MC68HC908GT16
MC68HC908GT8
MC68HC08GT16
Data Sheet
M68HC08
Microcontrollers
MC68HC908GT16
Rev. 5.0
04/2007
freescale.com
MC68HC908GT16
MC68HC908GT8
MC68HC08GT16
Data Sheet
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MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
3
Revision History
The following revision history table summarizes changes contained in this document. For your
convenience, the page number designators have been linked to the appropriate location.
Revision History (Sheet 1 of 2)
Date
Revision
Level
March,
2002
N/A
May,
2002
June,
2002
Page
Number(s)
Description
Original release
1.0
2.0
N/A
7.2 Features — Corrected third bulleted item to reflect ±4 percent variability
77
Figure 15-1. Forced Monitor Mode (Low) — Reworked for clarity
211
Figure 15-2. Forced Monitor Mode (High) — Reworked for clarity
211
Figure 15-3. Standard Monitor Mode — Reworked for clarity
212
Table 15-1. Monitor Mode Signal Requirements and Options — Reworked for
clarity
214
Figure 12-4. Port A I/O Circuit — Reworked to correct pullup resistor
143
Figure 12-11. Port C I/O Circuit — Reworked to correct pullup resistor
148
Figure 12-15. Port D I/O Circuit — Reworked to correct pullup resistor
151
Figure 2-2. Control, Status, and Data Registers — Corrected ESCI arbiter data
register (SCIADAT) to reflect read-only status
50
Figure 14-19. ESCI Arbiter Control Register (SCIACTL) — Corrected address
location designator from $0018 to $000A
170
Figure 14-20. ESCI Arbiter Data Register (SCIADAT) — Corrected address
location designator from $0019 to $000B
171
Reformatted to meet current publications standards
September,
2004
3.0
(Continued
on next
page)
Throughout
1.5.6 ADC Reference Pins (VREFH and VREFL) — Corrected connections
27
2.6.3 Flash Page Erase Operation — Updated procedure
41
2.6.4 Flash Mass Erase Operation — Updated procedure
42
2.6.5 Flash Program/Read Operation — Updated procedure
43
2.6.6 Flash Block Protection — Description updated for clarity
45
3.3.5 Conversion — Updated for clarity
52
3.6.3 ADC Voltage Reference High Pin (VREFH) — Corrected connections
53
3.6.4 ADC Voltage Reference Low Pin (VREFL) — Corrected connections
53
3.7.1 ADC Status and Control Register — Updated description of the COCO bit
54
Chapter 4 Configuration Register (CONFIG) — Updated COP tmeout selections
57, 59
Chapter 4 Configuration Register (CONFIG) — Updted SSREC bit usage
60
Chapter 5 Computer Operating Properly (COP) Module — Updated timeout
selections
62
Figure 5-1. COP Block Diagram — Updated illustration for clarity
61
Table 6-1. Instruction Set Summary — Updated definitions for STOP and WAIT
70
Figure 7-9. Code Example for Switching Clock Sources — Replaced example
code
89
Figure 7-10. Code Example for Enabling the Clock Monitor — Replaced example
code
90
Figure 14-18. ESCI Prescaler Register (SCPSC) — Corrected address location
172
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
Revision History
Revision History (Sheet 2 of 2)
Date
Revision
Level
Description
Chapter 15 System Integration Module (SIM) — Clarified SIM features and
functionality
September,
2004
March,
2006
April,
2007
4.0
5.0
179, 182,
183, 184
15.7.2 SIM Reset Status Register — Clarified SRSR operation
194
Table 19-1. Monitor Mode Signal Requirements and Options — Reworked
247
19.2.1 Functional Description — Corrected Break description
3.0
(Continued
from
previous
page)
Page
Number(s)
237, 240
19.3 Monitor Module (MON) — Reworked
243
Chapter 20 Electrical Specifications — Revised/added tables:
20.5 5.0-V DC Electrical Characteristics
20.6 3.0-V DC Electrical Characteristics
20.7 Supply Current Characteristics
20.8 5-V Control Timing
20.9 3-V Control Timing
257
258
259
260
260
20.20 Memory Characteristics — Updated memory table
273
Chapter 20 Electrical Specifications — Added figures:
Figure 20-1. RST and IRQ Timing
Figure 20-2. RST and IRQ Timing
260
260
Appendix A MC68HC08GT16 — Introduces the MC68HC08GT16, the ROM part
equivalent to the MC68HC908GT16.
281
4.2 Functional Description — In the description of the COP Rate Select Bit
corrected the values for COP timeout period
57
Figure 5-1. COP Block Diagram — Replaced BUSCLKX4 with COPCLK
61
14.9.1 ESCI Arbiter Control Register — Replaced one half with one quarter in
definition for ACLK = 0
176
14.9.3 Bit Time Measurement — Replaced one half with one quarter in definition
for ACLK = 0
177
Revised the following diagrams:
Figure 19-10. Forced Monitor Mode (Low)
Figure 19-11. Forced Monitor Mode (High)
Figure 19-12. Standard Monitor Mode
245
245
246
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
5
Revision History
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
6
Freescale Semiconductor
List of Chapters
Chapter 1 General Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Chapter 2 Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Chapter 3 Analog-to-Digital Converter (ADC). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Chapter 4 Configuration Register (CONFIG) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Chapter 5 Computer Operating Properly (COP) Module . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Chapter 6 Central Processor Unit (CPU). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Chapter 7 Internal Clock Generator (ICG) Module) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77
Chapter 8 External Interrupt (IRQ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Chapter 9 Keyboard Interrupt Module (KBI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Chapter 10 Low-Voltage Inhibit (LVI). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Chapter 11 Low-Power Modes (MODES). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Chapter 12 Input/Output (I/O) Ports (PORTS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
Chapter 13 Resets and Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .137
Chapter 14 Enhanced Serial Communications Interface (ESCI) Module . . . . . . . . . . . . . 149
Chapter 15 System Integration Module (SIM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
Chapter 16 Serial Peripheral Interface (SPI) Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
Chapter 17 Timebase Module (TBM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
Chapter 18 Timer Interface Module (TIM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
Chapter 19 Development Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
Chapter 20 Electrical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
Chapter 21 Ordering Information and Mechanical Specifications . . . . . . . . . . . . . . . . . . 275
Appendix A MC68HC08GT16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
7
List of Chapters
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
8
Freescale Semiconductor
Table of Contents
Chapter 1
General Description
1.1
1.2
1.2.1
1.2.2
1.3
1.4
1.5
1.5.1
1.5.2
1.5.3
1.5.4
1.5.5
1.5.6
1.5.7
1.5.8
1.5.9
1.5.10
1.5.11
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Standard Features of the MC68HC908GT16/MC68HC908GT8 . . . . . . . . . . . . . . . . . . . . .
Features of the CPU08 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MCU Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pin Assignments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pin Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power Supply Pins (VDD and VSS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Oscillator Pins (PTE4/OSC1 and PTE3/OSC2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
External Reset Pin (RST). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
External Interrupt Pin (IRQ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC and ICG Power Supply Pins (VDDA and VSSA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Reference Pins (VREFH and VREFL). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port A Input/Output (I/O) Pins (PTA7/KBD7–PTA0/KBD0) . . . . . . . . . . . . . . . . . . . . . . . . .
Port B I/O Pins (PTB7/AD7–PTB0/AD0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port C I/O Pins (PTC6–PTC0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port D I/O Pins (PTD7/T2CH1–PTD0/SS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port E I/O Pins (PTE4–PTE2, PTE1/RxD, and PTE0/TxD) . . . . . . . . . . . . . . . . . . . . . . . . .
21
21
21
23
23
25
26
26
27
27
27
27
27
28
28
28
28
28
Chapter 2
Memory
2.1
2.2
2.3
2.4
2.5
2.6
2.6.1
2.6.2
2.6.3
2.6.4
2.6.5
2.6.6
2.6.7
2.6.8
2.6.9
2.6.10
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Unimplemented Memory Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reserved Memory Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input/Output (I/O) Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Random-Access Memory (RAM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Flash Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Flash Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Flash Page Erase Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Flash Mass Erase Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Flash Program/Read Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Flash Block Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Flash Block Protect Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ICG User Trim Registers (ICGTR5 and ICGTR3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
29
29
29
29
40
40
40
41
41
42
43
45
45
46
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Table of Contents
Chapter 3
Analog-to-Digital Converter (ADC)
3.1
3.2
3.3
3.3.1
3.3.2
3.3.3
3.3.4
3.3.5
3.3.6
3.4
3.5
3.5.1
3.5.2
3.6
3.6.1
3.6.2
3.6.3
3.6.4
3.6.5
3.7
3.7.1
3.7.2
3.7.3
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Port I/O Pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Port I/O Pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Voltage Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Conversion Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Accuracy and Precision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Analog Power Pin (VDDA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Analog Ground Pin (VSSA). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Voltage Reference High Pin (VREFH). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Voltage Reference Low Pin (VREFL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Voltage In (VADIN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I/O Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Status and Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Data Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Clock Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
49
49
49
49
51
51
52
52
52
52
52
52
53
53
53
53
53
53
54
54
54
55
56
Chapter 4
Configuration Register (CONFIG)
4.1
4.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Chapter 5
Computer Operating Properly (COP) Module
5.1
5.2
5.3
5.3.1
5.3.2
5.3.3
5.3.4
5.3.5
5.3.6
5.3.7
5.3.8
5.4
5.5
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
COPCLK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
STOP Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
COPCTL Write . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power-On Reset. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Internal Reset. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reset Vector Fetch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
COPD (COP Disable). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
COPRS (COP Rate Select) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
COP Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
61
61
62
62
62
62
62
62
63
63
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5.6
5.7
5.7.1
5.7.2
5.8
Monitor Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
COP Module During Break Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
63
63
63
64
64
Chapter 6
Central Processor Unit (CPU)
6.1
6.2
6.3
6.3.1
6.3.2
6.3.3
6.3.4
6.3.5
6.4
6.5
6.5.1
6.5.2
6.6
6.7
6.8
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CPU Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Accumulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Index Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stack Pointer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Program Counter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Condition Code Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Arithmetic/Logic Unit (ALU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CPU During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Instruction Set Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Opcode Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
65
65
65
66
66
67
67
68
69
69
69
69
69
70
75
Chapter 7
Internal Clock Generator (ICG) Module)
7.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.2
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3.1
Clock Enable Circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3.2
Internal Clock Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3.2.1
Digitally Controlled Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3.2.2
Modulo N Divider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3.2.3
Frequency Comparator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3.2.4
Digital Loop Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3.3
External Clock Generator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3.3.1
External Oscillator Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3.3.2
External Clock Input Path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3.4
Clock Monitor Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3.4.1
Clock Monitor Reference Generator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3.4.2
Internal Clock Activity Detector. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3.4.3
External Clock Activity Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3.5
Clock Selection Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3.5.1
Clock Selection Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.3.5.2
Clock Switching Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
77
77
77
80
80
81
81
82
82
83
83
84
84
84
86
86
87
88
88
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
11
Table of Contents
7.4
Usage Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
7.4.1
Switching Clock Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
7.4.2
Enabling the Clock Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
7.4.3
Using Clock Monitor Interrupts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
7.4.4
Quantization Error in DCO Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
7.4.4.1
Digitally Controlled Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
7.4.4.2
Binary Weighted Divider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
7.4.4.3
Variable-Delay Ring Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
7.4.4.4
Ring Oscillator Fine-Adjust Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
7.4.5
Switching Internal Clock Frequencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
7.4.6
Nominal Frequency Settling Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
7.4.6.1
Settling to Within 15 Percent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
7.4.6.2
Settling to Within 5 Percent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
7.4.6.3
Total Settling Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
7.4.7
Trimming Frequency on the Internal Clock Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
7.5
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
7.5.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
7.5.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
7.6
CONFIG2 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
7.6.1
External Clock Enable (EXTCLKEN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
7.6.2
External Crystal Enable (EXTXTALEN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
7.6.3
Slow External Clock (EXTSLOW) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
7.6.4
Oscillator Enable In Stop (OSCENINSTOP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
7.7
Input/Output (I/O) Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
7.7.1
ICG Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
7.7.2
ICG Multiplier Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
7.7.3
ICG Trim Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
7.7.4
ICG DCO Divider Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
7.7.5
ICG DCO Stage Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Chapter 8
External Interrupt (IRQ)
8.1
8.2
8.3
8.4
8.5
8.6
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IRQ Pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IRQ Module During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IRQ Status and Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
101
101
101
103
104
104
Chapter 9
Keyboard Interrupt Module (KBI)
9.1
9.2
9.3
9.4
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Keyboard Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
107
107
107
110
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
12
Freescale Semiconductor
9.5
9.5.1
9.5.2
9.6
9.7
9.7.1
9.7.2
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Keyboard Module During Break Interrupts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I/O Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Keyboard Status and Control Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Keyboard Interrupt Enable Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
110
110
111
111
111
111
112
Chapter 10
Low-Voltage Inhibit (LVI)
10.1
10.2
10.3
10.3.1
10.3.2
10.3.3
10.3.4
10.4
10.5
10.6
10.6.1
10.6.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Polled LVI Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Forced Reset Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Voltage Hysteresis Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
LVI Trip Selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
LVI Status Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
LVI Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
113
113
113
114
114
114
115
115
115
115
115
116
Chapter 11
Low-Power Modes (MODES)
11.1
11.1.1
11.1.2
11.2
11.2.1
11.2.2
11.3
11.3.1
11.3.2
11.4
11.4.1
11.4.2
11.5
11.5.1
11.5.2
11.6
11.6.1
11.6.2
11.7
11.7.1
11.7.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Analog-to-Digital Converter (ADC). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Break Module (BRK) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Central Processor Unit (CPU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Internal Clock Generator Module (ICG) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Computer Operating Properly Module (COP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
External Interrupt Module (IRQ). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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117
117
117
117
117
117
117
118
118
118
118
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118
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119
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11.8 Keyboard Interrupt Module (KBI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.8.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.8.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.9 Low-Voltage Inhibit Module (LVI). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.9.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.9.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.10 Enhanced Serial Communications Interface Module (SCI) . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.10.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.10.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.11 Serial Peripheral Interface Module (SPI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.11.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.11.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.12 Timer Interface Module (TIM1 and TIM2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.12.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.12.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.13 Timebase Module (TBM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.13.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.13.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.14 Exiting Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11.15 Exiting Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
119
119
119
119
119
120
120
120
120
120
120
120
120
120
121
121
121
121
121
122
Chapter 12
Input/Output (I/O) Ports (PORTS)
12.1
12.2
12.2.1
12.2.2
12.2.3
12.3
12.3.1
12.3.2
12.4
12.4.1
12.4.2
12.4.3
12.5
12.5.1
12.5.2
12.5.3
12.6
12.6.1
12.6.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port A Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Data Direction Register A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port A Input Pullup Enable Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port B Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Data Direction Register B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port C Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Data Direction Register C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port C Input Pullup Enable Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port D. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port D Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Data Direction Register D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port D Input Pullup Enable Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Port E Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Data Direction Register E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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126
126
126
127
128
128
128
129
130
130
131
132
132
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Resets and Interrupts
13.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.2 Resets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.2.1
Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.2.2
External Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.2.3
Internal Reset. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.2.3.1
Power-On Reset (POR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.2.3.2
Computer Operating Properly (COP) Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.2.3.3
Low-Voltage Inhibit Reset. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.2.3.4
Illegal Opcode Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.2.3.5
Illegal Address Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.2.4
SIM Reset Status Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3 Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3.1
Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3.2
Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3.2.1
Software Interrupt (SWI) Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3.2.2
Break Interrupt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3.2.3
IRQ Pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3.2.4
Internal Clock Generator (ICG). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3.2.5
Timer Interface Module 1 (TIM1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3.2.6
Timer Interface Module 2 (TIM2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3.2.7
Serial Peripheral Interface (SPI). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3.2.8
Serial Communications Interface (SCI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3.2.9
KBD0–KBD7 Pins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3.2.10
Analog-to-Digital Converter (ADC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3.2.11
Timebase Module (TBM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3.3
Interrupt Status Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3.3.1
Interrupt Status Register 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3.3.2
Interrupt Status Register 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13.3.3.3
Interrupt Status Register 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
137
137
137
137
137
138
138
139
139
139
139
140
140
143
143
144
144
144
144
144
144
145
145
145
146
146
147
147
147
Chapter 14
Enhanced Serial Communications Interface (ESCI) Module
14.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.2 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.3 Pin Name Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.4 Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.4.1
Data Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.4.2
Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.4.2.1
Character Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.4.2.2
Character Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.4.2.3
Break Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.4.2.4
Idle Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.4.2.5
Inversion of Transmitted Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14.4.2.6
Transmitter Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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149
149
151
152
153
153
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14.4.3
Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
14.4.3.1
Character Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
14.4.3.2
Character Reception. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
14.4.3.3
Data Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
14.4.3.4
Framing Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
14.4.3.5
Baud Rate Tolerance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
14.4.3.6
Receiver Wakeup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
14.4.3.7
Receiver Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
14.4.3.8
Error Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
14.5 Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
14.5.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
14.5.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
14.6 ESCI During Break Module Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
14.7 I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
14.7.1
PTE0/TxD (Transmit Data). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
14.7.2
PTE1/RxD (Receive Data) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
14.8 I/O Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
14.8.1
ESCI Control Register 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
14.8.2
ESCI Control Register 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
14.8.3
ESCI Control Register 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
14.8.4
ESCI Status Register 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
14.8.5
ESCI Status Register 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
14.8.6
ESCI Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
14.8.7
ESCI Baud Rate Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
14.8.8
ESCI Prescaler Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
14.9 ESCI Arbiter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
14.9.1
ESCI Arbiter Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
14.9.2
ESCI Arbiter Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
14.9.3
Bit Time Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
14.9.4
Arbitration Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
Chapter 15
System Integration Module (SIM)
15.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.2 SIM Bus Clock Control and Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.2.1
Bus Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.2.2
Clock Startup from POR or LVI Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.2.3
Clocks in Stop Mode and Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.3 Reset and System Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.3.1
External Pin Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.3.2
Active Resets from Internal Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.3.2.1
Power-On Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.3.2.2
Computer Operating Properly (COP) Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.3.2.3
Illegal Opcode Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.3.2.4
Illegal Address Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.3.2.5
Low-Voltage Inhibit (LVI) Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.3.2.6
Monitor Mode Entry Module Reset (MODRST) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
15.4 SIM Counter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.4.1
SIM Counter During Power-On Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.4.2
SIM Counter During Stop Mode Recovery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.4.3
SIM Counter and Reset States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.5 Exception Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.5.1
Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.5.1.1
Hardware Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.5.1.2
SWI Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.5.1.3
Interrupt Status Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.5.2
Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.5.3
Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.5.4
Status Flag Protection in Break Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.6 Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.6.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.6.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.7 SIM Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.7.1
SIM Break Status Register. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.7.2
SIM Reset Status Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15.7.3
SIM Break Flag Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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185
185
185
186
186
187
188
188
190
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190
191
191
192
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194
195
Chapter 16
Serial Peripheral Interface (SPI) Module
16.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.2 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.3 Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.3.1
Master Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.3.2
Slave Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.4 Transmission Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.4.1
Clock Phase and Polarity Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.4.2
Transmission Format When CPHA = 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.4.3
Transmission Format When CPHA = 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.4.4
Transmission Initiation Latency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.5 Queuing Transmission Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.6 Error Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.6.1
Overflow Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.6.2
Mode Fault Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.7 Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.8 Resetting the SPI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.9 Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.9.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.9.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.10 SPI During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.11 I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.11.1
MISO (Master In/Slave Out). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.11.2
MOSI (Master Out/Slave In). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.11.3
SPSCK (Serial Clock) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.11.4
SS (Slave Select) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Table of Contents
16.12 I/O Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.12.1
SPI Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.12.2
SPI Status and Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16.12.3
SPI Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
213
213
214
216
Chapter 17
Timebase Module (TBM)
17.1
17.2
17.3
17.4
17.5
17.6
17.6.1
17.6.2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Timebase Register Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
217
217
217
218
219
220
220
220
Chapter 18
Timer Interface Module (TIM)
18.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.2 Features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.3 Pin Name Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.4 Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.4.1
TIM Counter Prescaler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.4.2
Input Capture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.4.3
Output Compare. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.4.3.1
Unbuffered Output Compare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.4.3.2
Buffered Output Compare . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.4.4
Pulse Width Modulation (PWM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.4.4.1
Unbuffered PWM Signal Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.4.4.2
Buffered PWM Signal Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.4.4.3
PWM Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.5 Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.6 Low-Power Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.6.1
Wait Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.6.2
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.7 TIM During Break Interrupts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.8 I/O Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.9 I/O Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.9.1
TIM Status and Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.9.2
TIM Counter Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.9.3
TIM Counter Modulo Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.9.4
TIM Channel Status and Control Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18.9.5
TIM Channel Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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223
223
223
225
225
226
226
226
227
227
228
228
229
229
229
230
230
230
230
231
232
233
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MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
Chapter 19
Development Support
19.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2 Break Module (BRK) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2.1
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2.1.1
Flag Protection During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2.1.2
TIM1 and TIM2 During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2.1.3
COP During Break Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2.2
Break Module Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2.2.1
Break Status and Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2.2.2
Break Address Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2.2.3
SIM Break Status Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.2.2.4
Break Flag Control Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3 Monitor Module (MON) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3.1
Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3.1.1
Normal Monitor Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3.1.2
Forced Monitor Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3.1.3
Monitor Vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3.1.4
Data Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3.1.5
Break Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3.1.6
Baud Rate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3.1.7
Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19.3.2
Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
237
237
237
240
240
240
240
241
241
242
242
243
243
247
248
248
249
249
249
249
252
Chapter 20
Electrical Specifications
20.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.2 Absolute Maximum Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.3 Functional Operating Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.4 Thermal Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.5 5.0-V DC Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.6 3.0-V DC Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.7 Supply Current Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.8 5-V Control Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.9 3-V Control Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.10 Internal Oscillator Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.11 External Oscillator Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.12 Trimmed Accuracy of the Internal Clock Generator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.12.1
2.7-Volt to 3.3-Volt Trimmed Internal Clock Generator Characteristics . . . . . . . . . . . . . . .
20.12.2
4.5-Volt to 5.5-Volt Trimmed Internal Clock Generator Characteristics . . . . . . . . . . . . . . .
20.13 Output High-Voltage Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.14 Output Low-Voltage Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.15 Typical Supply Currents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.16 ADC Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20.17 5.0-V SPI Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
255
255
256
256
257
258
259
260
260
261
261
262
262
262
263
265
267
268
269
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Freescale Semiconductor
19
Table of Contents
20.18 3.0-V SPI Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
20.19 Timer Interface Module Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
20.20 Memory Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
Chapter 21
Ordering Information and Mechanical Specifications
21.1
21.2
21.3
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
MC Order Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
Package Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
Appendix A
MC68HC08GT16
A.1
A.2
A.3
A.4
A.5
A.6
A.7
A.8
A.8.1
A.8.2
A.8.3
A.9
A.9.1
A.9.2
A.10
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MCU Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Memory Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reserved Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ICG Trim Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Monitor ROM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Reference Pins (VREFH and VREFL). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Electrical Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.0-V DC Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.0-V DC Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Supply Current Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Internal Oscillator Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Memory Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Order Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
281
281
281
281
284
284
284
284
285
286
287
288
289
289
289
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
Chapter 1
General Description
1.1 Introduction
The MC68HC908GT16, MC68HC908GT8, and MC68HC08GT16 are members of the low-cost,
high-performance M68HC08 Family of 8-bit microcontroller units (MCUs). All MCUs in the family use the
enhanced M68HC08 central processor unit (CPU08) and are available with a variety of modules, memory
sizes and types, and package types.
All references to the MC68HC908GT16 in this data book apply equally to the MC68HC908GT8, unless
otherwise stated.
This revision introduces the MC68HC08GT16, the ROM part equivalent to the MC68HC908GT16. The
entire data book applies to this ROM device, with the exceptions outlined in Appendix A MC68HC08GT16.
1.2 Features
For convenience, features have been organized to reflect:
• Standard features of the MC68HC908GT16/MC68HC908GT8
• Features of the CPU08
1.2.1 Standard Features of the MC68HC908GT16/MC68HC908GT8
•
•
•
•
•
•
•
High-performance M68HC08 architecture optimized for C-compilers
Fully upward-compatible object code with M6805, M146805, and M68HC05 Families
8-MHz internal bus frequency
Internal oscillator requiring no external components:
– Software selectable bus frequencies
– ±25 percent accuracy with trim capability to ±4 percent
– Clock monitor
– Option to allow use of external clock source or external crystal/ceramic resonator
Flash program memory security(1)
On-chip programming firmware for use with host personal computer which does not require high
voltage for entry
In-system programming (ISP)
1. No security feature is absolutely secure. However, Freescale’s strategy is to make reading or copying the Flash difficult for
unauthorized users.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
21
General Description
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
System protection features:
– Optional computer operating properly (COP) reset
– Low-voltage detection with optional reset and selectable trip points for 3.0-V and 5.0-V
operation
– Illegal opcode detection with reset
– Illegal address detection with reset
Low-power design; fully static with stop and wait modes
Standard low-power modes of operation:
– Wait mode
– Stop mode
Master reset pin and power-on reset (POR)
16 Kbytes of on-chip 100k cycle write/erase capable Flash memory (8 Kbytes on
MC68HC908GT8)
512 bytes of on-chip random-access memory (RAM)
720 bytes of Flash programming routines ROM
Serial peripheral interface module (SPI)
Serial communications interface module (SCI)
Two 16-bit, 2-channel timer interface modules (TIM1 and TIM2) with selectable input capture,
output compare, and pulse-width modulation (PWM) capability on each channel
8-channel, 8-bit successive approximation analog-to-digital converter (ADC)
Break module (BRK) to allow single breakpoint setting during in-circuit debugging
Internal pullups on IRQ and RST to reduce customer system cost
Up to 36 general-purpose input/output (I/O) pins, including:
– 28 shared-function I/O pins
– Six or eight dedicated I/O pins, depending on package choice
Selectable pullups on inputs only on ports A, C, and D. Selection is on an individual port bit basis.
During output mode, pullups are disengaged.
High current 10-mA sink/10-mA source capability on all port pins
Higher current 20-mA sink/source capability on PTC0–PTC4
Timebase module with clock prescaler circuitry for eight user selectable periodic real-time
interrupts with optional active clock source during stop mode for periodic wakeup from stop using
an external 32-kHz crystal or internal oscillator
User selection of having the oscillator enabled or disabled during stop mode
8-bit keyboard wakeup port
Available packages:
– 42-pin shrink dual in-line package (SDIP)
– 44-pin quad flat pack (QFP)
Specific features of the MC68HC908GT16 in 42-pin SDIP are:
– Port C is only 5 bits: PTC0–PTC4
– Port D is 8 bits: PTD0–PTD7; dual 2-channel TIM modules
Specific features of the MC68HC908GT16 in 44-pin QFP are:
– Port C is 7 bits: PTC0–PTC6
– Port D is 8 bits: PTD0–PTD7; dual 2-channel TIM modules
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
MCU Block Diagram
1.2.2 Features of the CPU08
Features of the CPU08 include:
• Enhanced HC05 programming model
• Extensive loop control functions
• 16 addressing modes (eight more than the HC05)
• 16-bit index register and stack pointer
• Memory-to-memory data transfers
• Fast 8 × 8 multiply instruction
• Fast 16/8 divide instruction
• Binary-coded decimal (BCD) instructions
• Optimization for controller applications
• Efficient C language support
1.3 MCU Block Diagram
Figure 1-1 shows the structure of the MC68HC908GT16.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
23
General Description
8-BIT KEYBOARD
INTERRUPT MODULE
FLASH PROGRAMMING ROUTINES
ROM — 720 BYTES
USER FLASH VECTOR SPACE — 36 BYTES
PTE4/OSC1
PTE3/OSC2
INTERNAL CLOCK
GENERATOR MODULE
RST(3)
SYSTEM INTEGRATION
MODULE
IRQ(3)
SINGLE EXTERNAL
INTERRUPT MODULE
VREFH
VREFL
2-CHANNEL TIMER INTERFACE
MODULE 2
DDRA
PTD7/T2CH1(1)
PTD6/T2CH0(1)
PTD5/T1CH1(1)
PTD4/T1CH0(1)
PTD3/SPSCK(1)
PTD2/MOSI(1)
PTD1/MISO(1)
PTD0/SS(1)
PTE2
PTE1/RxD
PTE0/TxD
SERIAL PERIPHERAL
INTERFACE MODULE
MONITOR MODULE
8-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
PTC6(1)
PTC5(1)
PTC4(1)(2)
PTC3(1)(2)
PTC2(1)(2)
PTC1(1)(2)
PTC0(1)(2)
SERIAL COMMUNICATIONS
INTERFACE MODULE
COMPUTER OPERATING
PROPERLY MODULE
POWER-ON RESET
MODULE
VDD
VSS
VDDA
VSSA
2-CHANNEL TIMER INTERFACE
MODULE 1
DDRD
MONITOR ROM — 304 BYTES
PORTA
USER RAM — 512 BYTES
PORTB
DUAL VOLTAGE
LOW-VOLTAGE INHIBIT MODULE
PTB7/AD7
PTB6/AD6
PTB5/AD5
PTB4/AD4
PTB3/AD3
PTB2/AD2
PTB1/AD1
PTB0/AD0
PORTC
USER FLASH
MC68HC908GT16 — 15,872 BYTES
MC68HC908GT8 — 7,680 BYTES
PTA7/KBD7–
PTA0/KBD0(1)
PORTD
SINGLE BREAKPOINT BREAK
MODULE
DDRB
CONTROL AND STATUS
REGISTERS — 64 BYTES
DDRC
PROGRAMMABLE TIMEBASE
MODULE
ARITHMETIC/LOGIC
UNIT (ALU)
MEMORY MAP
MODULE
DDRE
CPU
REGISTERS
PORTE
INTERNAL BUS
M68HC08 CPU
SECURITY
MODULE
CONFIGURATION REGISTER 1
MODULE
CONFIGURATION REGISTER 2
MODULE
MONITOR MODE ENTRY
MODULE
1. Ports are software configurable with pullup device if input port.
2. Higher current drive port pins
3. Pin contains integrated pullup device
Figure 1-1. MCU Block Diagram
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
Pin Assignments
1.4 Pin Assignments
VDDA (ADC/ICG)
1
42
PTA7/KBD7
VSSA (ADC/ICG)
2
41
PTA6/KBD6
PTE2
3
40
PTA5/KBD5
PTE3/OSC2
4
39
PTA4/KBD4
PTE4/OSC1
5
38
PTA3/KBD3
RST
6
37
PTA2/KBD2
PTC0
7
36
PTA1/KBD1
PTC1
8
35
PTA0/KBD0
PTC2
9
34
VREFL (ADC)
PTC3
10
33
VREFH (ADC)
PTC4
11
32
PTB7/AD7
PTE0/TxD
12
31
PTB6/AD6
PTE1/RxD
13
30
PTB5/AD5
IRQ
14
29
PTB4/AD4
PTD0/SS
15
28
PTB3/AD3
PTD1/MISO
16
27
PTB2/AD2
PTD2/MOSI
17
26
PTB1/AD1
PTD3/SPSCK
18
25
PTB0/AD0
VSS
19
24
PTD7/T2CH1
VDD
20
23
PTD6/T2CH0
PTD4/T1CH0
21
22
PTD5/T1CH1
Pins Not Available
on 42-Pin Package
Internal
Connection
PTC5
Connected to ground
PTC6
Connected to ground
Figure 1-2. 42-Pin SDIP Pin Assignments
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
25
PTA2/KBD2
34
PTA6/KBD6
38
PTA3/KBD3
PTA7/KBD7
39
35
VDDA
40
PTA4/KBD4
VSSA
41
36
PTE2
42
PTA5/KBD5
PTE3/OSC2
43
RST 1
37
PTE4/OSC1
44
General Description
33
PTA1/KBD1
27
PTB5/AD5
PTC6
8
26
PTB4/AD4
PTE0/TxD
9
25
PTB3/AD3
PTE1/RxD
10
24
PTB2/AD2
IRQ 11
22
7
PTB0/AD0
PTC5
21
PTB6/AD6
PTD7/T2CH1
28
20
6
PTD6/T2CH0
PTC4
19
PTB7/AD7
PTD5/T1CH1
29
18
5
PTD4/T1CH0
PTC3
17
VREFH
VDD
30
16
4
VSS
PTC2
15
VREFL
PTD3/SPSCK
31
14
3
PTD2/MOSI
PTC1
13
PTA0/KBD0
PTD1/MISO
32
12
2
PTD0/SS
PTC0
23
PTB1/AD1
Figure 1-3. 44-Pin QFP Pin Assignments
1.5 Pin Functions
Descriptions of the pin functions are provided here.
1.5.1 Power Supply Pins (VDD and VSS)
VDD and VSS are the power supply and ground pins. The MCU operates from a single power supply.
Fast signal transitions on MCU pins place high, short-duration current demands on the power supply. To
prevent noise problems, take special care to provide power supply bypassing at the MCU as Figure 1-4
shows. Place the C1 bypass capacitor as close to the MCU as possible. Use a high-frequency-response
ceramic capacitor for C1. C2 is an optional bulk current bypass capacitor for use in applications that
require the port pins to source high current levels.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
Pin Functions
MCU
VSS
VDD
C1
0.1 μF
+
C2
VDD
Note: Component values shown represent typical applications.
Figure 1-4. Power Supply Bypassing
1.5.2 Oscillator Pins (PTE4/OSC1 and PTE3/OSC2)
PTE4/OSC1 and PTE3/OSC2 are general-purpose, bidirectional I/O port pins. These pins can also be
programmed to be the connections for an external crystal, resonator or clock circuit. See Chapter 7
Internal Clock Generator (ICG) Module).
1.5.3 External Reset Pin (RST)
A logic 0 on the RST pin forces the MCU to a known startup state. RST is bidirectional, allowing a reset
of the entire system. It is driven low when any internal reset source is asserted. This pin contains an
internal pullup resistor. See Chapter 15 System Integration Module (SIM).
1.5.4 External Interrupt Pin (IRQ)
IRQ is an asynchronous external interrupt pin. This pin contains an internal pullup resistor. See
Chapter 8 External Interrupt (IRQ).
1.5.5 ADC and ICG Power Supply Pins (VDDA and VSSA)
VDDA and VSSA are the power supply pins for the analog-to-digital converter (ADC) and the internal clock
generator (ICG). Connect the VDDA pin to the same voltage potential as VDD, and the VSSA pin to the
same voltage potential as VSS. Decoupling of these pins should be as per the digital supply. See
Chapter 3 Analog-to-Digital Converter (ADC) and Chapter 7 Internal Clock Generator (ICG) Module).
1.5.6 ADC Reference Pins (VREFH and VREFL)
VREFH and VREFL are the reference voltage pins for the analog-to-digital converter (ADC). VREFH is the
high reference supply for the ADC and should be filtered. VREFH must be connected to the same voltage
potential as the analog supply pin, VDDA. VREFL is the low reference supply for the ADC and should be
externally filtered. VREFL must be connected to the same voltage potential as the analog supply pin VSSA.
See Chapter 3 Analog-to-Digital Converter (ADC).
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
27
General Description
1.5.7 Port A Input/Output (I/O) Pins (PTA7/KBD7–PTA0/KBD0)
PTA7–PTA0 are general-purpose, bidirectional I/O port pins. Any or all of the port A pins can be
programmed to serve as keyboard interrupt pins. See Chapter 12 Input/Output (I/O) Ports (PORTS) and
Chapter 9 Keyboard Interrupt Module (KBI).
These port pins also have selectable pullups when configured for input mode. The pullups are disengaged
when configured for output mode. The pullups are selectable on an individual port bit basis.
1.5.8 Port B I/O Pins (PTB7/AD7–PTB0/AD0)
PTB7–PTB0 are general-purpose, bidirectional I/O port pins that can also be used for analog-to-digital
converter (ADC) inputs. See Chapter 12 Input/Output (I/O) Ports (PORTS) and Chapter 3
Analog-to-Digital Converter (ADC).
1.5.9 Port C I/O Pins (PTC6–PTC0)
PTC6–PTC0 are general-purpose, bidirectional I/O port pins. PTC0–PTC4 have higher current
sink/source capability. PTC5 and PTC6 are only available on the 44-pin QFP package.
These port pins also have selectable pullups when configured for input mode. The pullups are disengaged
when configured for output mode. The pullups are selectable on an individual port bit basis. See
Chapter 12 Input/Output (I/O) Ports (PORTS).
1.5.10 Port D I/O Pins (PTD7/T2CH1–PTD0/SS)
PTD7–PTD0 are special-function, bidirectional I/O port pins. PTD0–PTD3 can be programmed to be
serial peripheral interface (SPI) pins, while PTD4–PTD7 can be individually programmed to be timer
interface module (TIM1 and TIM2) pins. See Chapter 18 Timer Interface Module (TIM), Chapter 16 Serial
Peripheral Interface (SPI) Module, and Chapter 12 Input/Output (I/O) Ports (PORTS).
These port pins also have selectable pullups when configured for input mode. The pullups are disengaged
when configured for output mode. The pullups are selectable on an individual port bit basis.
1.5.11 Port E I/O Pins (PTE4–PTE2, PTE1/RxD, and PTE0/TxD)
PTE0–PTE4 are general-purpose, bidirectional I/O port pins. PTE0–PTE1 can also be programmed to be
serial communications interface (SCI) pins. See Chapter 14 Enhanced Serial Communications Interface
(ESCI) Module and Chapter 12 Input/Output (I/O) Ports (PORTS).
PTE3 and PTE4 can also be programmed to be clock or oscillator pins. See Chapter 4 Configuration
Register (CONFIG) and Chapter 12 Input/Output (I/O) Ports (PORTS).
NOTE
Any unused inputs and I/O ports should be tied to an appropriate logic level
(either VDD or VSS). Although the I/O ports do not require termination,
termination is recommended to reduce the possibility of static damage.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
Chapter 2
Memory
2.1 Introduction
The CPU08 can address 64 Kbytes of memory space. The memory map, shown in Figure 2-1, includes:
• User Flash memory:
– MC68HC908GT16 — 15,872 bytes
– MC68HC908GT8 — 7,680 bytes
• 512 bytes of random-access memory (RAM)
• 720 bytes of Flash programming routines read-only memory (ROM)
• 36 bytes of user-defined vectors
• 304 bytes of monitor ROM
2.2 Unimplemented Memory Locations
Accessing an unimplemented location can cause an illegal address reset. In the memory map (Figure 2-1)
and in register figures in this document, unimplemented locations are shaded.
2.3 Reserved Memory Locations
Accessing a reserved location can have unpredictable effects on MCU operation. In the Figure 2-1 and
in register figures in this document, reserved locations are marked with the word Reserved or with the
letter R.
2.4 Input/Output (I/O) Section
Most of the control, status, and data registers are in the zero page area of $0000–$003F. Additional I/O
registers have these addresses:
• $FE00; SIM break status register, SBSR
• $FE01; SIM reset status register, SRSR
• $FE02; reserved, SUBAR
• $FE03; SIM break flag control register, SBFCR
• $FE04; interrupt status register 1, INT1
• $FE05; interrupt status register 2, INT2
• $FE06; interrupt status register 3, INT3
• $FE07; reserved
• $FE08; Flash control register, FLCR
• $FE09; break address register high, BRKH
• $FE0A; break address register low, BRKL
• $FE0B; break status and control register, BRKSCR
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
29
Memory
•
•
•
•
•
$FE0C; LVI status register, LVISR
$FF7E; Flash block protect register, FLBPR
$FF80; ICG user trim register 5V ICGTR5
$FF81; ICG user trim register 3V ICGTR3
$FFFF; COP control register, COPCTL
Data registers are shown in Figure 2-2. Table 2-1 is a list of vector locations.
$0000
↓
$003F
$0040
↓
$023F
$0240
↓
$1B4F
$1B50
↓
$1E1F
$1E20
↓
$BFFF
I/O REGISTERS
64 BYTES
RAM
512 BYTES
UNIMPLEMENTED
6416 BYTES
FLASH PROGRAMMING ROUTINES ROM
720 BYTES
UNIMPLEMENTED
41,440 BYTES
$C000
↓
FLASH MEMORY
MC68HC908GT16
15,872 BYTES
$FDFF
$FE00
SIM BREAK STATUS REGISTER (SBSR)
$FE01
SIM RESET STATUS REGISTER (SRSR)
$FE02
RESERVED (SUBAR)
$FE03
SIM BREAK FLAG CONTROL REGISTER (SBFCR)
$FE04
INTERRUPT STATUS REGISTER 1 (INT1)
$FE05
INTERRUPT STATUS REGISTER 2 (INT2)
$FE06
INTERRUPT STATUS REGISTER 3 (INT3)
$FE07
RESERVED
$FE08
FLASH CONTROL REGISTER (FLCR)
$FE09
BREAK ADDRESS REGISTER HIGH (BRKH)
$FE0A
BREAK ADDRESS REGISTER LOW (BRKL)
$FE0B
BREAK STATUS AND CONTROL REGISTER (BRKSCR)
RESERVED(1)
$C000
↓
$DFFF
FLASH MEMORY
MC68HC908GT8
7,680 BYTES
$E000
↓
$FDFF
1. Inadvertent access to
these locations will not
cause an illegal address
reset.
Figure is continued on the next page
Figure 2-1. Memory Map
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
30
Freescale Semiconductor
Input/Output (I/O) Section
$FE0C
LVI STATUS REGISTER (LVISR)
$FE0D
UNIMPLEMENTED
3 BYTES
↓
$FE0F
$FE10
↓
$FE1F
UNIMPLEMENTED
16 BYTES
RESERVED FOR COMPATIBILITY WITH MONITOR CODE
FOR A-FAMILY PART
$FE20
MONITOR ROM
304 BYTES
↓
$FF4F
$FF50
UNIMPLEMENTED
46 BYTES
↓
$FF7D
$FF7E
FLASH BLOCK PROTECT REGISTER (FLBPR)
$FF7F
UNIMPLEMENTED 1 BYTE
$FF80
ICG USER TRIM REGISTER 5V (ICGTR5)
$FF81
ICG USER TRIM REGISTER 3V (ICGTR3)
$FF82
UNIMPLEMENTED
90 BYTES
↓
$FFDB
$FFDC
FLASH VECTORS
36 BYTES
↓
$FFFF(2)
2. $FFF6–$FFFD reserved for eight security bytes
Figure 2-1. Memory Map (Continued)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
31
Memory
Addr.
$0000
Register Name
Port A Data Register Read:
(PTA) Write:
See page 126. Reset:
$0001
Port B Data Register Read:
(PTB) Write:
See page 128. Reset:
$0002
Port C Data Register Read:
(PTC) Write:
See page 130. Reset:
$0003
$0004
Port D Data Register ( Read:
PTD) Write:
See page 132. Reset:
Data Direction Register A Read:
(DDRA) Write:
See page 126. Reset:
$0005
Data Direction Register B Read:
(DDRB) Write:
See page 128. Reset:
$0006
Data Direction Register C Read:
(DDRC) Write:
See page 130. Reset:
$0007
$0008
Data Direction Register D Read:
(DDRD) Write:
See page 133. Reset:
Port E Data Register Read:
(PTE) Write:
See page 135. Reset:
$0009
ESCI Prescaler Register Read:
(SCPSC) Write:
See page 172. Reset:
$000A
ESCI Arbiter Control Read:
Register (SCIACTL) Write:
See page 176. Reset:
$000B
$000C
ESCI Arbiter Data Read:
Register (SCIADAT) Write:
See page 177. Reset:
Data Direction Register E Read:
(DDRE) Write:
See page 136. Reset:
Bit 7
6
5
4
3
2
1
Bit 0
PTA7
PTA6
PTA5
PTA4
PTA3
PTA2
PTA1
PTA0
PTB2
PTB1
PTB0
PTC2
PTC1
PTC0
PTD2
PTD1
PTD0
Unaffected by reset
PTB7
PTB6
PTB5
PTB4
PTB3
Unaffected by reset
0
PTC6
PTC5
PTC4
PTC3
Unaffected by reset
PTD7
PTD6
PTD5
PTD4
PTD3
Unaffected by reset
DDRA7
DDRA6
DDRA5
DDRA4
DDRA3
DDRA2
DDRA1
DDRA0
0
0
0
0
0
0
0
0
DDRB7
DDRB6
DDRB5
DDRB4
DDRB3
DDRB2
DDRB1
DDRB0
0
0
0
0
0
0
0
0
DDRC6
DDRC5
DDRC4
DDRC3
DDRC2
DDRC1
DDRC0
0
0
0
0
0
0
0
0
DDRD7
DDRD6
DDRD5
DDRD4
DDRD3
DDRD2
DDRD1
DDRD0
0
0
0
0
0
0
0
0
0
0
0
PTE4
PTE3
PTE2
PTE1
PTE0
PSSB2
PSSB1
PSSB0
0
Unaffected by reset
PDS2
0
AM1
PDS1
PDS0
PSSB4
0
0
0
ALOST
AM0
ACLK
PSSB3
0
0
0
0
AFIN
ARUN
AOVFL
ARD8
0
0
0
0
0
0
0
0
ARD7
ARD6
ARD5
ARD4
ARD3
ARD2
ARD1
ARD0
0
0
0
0
0
0
0
0
0
0
0
DDRE4
DDRE3
DDRE2
DDRE1
DDRE0
0
0
0
0
0
0
0
0
= Unimplemented
R = Reserved
U = Unaffected
Figure 2-2. Control, Status, and Data Registers (Sheet 1 of 7)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
32
Freescale Semiconductor
Input/Output (I/O) Section
Addr.
$000D
$000E
$000F
Register Name
Port C Input Pullup Enable Read:
Register (PTCPUE) Write:
See page 131. Reset:
$0010
$0011
SPI Status and Control Read:
Register (SPSCR) Write:
See page 214. Reset:
$0013
6
5
4
3
2
1
Bit 0
PTAPUE6
PTAPUE5
PTAPUE4
PTAPUE3
PTAPUE2
PTAPUE1
PTAPUE0
0
0
0
0
0
0
0
PTCPUE6
PTCPUE5
PTCPUE4
PTCPUE3
PTCPUE2
PTCPUE1
PTCPUE0
0
0
0
0
0
0
0
PTDPUE6
PTDPUE5
PTDPUE4
PTDPUE3
PTDPUE2
PTDPUE1
PTDPUE0
0
0
0
0
0
0
0
SPRIE
R
SPMSTR
CPOL
CPHA
SPWOM
SPE
SPTIE
0
0
0
0
0
MODFEN
SPR1
SPR0
0
0
Port D Input Pullup Enable Read: PTDPUE7
Register (PTDPUE) Write:
See page 134. Reset:
0
SPI Control Register Read:
(SPCR) Write:
See page 213. Reset:
$0012
Bit 7
Port A Input Pullup Enable Read: PTAPUE7
Register (PTAPUE) Write:
See page 127. Reset:
0
SPI Data Register Read:
(SPDR) Write:
See page 216. Reset:
ESCI Control Register 1 Read:
(SCC1) Write:
See page 163. Reset:
SPRF
ERRIE
1
0
1
OVRF
MODF
SPTE
0
0
0
0
1
0
0
0
R7
R6
R5
R4
R3
R2
R1
R0
T7
T6
T5
T4
T3
T2
T1
T0
Unaffected by reset
LOOPS
ENSCI
TXINV
M
WAKE
ILTY
PEN
PTY
0
0
0
0
0
0
0
0
SCTIE
TCIE
SCRIE
ILIE
TE
RE
RWU
SBK
0
0
0
0
0
0
0
0
T8
R
R
ORIE
NEIE
FEIE
PEIE
$0014
ESCI Control Register 2 Read:
(SCC2) Write:
See page 165. Reset:
R8
$0015
ESCI Control Register 3 Read:
(SCC3) Write:
See page 167. Reset:
U
U
0
0
0
0
0
0
ESCI Status Register 1 Read:
(SCS1) Write:
See page 168. Reset:
SCTE
TC
SCRF
IDLE
OR
NF
FE
PE
1
1
0
0
0
0
0
0
BKF
RPF
$0016
$0017
ESCI Status Register 2 Read:
(SCS2) Write:
See page 170. Reset:
$0018
ESCI Data Register Read:
(SCDR) Write:
See page 171. Reset:
$0019
ESCI Baud Rate Register Read:
(SCBR) Write:
See page 171. Reset:
0
0
0
0
0
0
0
0
R7
R6
R5
R4
R3
R2
R1
R0
T7
T6
T5
T4
T3
T2
T1
T0
Unaffected by reset
0
SCP1
SCP0
R
SCR2
SCR1
SCR0
0
0
0
0
0
0
0
= Unimplemented
R = Reserved
U = Unaffected
Figure 2-2. Control, Status, and Data Registers (Sheet 2 of 7)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
33
Memory
Addr.
$001A
$001B
$001C
$001D
$001E
$001F
Register Name
Keyboard Status Read:
and Control Register Write:
(INTKBSCR)
See page 111. Reset:
Keyboard Interrupt Enable Read:
Register (INTKBIER) Write:
See page 112. Reset:
Timebase Module Control Read:
Register (TBCR) Write:
See page 218. Reset:
IRQ Status and Control Read:
Register (INTSCR) Write:
See page 104. Reset:
Configuration Register 2 Read:
(CONFIG2)† Write:
See page 58.
Reset:
Configuration Register 1 Read:
(CONFIG1)† Write:
See page 58. Reset:
Bit 7
6
5
4
3
2
0
0
0
0
KEYF
0
ACKK
1
Bit 0
IMASKK
MODEK
0
0
0
0
0
0
0
0
KBIE7
KBIE6
KBIE5
KBIE4
KBIE3
KBIE2
KBIE1
KBIE0
0
0
0
0
0
0
0
0
TBR2
TBR1
TBR0
TBIE
TBON
R
0
0
0
0
0
0
0
0
0
0
0
0
IRQF1
0
IMASK1
MODE1
TBIF
0
TACK
ACK1
0
0
0
0
0
0
0
0
0
EXTXTALEN
EXT-SLOW
EXTCLKEN
0
OSCENINSTOP
R
0
0
0
0
0
0
0
0
COPRS
LVISTOP
LVIRSTD
SSREC
STOP
COPD
0
0
0
0
0
0
PS2
PS1
PS0
R
LVIPWRD LVI5OR3(1)
0
0
1. One-time writable register after each reset, except LVI5OR3 bit. LVI5OR3 bit is only reset via POR (power-on reset).
Timer 1 Status and Control Read:
Register (T1SC) Write:
See page 231. Reset:
TOF
0
0
TOIE
TSTOP
0
0
1
0
0
0
0
0
Bit 15
14
13
12
11
10
9
Bit 8
$0021
Timer 1 Counter Read:
Register High (T1CNTH) Write:
See page 232. Reset:
0
0
0
0
0
0
0
0
Bit 7
6
5
4
3
2
1
Bit 0
$0022
Timer 1 Counter Read:
Register Low (T1CNTL) Write:
See page 232. Reset:
0
0
0
0
0
0
0
0
Bit 15
14
13
12
11
10
9
Bit 8
1
1
1
1
1
1
1
1
Bit 7
6
5
4
3
2
1
Bit 0
1
1
1
1
1
1
1
1
CH0IE
MS0B
MS0A
ELS0B
ELS0A
TOV0
CH0MAX
0
0
0
0
0
0
0
$0020
$0023
$0024
Timer 1 Counter Modulo Read:
Register High (T1MODH) Write:
See page 233. Reset:
Timer 1 Counter Modulo Read:
Register Low (T1MODL) Write:
See page 233. Reset:
Timer 1 Channel 0 Status and Read:
$0025
Control Register (T1SC0) Write:
See page 233. Reset:
0
CH0F
0
0
= Unimplemented
TRST
R = Reserved
U = Unaffected
Figure 2-2. Control, Status, and Data Registers (Sheet 3 of 7)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
34
Freescale Semiconductor
Input/Output (I/O) Section
Addr.
$0026
$0027
Register Name
Timer 1 Channel 0 Read:
Register High (T1CH0H) Write:
See page 236. Reset:
Timer 1 Channel 0 Read:
Register Low (T1CH0L) Write:
See page 236. Reset:
Timer 1 Channel 1 Status and Read:
$0028
Control Register (T1SC1) Write:
See page 234. Reset:
$0029
Timer 1 Channel 1 Read:
Register High (T1CH1H) Write:
See page 236. Reset:
$002A
Timer 1 Channel 1 Read:
Register Low (T1CH1L) Write:
See page 236. Reset:
Bit 7
6
5
4
3
2
1
Bit 0
Bit 15
14
13
12
11
10
9
Bit 8
2
1
Bit 0
Indeterminate after reset
Bit 7
6
5
4
3
Indeterminate after reset
CH1F
0
0
CH1IE
MS1A
ELS1B
ELS1A
TOV1
CH1MAX
0
0
0
0
0
0
0
0
Bit 15
14
13
12
11
10
9
Bit 8
2
1
Bit 0
PS2
PS1
PS0
Indeterminate after reset
Bit 7
6
5
4
3
Indeterminate after reset
Timer 2 Status and Control Read:
Register (T2SC) Write:
See page 231. Reset:
TOF
0
0
TOIE
TSTOP
0
0
1
0
0
0
0
0
Timer 2 Counter Read:
Register High (T2CNTH) Write:
See page 232. Reset:
Bit 15
14
13
12
11
10
9
Bit 8
0
0
0
0
0
0
0
0
Bit 7
6
5
4
3
2
1
Bit 0
$002D
Timer 2 Counter Read:
Register Low (T2CNTL) Write:
See page 232. Reset:
0
0
0
0
0
0
0
0
$002E
Timer 2 Counter Modulo Read:
Register High (T2MODH) Write:
See page 233. Reset:
Bit 15
14
13
12
11
10
9
Bit 8
1
1
1
1
1
1
1
1
Bit 7
6
5
4
3
2
1
Bit 0
1
1
1
1
1
1
1
1
CH0IE
MS0B
MS0A
ELS0B
ELS0A
TOV0
CH0MAX
0
0
0
0
0
0
0
0
Bit 15
14
13
12
11
10
9
Bit 8
2
1
Bit 0
$002B
$002C
$002F
Timer 2 Counter Modulo Read:
Register Low (T2MODL) Write:
See page 233. Reset:
Timer 2 Channel 0 Status and Read:
$0030
Control Register (T2SC0) Write:
See page 233. Reset:
$0031
Timer 2 Channel 0 Read:
Register High (T2CH0H) Write:
See page 236. Reset:
$0032
Timer 2 Channel 0 Read:
Register Low (T2CH0L) Write:
See page 236. Reset:
0
CH0F
0
TRST
Indeterminate after reset
Bit 7
6
5
4
3
Indeterminate after reset
= Unimplemented
R = Reserved
U = Unaffected
Figure 2-2. Control, Status, and Data Registers (Sheet 4 of 7)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
35
Memory
Addr.
Register Name
Bit 7
Timer 2 Channel 1 Status and Read:
$0033
Control Register (T2SC1) Write:
See page 234. Reset:
CH1F
$0034
$0035
Timer 2 Channel 1 Read:
Register High (T2CH1H) Write:
See page 236. Reset:
Timer 2 Channel 1 Read:
Register Low (T2CH1L) Write:
See page 236. Reset:
$0036
ICG Control Register Read:
(ICGCR) Write:
See page 98. Reset:
$0037
ICG Multiplier Register Read:
(ICGMR) Write:
See page 99. Reset:
$0038
$0039
$003A
ICG Trim Register Read:
(ICGTR) Write:
See page 100. Reset:
ICG Divider Control Read:
Register (ICGDVR) Write:
See page 100. Reset:
ICG DCO Stage Control Read:
Register (ICGDSR) Write:
See page 100. Reset:
Read:
$003B
Reserved Write:
0
6
5
0
CH1IE
$003D
$003E
ADC Status and Control Read:
Register (ADSCR) Write:
See page 54. Reset:
ADC Data Register Read:
(ADR) Write:
See page 55. Reset:
ADC Clock Register Read:
(ADCLK) Write:
See page 56. Reset:
3
2
1
Bit 0
MS1A
ELS1B
ELS1A
TOV1
CH1MAX
0
0
0
0
0
0
0
0
Bit 15
14
13
12
11
10
9
Bit 8
2
1
Bit 0
Indeterminate after reset
Bit 7
6
5
4
3
Indeterminate after reset
CMIE
CMF
ICGS
CS
ICGON
0
0
0
1
0
0
0
N6
N5
N4
N3
N2
N1
N0
0
0
0
1
0
1
0
1
TRIM7
TRIM6
TRIM5
TRIM4
TRIM3
TRIM2
TRIM1
TRIM0
1
0
0
0
0
0
0
0
DDIV3
DDIV2
DDIV1
DDIV0
0
0
ECGON
ECGS
CMON
0
0
0
0
U
U
U
U
DSTG7
DSTG6
DSTG5
DSTG4
DSTG3
DSTG2
DSTG1
DSTG0
R
R
R
R
R
R
R
R
R
R
R
Unaffected by reset
R
R
R
Reset:
$003C
4
R
R
Indeterminate after reset
COCO
AIEN
ADCO
ADCH4
ADCH3
ADCH2
ADCH1
ADCH0
0
0
0
1
1
1
1
1
AD7
AD6
AD5
AD4
AD3
AD2
AD1
AD0
0
0
0
0
0
0
0
0
ADIV2
ADIV1
ADIV0
ADICLK
0
0
0
0
0
0
0
0
0
0
0
0
R
Read:
$003F
Unimplemented Write:
Reset:
= Unimplemented
R = Reserved
U = Unaffected
Figure 2-2. Control, Status, and Data Registers (Sheet 5 of 7)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
36
Freescale Semiconductor
Input/Output (I/O) Section
Addr.
$FE00
Register Name
Bit 7
SIM Break Status Register Read:
(SBSR) Write:
See page 242. Reset:
6
5
4
3
2
1
SBSW
Bit 0
R
R
R
R
R
R
0
0
0
0
0
0
0
0
POR
PIN
COP
ILOP
ILAD
MODRST
LVI
0
1
0
0
0
0
0
0
0
R
R
R
R
R
R
R
R
BCFE
R
R
R
R
R
R
R
NOTE
R
Note: Writing a 0 clears SBSW.
$FE01
SIM Reset Status Register Read:
(SRSR) Write:
See page 140. POR:
Read:
$FE02
$FE03
SIM Upper Byte Address
Write:
Register (SUBAR)
Reset:
SIM Break Flag Control Read:
Register (SBFCR) Write:
See page 242. Reset:
0
Interrupt Status Register 1 Read:
(INT1) Write:
See page 147. Reset:
IF6
IF5
IF4
IF3
IF2
IF1
0
0
R
R
R
R
R
R
R
R
0
0
0
0
0
0
0
0
IF14
IF13
IF12
IF11
IF10
IF9
IF8
IF7
$FE05
Interrupt Status Register 2 Read:
(INT2) Write:
See page 147. Reset:
R
R
R
R
R
R
R
R
0
0
0
0
0
0
0
0
0
0
0
0
0
0
IF16
IF15
$FE06
Interrupt Status Register 3 Read:
(INT3) Write:
See page 147. Reset:
R
R
R
R
R
R
R
R
0
0
0
0
0
0
0
0
R
R
R
R
R
R
R
R
Reset:
0
0
0
0
0
0
0
0
Flash Control Register Read:
(FLCR) Write:
See page 41. Reset:
0
0
0
0
HVEN
MASS
ERASE
PGM
0
0
0
0
0
0
0
0
Bit 15
14
13
12
11
10
9
Bit 8
0
0
0
0
0
0
0
0
Bit 7
6
5
4
3
2
1
Bit 0
0
0
0
0
0
0
0
0
BRKE
BRKA
0
0
0
0
0
0
0
0
0
0
0
0
0
0
$FE04
Read:
$FE07
$FE08
Reserved Write:
Break Address Register High Read:
$FE09
(BRKH) Write:
See page 241. Reset:
Break Address Register Low Read:
$FE0A
(BRKL) Write:
See page 241. Reset:
$FE0B
Break Status and Control Read:
Register (BRKSCR) Write:
See page 241. Reset:
= Unimplemented
R = Reserved
U = Unaffected
Figure 2-2. Control, Status, and Data Registers (Sheet 6 of 7)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
37
Memory
Addr.
Register Name
Read:
$FE0C
$FF7E
$FF80
$FF81
$FFFF
LVI Status Register (LVISR)
Write:
See page 115.
Reset:
Flash Block Protect Read:
Register (FLBPR)(1) Write:
See page 45. Reset:
ICG User Trim Read:
Register 5V (ICGTR5)(1) Write:
See page 46. Reset:
ICG User Trim Read:
Register 3V (ICGTR3)(1) Write:
See page 46. Reset:
Bit 7
6
5
4
3
2
1
Bit 0
LVIOUT
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
BPR7
BPR6
BPR5
BPR4
BPR3
BPR2
BPR1
BPR0
TRIM2
TRIM1
TRIM0
TRIM2
TRIM1
TRIM0
Unaffected by reset
TRIM7
TRIM6
TRIM5
TRIM4
TRIM3
Unaffected by reset
TRIM7
TRIM6
TRIM5
TRIM4
TRIM3
Unaffected by reset
COP Control Register Read:
(COPCTL) Write:
See page 63. Reset:
Low byte of reset vector
Writing clears COP counter (any value)
Unaffected by reset
1. Non-volatile Flash register
= Unimplemented
R = Reserved
U = Unaffected
Figure 2-2. Control, Status, and Data Registers (Sheet 7 of 7)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
38
Freescale Semiconductor
Input/Output (I/O) Section
.
Table 2-1. Vector Addresses
Vector Priority
Lowest
Vector
IF16
IF15
IF14
IF13
IF12
IF11
IF10
IF9
IF8
IF7
IF6
IF5
IF4
IF3
IF2
IF1
—
Highest
—
Address
Vector
$FFDC
Timebase Vector (High)
$FFDD
Timebase Vector (Low)
$FFDE
ADC Conversion Complete Vector (High)
$FFDF
ADC Conversion Complete Vector (Low)
$FFE0
Keyboard Vector (High)
$FFE1
Keyboard Vector (Low)
$FFE2
SCI Transmit Vector (High)
$FFE3
SCI Transmit Vector (Low)
$FFE4
SCI Receive Vector (High)
$FFE5
SCI Receive Vector (Low)
$FFE6
SCI Error Vector (High)
$FFE7
SCI Error Vector (Low)
$FFE8
SPI Transmit Vector (High)
$FFE9
SPI Transmit Vector (Low)
$FFEA
SPI Receive Vector (High)
$FFEB
SPI Receive Vector (Low)
$FFEC
TIM2 Overflow Vector (High)
$FFED
TIM2 Overflow Vector (Low)
$FFEE
TIM2 Channel 1 Vector (High)
$FFEF
TIM2 Channel 1 Vector (Low)
$FFF0
TIM2 Channel 0 Vector (High)
$FFF1
TIM2 Channel 0 Vector (Low)
$FFF2
TIM1 Overflow Vector (High)
$FFF3
TIM1 Overflow Vector (Low)
$FFF4
TIM1 Channel 1 Vector (High)
$FFF5
TIM1 Channel 1 Vector (Low)
$FFF6
TIM1 Channel 0 Vector (High)
$FFF7
TIM1 Channel 0 Vector (Low)
$FFF8
ICG Vector (High)
$FFF9
ICG Vector (Low)
$FFFA
IRQ Vector (High)
$FFFB
IRQ Vector (Low)
$FFFC
SWI Vector (High)
$FFFD
SWI Vector (Low)
$FFFE
Reset Vector (High)
$FFFF
Reset Vector (Low)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
39
Memory
2.5 Random-Access Memory (RAM)
Addresses $0040 through $023F are RAM locations. The location of the stack RAM is programmable.
The 16-bit stack pointer allows the stack to be anywhere in the 64-Kbyte memory space.
NOTE
For correct operation, the stack pointer must point only to RAM locations.
Within page zero are 192 bytes of RAM. Because the location of the stack RAM is programmable, all page
zero RAM locations can be used for I/O control and user data or code. When the stack pointer is moved
from its reset location at $00FF out of page zero, direct addressing mode instructions can efficiently
access all page zero RAM locations. Page zero RAM, therefore, provides ideal locations for frequently
accessed global variables.
Before processing an interrupt, the CPU uses five bytes of the stack to save the contents of the CPU
registers.
NOTE
For M6805 compatibility, the H register is not stacked.
During a subroutine call, the CPU uses two bytes of the stack to store the return address. The stack
pointer decrements during pushes and increments during pulls.
NOTE
Be careful when using nested subroutines. The CPU may overwrite data in
the RAM during a subroutine or during the interrupt stacking operation.
2.6 Flash Memory
This sub-section describes the operation of the embedded Flash memory. This memory can be read,
programmed, and erased from a single external supply. The program, erase, and read operations are
enabled through the use of an internal charge pump.
2.6.1 Functional Description
The Flash memory is an array of 15,872 bytes (7,680 bytes on MC68HC908GT8) with an additional
36 bytes of user vectors, one byte of block protection and two bytes of ICG user trim storage. An erased
bit reads as 1 and a programmed bit reads as a 0. Memory in the Flash array is organized into two rows
per page basis. The page size is 64 bytes per page and the row size is 32 bytes per row. Hence the
minimum erase page size is 64 bytes and the minimum program row size is 32 bytes. Program and erase
operation operations are facilitated through control bits in Flash control register (FLCR). Details for these
operations appear later in this section.
The address ranges for the user memory and vectors are:
• $C000–$FDFF; user memory ($E000–$FDFF on MC68HC908GT8)
• $FE08; Flash control register
• $FF7E; Flash block protect register
• $FF80; ICG user trim register (ICGTR5)
• $FF81; ICG user trim register (ICGTR3)
• $FFDC–$FFFF; these locations are reserved for user-defined interrupt and reset vectors
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
Flash Memory
2.6.2 Flash Control Register
The Flash control register (FLCR) controls Flash program and erase operations.
Address:
Read:
$FE08
Bit 7
6
5
4
0
0
0
0
0
0
0
0
Write:
Reset:
3
2
1
Bit 0
HVEN
MASS
ERASE
PGM
0
0
0
0
= Unimplemented
Figure 2-3. Flash Control Register (FLCR)
HVEN — High-Voltage Enable Bit
This read/write bit enables the charge pump to drive high voltages for program and erase operations
in the array. HVEN can only be set if either PGM = 1 or ERASE = 1 and the proper sequence for
program or erase is followed.
1 = High voltage enabled to array and charge pump on
0 = High voltage disabled to array and charge pump off
MASS — Mass Erase Control Bit
Setting this read/write bit configures the 16Kbyte Flash array for mass erase operation.
1 = MASS erase operation selected
0 = MASS erase operation unselected
ERASE — Erase Control Bit
This read/write bit configures the memory for erase operation. ERASE is interlocked with the PGM bit
such that both bits cannot be equal to 1 or set to 1 at the same time.
1 = Erase operation selected
0 = Erase operation unselected
PGM — Program Control Bit
This read/write bit configures the memory for program operation. PGM is interlocked with the ERASE
bit such that both bits cannot be equal to 1 or set to 1 at the same time.
1 = Program operation selected
0 = Program operation unselected
2.6.3 Flash Page Erase Operation
Use the following procedure to erase a page (64 bytes) of Flash memory. A page consists of 64
consecutive bytes starting from addresses $XX00, $XX40, $XX80, or $XXC0. The 36-byte user interrupt
vectors area also forms a page. Any Flash memory page can be erased alone.
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Freescale Semiconductor
41
Memory
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Set the ERASE bit and clear the MASS bit in the Flash control register.
Read the Flash block protect register.
Write any data to any Flash location within the address range of the block to be erased.
Wait for a time, tNVS (minimum 10 μs).
Set the HVEN bit.
Wait for a time, tErase (minimum 1 ms or 4 ms).
Clear the ERASE bit.
Wait for a time, tNVH (minimum 5 μs).
Clear the HVEN bit.
After time, tRCV (typical 1 μs), the memory can be accessed in read mode again.
NOTE
Programming and erasing of Flash locations cannot be performed by code
being executed from the Flash memory. While these operations must be
performed in the order as shown, but other unrelated operations may occur
between the steps.
CAUTION
A page erase of the vector page will erase the internal oscillator trim values
at $FF80 and $FF81.
In applications that require more than 1000 program/erase cycles, use the 4 ms page erase specification
to get improved long-term reliability. Any application can use this 4 ms page erase specification. However,
in applications where a Flash location will be erased and reprogrammed less than 1000 times, and speed
is important, use the 1 ms page erase specification to get a shorter cycle time.
2.6.4 Flash Mass Erase Operation
Use the following procedure to erase the entire Flash memory to read as a 1:
1. Set both the ERASE bit and the MASS bit in the Flash control register.
2. Read the Flash block protect register.
3. Write any data to any Flash address(1) within the Flash memory address range.
4. Wait for a time, tNVS (minimum 10 μs).
5. Set the HVEN bit.
6. Wait for a time, tMErase (minimum 4 ms).
7. Clear the ERASE and MASS bits.
NOTE
Mass erase is disabled whenever any block is protected (FLBPR does not
equal $FF).
8. Wait for a time, tNVHL (minimum 100 μs).
9. Clear the HVEN bit.
10. After time, tRCV (typical 1 μs), the memory can be accessed in read mode again.
NOTE
Programming and erasing of Flash locations cannot be performed by code
being executed from the Flash memory. While these operations must be
1. When in monitor mode, with security sequence failed (see 19.3.2 Security), write to the Flash block protect register instead
of any Flash address.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
Flash Memory
performed in the order as shown, but other unrelated operations may occur
between the steps.
CAUTION
A mass erase will erase the internal oscillator trim values at $FF80 and
$FF81.
2.6.5 Flash Program/Read Operation
Programming of the Flash memory is done on a row basis. A row consists of 32 consecutive bytes starting
from addresses $XX00, $XX20, $XX40, $XX60, $XX80, $XXA0, $XXC0, or $XXE0. Use the following
step-by-step procedure to program a row of Flash memory
Figure 2-4 is a flowchart of the programming algorithm.
NOTE
Only bytes which are currently $FF may be programmed.
1. Set the PGM bit. This configures the memory for program operation and enables the latching of
address and data for programming.
2. Read the Flash block protect register.
3. Write any data to any Flash location within the address range desired.
4. Wait for a time, tNVS (minimum 10 μs).
5. Set the HVEN bit.
6. Wait for a time, tPGS (minimum 5 μs).
7. Write data to the Flash address being programmed(1).
8. Wait for time, tPROG (minimum 30 μs).
9. Repeat step 7 and 8 until all desired bytes within the row are programmed.
10. Clear the PGM bit(1).
11. Wait for time, tNVH (minimum 5 μs).
12. Clear the HVEN bit.
13. After time, tRCV (typical 1 μs), the memory can be accessed in read mode again.
NOTE
The COP register at location $FFFF should not be written between steps
5-12, when the HVEN bit is set. Since this register is located at a valid Flash
address, unpredictable behavior may occur if this location is written while
HVEN is set.
This program sequence is repeated throughout the memory until all data is programmed.
NOTE
Programming and erasing of Flash locations cannot be performed by code
being executed from the Flash memory. While these operations must be
performed in the order shown, other unrelated operations may occur
between the steps. Do not exceed tPROG maximum, see 20.20 Memory
Characteristics.
1. The time between each Flash address change, or the time between the last Flash address programmed to clearing PGM
bit, must not exceed the maximum programming time, tPROG maximum.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
43
Memory
Algorithm for programming
a row (32 bytes) of FLASH memory
1
2
3
SET PGM BIT
READ THE FLASH BLOCK PROTECT REGISTER
WRITE ANY DATA TO ANY FLASH ADDRESS
WITHIN THE ROW ADDRESS RANGE DESIRED
4
5
6
7
8
WAIT FOR A TIME, tNVS
SET HVEN BIT
WAIT FOR A TIME, tPGS
WRITE DATA TO THE FLASH ADDRESS
TO BE PROGRAMMED
WAIT FOR A TIME, tPROG
COMPLETED
PROGRAMMING
THIS ROW?
Y
N
10
11
CLEAR PGM BIT
WAIT FOR A TIME, tNVH
Note:
The time between each Flash address change (step 7 to step 7),
or the time between the last Flash address programmed
to clearing PGM bit (step 7 to step 10)
must not exceed the maximum programming
time, tPROG max.
This row program algorithm assumes the row/s
to be programmed are initially erased.
12
13
CLEAR HVEN BIT
WAIT FOR A TIME, tRCV
END OF PROGRAMMING
Figure 2-4. Flash Programming Flowchart
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
Flash Memory
2.6.6 Flash Block Protection
Due to the ability of the on-board charge pump to erase and program the Flash memory in the target
application, provision is made for protecting a block of memory from unintentional erase or program
operations due to system malfunction. This protection is done by using of a Flash block protect register
(FLBPR). The FLBPR determines the range of the Flash memory which is to be protected. The range of
the protected area starts from a location defined by FLBPR and ends at the bottom of the Flash memory
($FFFF). When the memory is protected, the HVEN bit cannot be set in either ERASE or PROGRAM
operations.
NOTE
In performing a program or erase operation, the Flash block protect register
must be read after setting the PGM or ERASE bit and before asserting the
HVEN bit
When the FLBPR is program with all 0’s, the entire memory is protected from being programmed and
erased. When all the bits are erased (all 1’s), the entire memory is accessible for program and erase.
When bits within the FLBPR are programmed, they lock a block of memory, address ranges as shown in
2.6.7 Flash Block Protect Register. Once the FLBPR is programmed with a value other than $FF or $FE,
any erase or program of the FLBPR or the protected block of Flash memory is prohibited. Mass erase is
disabled whenever any block is protected (FLBPR does not equal $FF). The FLBPR itself can be erased
or programmed only with an external voltage, VTST, present on the IRQ pin. This voltage also allows entry
from reset into the monitor mode.
2.6.7 Flash Block Protect Register
The Flash block protect register (FLBPR) is implemented as a byte within the Flash memory, and
therefore can only be written during a programming sequence of the Flash memory. The value in this
register determines the starting location of the protected range within the Flash memory.
Address:
$FF7E
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
BPR7
BPR6
BPR5
BPR4
BPR3
BPR2
BPR1
BPR0
Unaffected by reset. Initial value from factory is 1.
Write to this register is by a programming sequence to the Flash memory.
Figure 2-5. Flash Block Protect Register (FLBPR)
BPR[7:0] — Flash Block Protect Bits
These eight bits represent bits [13:6] of a 16-bit memory address. Bit 15 and Bit 14 are 1s and bits [5:0]
are 0s.
The resultant 16-bit address is used for specifying the start address of the Flash memory for block
protection. The Flash is protected from this start address to the end of Flash memory, at $FFFF. With
this mechanism, the protect start address can be $XX00, $XX40, $XX80, and $XXC0 (64 bytes page
boundaries) within the Flash memory.
16-BIT MEMORY ADDRESS
START ADDRESS OF FLASH
1
BLOCK PROTECT
1
FLBPR VALUE
0
0
0
0
0
0
Figure 2-6. Flash Block Protect Start Address
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
45
Memory
Table 2-2. Examples of Protect Address Ranges
BPR[7:0]
Addresses of Protect Range
$00
The entire Flash memory is protected.
$01 (0000 0001)
$C040 (1100 0000 0100 0000) — $FFFF
$02 (0000 0010)
$C080 (1100 0000 1000 0000) — $FFFF
$03 (0000 0011)
$C0C0 (1100 0000 1100 0000) — $FFFF
$04 (0000 0100)
$C100 (1100 0001 0000 0000) — $FFFF
and so on...
$FC (1111 1100)
$FF00 (1111 1111 0000 0000) — FFFF
$FD (1111 1101)
$FF40 (1111 1111 0100 0000) — $FFFF
FLBPR and vectors are protected
$FE (1111 1110)
$FF80 (1111 1111 1000 0000) — FFFF
Vectors are protected
$FF
The entire Flash memory is not protected.
2.6.8 ICG User Trim Registers (ICGTR5 and ICGTR3)
The ICG user trim register are two normal bytes of Flash memory which are allocated for the user to store
copies of the ICG trim register (ICGTR) value. ICGTR5 is allocated for storage of the trim value when a
5-V supply is used, ICGTR3 for storage of the trim value when a 3-V supply is used. Representative trim
values are programmed into these locations by Freescale but they may be erased and reprogrammed by
the user at any time.
Storage and retrieval of data in these registers is not automatic and must be performed programmatically.
Typically, these locations are programmed by the user during an in-system calibration procedure and one
of them, depending on the application supply voltage, is subsequently used by the user’s initialization
code to configure the ICG each time following a reset.
ICGTR5 is used by the MC68HC908GT16 monitor ROM program during its initialization sequence if
monitor mode was entered while clocking from the ICG. If the contents of ICGTR5 are not $FF then the
contents are copied to ICGTR.
NOTE
The contents of ICGTR3 are not utilized by the monitor ROM program.
Address: ICGTR5, $FF80 and ICGTR3, $FF81
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
TRIM7
TRIM6
TRIM5
TRIM4
TRIM3
TRIM2
TRIM1
TRIM0
Unaffected by reset. Initial value from factory is 1.
Write to this register is by a programming sequence to the Flash memory.
Figure 2-7. ICG User Trim Registers (ICGTR5 and ICGTR3)
TRIM[7:0] — ICG Trim Factor Bits
These bits are copied by the monitor ROM program following a reset, if monitor mode was entered
while clocking from the ICG and may be copied by the user’s initialization code to the ICG trim register
(ICGTR).
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
46
Freescale Semiconductor
Flash Memory
2.6.9 Wait Mode
Putting the MCU into wait mode while the Flash is in read mode does not affect the operation of the Flash
memory directly, but there will not be any memory activity since the CPU is inactive.
The WAIT instruction should not be executed while performing a program or erase operation on the Flash,
otherwise the operation will discontinue, and the Flash will be on standby mode.
2.6.10 Stop Mode
Putting the MCU into stop mode while the Flash is in read mode does not affect the operation of the Flash
memory directly, but there will not be any memory activity since the CPU is inactive.
The STOP instruction should not be executed while performing a program or erase operation on the
Flash, otherwise the operation will discontinue, and the Flash will be on standby mode
NOTE
Standby mode is the power saving mode of the Flash module in which all
internal control signals to the Flash are inactive and the current
consumption of the Flash is at a minimum.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
47
Memory
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
Chapter 3
Analog-to-Digital Converter (ADC)
3.1 Introduction
This section describes the 8-bit analog-to-digital converter (ADC).
3.2 Features
Features of the ADC module include:
• Eight channels with multiplexed input
• Linear successive approximation with monotonicity
• 8-bit resolution
• Single or continuous conversion
• Conversion complete flag or conversion complete interrupt
• Selectable ADC clock
3.3 Functional Description
The ADC provides eight pins for sampling external sources at pins PTB7/AD7–PTB0/AD0. An analog
multiplexer allows the single ADC converter to select one of eight ADC channels as ADC voltage in
(VADIN). VADIN is converted by the successive approximation register-based analog-to-digital converter.
When the conversion is completed, ADC places the result in the ADC data register and sets a flag or
generates an interrupt. See Figure 3-2.
3.3.1 ADC Port I/O Pins
PTB7/AD7–PTB0/AD0 are general-purpose I/O (input/output) pins that share with the ADC channels. The
channel select bits define which ADC channel/port pin will be used as the input signal. The ADC overrides
the port I/O logic by forcing that pin as input to the ADC. The remaining ADC channels/port pins are
controlled by the port I/O logic and can be used as general-purpose I/O. Writes to the port register or data
direction register (DDR) will not have any affect on the port pin that is selected by the ADC. Read of a port
pin in use by the ADC will return a 0.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
49
Analog-to-Digital Converter (ADC)
8-BIT KEYBOARD
INTERRUPT MODULE
FLASH PROGRAMMING ROUTINES
ROM — 720 BYTES
USER FLASH VECTOR SPACE — 36 BYTES
PTE4/OSC1
PTE3/OSC2
INTERNAL CLOCK
GENERATOR MODULE
RST(3)
SYSTEM INTEGRATION
MODULE
IRQ(3)
SINGLE EXTERNAL
INTERRUPT MODULE
VREFH
VREFL
2-CHANNEL TIMER INTERFACE
MODULE 2
DDRA
PTD7/T2CH1(1)
PTD6/T2CH0(1)
PTD5/T1CH1(1)
PTD4/T1CH0(1)
PTD3/SPSCK(1)
PTD2/MOSI(1)
PTD1/MISO(1)
PTD0/SS(1)
PTE2
PTE1/RxD
PTE0/TxD
SERIAL PERIPHERAL
INTERFACE MODULE
MONITOR MODULE
8-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
PTC6(1)
PTC5(1)
PTC4(1)(2)
PTC3(1)(2)
PTC2(1)(2)
PTC1(1)(2)
PTC0(1)(2)
SERIAL COMMUNICATIONS
INTERFACE MODULE
COMPUTER OPERATING
PROPERLY MODULE
POWER-ON RESET
MODULE
VDD
VSS
VDDA
VSSA
2-CHANNEL TIMER INTERFACE
MODULE 1
DDRD
MONITOR ROM — 304 BYTES
PORTA
USER RAM — 512 BYTES
PORTB
DUAL VOLTAGE
LOW-VOLTAGE INHIBIT MODULE
PTB7/AD7
PTB6/AD6
PTB5/AD5
PTB4/AD4
PTB3/AD3
PTB2/AD2
PTB1/AD1
PTB0/AD0
PORTC
USER FLASH
MC68HC908GT16 — 15,872 BYTES
MC68HC908GT8 — 7,680 BYTES
PTA7/KBD7–
PTA0/KBD0(1)
PORTD
SINGLE BREAKPOINT BREAK
MODULE
DDRB
CONTROL AND STATUS
REGISTERS — 64 BYTES
DDRC
PROGRAMMABLE TIMEBASE
MODULE
ARITHMETIC/LOGIC
UNIT (ALU)
MEMORY MAP
MODULE
DDRE
CPU
REGISTERS
PORTE
INTERNAL BUS
M68HC08 CPU
SECURITY
MODULE
CONFIGURATION REGISTER 1
MODULE
CONFIGURATION REGISTER 2
MODULE
MONITOR MODE ENTRY
MODULE
1. Ports are software configurable with pullup device if input port.
2. Higher current drive port pins
3. Pin contains integrated pullup device
Figure 3-1. Block Diagram Highlighting ADC Block and Pins
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
50
Freescale Semiconductor
Functional Description
INTERNAL DATA BUS
READ DDRBx
WRITE DDRBx
DISABLE
DDRBx
RESET
WRITE PTBx
PTBx
PTBx
ADC CHANNEL x
READ PTBx
DISABLE
ADC DATA REGISTER
INTERRUPT
LOGIC
ADC
VOLTAGE IN
(VADIN)
CONVERSION
COMPLETE
CHANNEL
SELECT
ADCH4–ADCH0
VREFH
ADC
VREFL
AIEN
ADC CLOCK
COCO
CGMXCLK
BUS CLOCK
CLOCK
GENERATOR
ADIV2–ADIV0
ADICLK
Figure 3-2. ADC Block Diagram
3.3.2 ADC Port I/O Pins
PTB7/AD7–PTB0/AD0 are general-purpose I/O pins that share with the ADC channels. The channel
select bits define which ADC channel/port pin will be used as the input signal. The ADC overrides the port
I/O logic by forcing that pin as input to the ADC. The remaining ADC channels/port pins are controlled by
the port I/O logic and can be used as general-purpose I/O. Writes to the port register or data direction
register (DDR) will not have any affect on the port pin that is selected by the ADC. Read of a port pin in
use by the ADC will return a logic 0.
3.3.3 Voltage Conversion
When the input voltage to the ADC equals VREFH, the ADC converts the signal to $FF (full scale). If the
input voltage equals VREFL, the ADC converts it to $00. Input voltages between VREFH and VREFL are a
straight-line linear conversion.
NOTE
The ADC input voltage must always be greater than VSSA and less than
VDDA. VREFH must always be greater than or equal to VREFL.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
51
Analog-to-Digital Converter (ADC)
NOTE
Connect the VDDA pin to the same voltage potential as the VDD pin, and
connect the VSSA pin to the same voltage potential as the VSS pin. The
VDDA pin should be routed carefully for maximum noise immunity.
3.3.4 Conversion Time
Conversion starts after a write to the ADC status and control register (ADSCR). One conversion will take
between 16 and 17 ADC clock cycles. The ADIVx and ADICLK bits should be set to provide a 1-MHz ADC
clock frequency.
Conversion time =
16 to 17 ADC cycles
ADC frequency
Number of bus cycles = conversion time × bus frequency
3.3.5 Conversion
In continuous conversion mode, the ADC data register will be filled with new data after each conversion.
Data from the previous conversion will be overwritten whether that data has been read or not.
Conversions will continue until the ADCO bit is cleared. The COCO bit is set after the first conversion and
will stay set until the next read of the ADC data register.
In single conversion mode, conversion begins with a write to the ADSCR. Only one conversion occurs
between writes to the ADSCR.
When a conversion is in process and the ADSCR is written, the current conversion data should be
discarded to prevent an incorrect reading.
3.3.6 Accuracy and Precision
The conversion process is monotonic and has no missing codes.
3.4 Interrupts
When the AIEN bit is set, the ADC module is capable of generating CPU interrupts after each ADC
conversion. A CPU interrupt is generated if the COCO bit is at 0. The COCO bit is not used as a
conversion complete flag when interrupts are enabled.
3.5 Low-Power Modes
The WAIT and STOP instruction can put the MCU in low power-consumption standby modes.
3.5.1 Wait Mode
The ADC continues normal operation during wait mode. Any enabled CPU interrupt request from the ADC
can bring the MCU out of wait mode. If the ADC is not required to bring the MCU out of wait mode, power
down the ADC by setting ADCH4–ADCH0 bits in the ADC status and control register before executing the
WAIT instruction.
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I/O Signals
3.5.2 Stop Mode
The ADC module is inactive after the execution of a STOP instruction. Any pending conversion is aborted.
ADC conversions resume when the MCU exits stop mode after an external interrupt. Allow one
conversion cycle to stabilize the analog circuitry.
3.6 I/O Signals
The ADC module has eight pins shared with port B, PTB7/AD7–PTB0/AD0.
3.6.1 ADC Analog Power Pin (VDDA)
The ADC analog portion uses VDDA as its power pin. Connect the VDDA pin to the same voltage potential
as VDD. External filtering may be necessary to ensure clean VDDA for good results.
NOTE
For maximum noise immunity, route VDDA carefully and place bypass
capacitors as close as possible to the package.
3.6.2 ADC Analog Ground Pin (VSSA)
The ADC analog portion uses VSSA as its ground pin. Connect the VSSA pin to the same voltage potential
as VSS.
NOTE
Route VSSA cleanly to avoid any offset errors.
3.6.3 ADC Voltage Reference High Pin (VREFH)
The ADC analog portion uses VREFH as its upper voltage reference pin. The VREFH pin must be connected
to the same voltage potential as VDDA. External filtering is often necessary to ensure a clean VREFH for
good results. Any noise present on this pin will be reflected and possibly magnified in A/D conversion
values.
NOTE
For maximum noise immunity, route VREFH carefully and place bypass
capacitors as close as possible to the package. Routing VREFH close and
parallel to VREFL may improve common mode noise rejection.
3.6.4 ADC Voltage Reference Low Pin (VREFL)
The ADC analog portion uses VREFL as its lower voltage reference pin. The VREFL pin must be connected
to the same voltage potential as VSSA. External filtering is often necessary to ensure a clean VREFL for
good results. Any noise present on this pin will be reflected and possibly magnified in A/D conversion
values.
NOTE
For maximum noise immunity, route VREFL carefully and, if not connected
to VSS, place bypass capacitors as close as possible to the package.
Routing VREFH close and parallel to VREFL may improve common mode
noise rejection.
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Analog-to-Digital Converter (ADC)
3.6.5 ADC Voltage In (VADIN)
VADIN is the input voltage signal from one of the eight ADC channels to the ADC module.
3.7 I/O Registers
These I/O registers control and monitor ADC operation:
• ADC status and control register (ADSCR)
• ADC data register (ADR)
• ADC clock register (ADCLK)
3.7.1 ADC Status and Control Register
Function of the ADC status and control register (ADSCR) is described here.
Address:
$003C
Bit 7
6
5
4
3
2
1
Bit 0
AIEN
ADCO
ADCH4
ADCH3
ADCH2
ADCH1
ADCH0
0
1
1
1
1
1
Read:
COCO
Write:
R
Reset:
0
0
R
= Reserved
Figure 3-3. ADC Status and Control Register (ADSCR)
COCO — Conversions Complete Bit
In non-interrupt mode (AIEN = 0), COCO is a read-only bit that is set at the end of each conversion.
COCO will stay set until cleared by a read of the ADC data register. Reset clears this bit.
In interrupt mode (AIEN = 1), COCO is a read-only bit that is not set at the end of a conversion. It
always reads as a 0.
1 = Conversion completed (AIEN = 0)
0 = Conversion not completed (AIEN = 0) or CPU interrupt enabled (AIEN = 1)
NOTE
The write function of the COCO bit is reserved. When writing to the ADSCR
register, always have a 0 in the COCO bit position.
AIEN — ADC Interrupt Enable Bit
When this bit is set, an interrupt is generated at the end of an ADC conversion. The interrupt signal is
cleared when the data register is read or the status/control register is written. Reset clears the AIEN bit.
1 = ADC interrupt enabled
0 = ADC interrupt disabled
ADCO — ADC Continuous Conversion Bit
When set, the ADC will convert samples continuously and update the ADR register at the end of each
conversion. Only one conversion is completed between writes to the ADSCR when this bit is cleared.
Reset clears the ADCO bit.
1 = Continuous ADC conversion
0 = One ADC conversion
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I/O Registers
ADCH4–ADCH0 — ADC Channel Select Bits
ADCH4–ADCH0 form a 5-bit field which is used to select one of 16 ADC channels. Only eight
channels, AD7–AD0, are available on this MCU. The channels are detailed in Table 3-1. Care should
be taken when using a port pin as both an analog and digital input simultaneously to prevent switching
noise from corrupting the analog signal. See Table 3-1.
The ADC subsystem is turned off when the channel select bits are all set to 1. This feature allows for
reduced power consumption for the MCU when the ADC is not being used.
NOTE
Recovery from the disabled state requires one conversion cycle to stabilize.
The voltage levels supplied from internal reference nodes, as specified in
Table 3-1, are used to verify the operation of the ADC converter both in production test and for user
applications.
Table 3-1. Mux Channel Select(1)
ADCH4
ADCH3
ADCH2
ADCH1
ADCH0
Input Select
0
0
0
0
0
PTB0/AD0
0
0
0
0
1
PTB1/AD1
0
0
0
1
0
PTB1/AD2
0
0
0
1
1
PTB2/AD3
0
0
1
0
0
PTB4/AD4
0
0
1
0
1
PTB5/AD5
0
0
1
1
0
PTB6/AD6
0
0
1
1
1
PTB7/AD7
0
↓
1
1
↓
1
0
↓
1
0
↓
0
0
↓
0
Reserved
1
1
1
0
1
VREFH
1
1
1
1
0
VREFL
1
1
1
1
1
ADC power off
1. If any unused channels are selected, the resulting ADC conversion will be unknown or
reserved.
3.7.2 ADC Data Register
One 8-bit result register, ADC data register (ADR), is provided. This register is updated each time an ADC
conversion completes.
Address:
Read:
$003D
Bit 7
6
5
4
3
2
1
Bit 0
AD7
AD6
AD5
AD4
AD3
AD2
AD1
AD0
0
0
0
0
0
0
0
0
Write:
Reset:
= Unimplemented
Figure 3-4. ADC Data Register (ADR)
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Analog-to-Digital Converter (ADC)
3.7.3 ADC Clock Register
The ADC clock register (ADCLK) selects the clock frequency for the ADC.
Address:
Read:
Write:
Reset:
$003E
Bit 7
6
5
4
ADIV2
ADIV1
ADIV0
ADICLK
0
0
0
0
3
2
1
Bit 0
0
0
0
0
0
0
0
0
= Unimplemented
Figure 3-5. ADC Clock Register (ADCLK)
ADIV2–ADIV0 — ADC Clock Prescaler Bits
ADIV2–ADIV0 form a 3-bit field which selects the divide ratio used by the ADC to generate the internal
ADC clock. Table 3-2 shows the available clock configurations. The ADC clock should be set to
approximately 1 MHz.
Table 3-2. ADC Clock Divide Ratio
ADIV2
ADIV1
ADIV0
0
0
0
ADC input clock ÷ 1
0
0
1
ADC input clock ÷ 2
0
1
0
ADC input clock ÷ 4
0
1
1
ADC input clock ÷ 8
1
(1)
X(1)
ADC input clock ÷ 16
X
ADC Clock Rate
1. X = Don’t care
ADICLK — ADC Input Clock Select Bit
ADICLK selects either the bus clock or the oscillator output clock (CGMXCLK) as the input clock
source to generate the internal ADC clock. Reset selects CGMXCLK as the ADC clock source.
1 = Internal bus clock
0 = Oscillator output clock (CGMXCLK)
The ADC requires a clock rate of approximately 1 MHz for correct operation. If the selected clock source
is not fast enough, the ADC will generate incorrect conversions. See 20.16 ADC Characteristics.
fADIC =
fCGMXCLK or bus frequency
ADIV[2:0]
≅ 1 MHz
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Chapter 4
Configuration Register (CONFIG)
4.1 Introduction
This section describes the configuration registers, CONFIG1 and CONFIG2. The configuration registers
enable or disable these options:
• Stop mode recovery time (32 CGMXCLK cycles or 4096 CGMXCLK cycles)
• COP timeout period (262,128 or 8176 COPCLK cycles)
• STOP instruction
• Computer operating properly module (COP)
• Low-voltage inhibit (LVI) module control and voltage trip point selection
• Enable/disable the oscillator (OSC) during stop mode
• External clock, external crystal, or ICG clock source
4.2 Functional Description
The configuration registers are used in the initialization of various options. The configuration registers can
be written once after each reset. All of the configuration register bits are cleared during reset. Since the
various options affect the operation of the microcontroller unit (MCU), it is recommended that these
registers be written immediately after reset. The configuration registers are located at $001E and $001F
and may be read at anytime.
NOTE
On a Flash device, the options except LVI5OR3 are one-time writable by
the user after each reset. The LVI5OR3 bit is one-time writable by the user
only after each POR (power-on reset). The CONFIG registers are not in the
Flash memory but are special registers containing one-time writable
latches after each reset. Upon a reset, the CONFIG registers default to
predetermined settings as shown in Figure 4-1 and Figure 4-2.
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Configuration Register (CONFIG)
Address:
Read:
$001E
Bit 7
6
0
0
5
0
3
2
EXTXTALEN EXTSLOW EXTCLKEN
Write:
Reset:
4
0
0
= Unimplemented
0
0
R
= Reserved
0
1
Bit 0
OSCENINSTOP
R
0
0
0
Figure 4-1. Configuration Register 2 (CONFIG2)
Address:
Read:
Write:
Reset:
$001F
Bit 7
6
5
4
3
2
1
Bit 0
COPRS
LVISTOP
LVIRSTD
LVIPWRD
LVI5OR3
SSREC
STOP
COPD
0
0
0
0
See Note
0
0
0
Note: LVI5OR3 bit is only reset via POR (power-on reset)
Figure 4-2. Configuration Register 1 (CONFIG1)
EXTXTALEN — External Crystal Enable Bit
EXTXTALEN enables the external oscillator circuits to be configured for a crystal configuration where
the PTE4/OSC1 and PTE3/OSC2 pins are the connections for an external crystal.
Clearing the EXTXTALEN bit (default setting) allows the PTE3/OSC2 pin to function as a
general-purpose I/O pin. Refer to Table 4-1 for configuration options for the external source. See
Chapter 7 Internal Clock Generator (ICG) Module) for a more detailed description of the external clock
operation.
EXTXTALEN, when set, also configures the clock monitor to expect an external clock source in the
valid range of crystals (30 kHz to 100 kHz or 1 MHz to 8 MHz). When EXTXTALEN is clear, the clock
monitor will expect an external clock source in the valid range for externally generated clocks when
using the clock monitor (60 Hz to 32 MHz).
EXTXTALEN, when set, also configures the external clock stabilization divider in the clock monitor for
a 4096-cycle timeout to allow the proper stabilization time for a crystal. When EXTXTALEN is clear,
the stabilization divider is configured to 16 cycles since an external clock source does not need a
startup time.
1 = Allows PTE3/OSC2 to be an external crystal connection.
0 = PTE3/OSC2 functions as an I/O port pin (default).
EXTSLOW — Slow External Crystal Enable Bit
The EXTSLOW bit has two functions. It configures the ICG module for a fast (1 MHz to 8 MHz) or slow
(30 kHz to 100 kHz) speed crystal. The option also configures the clock monitor operation in the ICG
module to expect an external frequency higher (307.2 kHz to 32 MHz) or lower (60 Hz to 307.2 kHz)
than the base frequency of the internal oscillator. See Chapter 7 Internal Clock Generator (ICG)
Module).
1 = ICG set for slow external crystal operation
0 = ICG set for fast external crystal operation
NOTE
This bit does not function without setting the EXTCLKEN bit also.
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Functional Description
EXTCLKEN — External Clock Enable Bit
EXTCLKEN enables an external clock source or crystal/ceramic resonator to be used as a clock input.
Setting this bit enables PTE4/OSC1 pin to be a clock input pin. Clearing this bit (default setting) allows
the PTE4/OSC1 and PTE3/OSC2 pins to function as a general-purpose input/output (I/O) pin. Refer
to Table 4-1 for configuration options for the external source. See Chapter 7 Internal Clock Generator
(ICG) Module) for a more detailed description of the external clock operation.
1 = Allows PTE4/OSC1 to be an external clock connection
0 = PTE4/OSC1 and PTE3/OSC2 function as I/O port pins (default).
Table 4-1. External Clock Option Settings
External Clock
Configuration Bits
Pin
Function
Description
EXTCLKEN
EXTXTALEN
PTE4/OSC1
PTE3/OSC2
0
0
PTE4
PTE3
Default setting — external oscillator disabled
0
1
PTE4
PTE3
External oscillator disabled since EXTCLKEN not set
1
0
OSC1
PTE3
External oscillator configured for an external clock source
input (square wave) on OSC1
1
1
OSC1
OSC2
External oscillator configured for an external crystal
configuration on OSC1 and OSC2. System will also
operate with square-wave clock source in OSC1.
OSCENINSTOP — Oscillator Enable In Stop Mode Bit
OSCENINSTOP, when set, will enable the internal clock generator module to continue to generate
clocks (either internal, ICLK, or external, ECLK) in stop mode. See Chapter 7 Internal Clock Generator
(ICG) Module). This function is used to keep the timebase running while the rest of the microcontroller
stops. See Chapter 17 Timebase Module (TBM). When clear, all clock generation will cease and both
ICLK and ECLK will be forced low during stop mode. The default state for this option is clear, disabling
the ICG in stop mode.
1 = Oscillator enabled to operate during stop mode
0 = Oscillator disabled during stop mode (default)
NOTE
This bit has the same functionality as the OSCSTOPENB CONFIG bit in
MC68HC908GP32 and MC68HC908GR8 parts.
COPRS — COP Rate Select Bit
COPD selects the COP timeout period. Reset clears COPRS. See Chapter 5 Computer Operating
Properly (COP) Module
1 = COP timeout period = 8176 COPCLK cycles
0 = COP timeout period = 262,128 COPCLK cycles
LVISTOP — LVI Enable in Stop Mode Bit
When the LVIPWRD bit is clear, setting the LVISTOP bit enables the LVI to operate during stop mode.
Reset clears LVISTOP.
1 = LVI enabled during stop mode
0 = LVI disabled during stop mode
LVIRSTD — LVI Reset Disable Bit
LVIRSTD disables the reset signal from the LVI module. See Chapter 10 Low-Voltage Inhibit (LVI).
1 = LVI module resets disabled
0 = LVI module resets enabled
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Configuration Register (CONFIG)
LVIPWRD — LVI Power Disable Bit
LVIPWRD disables the LVI module. See Chapter 10 Low-Voltage Inhibit (LVI).
1 = LVI module power disabled
0 = LVI module power enabled
LVI5OR3 — LVI 5-V or 3-V Operating Mode Bit
LVI5OR3 selects the voltage operating mode of the LVI module. See Chapter 10 Low-Voltage Inhibit
(LVI) The voltage mode selected for the LVI should match the operating VDD. See Chapter 20
Electrical Specifications for the LVI’s voltage trip points for each of the modes.
1 = LVI operates in 5-V mode.
0 = LVI operates in 3-V mode.
NOTE
The LVI5OR3 bit is cleared by a power-on reset (POR) only. Other resets
will leave this bit unaffected.
SSREC — Short Stop Recovery Bit
SSREC enables the CPU to exit stop mode with a delay of 32 CGMXCLK cycles instead of a
4096-CGMXCLK cycle delay.
1 = Stop mode recovery after 32 CGMXCLK cycles
0 = Stop mode recovery after 4096 CGMXCLCK cycles
NOTE
Exiting stop mode by an LVI reset will result in the long stop recovery.
The short stop recovery delay can be enabled when using the internal oscillator, a crystal, or a ceramic
resonator and the OSCENINSTOP bit is set. The short stop recovery delay can be enabled when an
external oscillator is used, regardless of the OSCENINSTOP setting.
The short stop recovery delay must be disabled (SSREC = 0) when the OSCENINSTOP bit is cleared.
STOP — STOP Instruction Enable Bit
STOP enables the STOP instruction.
1 = STOP instruction enabled
0 = STOP instruction treated as illegal opcode
COPD — COP Disable Bit
COPD disables the COP module. See Chapter 5 Computer Operating Properly (COP) Module.
1 = COP module disabled
0 = COP module enabled
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Chapter 5
Computer Operating Properly (COP) Module
5.1 Introduction
The computer operating properly (COP) module contains a free-running counter that generates a reset if
allowed to overflow. The COP module helps software recover from runaway code. Prevent a COP reset
by clearing the COP counter periodically. The COP module can be disabled through the COPD bit in the
CONFIG register.
5.2 Functional Description
Figure 5-1 shows the structure of the COP module.
SIM MODULE
RESET VECTOR FETCH
RESET STATUS REGISTER
COP TIMEOUT
CLEAR STAGES 5–12
CLEAR ALL STAGES
INTERNAL RESET SOURCES
SIM RESET CIRCUIT
12-BIT SIM COUNTER
COPCLK
COPCTL WRITE
COP CLOCK
COP MODULE
6-BIT COP COUNTER
COPEN (FROM SIM)
COPD (FROM CONFIG1)
RESET
CLEAR
COP COUNTER
COPCTL WRITE
COP RATE SELECT
(COPRS FROM CONFIG1)
Figure 5-1. COP Block Diagram
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Computer Operating Properly (COP) Module
The COP counter is a free-running 6-bit counter preceded by a 12-bit prescaler counter. If not cleared by
software, the COP counter overflows and generates an asynchronous reset after 262,128 or 8176
COPCLK cycles, depending on the state of the COP rate select bit, COPRS, in the configuration register.
With a 8176 COPCLK cycle overflow option, a 32.768-kHz crystal gives a COP timeout period of 250 ms.
Writing any value to location $FFFF before an overflow occurs prevents a COP reset by clearing the COP
counter and stages 12 through 5 of the prescaler.
NOTE
Service the COP immediately after reset and before entering or after exiting
stop mode to guarantee the maximum time before the first COP counter
overflow.
A COP reset pulls the RST pin low for 32 COPCLK cycles and sets the COP bit in the reset status register
(RSR).
In monitor mode, the COP is disabled if the RST pin or the IRQ1 is held at VTST. During the break state,
VTST on the RST pin disables the COP.
NOTE
Place COP clearing instructions in the main program and not in an interrupt
subroutine. Such an interrupt subroutine could keep the COP from
generating a reset even while the main program is not working properly.
5.3 I/O Signals
The following paragraphs describe the signals shown in Figure 5-1.
5.3.1 COPCLK
COPCLK is a clock generated by the clock selection circuit in the internal clock generator (ICG). See 7.3.5
Clock Selection Circuit for more details.
5.3.2 STOP Instruction
The STOP instruction clears the COP prescaler.
5.3.3 COPCTL Write
Writing any value to the COP control register (COPCTL) (see 5.4 COP Control Register) clears the COP
counter and clears bits 12 through 5 of the prescaler. Reading the COP control register returns the low
byte of the reset vector.
5.3.4 Power-On Reset
The power-on reset (POR) circuit clears the COP prescaler 4096 CGMXCLK cycles after power-up.
5.3.5 Internal Reset
An internal reset clears the COP prescaler and the COP counter.
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COP Control Register
5.3.6 Reset Vector Fetch
A reset vector fetch occurs when the vector address appears on the data bus. A reset vector fetch clears
the COP prescaler.
5.3.7 COPD (COP Disable)
The COPD signal reflects the state of the COP disable bit (COPD) in the configuration register. See
Chapter 4 Configuration Register (CONFIG).
5.3.8 COPRS (COP Rate Select)
The COPRS signal reflects the state of the COP rate select bit (COPRS) in the configuration register. See
Chapter 4 Configuration Register (CONFIG).
5.4 COP Control Register
The COP control register is located at address $FFFF and overlaps the reset vector. Writing any value to
$FFFF clears the COP counter and starts a new timeout period. Reading location $FFFF returns the low
byte of the reset vector.
Address: $FFFF
Bit 7
6
5
4
3
Read:
Low byte of reset vector
Write:
Clear COP counter
Reset:
Unaffected by reset
2
1
Bit 0
Figure 5-2. COP Control Register (COPCTL)
5.5 Interrupts
The COP does not generate central processor unit (CPU) interrupt requests.
5.6 Monitor Mode
When monitor mode is entered with VTST on the IRQ pin, the COP is disabled as long as VTST remains
on the IRQ pin or the RST pin. When monitor mode is entered by having blank reset vectors and not
having VTST on the IRQ pin, the COP is automatically disabled until a POR occurs.
5.7 Low-Power Modes
The WAIT and STOP instructions put the microcontroller unit (MCU) in low power-consumption standby
modes.
5.7.1 Wait Mode
The COP remains active during wait mode. To prevent a COP reset during wait mode, periodically clear
the COP counter in a CPU interrupt routine.
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Computer Operating Properly (COP) Module
5.7.2 Stop Mode
Stop mode turns off the COPCLK input to the COP and clears the COP prescaler. Service the COP
immediately before entering or after exiting stop mode to ensure a full COP timeout period after entering
or exiting stop mode.
To prevent inadvertently turning off the COP with a STOP instruction, a configuration option is available
that disables the STOP instruction. When the STOP bit in the configuration register has the STOP
instruction is disabled, execution of a STOP instruction results in an illegal opcode reset.
5.8 COP Module During Break Mode
The COP is disabled during a break interrupt when VTST is present on the RST pin.
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Chapter 6
Central Processor Unit (CPU)
6.1 Introduction
The M68HC08 CPU (central processor unit) is an enhanced and fully object-code-compatible version of
the M68HC05 CPU. The CPU08 Reference Manual (document order number CPU08RM/AD) contains a
description of the CPU instruction set, addressing modes, and architecture.
6.2 Features
Features of the CPU include:
• Object code fully upward-compatible with M68HC05 Family
• 16-bit stack pointer with stack manipulation instructions
• 16-bit index register with x-register manipulation instructions
• 8-MHz CPU internal bus frequency
• 64-Kbyte program/data memory space
• 16 addressing modes
• Memory-to-memory data moves without using accumulator
• Fast 8-bit by 8-bit multiply and 16-bit by 8-bit divide instructions
• Enhanced binary-coded decimal (BCD) data handling
• Modular architecture with expandable internal bus definition for extension of addressing range
beyond 64 Kbytes
• Low-power stop and wait modes
6.3 CPU Registers
Figure 6-1 shows the five CPU registers. CPU registers are not part of the memory map.
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Central Processor Unit (CPU)
0
7
ACCUMULATOR (A)
0
15
H
X
INDEX REGISTER (H:X)
15
0
STACK POINTER (SP)
15
0
PROGRAM COUNTER (PC)
7
0
V 1 1 H I N Z C
CONDITION CODE REGISTER (CCR)
CARRY/BORROW FLAG
ZERO FLAG
NEGATIVE FLAG
INTERRUPT MASK
HALF-CARRY FLAG
TWO’S COMPLEMENT OVERFLOW FLAG
Figure 6-1. CPU Registers
6.3.1 Accumulator
The accumulator is a general-purpose 8-bit register. The CPU uses the accumulator to hold operands and
the results of arithmetic/logic operations.
Bit 7
6
5
4
3
2
1
Bit 0
Read:
Write:
Reset:
Unaffected by reset
Figure 6-2. Accumulator (A)
6.3.2 Index Register
The 16-bit index register allows indexed addressing of a 64-Kbyte memory space. H is the upper byte of
the index register, and X is the lower byte. H:X is the concatenated 16-bit index register.
In the indexed addressing modes, the CPU uses the contents of the index register to determine the
conditional address of the operand.
The index register can serve also as a temporary data storage location.
Bit
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
Bit
0
0
0
0
0
0
0
0
0
X
X
X
X
X
X
X
X
Read:
Write:
Reset:
X = Indeterminate
Figure 6-3. Index Register (H:X)
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CPU Registers
6.3.3 Stack Pointer
The stack pointer is a 16-bit register that contains the address of the next location on the stack. During a
reset, the stack pointer is preset to $00FF. The reset stack pointer (RSP) instruction sets the least
significant byte to $FF and does not affect the most significant byte. The stack pointer decrements as data
is pushed onto the stack and increments as data is pulled from the stack.
In the stack pointer 8-bit offset and 16-bit offset addressing modes, the stack pointer can function as an
index register to access data on the stack. The CPU uses the contents of the stack pointer to determine
the conditional address of the operand.
Bit
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
Bit
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
Read:
Write:
Reset:
Figure 6-4. Stack Pointer (SP)
NOTE
The location of the stack is arbitrary and may be relocated anywhere in
random-access memory (RAM). Moving the SP out of page 0 ($0000 to
$00FF) frees direct address (page 0) space. For correct operation, the
stack pointer must point only to RAM locations.
6.3.4 Program Counter
The program counter is a 16-bit register that contains the address of the next instruction or operand to be
fetched.
Normally, the program counter automatically increments to the next sequential memory location every
time an instruction or operand is fetched. Jump, branch, and interrupt operations load the program
counter with an address other than that of the next sequential location.
During reset, the program counter is loaded with the reset vector address located at $FFFE and $FFFF.
The vector address is the address of the first instruction to be executed after exiting the reset state.
Bit
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
Bit
0
Read:
Write:
Reset:
Loaded with vector from $FFFE and $FFFF
Figure 6-5. Program Counter (PC)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
67
Central Processor Unit (CPU)
6.3.5 Condition Code Register
The 8-bit condition code register contains the interrupt mask and five flags that indicate the results of the
instruction just executed. Bits 6 and 5 are set permanently to 1. The following paragraphs describe the
functions of the condition code register.
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
V
1
1
H
I
N
Z
C
X
1
1
X
1
X
X
X
X = Indeterminate
Figure 6-6. Condition Code Register (CCR)
V — Overflow Flag
The CPU sets the overflow flag when a two's complement overflow occurs. The signed branch
instructions BGT, BGE, BLE, and BLT use the overflow flag.
1 = Overflow
0 = No overflow
H — Half-Carry Flag
The CPU sets the half-carry flag when a carry occurs between accumulator bits 3 and 4 during an
add-without-carry (ADD) or add-with-carry (ADC) operation. The half-carry flag is required for
binary-coded decimal (BCD) arithmetic operations. The DAA instruction uses the states of the H and
C flags to determine the appropriate correction factor.
1 = Carry between bits 3 and 4
0 = No carry between bits 3 and 4
I — Interrupt Mask
When the interrupt mask is set, all maskable CPU interrupts are disabled. CPU interrupts are enabled
when the interrupt mask is cleared. When a CPU interrupt occurs, the interrupt mask is set
automatically after the CPU registers are saved on the stack, but before the interrupt vector is fetched.
1 = Interrupts disabled
0 = Interrupts enabled
NOTE
To maintain M6805 Family compatibility, the upper byte of the index
register (H) is not stacked automatically. If the interrupt service routine
modifies H, then the user must stack and unstack H using the PSHH and
PULH instructions.
After the I bit is cleared, the highest-priority interrupt request is serviced first.
A return-from-interrupt (RTI) instruction pulls the CPU registers from the stack and restores the
interrupt mask from the stack. After any reset, the interrupt mask is set and can be cleared only by the
clear interrupt mask software instruction (CLI).
N — Negative Flag
The CPU sets the negative flag when an arithmetic operation, logic operation, or data manipulation
produces a negative result, setting bit 7 of the result.
1 = Negative result
0 = Non-negative result
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
68
Freescale Semiconductor
Arithmetic/Logic Unit (ALU)
Z — Zero Flag
The CPU sets the zero flag when an arithmetic operation, logic operation, or data manipulation
produces a result of $00.
1 = Zero result
0 = Non-zero result
C — Carry/Borrow Flag
The CPU sets the carry/borrow flag when an addition operation produces a carry out of bit 7 of the
accumulator or when a subtraction operation requires a borrow. Some instructions — such as bit test
and branch, shift, and rotate — also clear or set the carry/borrow flag.
1 = Carry out of bit 7
0 = No carry out of bit 7
6.4 Arithmetic/Logic Unit (ALU)
The ALU performs the arithmetic and logic operations defined by the instruction set.
Refer to the CPU08 Reference Manual (document order number CPU08RM/AD) for a description of the
instructions and addressing modes and more detail about the architecture of the CPU.
6.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
6.5.1 Wait Mode
The WAIT instruction:
• Clears the interrupt mask (I bit) in the condition code register, enabling interrupts. After exit from
wait mode by interrupt, the I bit remains clear. After exit by reset, the I bit is set.
• Disables the CPU clock
6.5.2 Stop Mode
The STOP instruction:
• Clears the interrupt mask (I bit) in the condition code register, enabling external interrupts. After
exit from stop mode by external interrupt, the I bit remains clear. After exit by reset, the I bit is set.
• Disables the CPU clock
After exiting stop mode, the CPU clock begins running after the oscillator stabilization delay.
6.6 CPU During Break Interrupts
If a break module is present on the MCU, the CPU starts a break interrupt by:
• Loading the instruction register with the SWI instruction
• Loading the program counter with $FFFC:$FFFD or with $FEFC:$FEFD in monitor mode
The break interrupt begins after completion of the CPU instruction in progress. If the break address
register match occurs on the last cycle of a CPU instruction, the break interrupt begins immediately.
A return-from-interrupt instruction (RTI) in the break routine ends the break interrupt and returns the MCU
to normal operation if the break interrupt has been deasserted.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
69
Central Processor Unit (CPU)
6.7 Instruction Set Summary
Table 6-1 provides a summary of the M68HC08 instruction set.
ADC #opr
ADC opr
ADC opr
ADC opr,X
ADC opr,X
ADC ,X
ADC opr,SP
ADC opr,SP
ADD #opr
ADD opr
ADD opr
ADD opr,X
ADD opr,X
ADD ,X
ADD opr,SP
ADD opr,SP
V H I N Z C
A ← (A) + (M) + (C)
Add with Carry
A ← (A) + (M)
Add without Carry
IMM
DIR
EXT
IX2
–
IX1
IX
SP1
SP2
A9
B9
C9
D9
E9
F9
9EE9
9ED9
ii
dd
hh ll
ee ff
ff
IMM
DIR
EXT
– IX2
IX1
IX
SP1
SP2
AB
BB
CB
DB
EB
FB
9EEB
9EDB
ii
dd
hh ll
ee ff
ff
ff
ee ff
ff
ee ff
Cycles
Effect
on CCR
Description
Operand
Operation
Opcode
Source
Form
Address
Mode
Table 6-1. Instruction Set Summary (Sheet 1 of 6)
2
3
4
4
3
2
4
5
2
3
4
4
3
2
4
5
AIS #opr
Add Immediate Value (Signed) to SP
SP ← (SP) + (16 « M)
– – – – – – IMM
A7
ii
2
AIX #opr
Add Immediate Value (Signed) to H:X
H:X ← (H:X) + (16 « M)
– – – – – – IMM
AF
ii
2
A ← (A) & (M)
IMM
DIR
EXT
IX2
0 – – – IX1
IX
SP1
SP2
A4
B4
C4
D4
E4
F4
9EE4
9ED4
ii
dd
hh ll
ee ff
ff
2
3
4
4
3
2
4
5
DIR
INH
INH
– – IX1
IX
SP1
38 dd
48
58
68 ff
78
9E68 ff
4
1
1
4
3
5
DIR
INH
– – INH
IX1
IX
SP1
– – – – – – REL
37
47
57
67
77
9E67
24
ff
rr
4
1
1
4
3
5
3
11
13
15
17
19
1B
1D
1F
dd
dd
dd
dd
dd
dd
dd
dd
4
4
4
4
4
4
4
4
AND #opr
AND opr
AND opr
AND opr,X
AND opr,X
AND ,X
AND opr,SP
AND opr,SP
ASL opr
ASLA
ASLX
ASL opr,X
ASL ,X
ASL opr,SP
Logical AND
Arithmetic Shift Left
(Same as LSL)
ASR opr
ASRA
ASRX
ASR opr,X
ASR opr,X
ASR opr,SP
Arithmetic Shift Right
BCC rel
Branch if Carry Bit Clear
C
0
b7
b0
C
b7
b0
PC ← (PC) + 2 + rel ? (C) = 0
Mn ← 0
DIR (b0)
DIR (b1)
DIR (b2)
– – – – – – DIR (b3)
DIR (b4)
DIR (b5)
DIR (b6)
DIR (b7)
ff
ee ff
dd
ff
BCLR n, opr
Clear Bit n in M
BCS rel
Branch if Carry Bit Set (Same as BLO)
PC ← (PC) + 2 + rel ? (C) = 1
– – – – – – REL
25
rr
3
BEQ rel
Branch if Equal
PC ← (PC) + 2 + rel ? (Z) = 1
– – – – – – REL
27
rr
3
Branch if Greater Than or Equal To
– – – – – – REL
PC ← (PC) + 2 + rel ? (N ⊕ V) = 0
(Signed Operands)
Branch if Greater Than (Signed
PC ← (PC) + 2 + rel ? (Z) | (N ⊕ V) = 0 – – – – – – REL
Operands)
90
rr
3
92
rr
3
BGE opr
BGT opr
BHCC rel
Branch if Half Carry Bit Clear
PC ← (PC) + 2 + rel ? (H) = 0
– – – – – – REL
28
rr
BHCS rel
Branch if Half Carry Bit Set
PC ← (PC) + 2 + rel ? (H) = 1
– – – – – – REL
29
rr
BHI rel
Branch if Higher
PC ← (PC) + 2 + rel ? (C) | (Z) = 0
– – – – – – REL
22
rr
3
3
3
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
70
Freescale Semiconductor
Instruction Set Summary
Effect
on CCR
V H I N Z C
Cycles
Description
Operand
Operation
Opcode
Source
Form
Address
Mode
Table 6-1. Instruction Set Summary (Sheet 2 of 6)
Branch if Higher or Same
(Same as BCC)
PC ← (PC) + 2 + rel ? (C) = 0
– – – – – – REL
BIH rel
Branch if IRQ Pin High
PC ← (PC) + 2 + rel ? IRQ = 1
– – – – – – REL
2F
rr
3
BIL rel
Branch if IRQ Pin Low
PC ← (PC) + 2 + rel ? IRQ = 0
– – – – – – REL
2E
rr
3
(A) & (M)
IMM
DIR
EXT
0 – – – IX2
IX1
IX
SP1
SP2
A5
B5
C5
D5
E5
F5
9EE5
9ED5
ii
dd
hh ll
ee ff
ff
ff
ee ff
2
3
4
4
3
2
4
5
rr
3
BHS rel
BIT #opr
BIT opr
BIT opr
BIT opr,X
BIT opr,X
BIT ,X
BIT opr,SP
BIT opr,SP
Bit Test
PC ← (PC) + 2 + rel ? (Z) | (N ⊕ V) = 1 – – – – – – REL
24
rr
3
BLO rel
Branch if Less Than or Equal To
(Signed Operands)
Branch if Lower (Same as BCS)
PC ← (PC) + 2 + rel ? (C) = 1
– – – – – – REL
25
rr
3
BLS rel
Branch if Lower or Same
PC ← (PC) + 2 + rel ? (C) | (Z) = 1
– – – – – – REL
23
rr
3
BLE opr
93
BLT opr
Branch if Less Than (Signed Operands)
PC ← (PC) + 2 + rel ? (N ⊕ V) =1
– – – – – – REL
91
rr
3
BMC rel
Branch if Interrupt Mask Clear
PC ← (PC) + 2 + rel ? (I) = 0
– – – – – – REL
2C
rr
3
BMI rel
Branch if Minus
PC ← (PC) + 2 + rel ? (N) = 1
– – – – – – REL
2B
rr
3
BMS rel
Branch if Interrupt Mask Set
PC ← (PC) + 2 + rel ? (I) = 1
– – – – – – REL
2D
rr
3
BNE rel
Branch if Not Equal
PC ← (PC) + 2 + rel ? (Z) = 0
– – – – – – REL
26
rr
3
BPL rel
Branch if Plus
PC ← (PC) + 2 + rel ? (N) = 0
– – – – – – REL
2A
rr
3
BRA rel
Branch Always
PC ← (PC) + 2 + rel
– – – – – – REL
20
rr
3
DIR (b0)
DIR (b1)
DIR (b2)
DIR (b3)
– – – – – DIR (b4)
DIR (b5)
DIR (b6)
DIR (b7)
01
03
05
07
09
0B
0D
0F
dd rr
dd rr
dd rr
dd rr
dd rr
dd rr
dd rr
dd rr
5
5
5
5
5
5
5
5
– – – – – – REL
DIR (b0)
DIR (b1)
DIR (b2)
DIR (b3)
– – – – –
DIR (b4)
DIR (b5)
DIR (b6)
DIR (b7)
21
00
02
04
06
08
0A
0C
0E
rr
dd rr
dd rr
dd rr
dd rr
dd rr
dd rr
dd rr
dd rr
3
DIR (b0)
DIR (b1)
DIR (b2)
– – – – – – DIR (b3)
DIR (b4)
DIR (b5)
DIR (b6)
DIR (b7)
10
12
14
16
18
1A
1C
1E
dd
dd
dd
dd
dd
dd
dd
dd
4
4
4
4
4
4
4
4
PC ← (PC) + 2; push (PCL)
SP ← (SP) – 1; push (PCH)
SP ← (SP) – 1
PC ← (PC) + rel
– – – – – – REL
AD
rr
4
PC ← (PC) + 3 + rel ? (A) – (M) = $00
PC ← (PC) + 3 + rel ? (A) – (M) = $00
PC ← (PC) + 3 + rel ? (X) – (M) = $00
PC ← (PC) + 3 + rel ? (A) – (M) = $00
PC ← (PC) + 2 + rel ? (A) – (M) = $00
PC ← (PC) + 4 + rel ? (A) – (M) = $00
DIR
IMM
– – – – – – IMM
IX1+
IX+
SP1
31
41
51
61
71
9E61
dd rr
ii rr
ii rr
ff rr
rr
ff rr
5
4
4
5
4
6
C←0
– – – – – 0 INH
98
1
I←0
– – 0 – – – INH
9A
2
BRCLR n,opr,rel Branch if Bit n in M Clear
BRN rel
Branch Never
BRSET n,opr,rel Branch if Bit n in M Set
BSET n,opr
Set Bit n in M
BSR rel
Branch to Subroutine
CBEQ opr,rel
CBEQA #opr,rel
CBEQX #opr,rel Compare and Branch if Equal
CBEQ opr,X+,rel
CBEQ X+,rel
CBEQ opr,SP,rel
CLC
Clear Carry Bit
CLI
Clear Interrupt Mask
PC ← (PC) + 3 + rel ? (Mn) = 0
PC ← (PC) + 2
PC ← (PC) + 3 + rel ? (Mn) = 1
Mn ← 1
5
5
5
5
5
5
5
5
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
71
Central Processor Unit (CPU)
CLR opr
CLRA
CLRX
CLRH
CLR opr,X
CLR ,X
CLR opr,SP
CMP #opr
CMP opr
CMP opr
CMP opr,X
CMP opr,X
CMP ,X
CMP opr,SP
CMP opr,SP
COM opr
COMA
COMX
COM opr,X
COM ,X
COM opr,SP
CPHX #opr
CPHX opr
M ← $00
A ← $00
X ← $00
H ← $00
M ← $00
M ← $00
M ← $00
Clear
Compare A with M
Complement (One’s Complement)
Compare H:X with M
Compare X with M
DAA
Decimal Adjust A
DBNZ opr,rel
DBNZA rel
DBNZX rel
Decrement and Branch if Not Zero
DBNZ opr,X,rel
DBNZ X,rel
DBNZ opr,SP,rel
DEC opr
DECA
DECX
DEC opr,X
DEC ,X
DEC opr,SP
Decrement
DIV
Divide
INC opr
INCA
INCX
INC opr,X
INC ,X
INC opr,SP
Exclusive OR M with A
Increment
Cycles
Effect
on CCR
V H I N Z C
CPX #opr
CPX opr
CPX opr
CPX ,X
CPX opr,X
CPX opr,X
CPX opr,SP
CPX opr,SP
EOR #opr
EOR opr
EOR opr
EOR opr,X
EOR opr,X
EOR ,X
EOR opr,SP
EOR opr,SP
Description
Operand
Operation
Opcode
Source
Form
Address
Mode
Table 6-1. Instruction Set Summary (Sheet 3 of 6)
DIR
INH
INH
0 – – 0 1 – INH
IX1
IX
SP1
3F dd
4F
5F
8C
6F ff
7F
9E6F ff
3
1
1
1
3
2
4
IMM
DIR
EXT
IX2
– –
IX1
IX
SP1
SP2
DIR
INH
INH
0 – – 1
IX1
IX
SP1
A1
B1
C1
D1
E1
F1
9EE1
9ED1
33
43
53
63
73
9E63
ff
2
3
4
4
3
2
4
5
4
1
1
4
3
5
(H:X) – (M:M + 1)
IMM
– –
DIR
65
75
ii ii+1
dd
3
4
(X) – (M)
IMM
DIR
EXT
IX2
– – IX1
IX
SP1
SP2
A3
B3
C3
D3
E3
F3
9EE3
9ED3
ii
dd
hh ll
ee ff
ff
2
3
4
4
3
2
4
5
U – – INH
72
(A) – (M)
M ← (M) = $FF – (M)
A ← (A) = $FF – (M)
X ← (X) = $FF – (M)
M ← (M) = $FF – (M)
M ← (M) = $FF – (M)
M ← (M) = $FF – (M)
(A)10
A ← (A) – 1 or M ← (M) – 1 or X ← (X) – 1
PC ← (PC) + 3 + rel ? (result) ≠ 0
DIR
PC ← (PC) + 2 + rel ? (result) ≠ 0
INH
PC ← (PC) + 2 + rel ? (result) ≠ 0
– – – – – – INH
PC ← (PC) + 3 + rel ? (result) ≠ 0
IX1
PC ← (PC) + 2 + rel ? (result) ≠ 0
IX
PC ← (PC) + 4 + rel ? (result) ≠ 0
SP1
3B
4B
5B
6B
7B
9E6B
ii
dd
hh ll
ee ff
ff
ff
ee ff
dd
ff
ff
ee ff
2
dd rr
rr
rr
ff rr
rr
ff rr
M ← (M) – 1
A ← (A) – 1
X ← (X) – 1
M ← (M) – 1
M ← (M) – 1
M ← (M) – 1
DIR
INH
INH
– – –
IX1
IX
SP1
A ← (H:A)/(X)
H ← Remainder
– – – – INH
52
A ← (A ⊕ M)
IMM
DIR
EXT
0 – – – IX2
IX1
IX
SP1
SP2
A8
B8
C8
D8
E8
F8
9EE8
9ED8
DIR
INH
– – – INH
IX1
IX
SP1
3C dd
4C
5C
6C ff
7C
9E6C ff
M ← (M) + 1
A ← (A) + 1
X ← (X) + 1
M ← (M) + 1
M ← (M) + 1
M ← (M) + 1
3A dd
4A
5A
6A ff
7A
9E6A ff
5
3
3
5
4
6
4
1
1
4
3
5
7
ii
dd
hh ll
ee ff
ff
ff
ee ff
2
3
4
4
3
2
4
5
4
1
1
4
3
5
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
72
Freescale Semiconductor
Instruction Set Summary
JSR opr
JSR opr
JSR opr,X
JSR opr,X
JSR ,X
LDA #opr
LDA opr
LDA opr
LDA opr,X
LDA opr,X
LDA ,X
LDA opr,SP
LDA opr,SP
LDHX #opr
LDHX opr
LDX #opr
LDX opr
LDX opr
LDX opr,X
LDX opr,X
LDX ,X
LDX opr,SP
LDX opr,SP
LSL opr
LSLA
LSLX
LSL opr,X
LSL ,X
LSL opr,SP
LSR opr
LSRA
LSRX
LSR opr,X
LSR ,X
LSR opr,SP
MOV opr,opr
MOV opr,X+
MOV #opr,opr
MOV X+,opr
MUL
NEG opr
NEGA
NEGX
NEG opr,X
NEG ,X
NEG opr,SP
PC ← Jump Address
DIR
EXT
– – – – – – IX2
IX1
IX
BC
CC
DC
EC
FC
dd
hh ll
ee ff
ff
2
3
4
3
2
PC ← (PC) + n (n = 1, 2, or 3)
Push (PCL); SP ← (SP) – 1
Push (PCH); SP ← (SP) – 1
PC ← Unconditional Address
DIR
EXT
– – – – – – IX2
IX1
IX
BD
CD
DD
ED
FD
dd
hh ll
ee ff
ff
4
5
6
5
4
IMM
DIR
EXT
IX2
0 – – – IX1
IX
SP1
SP2
IMM
0 – – –
DIR
A6
B6
C6
D6
E6
F6
9EE6
9ED6
45
55
ii
dd
hh ll
ee ff
ff
2
3
4
4
3
2
4
5
3
4
IMM
DIR
EXT
IX2
0 – – – IX1
IX
SP1
SP2
AE
BE
CE
DE
EE
FE
9EEE
9EDE
DIR
INH
INH
– – IX1
IX
SP1
38 dd
48
58
68 ff
78
9E68 ff
H:X ← (H:X) + 1 (IX+D, DIX+)
DIR
INH
– – 0 INH
IX1
IX
SP1
DD
DIX+
0 – – – IMD
IX+D
34
44
54
64
74
9E64
4E
5E
6E
7E
X:A ← (X) × (A)
– 0 – – – 0 INH
M ← –(M) = $00 – (M)
A ← –(A) = $00 – (A)
X ← –(X) = $00 – (X)
M ← –(M) = $00 – (M)
M ← –(M) = $00 – (M)
DIR
INH
INH
– –
IX1
IX
SP1
Effect
on CCR
Description
V H I N Z C
Jump
Jump to Subroutine
A ← (M)
Load A from M
H:X ← (M:M + 1)
Load H:X from M
X ← (M)
Load X from M
Logical Shift Left
(Same as ASL)
Logical Shift Right
C
0
b7
b0
0
C
b7
b0
(M)Destination ← (M)Source
Move
Unsigned multiply
Negate (Two’s Complement)
ff
ee ff
ii jj
dd
ii
dd
hh ll
ee ff
ff
ff
ee ff
Cycles
Operand
JMP opr
JMP opr
JMP opr,X
JMP opr,X
JMP ,X
Operation
Address
Mode
Source
Form
Opcode
Table 6-1. Instruction Set Summary (Sheet 4 of 6)
2
3
4
4
3
2
4
5
4
1
1
4
3
5
dd
4
1
1
ff
4
3
ff
5
dd dd 5
dd
4
ii dd
4
dd
4
42
5
30 dd
40
50
60 ff
70
9E60 ff
4
1
1
4
3
5
NOP
No Operation
None
– – – – – – INH
9D
1
NSA
Nibble Swap A
A ← (A[3:0]:A[7:4])
– – – – – – INH
62
3
A ← (A) | (M)
IMM
DIR
EXT
IX2
0 – – –
IX1
IX
SP1
SP2
ORA #opr
ORA opr
ORA opr
ORA opr,X
ORA opr,X
ORA ,X
ORA opr,SP
ORA opr,SP
ii
dd
hh ll
ee ff
ff
2
3
4
4
3
2
4
5
PSHA
Push A onto Stack
Push (A); SP ← (SP) – 1
– – – – – – INH
AA
BA
CA
DA
EA
FA
9EEA
9EDA
87
PSHH
Push H onto Stack
Push (H); SP ← (SP) – 1
– – – – – – INH
8B
2
PSHX
Push X onto Stack
Push (X); SP ← (SP) – 1
– – – – – – INH
89
2
Inclusive OR A and M
ff
ee ff
2
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
73
Central Processor Unit (CPU)
V H I N Z C
Cycles
Effect
on CCR
Description
Operand
Operation
Opcode
Source
Form
Address
Mode
Table 6-1. Instruction Set Summary (Sheet 5 of 6)
PULA
Pull A from Stack
SP ← (SP + 1); Pull (A)
– – – – – – INH
86
2
PULH
Pull H from Stack
SP ← (SP + 1); Pull (H)
– – – – – – INH
8A
2
PULX
Pull X from Stack
SP ← (SP + 1); Pull (X)
– – – – – – INH
88
2
C
DIR
INH
INH
– – IX1
IX
SP1
39 dd
49
59
69 ff
79
9E69 ff
4
1
1
4
3
5
DIR
INH
– – INH
IX1
IX
SP1
36 dd
46
56
66 ff
76
9E66 ff
4
1
1
4
3
5
ROL opr
ROLA
ROLX
ROL opr,X
ROL ,X
ROL opr,SP
Rotate Left through Carry
b7
b0
ROR opr
RORA
RORX
ROR opr,X
ROR ,X
ROR opr,SP
Rotate Right through Carry
RSP
Reset Stack Pointer
SP ← $FF
– – – – – – INH
9C
1
RTI
Return from Interrupt
SP ← (SP) + 1; Pull (CCR)
SP ← (SP) + 1; Pull (A)
SP ← (SP) + 1; Pull (X)
SP ← (SP) + 1; Pull (PCH)
SP ← (SP) + 1; Pull (PCL)
INH
80
7
RTS
Return from Subroutine
SP ← SP + 1; Pull (PCH)
SP ← SP + 1; Pull (PCL)
– – – – – – INH
81
4
A ← (A) – (M) – (C)
IMM
DIR
EXT
– – IX2
IX1
IX
SP1
SP2
A2
B2
C2
D2
E2
F2
9EE2
9ED2
C
b7
b0
SBC #opr
SBC opr
SBC opr
SBC opr,X
SBC opr,X
SBC ,X
SBC opr,SP
SBC opr,SP
Subtract with Carry
SEC
Set Carry Bit
C←1
– – – – – 1 INH
99
1
SEI
Set Interrupt Mask
I←1
– – 1 – – – INH
9B
2
(M:M + 1) ← (H:X)
DIR
EXT
IX2
0 – – – IX1
IX
SP1
SP2
0 – – – DIR
B7
C7
D7
E7
F7
9EE7
9ED7
35
I ← 0; Stop Processing
– – 0 – – – INH
8E
M ← (X)
DIR
EXT
IX2
0 – – – IX1
IX
SP1
SP2
BF
CF
DF
EF
FF
9EEF
9EDF
dd
hh ll
ee ff
ff
IMM
DIR
EXT
– – IX2
IX1
IX
SP1
SP2
A0
B0
C0
D0
E0
F0
9EE0
9ED0
ii
dd
hh ll
ee ff
ff
STA opr
STA opr
STA opr,X
STA opr,X
STA ,X
STA opr,SP
STA opr,SP
STHX opr
STOP
STX opr
STX opr
STX opr,X
STX opr,X
STX ,X
STX opr,SP
STX opr,SP
SUB #opr
SUB opr
SUB opr
SUB opr,X
SUB opr,X
SUB ,X
SUB opr,SP
SUB opr,SP
Store A in M
Store H:X in M
Enable Interrupts, Stop Processing,
Refer to MCU Documentation
Store X in M
Subtract
M ← (A)
A ← (A) – (M)
ii
dd
hh ll
ee ff
ff
ff
ee ff
dd
hh ll
ee ff
ff
ff
ee ff
dd
2
3
4
4
3
2
4
5
3
4
4
3
2
4
5
4
1
ff
ee ff
ff
ee ff
3
4
4
3
2
4
5
2
3
4
4
3
2
4
5
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
74
Freescale Semiconductor
Opcode Map
V H I N Z C
Cycles
Effect
on CCR
Description
Operand
Operation
Opcode
Source
Form
Address
Mode
Table 6-1. Instruction Set Summary (Sheet 6 of 6)
SWI
Software Interrupt
PC ← (PC) + 1; Push (PCL)
SP ← (SP) – 1; Push (PCH)
SP ← (SP) – 1; Push (X)
SP ← (SP) – 1; Push (A)
SP ← (SP) – 1; Push (CCR)
SP ← (SP) – 1; I ← 1
PCH ← Interrupt Vector High Byte
PCL ← Interrupt Vector Low Byte
TAP
Transfer A to CCR
CCR ← (A)
INH
84
2
TAX
Transfer A to X
X ← (A)
– – – – – – INH
97
1
TPA
Transfer CCR to A
A ← (CCR)
– – – – – – INH
85
(A) – $00 or (X) – $00 or (M) – $00
DIR
INH
INH
0 – – –
IX1
IX
SP1
H:X ← (SP) + 1
– – – – – – INH
95
2
A ← (X)
– – – – – – INH
9F
1
(SP) ← (H:X) – 1
– – – – – – INH
94
2
I bit ← 0; Inhibit CPU clocking
until interrupted
– – 0 – – – INH
8F
1
TST opr
TSTA
TSTX
TST opr,X
TST ,X
TST opr,SP
Test for Negative or Zero
TSX
Transfer SP to H:X
TXA
Transfer X to A
TXS
Transfer H:X to SP
WAIT
A
C
CCR
dd
dd rr
DD
DIR
DIX+
ee ff
EXT
ff
H
H
hh ll
I
ii
IMD
IMM
INH
IX
IX+
IX+D
IX1
IX1+
IX2
M
N
Enable Interrupts; Wait for Interrupt
Accumulator
Carry/borrow bit
Condition code register
Direct address of operand
Direct address of operand and relative offset of branch instruction
Direct to direct addressing mode
Direct addressing mode
Direct to indexed with post increment addressing mode
High and low bytes of offset in indexed, 16-bit offset addressing
Extended addressing mode
Offset byte in indexed, 8-bit offset addressing
Half-carry bit
Index register high byte
High and low bytes of operand address in extended addressing
Interrupt mask
Immediate operand byte
Immediate source to direct destination addressing mode
Immediate addressing mode
Inherent addressing mode
Indexed, no offset addressing mode
Indexed, no offset, post increment addressing mode
Indexed with post increment to direct addressing mode
Indexed, 8-bit offset addressing mode
Indexed, 8-bit offset, post increment addressing mode
Indexed, 16-bit offset addressing mode
Memory location
Negative bit
n
opr
PC
PCH
PCL
REL
rel
rr
SP1
SP2
SP
U
V
X
Z
&
|
⊕
()
–( )
#
«
←
?
:
—
– – 1 – – – INH
83
9
3D dd
4D
5D
6D ff
7D
9E6D ff
1
3
1
1
3
2
4
Any bit
Operand (one or two bytes)
Program counter
Program counter high byte
Program counter low byte
Relative addressing mode
Relative program counter offset byte
Relative program counter offset byte
Stack pointer, 8-bit offset addressing mode
Stack pointer 16-bit offset addressing mode
Stack pointer
Undefined
Overflow bit
Index register low byte
Zero bit
Logical AND
Logical OR
Logical EXCLUSIVE OR
Contents of
Negation (two’s complement)
Immediate value
Sign extend
Loaded with
If
Concatenated with
Set or cleared
Not affected
6.8 Opcode Map
See Table 6-2.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
75
MSB
Branch
REL
DIR
INH
3
4
0
1
2
5
BRSET0
3 DIR
5
BRCLR0
3 DIR
5
BRSET1
3 DIR
5
BRCLR1
3 DIR
5
BRSET2
3 DIR
5
BRCLR2
3 DIR
5
BRSET3
3 DIR
5
BRCLR3
3 DIR
5
BRSET4
3 DIR
5
BRCLR4
3 DIR
5
BRSET5
3 DIR
5
BRCLR5
3 DIR
5
BRSET6
3 DIR
5
BRCLR6
3 DIR
5
BRSET7
3 DIR
5
BRCLR7
3 DIR
4
BSET0
2 DIR
4
BCLR0
2 DIR
4
BSET1
2 DIR
4
BCLR1
2 DIR
4
BSET2
2 DIR
4
BCLR2
2 DIR
4
BSET3
2 DIR
4
BCLR3
2 DIR
4
BSET4
2 DIR
4
BCLR4
2 DIR
4
BSET5
2 DIR
4
BCLR5
2 DIR
4
BSET6
2 DIR
4
BCLR6
2 DIR
4
BSET7
2 DIR
4
BCLR7
2 DIR
3
BRA
2 REL
3
BRN
2 REL
3
BHI
2 REL
3
BLS
2 REL
3
BCC
2 REL
3
BCS
2 REL
3
BNE
2 REL
3
BEQ
2 REL
3
BHCC
2 REL
3
BHCS
2 REL
3
BPL
2 REL
3
BMI
2 REL
3
BMC
2 REL
3
BMS
2 REL
3
BIL
2 REL
3
BIH
2 REL
Read-Modify-Write
INH
IX1
5
6
1
NEGX
1 INH
4
CBEQX
3 IMM
7
DIV
1 INH
1
COMX
1 INH
1
LSRX
1 INH
4
LDHX
2 DIR
1
RORX
1 INH
1
ASRX
1 INH
1
LSLX
1 INH
1
ROLX
1 INH
1
DECX
1 INH
3
DBNZX
2 INH
1
INCX
1 INH
1
TSTX
1 INH
4
MOV
2 DIX+
1
CLRX
1 INH
4
NEG
2
IX1
5
CBEQ
3 IX1+
3
NSA
1 INH
4
COM
2 IX1
4
LSR
2 IX1
3
CPHX
3 IMM
4
ROR
2 IX1
4
ASR
2 IX1
4
LSL
2 IX1
4
ROL
2 IX1
4
DEC
2 IX1
5
DBNZ
3 IX1
4
INC
2 IX1
3
TST
2 IX1
4
MOV
3 IMD
3
CLR
2 IX1
SP1
IX
9E6
7
Control
INH
INH
8
9
Register/Memory
IX2
SP2
IMM
DIR
EXT
A
B
C
D
9ED
4
SUB
3 EXT
4
CMP
3 EXT
4
SBC
3 EXT
4
CPX
3 EXT
4
AND
3 EXT
4
BIT
3 EXT
4
LDA
3 EXT
4
STA
3 EXT
4
EOR
3 EXT
4
ADC
3 EXT
4
ORA
3 EXT
4
ADD
3 EXT
3
JMP
3 EXT
5
JSR
3 EXT
4
LDX
3 EXT
4
STX
3 EXT
4
SUB
3 IX2
4
CMP
3 IX2
4
SBC
3 IX2
4
CPX
3 IX2
4
AND
3 IX2
4
BIT
3 IX2
4
LDA
3 IX2
4
STA
3 IX2
4
EOR
3 IX2
4
ADC
3 IX2
4
ORA
3 IX2
4
ADD
3 IX2
4
JMP
3 IX2
6
JSR
3 IX2
4
LDX
3 IX2
4
STX
3 IX2
5
SUB
4 SP2
5
CMP
4 SP2
5
SBC
4 SP2
5
CPX
4 SP2
5
AND
4 SP2
5
BIT
4 SP2
5
LDA
4 SP2
5
STA
4 SP2
5
EOR
4 SP2
5
ADC
4 SP2
5
ORA
4 SP2
5
ADD
4 SP2
IX1
SP1
IX
E
9EE
F
LSB
0
Freescale Semiconductor
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F
4
1
NEG
NEGA
2 DIR 1 INH
5
4
CBEQ CBEQA
3 DIR 3 IMM
5
MUL
1 INH
4
1
COM
COMA
2 DIR 1 INH
4
1
LSR
LSRA
2 DIR 1 INH
4
3
STHX
LDHX
2 DIR 3 IMM
4
1
ROR
RORA
2 DIR 1 INH
4
1
ASR
ASRA
2 DIR 1 INH
4
1
LSL
LSLA
2 DIR 1 INH
4
1
ROL
ROLA
2 DIR 1 INH
4
1
DEC
DECA
2 DIR 1 INH
5
3
DBNZ DBNZA
3 DIR 2 INH
4
1
INC
INCA
2 DIR 1 INH
3
1
TST
TSTA
2 DIR 1 INH
5
MOV
3 DD
3
1
CLR
CLRA
2 DIR 1 INH
INH Inherent
REL Relative
IMM Immediate
IX
Indexed, No Offset
DIR Direct
IX1 Indexed, 8-Bit Offset
EXT Extended
IX2 Indexed, 16-Bit Offset
DD Direct-Direct
IMD Immediate-Direct
IX+D Indexed-Direct DIX+ Direct-Indexed
*Pre-byte for stack pointer indexed instructions
5
3
NEG
NEG
3 SP1 1 IX
6
4
CBEQ
CBEQ
4 SP1 2 IX+
2
DAA
1 INH
5
3
COM
COM
3 SP1 1 IX
5
3
LSR
LSR
3 SP1 1 IX
4
CPHX
2 DIR
5
3
ROR
ROR
3 SP1 1 IX
5
3
ASR
ASR
3 SP1 1 IX
5
3
LSL
LSL
3 SP1 1 IX
5
3
ROL
ROL
3 SP1 1 IX
5
3
DEC
DEC
3 SP1 1 IX
6
4
DBNZ
DBNZ
4 SP1 2 IX
5
3
INC
INC
3 SP1 1 IX
4
2
TST
TST
3 SP1 1 IX
4
MOV
2 IX+D
4
2
CLR
CLR
3 SP1 1 IX
SP1 Stack Pointer, 8-Bit Offset
SP2 Stack Pointer, 16-Bit Offset
IX+ Indexed, No Offset with
Post Increment
IX1+ Indexed, 1-Byte Offset with
Post Increment
7
3
RTI
BGE
1 INH 2 REL
4
3
RTS
BLT
1 INH 2 REL
3
BGT
2 REL
9
3
SWI
BLE
1 INH 2 REL
2
2
TAP
TXS
1 INH 1 INH
1
2
TPA
TSX
1 INH 1 INH
2
PULA
1 INH
2
1
PSHA
TAX
1 INH 1 INH
2
1
PULX
CLC
1 INH 1 INH
2
1
PSHX
SEC
1 INH 1 INH
2
2
PULH
CLI
1 INH 1 INH
2
2
PSHH
SEI
1 INH 1 INH
1
1
CLRH
RSP
1 INH 1 INH
1
NOP
1 INH
1
STOP
*
1 INH
1
1
WAIT
TXA
1 INH 1 INH
2
SUB
2 IMM
2
CMP
2 IMM
2
SBC
2 IMM
2
CPX
2 IMM
2
AND
2 IMM
2
BIT
2 IMM
2
LDA
2 IMM
2
AIS
2 IMM
2
EOR
2 IMM
2
ADC
2 IMM
2
ORA
2 IMM
2
ADD
2 IMM
3
SUB
2 DIR
3
CMP
2 DIR
3
SBC
2 DIR
3
CPX
2 DIR
3
AND
2 DIR
3
BIT
2 DIR
3
LDA
2 DIR
3
STA
2 DIR
3
EOR
2 DIR
3
ADC
2 DIR
3
ORA
2 DIR
3
ADD
2 DIR
2
JMP
2 DIR
4
4
BSR
JSR
2 REL 2 DIR
2
3
LDX
LDX
2 IMM 2 DIR
2
3
AIX
STX
2 IMM 2 DIR
MSB
0
3
SUB
2 IX1
3
CMP
2 IX1
3
SBC
2 IX1
3
CPX
2 IX1
3
AND
2 IX1
3
BIT
2 IX1
3
LDA
2 IX1
3
STA
2 IX1
3
EOR
2 IX1
3
ADC
2 IX1
3
ORA
2 IX1
3
ADD
2 IX1
3
JMP
2 IX1
5
JSR
2 IX1
5
3
LDX
LDX
4 SP2 2 IX1
5
3
STX
STX
4 SP2 2 IX1
4
SUB
3 SP1
4
CMP
3 SP1
4
SBC
3 SP1
4
CPX
3 SP1
4
AND
3 SP1
4
BIT
3 SP1
4
LDA
3 SP1
4
STA
3 SP1
4
EOR
3 SP1
4
ADC
3 SP1
4
ORA
3 SP1
4
ADD
3 SP1
2
SUB
1 IX
2
CMP
1 IX
2
SBC
1 IX
2
CPX
1 IX
2
AND
1 IX
2
BIT
1 IX
2
LDA
1 IX
2
STA
1 IX
2
EOR
1 IX
2
ADC
1 IX
2
ORA
1 IX
2
ADD
1 IX
2
JMP
1 IX
4
JSR
1 IX
4
2
LDX
LDX
3 SP1 1 IX
4
2
STX
STX
3 SP1 1 IX
High Byte of Opcode in Hexadecimal
LSB
Low Byte of Opcode in Hexadecimal
0
5
Cycles
BRSET0 Opcode Mnemonic
3 DIR Number of Bytes / Addressing Mode
Central Processor Unit (CPU)
76
Table 6-2. Opcode Map
Bit Manipulation
DIR
DIR
Chapter 7
Internal Clock Generator (ICG) Module)
7.1 Introduction
The internal clock generator module (ICG) is used to create a stable clock source for the microcontroller
without using any external components. The ICG generates the oscillator output clock (CGMXCLK),
which is used by the low-voltage inhibit (LVI) and other modules. The ICG also generates the clock
generator output (CGMOUT), which is fed to the system integration module (SIM) to create the bus
clocks. The bus frequency will be one-fourth the frequency of CGMXCLK and one-half the frequency of
CGMOUT. Finally, the ICG generates the timebase clock (TBMCLK), which is used in the timebase
module (TBM) and the computer operating properly (COP) clock (COPCLK) which is used by the COP
module.
7.2 Features
The ICG has these features:
• Selectable external clock generator, either 1-pin external source or 2-pin crystal, multiplexed with
port pins
• Internal clock generator with programmable frequency output in integer multiples of a nominal
frequency (307.2 kHz ± 25 percent)
• Frequency adjust (trim) register to improve variability to ±4 percent
• Bus clock software selectable from either internal or external clock (bus frequency range from
76.8 kHz ± 25 percent to 9.75 MHz ± 25 percent in 76.8-kHz increments
NOTE
Do not exceed the maximum bus frequency of 8 MHz at 5.0 V and 4 MHz
at 3.0 V.
•
•
Timebase clock automatically selected from external if external clock is available
Clock monitor for both internal and external clocks
7.3 Functional Description
The ICG, shown in Figure 7-2, contains these major submodules:
• Clock enable circuit
• Internal clock generator
• External clock generator
• Clock monitor circuit
• Clock selection circuit
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
77
Internal Clock Generator (ICG) Module)
8-BIT KEYBOARD
INTERRUPT MODULE
FLASH PROGRAMMING ROUTINES
ROM — 720 BYTES
USER FLASH VECTOR SPACE — 36 BYTES
PTE4/OSC1
PTE3/OSC2
INTERNAL CLOCK
GENERATOR MODULE
RST(3)
SYSTEM INTEGRATION
MODULE
IRQ(3)
SINGLE EXTERNAL
INTERRUPT MODULE
VREFH
VREFL
2-CHANNEL TIMER INTERFACE
MODULE 2
DDRA
PTD7/T2CH1(1)
PTD6/T2CH0(1)
PTD5/T1CH1(1)
PTD4/T1CH0(1)
PTD3/SPSCK(1)
PTD2/MOSI(1)
PTD1/MISO(1)
PTD0/SS(1)
PTE2
PTE1/RxD
PTE0/TxD
SERIAL PERIPHERAL
INTERFACE MODULE
MONITOR MODULE
8-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
PTC6(1)
PTC5(1)
PTC4(1)(2)
PTC3(1)(2)
PTC2(1)(2)
PTC1(1)(2)
PTC0(1)(2)
SERIAL COMMUNICATIONS
INTERFACE MODULE
COMPUTER OPERATING
PROPERLY MODULE
POWER-ON RESET
MODULE
VDD
VSS
VDDA
VSSA
2-CHANNEL TIMER INTERFACE
MODULE 1
DDRD
MONITOR ROM — 304 BYTES
PORTA
USER RAM — 512 BYTES
PORTB
DUAL VOLTAGE
LOW-VOLTAGE INHIBIT MODULE
PTB7/AD7
PTB6/AD6
PTB5/AD5
PTB4/AD4
PTB3/AD3
PTB2/AD2
PTB1/AD1
PTB0/AD0
PORTC
USER FLASH
MC68HC908GT16 — 15,872 BYTES
MC68HC908GT8 — 7,680 BYTES
PTA7/KBD7–
PTA0/KBD0(1)
PORTD
SINGLE BREAKPOINT BREAK
MODULE
DDRB
CONTROL AND STATUS
REGISTERS — 64 BYTES
DDRC
PROGRAMMABLE TIMEBASE
MODULE
ARITHMETIC/LOGIC
UNIT (ALU)
MEMORY MAP
MODULE
DDRE
CPU
REGISTERS
PORTE
INTERNAL BUS
M68HC08 CPU
SECURITY
MODULE
CONFIGURATION REGISTER 1
MODULE
CONFIGURATION REGISTER 2
MODULE
MONITOR MODE ENTRY
MODULE
1. Ports are software configurable with pullup device if input port.
2. Higher current drive port pins
3. Pin contains integrated pullup device
Figure 7-1. Block Diagram Highlighting ICG Module and Pins
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
78
Freescale Semiconductor
Functional Description
CS
CGMOUT
RESET
CGMXCLK
CLOCK
SELECTION
CIRCUIT
TBMCLK
COPCLK
IOFF
EOFF
CMON
ECGS
ICGS
CLOCK
MONITOR
CIRCUIT
FICGS
DDIV[3:0]
INTERNAL CLOCK
GENERATOR
N[6:0}
TRIM[7:0]
DSTG[7:0]
ICLK
IBASE
ICGEN
SIMOSCEN
CLOCK/PIN
ENABLE
CIRCUIT
OSCENINSTOP
EXTCLKEN
ECGON
ICGON
ECGEN
EXTXTALEN
EXTERNAL CLOCK
GENERATOR
EXTSLOW
INTERNAL
TO MCU
PTE4
LOGIC
OSC1
PTE4
OSC2
PTE3
ECLK
PTE3
LOGIC
EXTERNAL
NAME
CONFIG2 REGISTER BIT
NAME
REGISTER BIT
NAME
TOP LEVEL SIGNAL
NAME
MODULE SIGNAL
Figure 7-2. ICG Module Block Diagram
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
79
Internal Clock Generator (ICG) Module)
7.3.1 Clock Enable Circuit
The clock enable circuit is used to enable the internal clock (ICLK) or external clock (ECLK) and the port
logic which is shared with the oscillator pins (OSC1 and OSC2). The clock enable circuit generates an
ICG stop (ICGSTOP) signal which stops all clocks (ICLK, ECLK, and the low-frequency base clock,
IBASE). ICGSTOP is set and the ICG is disabled in stop mode if the oscillator enable stop bit
(OSCENINSTOP) in the CONFIG2 register is clear. The ICG clocks will be enabled in stop mode if
OSCENINSTOP is high.
The internal clock enable signal (ICGEN) turns on the internal clock generator which generates ICLK.
ICGEN is set (active) whenever the ICGON bit is set and the ICGSTOP signal is clear. When ICGEN is
clear, ICLK and IBASE are both low.
The external clock enable signal (ECGEN) turns on the external clock generator which generates ECLK.
ECGEN is set (active) whenever the ECGON bit is set and the ICGSTOP signal is clear. ECGON cannot
be set unless the external clock enable (EXTCLKEN) bit in the CONFIG2 register is set. when ECGEN is
clear, ECLK is low.
The port E4 enable signal (PE4EN) turns on the port E4 logic. Since port E4 is on the same pin as OSC1,
this signal is only active (set) when the external clock function is not desired. Therefore, PE4EN is clear
when ECGON is set. PE4EN is not gated with ICGSTOP, which means that if the ECGON bit is set, the
port E4 logic will remain disabled in stop mode.
The port E3 enable signal (PE3EN) turns on the port E3 logic. Since port E3 is on the same pin as OSC2,
this signal is only active (set) when 2-pin oscillator function is not desired. Therefore, PE3EN is clear when
ECGON and the external crystal enable (EXTXTALEN) bit in the CONFIG2 register are both set. PE3EN
is not gated with ICGSTOP, which means that if ECGON and EXTXTALEN are set, the port E3 logic will
remain disabled in stop mode.
7.3.2 Internal Clock Generator
The internal clock generator, shown in Figure 7-3, creates a low frequency base clock (IBASE), which
operates at a nominal frequency (fNOM) of 307.2 kHz ± 25 percent, and an internal clock (ICLK) which is
an integer multiple of IBASE. This multiple is the ICG multiplier factor (N), which is programmed in the
ICG multiplier register (ICGMR). The internal clock generator is turned off and the output clocks (IBASE
and ICLK) are held low when the internal clock generator enable signal (ICGEN) is clear.
The internal clock generator contains:
• A digitally controlled oscillator
• A modulo N divider
• A frequency comparator, which contains voltage and current references, a frequency to voltage
converter, and comparators
• A digital loop filter
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
80
Freescale Semiconductor
Functional Description
ICGEN
VOLTAGE AND
CURRENT
REFERENCES
FICGS
++
DSTG[7:0]
+
DIGITAL
LOOP
FILTER
–
DDIV[3:0]
DIGITALLY
CONTROLLED
OSCILLATOR
ICLK
––
TRIM[7:0]
FREQUENCY
COMPARATOR
CLOCK GENERATOR
N[6:0]
MODULO
N
DIVIDER
IBASE
NAME
CONFIG2 REGISTER BIT
NAME
REGISTER BIT
NAME
TOP LEVEL SIGNAL
NAME
MODULE SIGNAL
Figure 7-3. Internal Clock Generator Block Diagram
7.3.2.1 Digitally Controlled Oscillator
The digitally controlled oscillator (DCO) is an inaccurate oscillator which generates the internal clock
(ICLK). The clock period of ICLK is dependent on the digital loop filter outputs (DSTG[7:0] and DDIV[3:0]).
Because of only a limited number of bits in DDIV and DSTG, the precision of the output (ICLK) is restricted
to a precision of approximately ±0.202 percent to ±0.368 percent when measured over several cycles (of
the desired frequency). Additionally, since the propagation delays of the devices used in the DCO ring
oscillator are a measurable fraction of the bus clock period, reaching the long-term precision may require
alternately running faster and slower than desired, making the worst case cycle-to-cycle frequency
variation ±6.45 percent to ±11.8 percent (of the desired frequency). The valid values of DDIV:DSTG range
from $000 to $9FF. For more information on the quantization error in the DCO, see 7.4.4 Quantization
Error in DCO Output.
7.3.2.2 Modulo N Divider
The modulo N divider creates the low-frequency base clock (IBASE) by dividing the internal clock (ICLK)
by the ICG multiplier factor (N), contained in the ICG multiplier register (ICGMR). When N is programmed
to a $01 or $00, the divider is disabled and ICLK is passed through to IBASE undivided. When the internal
clock generator is stable, the frequency of IBASE will be equal to the nominal frequency (fNOM) of 307.2
kHz ± 25 percent.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
81
Internal Clock Generator (ICG) Module)
7.3.2.3 Frequency Comparator
The frequency comparator effectively compares the low-frequency base clock (IBASE) to a nominal
frequency, fNOM. First, the frequency comparator converts IBASE to a voltage by charging a known
capacitor with a current reference for a period dependent on IBASE. This voltage is compared to a voltage
reference with comparators, whose outputs are fed to the digital loop filter. The dependence of these
outputs on the capacitor size, current reference, and voltage reference causes up to ±25 percent error in
fNOM.
7.3.2.4 Digital Loop Filter
The digital loop filter (DLF) uses the outputs of the frequency comparator to adjust the internal clock
(ICLK) clock period. The DLF generates the DCO divider control bits (DDIV[3:0]) and the DCO stage
control bits (DSTG[7:0]), which are fed to the DCO. The DLF first concatenates the DDIV and DSTG
registers (DDIV[3:0]:DSTG[7:0]) and then adds or subtracts a value dependent on the relative error in the
low-frequency base clock’s period, as shown in Table 7-1. In some extreme error conditions, such as
operating at a VDD level which is out of specification, the DLF may attempt to use a value above the
maximum ($9FF) or below the minimum ($000). In both cases, the value for DDIV will be between $A and
$F. In this range, the DDIV value will be interpreted the same as $9 (the slowest condition). Recovering
from this condition requires subtracting (increasing frequency) in the normal fashion until the value is
again below $9FF. (If the desired value is $9xx, the value may settle at $Axx through $Fxx. This is an
acceptable operating condition.) If the error is less than ±5 percent, the internal clock generator’s filter
stable indicator (FICGS) is set, indicating relative frequency accuracy to the clock monitor.
Table 7-1. Correction Sizes from DLF to DCO
Frequency Error of IBASE
Compared to fNOM
DDVI[3:0]:DSTG[7:0]
Correction
IBASE < 0.85 fNOM
–32 (–$020)
0.85 fNOM < IBASE
IBASE < 0.95 fNOM
–8 (–$008)
0.95 fNOM < IBASE
IBASE < fNOM
–1 (–$001)
fNOM < IBASE
IBASE < 1.05 fNOM
+1 (+$001)
1.05 fNOM < IBASE
IBASE < 1.15 fNOM
+8 (+$008)
1.15 fNOM < IBASE
+32 (+$020)
Current to New
DDIV[3:0]:DSTG[7:0](1)
Relative Correction
in DCO
Minimum
$xFF to $xDF
–2/31
–6.45%
Maximum
$x20 to $x00
–2/19
–10.5%
Minimum
$xFF to $xF7
–0.5/31
–1.61%
Maximum
$x08 to $x00
–0.5/17.5
–2.86%
Minimum
$xFF to $xFE
–0.0625/31
–0.202%
Maximum
$x01 to $x00
–0.0625/17.0625
–0.366%
Minimum
$xFE to $xFF
+0.0625/30.9375
+0.202%
Maximum
$x00 to $x01
+0.0625/17
+0.368%
Minimum
$xF7 to $xFF
+0.5/30.5
+1.64%
Maximum
$x00 to $x08
+0.5/17
+2.94%
Minimum
$xDF to $xFF
+2/29
+6.90%
Maximum
$x00 to $x20
+2/17
+11.8%
1. x = Maximum error is independent of value in DDIV[3:0]. DDIV increments or decrements when an addition to DSTG[7:0]
carries or borrows.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
82
Freescale Semiconductor
Functional Description
7.3.3 External Clock Generator
The ICG also provides for an external oscillator or external clock source, if desired. The external clock
generator, shown in Figure 7-4, contains an external oscillator amplifier and an external clock input path.
ECGEN
INPUT PATH
ECLK
EXTXTALEN
AMPLIFIER
EXTERNAL
CLOCK
GENERATOR
EXTSLOW
INTERNAL TO MCU
OSC1
PTE4
OSC2
PTE3
EXTERNAL
NAME
NAME
RB
R S*
CONFIG2 BIT
X1
TOP LEVEL SIGNAL
NAME
REGISTER BIT
NAME
MODULE SIGNAL
C1
*RS can be 0 (shorted)
when used with higherfrequency crystals. Refer
to manufacturer’s data.
C2
These components are required
for external crystal use only.
Figure 7-4. External Clock Generator Block Diagram
7.3.3.1 External Oscillator Amplifier
The external oscillator amplifier provides the gain required by an external crystal connected in a Pierce
oscillator configuration. The amount of this gain is controlled by the slow external (EXTSLOW) bit in the
CONFIG2 register. When EXTSLOW is set, the amplifier gain is reduced for operating low-frequency
crystals (32 kHz to 100 kHz). When EXTSLOW is clear, the amplifier gain will be sufficient for 1-MHz to
8-MHz crystals. EXTSLOW must be configured correctly for the given crystal or the circuit may not
operate.
The amplifier is enabled when the external clock generator enable (ECGEN) signal is set and when the
external crystal enable (EXTXTALEN) bit in the CONFIG2 register is set. ECGEN is controlled by the
clock enable circuit (see 7.3.1 Clock Enable Circuit) and indicates that the external clock function is
desired. When enabled, the amplifier will be connected between the PTE4/OSC1 and PTE3/OSC2 pins.
Otherwise, the PTE3/OSC2 pin reverts to its port function.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
83
Internal Clock Generator (ICG) Module)
In its typical configuration, the external oscillator requires five external components:
1. Crystal, X1
2. Fixed capacitor, C1
3. Tuning capacitor, C2 (can also be a fixed capacitor)
4. Feedback resistor, RB
5. Series resistor, RS (Included in Figure 7-4 to follow strict Pierce oscillator guidelines and may not
be required for all ranges of operation, especially with high frequency crystals. Refer to the crystal
manufacturer’s data for more information.)
7.3.3.2 External Clock Input Path
The external clock input path is the means by which the microcontroller uses an external clock source.
The input to the path is the PTE4/OSC1 pin and the output is the external clock (ECLK). The path, which
contains input buffering, is enabled when the external clock generator enable signal (ECGEN) is set.
When not enabled, the PTE4/OSC1 pin reverts to its port function.
7.3.4 Clock Monitor Circuit
The ICG contains a clock monitor circuit which, when enabled, will continuously monitor both the external
clock (ECLK) and the internal clock (ICLK) to determine if either clock source has been corrupted. The
clock monitor circuit, shown in Figure 7-5, contains these blocks:
• Clock monitor reference generator
• Internal clock activity detector
• External clock activity detector
7.3.4.1 Clock Monitor Reference Generator
The clock monitor uses a reference based on one clock source to monitor the other clock source. The
clock monitor reference generator generates the external reference clock (EREF) based on the external
clock (ECLK) and the internal reference clock (IREF) based on the internal clock (ICLK). To simplify the
circuit, the low-frequency base clock (IBASE) is used in place of ICLK because it always operates at or
near 307.2 kHz. For proper operation, EREF must be at least twice as slow as IBASE and IREF must be
at least twice as slow as ECLK.
To guarantee that IREF is slower than ECLK and EREF is slower than IBASE, one of the signals is divided
down. Which signal is divided and by how much is determined by the external slow (EXTSLOW) and
external crystal enable (EXTXTALEN) bits in the CONFIG2 register, according to the rules in Table 7-2.
NOTE
Each signal (IBASE and ECLK) is always divided by four. A longer divider
is used on either IBASE or ECLK based on the EXTSLOW bit.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
84
Freescale Semiconductor
Functional Description
IOFF
IOFF
EREF
ICGS
ICGS
IBASE
EREF
CMON
CMON
FICGS
FICGS
IBASE
IBASE
ICGEN
ICGEN
ICLK
ACTIVITY
DETECTOR
ICGON
EXTXTALEN
EXTSLOW
EXTXTALEN
EXTSLOW
REFERENCE
GENERATOR
ECGS
ESTBCLK
ECLK
ECGEN
IREF
ESTBCLK
ECGS
ECGS
IREF
ECGEN
ECLK
ECGEN
ECLK
CMON
ECLK
ACTIVITY
DETECTOR
EOFF
EOFF
NAME
CONFIG2 REGISTER BIT
NAME
REGISTER BIT
NAME
TOP LEVEL SIGNAL
NAME
MODULE SIGNAL
Figure 7-5. Clock Monitor Block Diagram
To conserve size, the long divider (divide by 4096) is also used as an external crystal stabilization divider.
The divider is reset when the external clock generator is turned off or in stop mode (ECGEN is clear).
When the external clock generator is first turned on, the external clock generator stable bit (ECGS) will
be clear. This condition automatically selects ECLK as the input to the long divider. The external
stabilization clock (ESTBCLK) will be ECLK divided by 16 when EXTXTALEN is low or 4096 when
EXTXTALEN is high. This timeout allows the crystal to stabilize. The falling edge of ESTBCLK is used to
set ECGS, which will set after a full 16 or 4096 cycles. When ECGS is set, the divider returns to its normal
function. ESTBCLK may be generated by either IBASE or ECLK, but any clocking will only reinforce the
set condition. If ECGS is cleared because the clock monitor determined that ECLK was inactive, the
divider will revert to a stabilization divider. Since this will change the EREF and IREF divide ratios, it is
important to turn the clock monitor off (CMON = 0) after inactivity is detected to ensure valid recovery.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
85
Internal Clock Generator (ICG) Module)
7.3.4.2 Internal Clock Activity Detector
The internal clock activity detector, shown in Figure 7-6, looks for at least one falling edge on the
low-frequency base clock (IBASE) every time the external reference (EREF) is low. Since EREF is less
than half the frequency of IBASE, this should occur every time. If it does not occur two consecutive times,
the internal clock inactivity indicator (IOFF) is set. IOFF will be cleared the next time there is a falling edge
of IBASE while EREF is low.
CMON
CK
EREF
IOFF
Q
1/4
R
R
R
D
D
DFFRS
IBASE
CK
Q
S
R
Q
DFFRR
CK
D
Q
ICGS
DFFRR
CK
R
R
DLF MEASURE
OUTPUT CLOCK
ICGEN
FICGS
NAME
CONFIG2 REGISTER BIT
NAME
REGISTER BIT
NAME
TOP LEVEL SIGNAL
NAME
MODULE SIGNAL
Figure 7-6. Internal Clock Activity Detector
The internal clock stable bit (ICGS) is also generated in the internal clock activity detector. ICGS is set
when the internal clock generator’s filter stable signal (FICGS) indicates that IBASE is within about 5
percent of the target 307.2 kHz ± 25 percent for two consecutive measurements. ICGS is cleared when
FICGS is clear, the internal clock generator is turned off or is in stop mode (ICGEN is clear), or when IOFF
is set.
7.3.4.3 External Clock Activity Detector
The external clock activity detector, shown in Figure 7-7, looks for at least one falling edge on the external
clock (ECLK) every time the internal reference (IREF) is low. Since IREF is less than half the frequency
of ECLK, this should occur every time. If it does not occur two consecutive times, the external clock
inactivity indicator (EOFF) is set. EOFF will be cleared the next time there is a falling edge of ECLK while
IREF is low.
The external clock stable bit (ECGS) is also generated in the external clock activity detector. ECGS is set
on a falling edge of the external stabilization clock (ESTBCLK). This will be 4096 ECLK cycles after the
external clock generator on bit is set, or the MCU exits stop mode (ECGEN = 1) if the external crystal
enable (EXTXTALEN) in the CONFIG2 register is set, or 16 cycles when EXTXTALEN is clear. ECGS is
cleared when the external clock generator is turned off or in stop mode (ECGEN is clear) or when EOFF
is set.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
86
Freescale Semiconductor
Functional Description
CMON
CK
IREF
EOFF
Q
1/4
R
R
R
D
D
DFFRR
DFFRS
CK
ECLK
CK
Q
Q
EGGS
R
S
ESTBCLK
ECGEN
NAME
CONFIG2 REGISTER BIT
NAME
REGISTER BIT
NAME
TOP LEVEL SIGNAL
NAME
MODULE SIGNAL
Figure 7-7. External Clock Activity Detector
7.3.5 Clock Selection Circuit
The clock selection circuit, shown in Figure 7-8, contains two clock switches which generate the oscillator
output clock (CGMXCLK) and the timebase clock (TBMCLK) from either the internal clock (ICLK) or the
external clock (ECLK). The COP clock (COPCLK) is identical to TBMCLK. The clock selection circuit also
contains a divide-by-two circuit which creates the clock generator output clock (CGMOUT), which
generates the bus clocks.
CS
SELECT
ICLK
ICLK
ECLK
ECLK
IOFF
IOFF
EOFF
EOFF
CGMXCLK
OUTPUT
SYNCHRONIZING
CLOCK
SWITCHER
DIV2
CGMOUT
FORCE_I
RESET
VSS
FORCE_E
ECGON
SELECT
TBMCLK
OUTPUT
COPCLK
ICLK
ECLK
IOFF
EOFF
SYNCHRONIZING
CLOCK
SWITCHER
FORCE_I
FORCE_E
NAME
CONFIG2 REGISTER BIT
NAME
REGISTER BIT
NAME
TOP LEVEL SIGNAL
NAME
MODULE SIGNAL
Figure 7-8. Clock Selection Circuit Block Diagram
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
87
Internal Clock Generator (ICG) Module)
7.3.5.1 Clock Selection Switches
The first switch creates the oscillator output clock (CGMXCLK) from either the internal clock (ICLK) or the
external clock (ECLK), based on the clock select bit (CS; set selects ECLK, clear selects ICLK). When
switching the CS bit, both ICLK and ECLK must be on (ICGON and ECGON set). The clock being
switched to also must be stable (ICGS or ECGS set).
The second switch creates the timebase clock (TBMCLK) and the COP clock (COPCLK) from ICLK or
ECLK based on the external clock on bit. When ECGON is set, the switch automatically selects the
external clock, regardless of the state of the ECGS bit.
7.3.5.2 Clock Switching Circuit
To robustly switch between the internal clock (ICLK) and the external clock (ECLK), the switch assumes
the clocks are completely asynchronous, so a synchronizing circuit is required to make the transition.
When the select input (the clock select bit for the oscillator output clock switch or the external clock on bit
for the timebase clock switch) is changed, the switch will continue to operate off the original clock for
between one and two cycles as the select input is transitioned through one side of the synchronizer. Next,
the output will be held low for between one and two cycles of the new clock as the select input transitions
through the other side. Then the output starts switching at the new clock’s frequency. This transition
guarantees that no glitches will be seen on the output even though the select input may change
asynchronously to the clocks. The unpredictably of the transition period is a necessary result of the
asynchronicity.
The switch automatically selects ICLK during reset. When the clock monitor is on (CMON is set) and it
determines one of the clock sources is inactive (as indicated by the IOFF or EOFF signals), the circuit is
forced to select the active clock. There are no clocks for the inactive side of the synchronizer to properly
operate, so that side is forced deselected. However, the active side will not be selected until one to two
clock cycles after the IOFF or EOFF signal transitions.
7.4 Usage Notes
The ICG has several features which can provide protection to the microcontroller if properly used. Other
features can greatly simplify usage of the ICG if certain techniques are employed. This section describes
several possible ways to use the ICG and its features. These techniques are not the only ways to use the
ICG and may not be optimum for all environments. In any case, these techniques should be used only as
a template, and the user should modify them according to the application’s requirements.
These notes include:
• Switching clock sources
• Enabling the clock monitor
• Using clock monitor interrupts
• Quantization error in digitally controlled oscillator (DCO) output
• Switching internal clock frequencies
• Nominal frequency settling time
• Improving frequency settling time
• Trimming frequency
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
88
Freescale Semiconductor
Usage Notes
7.4.1 Switching Clock Sources
•
•
•
•
•
Switching from one clock source to another requires both clock sources to be enabled and stable.
A simple flow requires:
Enable desired clock source
Wait for it to become stable
Switch clocks
Disable previous clock source
The key point to remember in this flow is that the clock source cannot be switched (CS cannot be written)
unless the desired clock is on and stable. A short assembly code example of how to employ this flow is
shown in Figure 7-9.
;* Clock Switching Code Example
;* This code switches from internal to external clock
;* Clock monitor and interrupts are not enabled
;* ICG Clock Switch
SwitchItoE:
bset
ECGON,ICGCR
brclr
ECGS,ICGCR,*
bset
CS,ICGCR
bclr
ICGON,ICGCR
;
;
;
;
turn on external oscillator
wait until external clock engaged
select external clock for bus
turn off internal clock (if desired)
Figure 7-9. Code Example for Switching Clock Sources
7.4.2 Enabling the Clock Monitor
Many applications require the clock monitor to determine if one of the clock sources has become inactive,
so the other can be used to recover from a potentially dangerous situation. Using the clock monitor
requires both clocks to be active (ECGON and ICGON both set). To enable the clock monitor, both clocks
also must be stable (ECGS and ICGS both set). This is to prevent the use of the clock monitor when a
clock is first turned on and potentially unstable.
Enabling the clock monitor and clock monitor interrupts requires a flow similar to this:
• Enable the alternate clock source
• Wait for both clock sources to be stable
• Switch to the desired clock source if necessary
• Enable the clock monitor
• Enable clock monitor interrupts
These events must happen in sequence. A short assembly code example of how to employ this flow is
shown in Figure 7-10.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
89
Internal Clock Generator (ICG) Module)
;* Clock Monitor Enable Code Example
;* This code turns on both clocks, selects the desired one,
;* then turns on the Clock Monitor and CM Interrupt
;* ICG Clock Monitor Enable
CMEnable:
bset
ECGON,ICGCR
brclr
bset
bset
bset
ECGS,ICGCR,*
CS,ICGCR
CMON,ICGCR
CMIE,ICGCR
;
;
;
;
;
;
turn on external oscillator
(assumes internal osc is on)
wait until external clock engaged
select external clock for bus
enable Clock Monitor
enable CM interrupt
Figure 7-10. Code Example for Enabling the Clock Monitor
7.4.3 Using Clock Monitor Interrupts
The clock monitor circuit can be used to recover from perilous situations such as crystal loss. To use the
clock monitor effectively, these points should be observed:
• Enable the clock monitor and clock monitor interrupts.
• The first statement in the clock monitor interrupt service routine (CMISR) should be a read to the
ICG control register (ICGCR) to verify that the clock monitor flag (CMF) is set. This is also the first
step in clearing the CMF bit.
• The second statement in the CMISR should be a write to the ICGCR to clear the CMF bit (write the
bit low). Writing the bit high will not affect it. This statement does not need to immediately follow
the first, but must be contained in the CMISR.
• The third statement in the CMISR should be to clear the CMON bit. This is required to ensure
proper reconfiguration of the reference dividers. This statement also must be contained in the
CMISR.
• Although the clock monitor can be enabled only when both clocks are stable (ICGS is set or ECGS
is set), it will remain set if one of the clocks goes unstable.
• The clock monitor only works if the external slow (EXTSLOW) bit in the CONFIG2 register is set to
the correct value.
• The internal and external clocks must both be enabled and running to use the clock monitor.
• When the clock monitor detects inactivity, the inactive clock is automatically deselected and the
active clock selected as the source for CGMXCLK and TBMCLK. The CMISR can use the state of
the CS bit to check which clock is inactive.
• When the clock monitor detects inactivity, the application may have been subjected to extreme
conditions which may have affected other circuits. The CMISR should take any appropriate
precautions.
7.4.4 Quantization Error in DCO Output
The digitally controlled oscillator (DCO) is comprised of three major sub-blocks:
1. Binary weighted divider
2. Variable-delay ring oscillator
3. Ring oscillator fine-adjust circuit
Each of these blocks affects the clock period of the internal clock (ICLK). Since these blocks are controlled
by the digital loop filter (DLF) outputs DDIV and DSTG, the output of the DCO can change only in
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
90
Freescale Semiconductor
Usage Notes
quantized steps as the DLF increments or decrements its output. The following sections describe how
each block will affect the output frequency.
7.4.4.1 Digitally Controlled Oscillator
The digitally controlled oscillator (DCO) is an inaccurate oscillator which generates the internal clock
(ICLK), whose clock period is dependent on the digital loop filter outputs (DSTG[7:0] and DDIV[3:0]).
Because of the digital nature of the DCO, the clock period of ICLK will change in quantized steps. This
will create a clock period difference or quantization error (Q-ERR) from one cycle to the next. Over several
cycles or for longer periods, this error is divided out until it reaches a minimum error of 0.202 percent to
0.368 percent. The dependence of this error on the DDIV[3:0] value and the number of cycles the error is
measured over is shown in Table 7-2.
Table 7-2. Quantization Error in ICLK
DDIV[3:0]
ICLK Cycles
Bus Cycles
τICLK Q-ERR
%0000 (min)
1
NA
6.45%–11.8%
%0000 (min)
4
1
1.61%–2.94%
%0000 (min)
≥ 32
≥8
0.202%–0.368%
%0001
1
NA
3.23%–5.88%
%0001
4
1
0.806%–1.47%
%0001
≥ 16
≥4
0.202%–0.368%
%0010
1
NA
1.61%–2.94%
%0010
4
1
0.403%–0.735%
%0010
≥8
≥2
0.202%–0.368%
%0011
1
NA
0.806%–1.47%
%0011
≥4
≥1
0.202%–0.368%
%0100
1
NA
0.403%–0.735%
%0100
≥2
≥1
0.202%–0.368%
%0101–%1001 (max)
≥1
≥1
0.202%–0.368%
7.4.4.2 Binary Weighted Divider
The binary weighted divider divides the output of the ring oscillator by a power of two, specified by the
DCO divider control bits (DDIV[3:0]). DDIV maximizes at %1001 (values of %1010 through %1111 are
interpreted as %1001), which corresponds to a divide by 512. When DDIV is %0000, the ring oscillator’s
output is divided by 1. Incrementing DDIV by one will double the period; decrementing DDIV will halve the
period. The DLF cannot directly increment or decrement DDIV; DDIV is only incremented or decremented
when an addition or subtraction to DSTG carries or borrows.
7.4.4.3 Variable-Delay Ring Oscillator
The variable-delay ring oscillator’s period is adjustable from 17 to 31 stage delays, in increments of two,
based on the upper three DCO stage control bits (DSTG[7:5]). A DSTG[7:5] of %000 corresponds to 17
stage delays; DSTG[7:5] of %111 corresponds to 31 stage delays. Adjusting the DSTG[5] bit has a 6.45
percent to 11.8 percent effect on the output frequency. This also corresponds to the size correction made
when the frequency error is greater than ±15 percent. The value of the binary weighted divider does not
affect the relative change in output clock period for a given change in DSTG[7:5].
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
91
Internal Clock Generator (ICG) Module)
7.4.4.4 Ring Oscillator Fine-Adjust Circuit
The ring oscillator fine-adjust circuit causes the ring oscillator to effectively operate at non-integer
numbers of stage delays by operating at two different points for a variable number of cycles specified by
the lower five DCO stage control bits (DSTG[4:0]). For example:
• When DSTG[7:5] is %011, the ring oscillator nominally operates at 23 stage delays.
• When DSTG[4:0] is %00000, the ring will always operate at 23 stage delays.
• When DSTG[4:0] is %00001, the ring will operate at 25 stage delays for one of 32 cycles and at 23
stage delays for 31 of 32 cycles.
• Likewise, when DSTG[4:0] is %11111, the ring operates at 25 stage delays for 31 of 32 cycles and
at 23 stage delays for one of 32 cycles.
• When DSTG[7:5] is %111, similar results are achieved by including a variable divide-by-two, so the
ring operates at 31 stages for some cycles and at 17 stage delays, with a divide-by-two for an
effective 34 stage delays, for the remainder of the cycles.
Adjusting the DSTG[0] bit has a 0.202 percent to 0.368 percent effect on the output clock period. This
corresponds to the minimum size correction made by the DLF, and the inherent, long-term quantization
error in the output frequency.
7.4.5 Switching Internal Clock Frequencies
The frequency of the internal clock (ICLK) may need to be changed for some applications. For example,
if the reset condition does not provide the correct frequency, or if the clock is slowed down for a low-power
mode (or sped up after a low-power mode), the frequency must be changed by programming the internal
clock multiplier factor (N). The frequency of ICLK is N times the frequency of IBASE, which is 307.2 kHz
±25 percent.
Before switching frequencies by changing the N value, the clock monitor must be disabled. This is
because when N is changed, the frequency of the low-frequency base clock (IBASE) will change
proportionally until the digital loop filter has corrected the error. Since the clock monitor uses IBASE, it
could erroneously detect an inactive clock. The clock monitor cannot be re-enabled until the internal clock
is stable again (ICGS is set).
The following flow is an example of how to change the clock frequency:
• Verify there is no clock monitor interrupt by reading the CMF bit.
• Turn off the clock monitor.
• If desired, switch to the external clock (see 7.4.1 Switching Clock Sources).
• Change the value of N.
• Switch back to internal (see 7.4.1 Switching Clock Sources), if desired.
• Turn on the clock monitor (see 7.4.2 Enabling the Clock Monitor), if desired.
7.4.6 Nominal Frequency Settling Time
Because the clock period of the internal clock (ICLK) is dependent on the digital loop filter outputs (DDIV
and DSTG) which cannot change instantaneously, ICLK temporarily will operate at an incorrect clock
period when any operating condition changes. This happens whenever the part is reset, the ICG multiply
factor (N) is changed, the ICG trim factor (TRIM) is changed, or the internal clock is enabled after inactivity
(stop mode or disabled operation). The time that the ICLK takes to adjust to the correct period is known
as the settling time.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
92
Freescale Semiconductor
Usage Notes
Settling time depends primarily on how many corrections it takes to change the clock period and the
period of each correction. Since the corrections require four periods of the low-frequency base clock
(4*τIBASE), and since ICLK is N (the ICG multiply factor for the desired frequency) times faster than
IBASE, each correction takes 4*N*τICLK. The period of ICLK, however, will vary as the corrections occur.
7.4.6.1 Settling to Within 15 Percent
When the error is greater than 15 percent, the filter takes eight corrections to double or halve the clock
period. Due to how the DCO increases or decreases the clock period, the total period of these eight
corrections is approximately 11 times the period of the fastest correction. (If the corrections were perfectly
linear, the total period would be 11.5 times the minimum period; however, the ring must be slightly
nonlinear.) Therefore, the total time it takes to double or halve the clock period is 44*N*τICLKFAST.
If the clock period needs more than doubled or halved, the same relationship applies, only for each time
the clock period needs doubled, the total number of cycles doubles. That is, when transitioning from fast
to slow, going from the initial speed to half speed takes 44*N*τICLKFAST; from half speed to quarter speed
takes 88*N*τICLKFAST; going from quarter speed to eighth speed takes 176*N*τICLKFAST; and so on. This
series can be expressed as (2x–1)*44*N*τICLKFAST, where x is the number of times the speed needs
doubled or halved. Since 2x happens to be equal to τICLKSLOW/τICLKFAST, the equation reduces to
44*N*(τICLKSLOW–τICLKFAST).
Note that increasing speed takes much longer than decreasing speed since N is higher. This can be
expressed in terms of the initial clock period (τ1) minus the final clock period (τ2) as such:
τ 15 = abs [ 44N ( τ 1 – τ 2 ) ]
7.4.6.2 Settling to Within 5 Percent
Once the clock period is within 15 percent of the desired clock period, the filter starts making smaller
adjustments. When between 15 percent and 5 percent error, each correction will adjust the clock period
between 1.61 percent and 2.94 percent. In this mode, a maximum of eight corrections will be required to
get to less than 5 percent error. Since the clock period is relatively close to desired, each correction takes
approximately the same period of time, or 4*τIBASE. At this point, the internal clock stable bit (ICGS) will
be set and the clock frequency is usable, although the error will be as high as 5 percent. The total time to
this point is:
τ 5 = abs [ 44N ( τ 1 – τ 2 ) ] + 32τ IBASE
7.4.6.3 Total Settling Time
Once the clock period is within 5 percent of the desired clock period, the filter starts making minimum
adjustments. In this mode, each correction will adjust the frequency between 0.202 percent and 0.368
percent. A maximum of 24 corrections will be required to get to the minimum error. Each correction takes
approximately the same period of time, or 4*τIBASE. Added to the corrections for 15 percent to 5 percent,
this makes 32 corrections (128*τIBASE) to get from 15 percent to the minimum error. The total time to the
minimum error is:
τ tot = abs [ 44N ( τ 1 – τ 2 ) ] + 128τ IBASE
The equations for τ15, τ5, and τtot are dependent on the actual initial and final clock periods τ1 and τ2, not
the nominal. This means the variability in the ICLK frequency due to process, temperature, and voltage
must be considered. Additionally, other process factors and noise can affect the actual tolerances of the
points at which the filter changes modes. This means a worst case adjustment of up to 35 percent (ICLK
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
93
Internal Clock Generator (ICG) Module)
clock period tolerance plus 10 percent) must be added. This adjustment can be reduced with trimming.
Table 7-3 shows some typical values for settling time.
Table 7-3. Typical Settling Time Examples
τ1
τ2
N
τ15
τ5
τtot
1/ (6.45 MHz)
1/ (25.8 MHz)
84
430 μs
535 μs
850 μs
1/ (25.8 MHz)
1/ (6.45 MHz)
21
107 μs
212 μs
525 μs
1/ (25.8 MHz)
1/ (307.2 kHz)
1
141 μs
246 μs
560 μs
1/ (307.2 kHz)
1/ (25.8 MHz)
84
11.9 ms
12.0 ms
12.3 ms
7.4.7 Trimming Frequency on the Internal Clock Generator
The unadjusted frequency of the low-frequency base clock (IBASE), when the comparators in the
frequency comparator indicate zero error, will vary as much as ±25 percent due to process, temperature,
and voltage dependencies. These dependencies are in the voltage and current references, the offset of
the comparators, and the internal capacitor.
The method of changing the unadjusted operating point is by changing the size of the capacitor. This
capacitor is designed with 639 equally sized units. Of that number, 384 of these units are always
connected. The remaining 255 units are put in by adjusting the ICG trim factor (TRIM). The default value
for TRIM is $80, or 128 units, making the default capacitor size 512. Each unit added or removed will
adjust the output frequency by about ±0.195 percent of the unadjusted frequency (adding to TRIM will
decrease frequency). Therefore, the frequency of IBASE can be changed to ±25 percent of its unadjusted
value, which is enough to cancel the process variability mentioned before.
The best way to trim the internal clock is to use the timer to measure the width of an input pulse on an
input capture pin (this pulse must be supplied by the application and should be as long or wide as
possible). Considering the prescale value of the timer and the theoretical (zero error) frequency of the bus
(307.2 kHz *N/4), the error can be calculated. This error, expressed as a percentage, can be divided by
0.195 percent and the resultant factor added or subtracted from TRIM. This process should be repeated
to eliminate any residual error.
7.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power- consumption standby modes.
7.5.1 Wait Mode
The ICG remains active in wait mode. If enabled, the ICG interrupt to the CPU can bring the MCU out of
wait mode.
In some applications, low power-consumption is desired in wait mode and a high-frequency clock is not
needed. In these applications, reduce power consumption by either selecting a low-frequency external
clock and turn the internal clock generator off or reduce the bus frequency by minimizing the ICG multiplier
factor (N) before executing the WAIT instruction.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
94
Freescale Semiconductor
CONFIG2 Options
7.5.2 Stop Mode
The value of the oscillator enable in stop (OSCENINSTOP) bit in the CONFIG2 register determines the
behavior of the ICG in stop mode. If OSCENINSTOP is low, the ICG is disabled in stop and, upon
execution of the STOP instruction, all ICG activity will cease and the output clocks (CGMXCLK,
CGMOUT, COPCLK, and TBMCLK) will be held low. Power consumption will be minimal.
If OSCENINSTOP is high, the ICG is enabled in stop and activity will continue. This is useful if the
timebase module (TBM) is required to bring the MCU out of stop mode. ICG interrupts will not bring the
MCU out of stop mode in this case.
During stop mode, if OSCENINSTOP is low, several functions in the ICG are affected. The stable bits
(ECGS and ICGS) are cleared, which will enable the external clock stabilization divider upon recovery.
The clock monitor is disabled (CMON = 0) which will also clear the clock monitor interrupt enable (CMIE)
and clock monitor flag (CMF) bits. The CS, ICGON, ECGON, N, TRIM, DDIV, and DSTG bits are
unaffected.
7.6 CONFIG2 Options
Four CONFIG2 register options affect the functionality of the ICG. These options are:
1. EXTCLKEN, external clock enable
2. EXTXTALEN, external crystal enable
3. EXTSLOW, slow external clock
4. OSCENINSTOP, oscillator enable in stop
All CONFIG2 options will have a default setting. Refer to Chapter 4 Configuration Register (CONFIG) on
how the CONFIG2 register is used.
7.6.1 External Clock Enable (EXTCLKEN)
External clock enable (EXTCLKEN), when set, enables the ECGON bit to be set. ECGON turns on the
external clock input path through the PTE4/OSC1 pin. When EXTCLKEN is clear, ECGON cannot be set
and PTE4/OSC1 will always perform the PTE4 function.
The default state for this option is clear.
7.6.2 External Crystal Enable (EXTXTALEN)
External crystal enable (EXTXTALEN), when set, will enable an amplifier to drive the PTE3/OSC2 pin
from the PTE4/OSC1 pin. The amplifier will drive only if the external clock enable (EXTCLKEN) bit and
the ECGON bit are also set. If EXTCLKEN or ECGON are clear, PTE3/OSC2 will perform the PTE3
function. When EXTXTALEN is clear, PTE3/OSC2 will always perform the PTE3 function.
EXTXTALEN, when set, also configures the clock monitor to expect an external clock source in the valid
range of crystals (30 kHz to 100 kHz or 1 MHz to 8 MHz). When EXTXTALEN is clear, the clock monitor
will expect an external clock source in the valid range for externally generated clocks when using the clock
monitor (60 Hz to 32 MHz).
EXTXTALEN, when set, also configures the external clock stabilization divider in the clock monitor for a
4096 cycle timeout to allow the proper stabilization time for a crystal. When EXTXTALEN is clear, the
stabilization divider is configured to 16 cycles since an external clock source does not need a startup time.
The default state for this option is clear.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
95
Internal Clock Generator (ICG) Module)
7.6.3 Slow External Clock (EXTSLOW)
Slow external clock (EXTSLOW), when set, will decrease the drive strength of the oscillator amplifier,
enabling low-frequency crystal operation (30 kHz–100 kHz) if properly enabled with the external clock
enable (EXTCLKEN) and external crystal enable (EXTXTALEN) bits. When clear, EXTSLOW enables
high-frequency crystal operation (1 MHz to 8 MHz).
EXTSLOW, when set, also configures the clock monitor to expect an external clock source that is slower
than the low-frequency base clock (60 Hz to 307.2 kHz). When EXTSLOW is clear, the clock monitor will
expect an external clock faster than the low-frequency base clock (307.2 kHz to 32 MHz).
The default state for this option is clear.
7.6.4 Oscillator Enable In Stop (OSCENINSTOP)
Oscillator enable in stop (OSCENINSTOP), when set, will enable the ICG to continue to generate clocks
(either CGMXCLK, CGMOUT, COPCLK, or TBMCLK) in stop mode. This function is used to keep the
timebase and COP running while the rest of the microcontroller stops. The clock monitor and
autoswitching functions remain operative.
When OSCENINSTOP is clear, all clock generation will cease and CGMXCLK, CGMOUT, COPCLK, and
TBMCLK will be forced low during stop mode. The clock monitor and autoswitching functions become
inoperative.
The default state for this option is clear.
7.7 Input/Output (I/O) Registers
The ICG contains five registers, summarized in Figure 7-11. These registers are:
1. ICG control register (ICGCR)
2. ICG multiplier register (ICGMR)
3. ICG trim register (ICGTR)
4. ICG DCO divider control register (ICGDVR)
5. ICG DCO stage control register (ICGDSR)
Several of the bits in these registers have interaction where the state of one bit may force another bit to
a particular state or prevent another bit from being set or cleared. A summary of this interaction is shown
in Table 7-4.
Addr.
6
CMF
ICG Control Register Read:
CMIE
$0036
(ICGCR) Write:
0(1)
See page 98. Reset:
0
0
1. See 7.7.1 ICG Control Register for method of clearing the CMF bit.
$0037
Register Name
Bit 7
ICG Multiply Register Read:
(ICGMR) Write:
See page 99. Reset:
0
5
4
3
CMON
CS
ICGON
0
0
1
0
0
0
N6
N5
N4
N3
N2
N1
N0
0
0
1
0
1
0
1
R
= Reserved
= Unimplemented
2
ICGS
1
ECGON
Bit 0
ECGS
U = Unaffected
Figure 7-11. ICG Module I/O Register Summary
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
96
Freescale Semiconductor
Input/Output (I/O) Registers
Addr.
Register Name
ICG Trim Register Read:
(ICGTR) Write:
See page 100. Reset:
$0038
ICG Divider Control Read:
Register (ICGDVR) Write:
See page 100. Reset:
$0039
ICG DCO Stage Control Read:
Register (ICGDSR) Write:
See page 100. Reset:
$003A
Bit 7
6
5
4
3
2
1
Bit 0
TRIM7
TRIM6
TRIM5
TRIM4
TRIM3
TRIM2
TRIM1
TRIM0
1
0
0
0
0
0
0
0
DDIV3
DDIV2
DDIV1
DDIV0
U
U
U
U
DSTG2
R
DSTG1
R
DSTG0
R
0
0
0
DSTG7
R
DSTG6
R
DSTG5
R
0
DSTG4
DSTG3
R
R
Unaffected by reset
= Unimplemented
R
= Reserved
U = Unaffected
Figure 7-11. ICG Module I/O Register Summary (Continued)
Table 7-4. ICG Module Register Bit Interaction Summary
CMIE
CMF
CMON
CS
ICGON
ICGS
ECGON
ECGS
N[6:0]
TRIM[7:0]
DDIV[3:0]
DSTG[7:0]
Register Bit Results for Given Condition
Reset
0
0
0
0
1
0
0
0
$15
$80
—
—
OSCENINSTOP = 0,
STOP = 1
0
0
0
—
—
0
—
0
—
—
—
—
EXTCLKEN = 0
0
0
0
0
1
—
0
0
—
—
uw
uw
CMF = 1
—
(1)
1
—
1
—
1
—
uw
uw
uw
uw
CMON = 0
0
0
(0)
—
—
—
—
—
—
—
—
—
CMON = 1
—
—
(1)
—
1
—
1
—
uw
uw
uw
uw
CS = 0
—
—
—
(0)
1
—
—
—
—
—
uw
uw
CS = 1
—
—
—
(1)
—
—
1
—
—
—
—
—
ICGON = 0
0
0
0
1
(0)
0
1
—
—
—
—
—
ICGON = 1
—
—
—
—
(1)
—
—
—
—
—
uw
uw
ICGS = 0
us
—
us
uc
—
(0)
—
—
—
—
—
—
ECGON = 0
0
0
0
0
1
—
(0)
0
—
—
uw
uw
ECGS = 0
us
—
us
us
—
—
—
(0)
—
—
—
—
IOFF = 1
—
1*
(1)
1
(1)
0
(1)
—
uw
uw
uw
uw
EOFF = 1
—
1*
(1)
0
(1)
—
(1)
0
uw
uw
uw
uw
N = written
(0)
(0)
(0)
—
—
0*
—
—
—
—
—
—
TRIM = written
(0)
(0)
(0)
—
—
0*
—
—
—
—
—
—
Condition
—
0, 1
0*, 1*
(0), (1)
us, uc, uw
Register bit is unaffected by the given condition.
Register bit is forced clear or set (respectively) in the given condition.
Register bit is temporarily forced clear or set (respectively) in the given condition.
Register bit must be clear or set (respectively) for the given condition to occur.
Register bit cannot be set, cleared, or written (respectively) in the given condition.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
97
Internal Clock Generator (ICG) Module)
7.7.1 ICG Control Register
The ICG control register (ICGCR) contains the control and status bits for the internal clock generator,
external clock generator, and clock monitor as well as the clock select and interrupt enable bits.
Address: $0036
Bit 7
Read:
Write:
Reset:
CMIE
0
6
CMF
0(1)
5
4
3
CMON
CS
ICGON
0
0
1
0
2
ICGS
0
1
Bit 0
ECGS
ECGON
0
0
1. See CMF bit description for method of clearing CMF bit.
= Unimplemented
Figure 7-12. ICG Control Register (ICGCR)
CMIE — Clock Monitor Interrupt Enable Bit
This read/write bit enables clock monitor interrupts. An interrupt will occur when both CMIE and CMF
are set. CMIE can be set when the CMON bit has been set for at least one cycle. CMIE is forced clear
when CMON is clear or during reset.
1 = Clock monitor interrupts enabled
0 = Clock monitor interrupts disabled
CMF — Clock Monitor Interrupt Flag
This read-only bit is set when the clock monitor determines that either ICLK or ECLK becomes inactive
and the CMON bit is set. This bit is cleared by first reading the bit while it is set, followed by writing the
bit low. This bit is forced clear when CMON is clear or during reset.
1 = Either ICLK or ECLK has become inactive.
0 = ICLK and ECLK have not become inactive since the last read of the ICGCR, or the clock monitor
is disabled.
CMON — Clock Monitor On Bit
This read/write bit enables the clock monitor. CMON can be set when both ICLK and ECLK have been
on and stable for at least one bus cycle. (ICGON, ECGON, ICGS, and ECGS are all set.) CMON is
forced set when CMF is set, to avoid inadvertent clearing of CMF. CMON is forced clear when either
ICGON or ECGON is clear, during stop mode with OSCENINSTOP low, or during reset.
1 = Clock monitor output enabled
0 = Clock monitor output disabled
CS — Clock Select Bit
This read/write bit determines which clock will generate the oscillator output clock (CGMXCLK). This
bit can be set when ECGON and ECGS have been set for at least one bus cycle and can be cleared
when ICGON and ICGS have been set for at least one bus cycle. This bit is forced set when the clock
monitor determines the internal clock (ICLK) is inactive or when ICGON is clear. This bit is forced clear
when the clock monitor determines that the external clock (ECLK) is inactive, when ECGON is clear,
or during reset.
1 = External clock (ECLK) sources CGMXCLK
0 = Internal clock (ICLK) sources CGMXCLK
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
98
Freescale Semiconductor
Input/Output (I/O) Registers
ICGON — Internal Clock Generator On Bit
This read/write bit enables the internal clock generator. ICGON can be cleared when the CS bit has
been set and the CMON bit has been clear for at least one bus cycle. ICGON is forced set when the
CMON bit is set, the CS bit is clear, or during reset.
1 = Internal clock generator enabled
0 = Internal clock generator disabled
ICGS — Internal Clock Generator Stable Bit
This read-only bit indicates when the internal clock generator has determined that the internal clock
(ICLK) is within about 5 percent of the desired value. This bit is forced clear when the clock monitor
determines the ICLK is inactive, when ICGON is clear, when the ICG multiplier register (ICGMR) is
written, when the ICG TRIM register (ICGTR) is written, during stop mode with OSCENINSTOP low,
or during reset.
1 = Internal clock is within 5 percent of the desired value.
0 = Internal clock may not be within 5 percent of the desired value.
ECGON — External Clock Generator On Bit
This read/write bit enables the external clock generator. ECGON can be cleared when the CS and
CMON bits have been clear for at least one bus cycle. ECGON is forced set when the CMON bit or the
CS bit is set. ECGON is forced clear during reset.
1 = External clock generator enabled
0 = External clock generator disabled
ECGS — External Clock Generator Stable Bit
This read-only bit indicates when at least 4096 external clock (ECLK) cycles have elapsed since the
external clock generator was enabled. This is not an assurance of the stability of ECLK but is meant
to provide a startup delay. This bit is forced clear when the clock monitor determines ECLK is inactive,
when ECGON is clear, during stop mode with OSCENINSTOP low, or during reset.
1 = 4096 ECLK cycles have elapsed since ECGON was set.
0 = External clock is unstable, inactive, or disabled.
7.7.2 ICG Multiplier Register
Address: $0037
Bit 7
Read:
Write:
Reset:
0
6
5
4
3
2
1
Bit 0
N6
N5
N4
N3
N2
N1
N0
0
0
1
0
1
0
1
= Unimplemented
Figure 7-13. ICG Multiplier Register (ICGMR)
N6:N0 — ICG Multiplier Factor Bits
These read/write bits change the multiplier used by the internal clock generator. The internal clock
(ICLK) will be:
(307.2 kHz ± 25 percent) * N
A value of $00 in this register is interpreted the same as a value of $01. This register cannot be written
when the CMON bit is set. Reset sets this factor to $15 (decimal 21) for default frequency of 6.45 MHz
± 25 percent (1.613 MHz ± 25 percent bus).
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
99
Internal Clock Generator (ICG) Module)
7.7.3 ICG Trim Register
Address: $0038
Bit 7
Read:
TRIM7
Write:
Reset:
1
6
5
4
3
2
1
Bit 0
TRIM6
TRIM5
TRIM4
TRIM3
TRIM2
TRIM1
TRIM0
0
0
0
0
0
0
0
Figure 7-14. ICG Trim Register (ICGTR)
TRIM7:TRIM0 — ICG Trim Factor Bits
These read/write bits change the size of the internal capacitor used by the internal clock generator. By
testing the frequency of the internal clock and incrementing or decrementing this factor accordingly,
the accuracy of the internal clock can be improved to ± 2 percent. Incrementing this register by one
decreases the frequency by 0.195 percent of the unadjusted value. Decrementing this register by one
increases the frequency by 0.195 percent. This register cannot be written when the CMON bit is set.
Reset sets these bits to $80, centering the range of possible adjustment.
7.7.4 ICG DCO Divider Register
Address: $0039
Bit 7
Read:
Write:
Reset:
0
6
5
4
0
0
= Unimplemented
0
3
DDIV3
U
U = Unaffected
2
DDIV2
1
DDIV1
Bit 0
DDIV0
U
U
U
Figure 7-15. ICG DCO Divider Control Register (ICGDVR)
DDIV3:DDIV0 — ICG DCO Divider Control Bits
These bits indicate the number of divide-by-twos (DDIV) that follow the digitally controlled oscillator.
When ICGON is set, DDIV is controlled by the digital loop filter. The range of valid values for DDIV is
from $0 to $9. Values of $A through $F are interpreted the same as $9. Since the DCO is active during
reset, reset has no effect on DSTG and the value may vary.
7.7.5 ICG DCO Stage Register
Address: $003A
Bit 7
Read: DSTG7
Write:
R
Reset:
R
6
DSTG6
R
5
DSTG5
R
4
3
DSTG4
DSTG3
R
R
Unaffected by reset
2
DSTG2
R
1
DSTG1
R
Bit 0
DSTG0
R
= Reserved
Figure 7-16. ICG DCO Stage Control Register (ICGDSR)
DSTG7:DSTG0 — ICG DCO Stage Control Bits
These bits indicate the number of stages (above the minimum) in the digitally controlled oscillator. The
total number of stages is approximately equal to $1FF, so changing DSTG from $00 to $FF will
approximately double the period. Incrementing DSTG will increase the period (decrease the
frequency) by 0.202 percent to 0.368 percent (decrementing has the opposite effect). DSTG cannot
be written when ICGON is set to prevent inadvertent frequency shifting. When ICGON is set, DSTG is
controlled by the digital loop filter. Since the DCO is active during reset, reset has no effect on DSTG
and the value may vary.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
Chapter 8
External Interrupt (IRQ)
8.1 Introduction
The IRQ (external interrupt) module provides a maskable interrupt input.
8.2 Features
Features of the IRQ module include:
• A dedicated external interrupt pin (IRQ)
• IRQ interrupt control bits
• Hysteresis buffer
• Programmable edge-only or edge and level interrupt sensitivity
• Automatic interrupt acknowledge
• Internal pullup resistor
8.3 Functional Description
A logic 0 applied to the external interrupt pin can latch a central processor unit (CPU) interrupt request.
Figure 8-2 shows the structure of the IRQ module.
Interrupt signals on the IRQ pin are latched into the IRQ latch. An interrupt latch remains set until one of
the following actions occurs:
• Vector fetch — A vector fetch automatically generates an interrupt acknowledge signal that clears
the latch that caused the vector fetch.
• Software clear — Software can clear an interrupt latch by writing to the appropriate acknowledge
bit in the interrupt status and control register (INTSCR). Writing a 1 to the ACK bit clears the IRQ
latch.
• Reset — A reset automatically clears the interrupt latch.
The external interrupt pin is falling-edge triggered and is software-configurable to be either falling-edge
or falling-edge and low-level triggered. The MODE bit in the INTSCR controls the triggering sensitivity of
the IRQ pin.
When an interrupt pin is edge-triggered only, the interrupt remains set until a vector fetch, software clear,
or reset occurs.
When an interrupt pin is both falling-edge and low-level triggered, the interrupt remains set until both of
these events occur:
• Vector fetch or software clear
• Return of the interrupt pin to logic 1
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
101
External Interrupt (IRQ)
8-BIT KEYBOARD
INTERRUPT MODULE
FLASH PROGRAMMING ROUTINES
ROM — 720 BYTES
USER FLASH VECTOR SPACE — 36 BYTES
PTE4/OSC1
PTE3/OSC2
INTERNAL CLOCK
GENERATOR MODULE
RST(3)
SYSTEM INTEGRATION
MODULE
IRQ(3)
SINGLE EXTERNAL
INTERRUPT MODULE
VREFH
VREFL
2-CHANNEL TIMER INTERFACE
MODULE 2
DDRA
PTD7/T2CH1(1)
PTD6/T2CH0(1)
PTD5/T1CH1(1)
PTD4/T1CH0(1)
PTD3/SPSCK(1)
PTD2/MOSI(1)
PTD1/MISO(1)
PTD0/SS(1)
PTE2
PTE1/RxD
PTE0/TxD
SERIAL PERIPHERAL
INTERFACE MODULE
MONITOR MODULE
8-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
PTC6(1)
PTC5(1)
PTC4(1)(2)
PTC3(1)(2)
PTC2(1)(2)
PTC1(1)(2)
PTC0(1)(2)
SERIAL COMMUNICATIONS
INTERFACE MODULE
COMPUTER OPERATING
PROPERLY MODULE
POWER-ON RESET
MODULE
VDD
VSS
VDDA
VSSA
2-CHANNEL TIMER INTERFACE
MODULE 1
DDRD
MONITOR ROM — 304 BYTES
PORTA
USER RAM — 512 BYTES
PORTB
DUAL VOLTAGE
LOW-VOLTAGE INHIBIT MODULE
PTB7/AD7
PTB6/AD6
PTB5/AD5
PTB4/AD4
PTB3/AD3
PTB2/AD2
PTB1/AD1
PTB0/AD0
PORTC
USER FLASH
MC68HC908GT16 — 15,872 BYTES
MC68HC908GT8 — 7,680 BYTES
PTA7/KBD7–
PTA0/KBD0(1)
PORTD
SINGLE BREAKPOINT BREAK
MODULE
DDRB
CONTROL AND STATUS
REGISTERS — 64 BYTES
DDRC
PROGRAMMABLE TIMEBASE
MODULE
ARITHMETIC/LOGIC
UNIT (ALU)
MEMORY MAP
MODULE
DDRE
CPU
REGISTERS
PORTE
INTERNAL BUS
M68HC08 CPU
SECURITY
MODULE
CONFIGURATION REGISTER 1
MODULE
CONFIGURATION REGISTER 2
MODULE
MONITOR MODE ENTRY
MODULE
1. Ports are software configurable with pullup device if input port.
2. Higher current drive port pins
3. Pin contains integrated pullup device
Figure 8-1. Block Diagram Highlighting IRQ Block and Pins
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
102
Freescale Semiconductor
IRQ Pin
RESET
ACK
TO CPU FOR
BIL/BIH
INSTRUCTIONS
INTERNAL ADDRESS BUS
VECTOR
FETCH
DECODER
VDD
INTERNAL
PULLUP
DEVICE
VDD
IRQF
D
CLR
Q
IRQ
INTERRUPT
REQUEST
SYNCHRONIZER
CK
IRQ
IMASK
MODE
TO MODE
SELECT
LOGIC
HIGH
VOLTAGE
DETECT
Figure 8-2. IRQ Module Block Diagram
The vector fetch or software clear may occur before or after the interrupt pin returns to logic 1. As long as
the pin is low, the interrupt request remains pending. A reset will clear the latch and the MODE control bit,
thereby clearing the interrupt even if the pin stays low.
When set, the IMASK bit in the INTSCR mask all external interrupt requests. A latched interrupt request
is not presented to the interrupt priority logic unless the IMASK bit is clear.
NOTE
The interrupt mask (I) in the condition code register (CCR) masks all
interrupt requests, including external interrupt requests.
Addr.
Register Name
$001D
IRQ Status and Control Read:
Register (INTSCR) Write:
See page 104. Reset:
Bit 7
6
5
4
3
2
0
0
0
0
IRQF
0
ACK
0
0
0
0
0
0
1
Bit 0
IMASK
MODE
0
0
= Unimplemented
Figure 8-3. IRQ I/O Register Summary
8.4 IRQ Pin
A logic 0 on the IRQ pin can latch an interrupt request into the IRQ latch. A vector fetch, software clear,
or reset clears the IRQ latch.
If the MODE bit is set, the IRQ pin is both falling-edge-sensitive and low-level-sensitive. With MODE set,
both of the following actions must occur to clear IRQ:
• Vector fetch or software clear — A vector fetch generates an interrupt acknowledge signal to clear
the latch. Software may generate the interrupt acknowledge signal by writing a 1 to the ACK bit in
the interrupt status and control register (INTSCR). The ACK bit is useful in applications that poll the
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
103
External Interrupt (IRQ)
•
IRQ pin and require software to clear the IRQ latch. Writing to the ACK bit prior to leaving an
interrupt service routine can also prevent spurious interrupts due to noise. Setting ACK does not
affect subsequent transitions on the IRQ pin. A falling edge that occurs after writing to the ACK bit
another interrupt request. If the IRQ mask bit, IMASK, is clear, the CPU loads the program counter
with the vector address at locations $FFFA and $FFFB.
Return of the IRQ pin to logic 1 — As long as the IRQ pin is at logic 0, IRQ remains active.
The vector fetch or software clear and the return of the IRQ pin to logic 1 may occur in any order. The
interrupt request remains pending as long as the IRQ pin is at logic 0. A reset will clear the latch and the
MODE control bit, thereby clearing the interrupt even if the pin stays low.
If the MODE bit is clear, the IRQ pin is falling-edge-sensitive only. With MODE clear, a vector fetch or
software clear immediately clears the IRQ latch.
The IRQF bit in the INTSCR register can be used to check for pending interrupts. The IRQF bit is not
affected by the IMASK bit, which makes it useful in applications where polling is preferred.
Use the BIH or BIL instruction to read the logic level on the IRQ pin.
NOTE
When using the level-sensitive interrupt trigger, avoid false interrupts by
masking interrupt requests in the interrupt routine.
8.5 IRQ Module During Break Interrupts
The BCFE bit in the SIM break flag control register (SBFCR) enables software to clear the latch during
the break state. See Chapter 19 Development Support.
To allow software to clear the IRQ latch during a break interrupt, write a 1 to the BCFE bit. If a latch is
cleared during the break state, it remains cleared when the MCU exits the break state.
To protect CPU interrupt flags during the break state, write a 0 to the BCFE bit. With BCFE at 0 (its default
state), writing to the ACK bit in the IRQ status and control register during the break state has no effect on
the IRQ interrupt flags.
8.6 IRQ Status and Control Register
The IRQ status and control register (INTSCR) controls and monitors operation of the IRQ module. The
INTSCR:
• Shows the state of the IRQ flag
• Clears the IRQ latch
• Masks IRQ interrupt request
• Controls triggering sensitivity of the IRQ interrupt pin
Address:
Read:
Write:
Reset:
$001D
Bit 7
0
6
5
0
0
= Unimplemented
4
0
3
IRQF
0
2
0
ACK
0
1
Bit 0
IMASK
MODE
0
0
Figure 8-4. IRQ Status and Control Register (INTSCR)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
104
Freescale Semiconductor
IRQ Status and Control Register
IRQF — IRQ Flag Bit
This read-only status bit is high when the IRQ interrupt is pending.
1 = IRQ interrupt pending
0 = IRQ interrupt not pending
ACK — IRQ Interrupt Request Acknowledge Bit
Writing a 1 to this write-only bit clears the IRQ latch. ACK always reads as 0. Reset clears ACK.
IMASK — IRQ Interrupt Mask Bit
Writing a 1 to this read/write bit disables IRQ interrupt requests. Reset clears IMASK.
1 = IRQ interrupt requests disabled
0 = IRQ interrupt requests enabled
MODE — IRQ Edge/Level Select Bit
This read/write bit controls the triggering sensitivity of the IRQ pin. Reset clears MODE.
1 = IRQ interrupt requests on falling edges and low levels
0 = IRQ interrupt requests on falling edges only
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
105
External Interrupt (IRQ)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
106
Freescale Semiconductor
Chapter 9
Keyboard Interrupt Module (KBI)
9.1 Introduction
The keyboard interrupt module (KBI) provides eight independently maskable external interrupts which are
accessible via PTA0–PTA7. When a port pin is enabled for keyboard interrupt function, an internal pullup
device is also enabled on the pin.
9.2 Features
Features include:
• Eight keyboard interrupt pins with separate keyboard interrupt enable bits and one keyboard
interrupt mask
• Hysteresis buffers
• Programmable edge-only or edge- and level- interrupt sensitivity
• Exit from low-power modes
• I/O (input/output) port bit(s) software configurable with pullup device(s) if configured as input port
bit(s)
9.3 Functional Description
Writing to the KBIE7–KBIE0 bits in the keyboard interrupt enable register independently enables or
disables each port A pin as a keyboard interrupt pin. Enabling a keyboard interrupt pin also enables its
internal pullup device. A logic 0 applied to an enabled keyboard interrupt pin latches a keyboard interrupt
request.
A keyboard interrupt is latched when one or more keyboard pins goes low after all were high. The MODEK
bit in the keyboard status and control register controls the triggering mode of the keyboard interrupt.
• If the keyboard interrupt is edge-sensitive only, a falling edge on a keyboard pin does not latch an
interrupt request if another keyboard pin is already low. To prevent losing an interrupt request on
one pin because another pin is still low, software can disable the latter pin while it is low.
• If the keyboard interrupt is falling edge- and low-level sensitive, an interrupt request is present as
long as any keyboard interrupt pin is low and the pin is keyboard interrupt enabled.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
107
Keyboard Interrupt Module (KBI)
8-BIT KEYBOARD
INTERRUPT MODULE
FLASH PROGRAMMING ROUTINES
ROM — 720 BYTES
USER FLASH VECTOR SPACE — 36 BYTES
PTE4/OSC1
PTE3/OSC2
INTERNAL CLOCK
GENERATOR MODULE
RST(3)
SYSTEM INTEGRATION
MODULE
IRQ(3)
SINGLE EXTERNAL
INTERRUPT MODULE
VREFH
VREFL
2-CHANNEL TIMER INTERFACE
MODULE 2
DDRA
PTD7/T2CH1(1)
PTD6/T2CH0(1)
PTD5/T1CH1(1)
PTD4/T1CH0(1)
PTD3/SPSCK(1)
PTD2/MOSI(1)
PTD1/MISO(1)
PTD0/SS(1)
PTE2
PTE1/RxD
PTE0/TxD
SERIAL PERIPHERAL
INTERFACE MODULE
MONITOR MODULE
8-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
PTC6(1)
PTC5(1)
PTC4(1)(2)
PTC3(1)(2)
PTC2(1)(2)
PTC1(1)(2)
PTC0(1)(2)
SERIAL COMMUNICATIONS
INTERFACE MODULE
COMPUTER OPERATING
PROPERLY MODULE
POWER-ON RESET
MODULE
VDD
VSS
VDDA
VSSA
2-CHANNEL TIMER INTERFACE
MODULE 1
DDRD
MONITOR ROM — 304 BYTES
PORTA
USER RAM — 512 BYTES
PORTB
DUAL VOLTAGE
LOW-VOLTAGE INHIBIT MODULE
PTB7/AD7
PTB6/AD6
PTB5/AD5
PTB4/AD4
PTB3/AD3
PTB2/AD2
PTB1/AD1
PTB0/AD0
PORTC
USER FLASH
MC68HC908GT16 — 15,872 BYTES
MC68HC908GT8 — 7,680 BYTES
PTA7/KBD7–
PTA0/KBD0(1)
PORTD
SINGLE BREAKPOINT BREAK
MODULE
DDRB
CONTROL AND STATUS
REGISTERS — 64 BYTES
DDRC
PROGRAMMABLE TIMEBASE
MODULE
ARITHMETIC/LOGIC
UNIT (ALU)
MEMORY MAP
MODULE
DDRE
CPU
REGISTERS
PORTE
INTERNAL BUS
M68HC08 CPU
SECURITY
MODULE
CONFIGURATION REGISTER 1
MODULE
CONFIGURATION REGISTER 2
MODULE
MONITOR MODE ENTRY
MODULE
1. Ports are software configurable with pullup device if input port.
2. Higher current drive port pins
3. Pin contains integrated pullup device
Figure 9-1. Block Diagram Highlighting KBI Block and Pins
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
108
Freescale Semiconductor
Functional Description
INTERNAL BUS
ACKK
KBD0
RESET
VDD
.
TO PULLUP ENABLE
KB0IE
D
.
VECTOR FETCH
DECODER
CLR
KEYF
Q
SYNCHRONIZER
CK
.
KEYBOARD
INTERRUPT
REQUEST
IMASKK
KBD7
MODEK
TO PULLUP ENABLE
KB7IE
Figure 9-2. Keyboard Module Block Diagram
Addr.
$001A
$001B
Register Name
Keyboard Status Read:
and Control Register Write:
(INTKBSCR)
See page 111. Reset:
Keyboard Interrupt Enable Read:
Register Write:
(INTKBIER)
See page 112. Reset:
Bit 7
6
5
4
3
0
0
0
0
KEYF
2
0
ACKK
1
Bit 0
IMASKK
MODEK
0
0
0
0
0
0
0
0
KBIE7
KBIE6
KBIE5
KBIE4
KBIE3
KBIE2
KBIE1
KBIE0
0
0
0
0
0
0
0
0
= Unimplemented
Figure 9-3. I/O Register Summary
If the MODEK bit is set, the keyboard interrupt pins are both falling edge- and low-level sensitive, and both
of the following actions must occur to clear a keyboard interrupt request:
• Vector fetch or software clear — A vector fetch generates an interrupt acknowledge signal to clear
the interrupt request. Software may generate the interrupt acknowledge signal by writing a 1 to the
ACKK bit in the keyboard status and control register (INTKBSCR). The ACKK bit is useful in
applications that poll the keyboard interrupt pins and require software to clear the keyboard
interrupt request. Writing to the ACKK bit prior to leaving an interrupt service routine can also
prevent spurious interrupts due to noise. Setting ACKK does not affect subsequent transitions on
the keyboard interrupt pins. A falling edge that occurs after writing to the ACKK bit latches another
interrupt request. If the keyboard interrupt mask bit, IMASKK, is clear, the CPU loads the program
counter with the vector address at locations $FFE0 and $FFE1.
• Return of all enabled keyboard interrupt pins to logic 1 — As long as any enabled keyboard
interrupt pin is at logic 0, the keyboard interrupt remains set.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
109
Keyboard Interrupt Module (KBI)
The vector fetch or software clear and the return of all enabled keyboard interrupt pins to logic 1 may occur
in any order.
If the MODEK bit is clear, the keyboard interrupt pin is falling-edge-sensitive only. With MODEK clear, a
vector fetch or software clear immediately clears the keyboard interrupt request.
Reset clears the keyboard interrupt request and the MODEK bit, clearing the interrupt request even if a
keyboard interrupt pin stays at logic 0.
The keyboard flag bit (KEYF) in the keyboard status and control register can be used to see if a pending
interrupt exists. The KEYF bit is not affected by the keyboard interrupt mask bit (IMASKK) which makes
it useful in applications where polling is preferred.
To determine the logic level on a keyboard interrupt pin, use the data direction register to configure the
pin as an input and read the data register.
NOTE
Setting a keyboard interrupt enable bit (KBIEx) forces the corresponding
keyboard interrupt pin to be an input, overriding the data direction register.
However, the data direction register bit must be a 0 for software to read the
pin.
9.4 Keyboard Initialization
When a keyboard interrupt pin is enabled, it takes time for the internal pullup to reach a logic 1. Therefore,
a false interrupt can occur as soon as the pin is enabled.
To prevent a false interrupt on keyboard initialization:
1. Mask keyboard interrupts by setting the IMASKK bit in the keyboard status and control register.
2. Enable the KBI pins by setting the appropriate KBIEx bits in the keyboard interrupt enable register.
3. Write to the ACKK bit in the keyboard status and control register to clear any false interrupts.
4. Clear the IMASKK bit.
An interrupt signal on an edge-triggered pin can be acknowledged immediately after enabling the pin. An
interrupt signal on an edge- and level-triggered interrupt pin must be acknowledged after a delay that
depends on the external load.
Another way to avoid a false interrupt:
1. Configure the keyboard pins as outputs by setting the appropriate DDRA bits in data direction
register A.
2. Write 1s to the appropriate port A data register bits.
3. Enable the KBI pins by setting the appropriate KBIEx bits in the keyboard interrupt enable register.
9.5 Low-Power Modes
The WAIT and STOP instructions put the microcontroller unit (MCU) in low power-consumption standby
modes.
9.5.1 Wait Mode
The keyboard module remains active in wait mode. Clearing the IMASKK bit in the keyboard status and
control register enables keyboard interrupt requests to bring the MCU out of wait mode.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
110
Freescale Semiconductor
Keyboard Module During Break Interrupts
9.5.2 Stop Mode
The keyboard module remains active in stop mode. Clearing the IMASKK bit in the keyboard status and
control register enables keyboard interrupt requests to bring the MCU out of stop mode.
9.6 Keyboard Module During Break Interrupts
The system integration module (SIM) controls whether the keyboard interrupt latch can be cleared during
the break state. The BCFE bit in the SIM break flag control register (SBFCR) enables software to clear
status bits during the break state.
To allow software to clear the keyboard interrupt latch during a break interrupt, write a 1 to the BCFE bit.
If a latch is cleared during the break state, it remains cleared when the MCU exits the break state.
To protect the latch during the break state, write a 0 to the BCFE bit. With BCFE at 0 (its default state),
writing to the keyboard acknowledge bit (ACKK) in the keyboard status and control register during the
break state has no effect. See 9.7.1 Keyboard Status and Control Register.
9.7 I/O Registers
These registers control and monitor operation of the keyboard module:
• Keyboard status and control register (INTKBSCR)
• Keyboard interrupt enable register (INTKBIER)
9.7.1 Keyboard Status and Control Register
The keyboard status and control register:
• Flags keyboard interrupt requests
• Acknowledges keyboard interrupt requests
• Masks keyboard interrupt requests
• Controls keyboard interrupt triggering sensitivity
Address: $001A
Read:
Bit 7
6
5
4
3
0
0
0
0
KEYF
0
ACKK
Write:
Reset:
2
0
0
0
0
0
0
1
Bit 0
IMASKK
MODEK
0
0
= Unimplemented
Figure 9-4. Keyboard Status and Control Register (INTKBSCR)
Bits 7–4 — Not used
These read-only bits always read as 0s.
KEYF — Keyboard Flag Bit
This read-only bit is set when a keyboard interrupt is pending. Reset clears the KEYF bit.
1 = Keyboard interrupt pending
0 = No keyboard interrupt pending
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
111
Keyboard Interrupt Module (KBI)
ACKK — Keyboard Acknowledge Bit
Writing a 1 to this write-only bit clears the keyboard interrupt request. ACKK always reads as 0. Reset
clears ACKK.
IMASKK — Keyboard Interrupt Mask Bit
Writing a 1 to this read/write bit prevents the output of the keyboard interrupt mask from generating
interrupt requests. Reset clears the IMASKK bit.
1 = Keyboard interrupt requests masked
0 = Keyboard interrupt requests not masked
MODEK — Keyboard Triggering Sensitivity Bit
This read/write bit controls the triggering sensitivity of the keyboard interrupt pins. Reset clears
MODEK.
1 = Keyboard interrupt requests on falling edges and low levels
0 = Keyboard interrupt requests on falling edges only
9.7.2 Keyboard Interrupt Enable Register
The keyboard interrupt enable register enables or disables each port A pin to operate as a keyboard
interrupt pin
.
Address: $001B
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
KBIE7
KBIE6
KBIE5
KBIE4
KBIE3
KBIE2
KBIE1
KBIE0
0
0
0
0
0
0
0
0
Figure 9-5. Keyboard Interrupt Enable Register (INTKBIER)
KBIE7–KBIE0 — Keyboard Interrupt Enable Bits
Each of these read/write bits enables the corresponding keyboard interrupt pin to latch interrupt
requests. Reset clears the keyboard interrupt enable register.
1 = PTAx pin enabled as keyboard interrupt pin
0 = PTAx pin not enabled as keyboard interrupt pin
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Chapter 10
Low-Voltage Inhibit (LVI)
10.1 Introduction
This section describes the low-voltage inhibit (LVI) module, which monitors the voltage on the VDD pin
and can force a reset when the VDD voltage falls below the LVI trip falling voltage, VTRIPF.
10.2 Features
Features of the LVI module include:
• Programmable LVI reset
• Selectable LVI trip voltage
• Programmable stop mode operation
10.3 Functional Description
Figure 10-1 shows the structure of the LVI module. The LVI is enabled out of reset. The LVI module
contains a bandgap reference circuit and comparator. Clearing the LVI power disable bit, LVIPWRD,
enables the LVI to monitor VDD voltage. Clearing the LVI reset disable bit, LVIRSTD, enables the LVI
module to generate a reset when VDD falls below a voltage, VTRIPF. Setting the LVI enable in stop mode
bit, LVISTOP, enables the LVI to operate in stop mode. Setting the LVI 5-V or 3-V trip point bit, LVI5OR3,
enables the trip point voltage, VTRIPF, to be configured for 5-V operation. Clearing the LVI5OR3 bit
enables the trip point voltage, VTRIPF, to be configured for 3-V operation. The actual trip points are shown
in Chapter 20 Electrical Specifications.
NOTE
After a power-on reset (POR) the LVI’s default mode of operation is 3 V. If
a 5-V system is used, the user must set the LVI5OR3 bit to raise the trip
point to 5-V operation. Note that this must be done after every power-on
reset since the default will revert back to 3-V mode after each power-on
reset. If the VDD supply is below the 5-V mode trip voltage but above the
3-V mode trip voltage when POR is released, the part will operate because
VTRIPF defaults to 3-V mode after a POR. So, in a 5-V system care must be
taken to ensure that VDD is above the 5-V mode trip voltage after POR is
released.
If the user requires 5-V mode and sets the LVI5OR3 bit after a power-on
reset while the VDD supply is not above the VTRIPR for 5-V mode, the
microcontroller unit (MCU) will immediately go into reset. The LVI in this
case will hold the part in reset until either VDD goes above the rising 5-V trip
point, VTRIPR, which will release reset or VDD decreases to approximately 0
V which will re-trigger the power-on reset and reset the trip point to 3-V
operation.
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Low-Voltage Inhibit (LVI)
LVISTOP, LVIPWRD, LVI5OR3, and LVIRSTD are in the configuration register (CONFIG1). See Figure
4-2. Configuration Register 1 (CONFIG1) for details of the LVI’s configuration bits. Once an LVI reset
occurs, the MCU remains in reset until VDD rises above a voltage, VTRIPR, which causes the MCU to exit
reset. See 15.3.2.5 Low-Voltage Inhibit (LVI) Reset for details of the interaction between the SIM and the
LVI. The output of the comparator controls the state of the LVIOUT flag in the LVI status register (LVISR).
An LVI reset also drives the RST pin low to provide low-voltage protection to external peripheral devices.
VDD
STOP INSTRUCTION
LVISTOP
FROM CONFIG1
FROM CONFIG1
LVIRSTD
LVIPWRD
FROM CONFIG
LOW VDD
DETECTOR
VDD > LVITrip = 0
LVI RESET
VDD ≤ LVITrip = 1
LVIOUT
LVI5OR3
FROM CONFIG1
Figure 10-1. LVI Module Block Diagram
Addr.
$FE0C
Register Name
LVI Status Register Read:
(LVISR) Write:
See page 115. Reset:
Bit 7
6
5
4
3
2
1
Bit 0
LVIOUT
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
= Unimplemented
Figure 10-2. LVI I/O Register Summary
10.3.1 Polled LVI Operation
In applications that can operate at VDD levels below the VTRIPF level, software can monitor VDD by polling
the LVIOUT bit. In the configuration register, the LVIPWRD bit must be at 0 to enable the LVI module, and
the LVIRSTD bit must be at 1 to disable LVI resets.
10.3.2 Forced Reset Operation
In applications that require VDD to remain above the VTRIPF level, enabling LVI resets allows the LVI
module to reset the MCU when VDD falls below the VTRIPF level. In the configuration register, the
LVIPWRD and LVIRSTD bits must be at 0 to enable the LVI module and to enable LVI resets.
10.3.3 Voltage Hysteresis Protection
Once the LVI has triggered (by having VDD fall below VTRIPF), the LVI will maintain a reset condition until
VDD rises above the rising trip point voltage, VTRIPR. This prevents a condition in which the MCU is
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LVI Status Register
continually entering and exiting reset if VDD is approximately equal to VTRIPF. VTRIPR is greater than
VTRIPF by the hysteresis voltage, VHYS.
10.3.4 LVI Trip Selection
The LVI5OR3 bit in the configuration register selects whether the LVI is configured for 5-V or 3-V
protection.
NOTE
The microcontroller is guaranteed to operate at a minimum supply voltage.
The trip point (VTRIPF [5 V] or VTRIPF [3 V]) may be lower than this. (See
Chapter 20 Electrical Specifications for the actual trip point voltages.)
10.4 LVI Status Register
The LVI status register (LVISR) indicates if the VDD voltage was detected below the VTRIPF level.
Address:
Read:
$FE0C
Bit 7
6
5
4
3
2
1
Bit 0
LVIOUT
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Write:
Reset:
= Unimplemented
Figure 10-3. LVI Status Register (LVISR)
LVIOUT — LVI Output Bit
This read-only flag becomes set when the VDD voltage falls below the VTRIPF trip voltage (see
Table 10-1). Reset clears the LVIOUT bit.
Table 10-1. LVIOUT Bit Indication
VDD
LVIOUT
VDD > VTRIPR
0
VDD < VTRIPF
1
VTRIPF < VDD < VTRIPR
Previous value
10.5 LVI Interrupts
The LVI module does not generate interrupt requests.
10.6 Low-Power Modes
The STOP and WAIT instructions put the MCU in low power-consumption standby modes.
10.6.1 Wait Mode
If enabled, the LVI module remains active in wait mode. If enabled to generate resets, the LVI module can
generate a reset and bring the MCU out of wait mode.
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Low-Voltage Inhibit (LVI)
10.6.2 Stop Mode
If enabled in stop mode (LVISTOP set), the LVI module remains active in stop mode. If enabled to
generate resets, the LVI module can generate a reset and bring the MCU out of stop mode.
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Chapter 11
Low-Power Modes (MODES)
11.1 Introduction
The microcontroller (MCU) may enter two low-power modes: wait mode and stop mode. They are
common to all HC08 MCUs and are entered through instruction execution. This section describes how
each module acts in the low-power modes.
11.1.1 Wait Mode
The WAIT instruction puts the MCU in a low-power standby mode in which the central processor unit
(CPU) clock is disabled but the bus clock continues to run. Power consumption can be further reduced by
disabling the LVI module and/or the timebase module through bits in the CONFIG1 register. (See
Chapter 4 Configuration Register (CONFIG).)
11.1.2 Stop Mode
Stop mode is entered when a STOP instruction is executed. The CPU clock is disabled and the bus clock
is disabled if the OSCENINSTOP bit in the CONFIG2 register is at a 0. (See Chapter 4 Configuration
Register (CONFIG).)
11.2 Analog-to-Digital Converter (ADC)
11.2.1 Wait Mode
The analog-to-digital converter (ADC) continues normal operation during wait mode. Any enabled CPU
interrupt request from the ADC can bring the MCU out of wait mode. If the ADC is not required to bring
the MCU out of wait mode, power down the ADC by setting ADCH4–ADCH0 bits in the ADC status and
control register before executing the WAIT instruction.
11.2.2 Stop Mode
The ADC module is inactive after the execution of a STOP instruction. Any pending conversion is aborted.
ADC conversions resume when the MCU exits stop mode after an external interrupt. Allow one
conversion cycle to stabilize the analog circuitry.
11.3 Break Module (BRK)
11.3.1 Wait Mode
If enabled, the break (BRK) module is active in wait mode. In the break routine, the user can subtract one
from the return address on the stack if the SBSW bit in the break status register is set.
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Low-Power Modes (MODES)
11.3.2 Stop Mode
The break module is inactive in stop mode. A break interrupt causes exit from stop mode and sets the
SBSW bit in the break status register. The STOP instruction does not affect break module register states.
11.4 Central Processor Unit (CPU)
11.4.1 Wait Mode
The WAIT instruction:
• Clears the interrupt mask (I bit) in the condition code register, enabling interrupts. After exit from
wait mode by interrupt, the I bit remains clear. After exit by reset, the I bit is set.
• Disables the CPU clock
11.4.2 Stop Mode
The STOP instruction:
• Clears the interrupt mask (I bit) in the condition code register, enabling external interrupts. After
exit from stop mode by external interrupt, the I bit remains clear. After exit by reset, the I bit is set.
• Disables the CPU clock
After exiting stop mode, the CPU clock begins running after the oscillator stabilization delay.
11.5 Internal Clock Generator Module (ICG)
11.5.1 Wait Mode
The internal clock generator (ICG) module remains active in wait mode. If enabled, the ICG interrupt to
the CPU can bring the MCU out of wait mode.
In some applications, low power-consumption is desired in wait mode and a high-frequency clock is not
needed. In these applications, reduce power consumption by either selecting a low-frequency external
clock and turn the internal clock generator off or reduce the bus frequency by minimizing the ICG multiplier
factor (N) before executing the WAIT instruction.
11.5.2 Stop Mode
The value of the oscillator enable in stop (OSCENINSTOP) bit in the CONFIG2 register determines the
behavior of the ICG in stop mode. If OSCENINSTOP is low, the ICG is disabled in stop and, upon
execution of the STOP instruction, all ICG activity will cease and the output clocks (CGMXCLK,
CGMOUT, COPCLK, and TBMCLK) will be held low. Power consumption will be minimal.
If OSCENINSTOP is high, the ICG is enabled in stop and activity will continue. This is useful if the
timebase module (TBM) is required to bring the MCU out of stop mode. ICG interrupts will not bring the
MCU out of stop mode in this case.
During stop mode, if OSCENINSTOP is low, several functions in the ICG are affected. The stable bits
(ECGS and ICGS) are cleared, which will enable the external clock stabilization divider upon recovery.
The clock monitor is disabled (CMON = 0) which will also clear the clock monitor interrupt enable (CMIE)
and clock monitor flag (CMF) bits. The CS, ICGON, ECGON, N, TRIM, DDIV, and DSTG bits are
unaffected.
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Computer Operating Properly Module (COP)
11.6 Computer Operating Properly Module (COP)
11.6.1 Wait Mode
The computer operating properly (COP) module remains active in wait mode. To prevent a COP reset
during wait mode, periodically clear the COP counter in a CPU interrupt routine.
11.6.2 Stop Mode
Stop mode turns off the COPCLK input to the COP and clears the COP prescaler. Service the COP
immediately before entering or after exiting stop mode to ensure a full COP timeout period after entering
or exiting stop mode.
The STOP bit in the CONFIG1 register enables the STOP instruction. To prevent inadvertently turning off
the COP with a STOP instruction, disable the STOP instruction by clearing the STOP bit.
11.7 External Interrupt Module (IRQ)
11.7.1 Wait Mode
The external interrupt (IRQ) module remains active in wait mode. Clearing the IMASK1 bit in the IRQ
status and control register enables IRQ CPU interrupt requests to bring the MCU out of wait mode.
11.7.2 Stop Mode
The IRQ module remains active in stop mode. Clearing the IMASK1 bit in the IRQ status and control
register enables IRQ CPU interrupt requests to bring the MCU out of stop mode.
11.8 Keyboard Interrupt Module (KBI)
11.8.1 Wait Mode
The keyboard interrupt (KBI) module remains active in wait mode. Clearing the IMASKK bit in the
keyboard status and control register enables keyboard interrupt requests to bring the MCU out of wait
mode.
11.8.2 Stop Mode
The keyboard module remains active in stop mode. Clearing the IMASKK bit in the keyboard status and
control register enables keyboard interrupt requests to bring the MCU out of stop mode.
11.9 Low-Voltage Inhibit Module (LVI)
11.9.1 Wait Mode
If enabled, the low-voltage inhibit (LVI) module remains active in wait mode. If enabled to generate resets,
the LVI module can generate a reset and bring the MCU out of wait mode.
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Low-Power Modes (MODES)
11.9.2 Stop Mode
If enabled, the LVI module remains active in stop mode. If enabled to generate resets, the LVI module
can generate a reset and bring the MCU out of stop mode.
11.10 Enhanced Serial Communications Interface Module (SCI)
11.10.1 Wait Mode
The enhanced serial communications interface (ESCI), or SCI module for short, module remains active
in wait mode. Any enabled CPU interrupt request from the SCI module can bring the MCU out of wait
mode.
If SCI module functions are not required during wait mode, reduce power consumption by disabling the
module before executing the WAIT instruction.
11.10.2 Stop Mode
The SCI module is inactive in stop mode. The STOP instruction does not affect SCI register states. SCI
module operation resumes after the MCU exits stop mode.
Because the internal clock is inactive during stop mode, entering stop mode during an SCI transmission
or reception results in invalid data.
11.11 Serial Peripheral Interface Module (SPI)
11.11.1 Wait Mode
The serial peripheral interface (SPI) module remains active in wait mode. Any enabled CPU interrupt
request from the SPI module can bring the MCU out of wait mode.
If SPI module functions are not required during wait mode, reduce power consumption by disabling the
SPI module before executing the WAIT instruction.
11.11.2 Stop Mode
The SPI module is inactive in stop mode. The STOP instruction does not affect SPI register states. SPI
operation resumes after an external interrupt. If stop mode is exited by reset, any transfer in progress is
aborted, and the SPI is reset.
11.12 Timer Interface Module (TIM1 and TIM2)
11.12.1 Wait Mode
The timer interface modules (TIM) remain active in wait mode. Any enabled CPU interrupt request from
the TIM can bring the MCU out of wait mode.
If TIM functions are not required during wait mode, reduce power consumption by stopping the TIM before
executing the WAIT instruction.
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Timebase Module (TBM)
11.12.2 Stop Mode
The TIM is inactive in stop mode. The STOP instruction does not affect register states or the state of the
TIM counter. TIM operation resumes when the MCU exits stop mode after an external interrupt.
11.13 Timebase Module (TBM)
11.13.1 Wait Mode
The timebase module (TBM) remains active after execution of the WAIT instruction. In wait mode, the
timebase register is not accessible by the CPU.
If the timebase functions are not required during wait mode, reduce the power consumption by stopping
the timebase before enabling the WAIT instruction.
11.13.2 Stop Mode
The timebase module may remain active after execution of the STOP instruction if the oscillator has been
enabled to operate during stop mode through the OSCENINSTOP bit in the CONFIG2 register. The
timebase module can be used in this mode to generate a periodic wakeup from stop mode.
If the oscillator has not been enabled to operate in stop mode, the timebase module will not be active
during stop mode. In stop mode, the timebase register is not accessible by the CPU.
If the timebase functions are not required during stop mode, reduce the power consumption by stopping
the timebase before enabling the STOP instruction.
11.14 Exiting Wait Mode
These events restart the CPU clock and load the program counter with the reset vector or with an interrupt
vector:
• External reset — A logic 0 on the RST pin resets the MCU and loads the program counter with the
contents of locations $FFFE and $FFFF.
• External interrupt — A high-to-low transition on an external interrupt pin (IRQ pin) loads the
program counter with the contents of locations: $FFFA and $FFFB; IRQ pin.
• Break interrupt — A break interrupt loads the program counter with the contents of $FFFC and
$FFFD.
• Computer operating properly module (COP) reset — A timeout of the COP counter resets the MCU
and loads the program counter with the contents of $FFFE and $FFFF.
• Low-voltage inhibit module (LVI) reset — A power supply voltage below the VTRIPF voltage resets
the MCU and loads the program counter with the contents of locations $FFFE and $FFFF.
• Internal Clock Generator module (ICG) interrupt — A CPU interrupt request from the ICG loads the
program counter with the contents of $FFF8 and $FFF9.
• Keyboard module (KBI) interrupt — A CPU interrupt request from the KBI module loads the
program counter with the contents of $FFE0 and $FFE1.
• Timer 1 interface module (TIM1) interrupt — A CPU interrupt request from the TIM1 loads the
program counter with the contents of:
– $FFF2 and $FFF3; TIM1 overflow
– $FFF4 and $FFF5; TIM1 channel 1
– $FFF6 and $FFF7; TIM1 channel 0
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Low-Power Modes (MODES)
•
•
•
•
•
Timer 2 interface module (TIM2) interrupt — A CPU interrupt request from the TIM2 loads the
program counter with the contents of:
– $FFEC and $FFED; TIM2 overflow
– $FFEE and $FFEF; TIM2 channel 1
– $FFF0 and $FFF1; TIM2 channel 0
Serial peripheral interface module (SPI) interrupt — A CPU interrupt request from the SPI loads
the program counter with the contents of:
– $FFE8 and $FFE9; SPI transmitter
– $FFEA and $FFEB; SPI receiver
Serial communications interface module (SCI) interrupt — A CPU interrupt request from the SCI
loads the program counter with the contents of:
– $FFE2 and $FFE3; SCI transmitter
– $FFE4 and $FFE5; SCI receiver
– $FFE6 and $FFE7; SCI receiver error
Analog-to-digital converter module (ADC) interrupt — A CPU interrupt request from the ADC loads
the program counter with the contents of: $FFDE and $FFDF; ADC conversion complete.
Timebase module (TBM) interrupt — A CPU interrupt request from the TBM loads the program
counter with the contents of: $FFDC and $FFDD; TBM interrupt.
11.15 Exiting Stop Mode
These events restart the system clocks and load the program counter with the reset vector or with an
interrupt vector:
• External reset — A logic 0 on the RST pin resets the MCU and loads the program counter with the
contents of locations $FFFE and $FFFF.
• External interrupt — A high-to-low transition on an external interrupt pin loads the program counter
with the contents of locations:
– $FFFA and $FFFB; IRQ pin
– $FFE0 and $FFE1; keyboard interrupt pins
• Low-voltage inhibit (LVI) reset — A power supply voltage below the LVITRIPF voltage resets the
MCU and loads the program counter with the contents of locations $FFFE and $FFFF.
• Break interrupt — A break interrupt loads the program counter with the contents of locations $FFFC
and $FFFD.
• Timebase module (TBM) interrupt — A TBM interrupt loads the program counter with the contents
of locations $FFDC and $FFDD when the timebase counter has rolled over. This allows the TBM
to generate a periodic wakeup from stop mode.
Upon exit from stop mode, the system clocks begin running after an oscillator stabilization delay. A 12-bit
stop recovery counter inhibits the system clocks for 4096 CGMXCLK cycles after the reset or external
interrupt.
The short stop recovery bit, SSREC, in the CONFIG1 register controls the oscillator stabilization delay
during stop recovery. Setting SSREC reduces stop recovery time from 4096 CGMXCLK cycles to 32
CGMXCLK cycles.
NOTE
Use the full stop recovery time (SSREC = 0) in applications that use an
external crystal.
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Chapter 12
Input/Output (I/O) Ports (PORTS)
12.1 Introduction
Bidirectional input-output (I/O) pins form five parallel ports. All I/O pins are programmable as inputs or
outputs. All individual bits within port A, port C, and port D are software configurable with pullup devices
if configured as input port bits. The pullup devices are automatically and dynamically disabled when a port
bit is switched to output mode.
NOTE
Connect any unused I/O pins to an appropriate logic level, either VDD or
VSS. Although the I/O ports do not require termination for proper operation,
termination reduces excess current consumption and the possibility of
electrostatic damage.
Addr.
$0000
$0001
$0002
$0003
$0004
$0005
Register Name
Read:
Port A Data Register
(PTA) Write:
See page 126.
Reset:
Read:
Port B Data Register
(PTB) Write:
See page 128.
Reset:
Read:
Port C Data Register
(PTC) Write:
See page 130.
Reset:
Read:
Port D Data Register
(PTD) Write:
See page 132.
Reset:
Read:
Data Direction Register A
(DDRA) Write:
See page 126.
Reset:
Read:
Data Direction Register B
(DDRB) Write:
See page 128.
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
PTA7
PTA6
PTA5
PTA4
PTA3
PTA2
PTA1
PTA0
PTB2
PTB1
PTB0
PTC2
PTC1
PTC0
PTD2
PTD1
PTD0
Unaffected by reset
PTB7
PTB6
PTB5
PTB4
PTB3
Unaffected by reset
0
PTC6
PTC5
PTC4
PTC3
Unaffected by reset
PTD7
PTD6
PTD5
PTD4
PTD3
Unaffected by reset
DDRA7
DDRA6
DDRA5
DDRA4
DDRA3
DDRA2
DDRA1
DDRA0
0
0
0
0
0
0
0
0
DDRB7
DDRB6
DDRB5
DDRB4
DDRB3
DDRB2
DDRB1
DDRB0
0
0
0
0
0
0
0
0
= Unimplemented
Figure 12-1. I/O Port Register Summary
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Input/Output (I/O) Ports (PORTS)
Addr.
$0006
$0007
$0008
$000C
$000D
$000E
$000F
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
DDRC6
DDRC5
DDRC4
DDRC3
DDRC2
DDRC1
DDRC0
0
0
0
0
0
0
0
0
DDRD7
DDRD6
DDRD5
DDRD4
DDRD3
DDRD2
DDRD1
DDRD0
0
0
0
0
0
0
0
0
Read:
Port E Data Register
(PTE) Write:
See page 135.
Reset:
0
0
0
PTE4
PTE3
PTE2
PTE1
PTE0
Read:
Data Direction Register E
(DDRE) Write:
See page 136.
Reset:
0
0
0
0
0
Read:
Data Direction Register C
(DDRC) Write:
See page 130.
Reset:
Read:
Data Direction Register D
(DDRD) Write:
See page 133.
Reset:
0
Unaffected by reset
Read:
Port A Input Pullup Enable
PTAPUE7
Register (PTAPUE) Write:
See page 127.
Reset:
0
Read:
Port C Input Pullup Enable
Register (PTCPUE) Write:
See page 131.
Reset:
0
0
Read:
Port D Input Pullup Enable
PTDPUE7
Register (PTDPUE) Write:
See page 134.
Reset:
0
DDRE4
DDRE3
DDRE2
DDRE1
DDRE0
0
0
0
0
0
0
PTAPUE6
PTAPUE5
PTAPUE4
PTAPUE3
PTAPUE2
PTAPUE1
PTAPUE0
0
0
0
0
0
0
0
PTCPUE6
PTCPUE5
PTCPUE4
PTCPUE3
PTCPUE2
PTCPUE1
PTCPUE0
0
0
0
0
0
0
0
PTDPUE6
PTDPUE5
PTDPUE4
PTDPUE3
PTDPUE2
PTDPUE1
PTDPUE0
0
0
0
0
0
0
0
= Unimplemented
Figure 12-1. I/O Port Register Summary (Continued)
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Introduction
Table 12-1. Port Control Register Bits Summary
Port
A
B
C
D
E
Bit
DDR
Module Control
0
DDRA0
KBIE0
PTA0/KBD0
1
DDRA1
KBIE1
PTA1/KBD1
2
DDRA2
KBIE2
PTA2/KBD2
3
DDRA3
KBIE3
PTA3/KBD3
4
DDRA4
KBIE4
PTA4/KBD4
5
DDRA5
KBIE5
PTA5/KBD5
6
DDRA6
KBIE6
PTA6/KBD6
7
DDRA7
KBIE7
PTA7/KBD7
KBD
Pin
0
DDRB0
PTB0/AD0
1
DDRB1
PTB1/AD1
2
DDRB2
PTB2/AD2
3
DDRB3
4
DDRB4
5
DDRB5
PTB5/AD5
6
DDRB6
PTB6/AD6
7
DDRB7
PTB7/AD7
0
DDRC0
PTC0
1
DDRC1
PTC1
2
DDRC2
PTC2
3
DDRC3
PTC3
4
DDRC4
PTC4
5
DDRC5
PTC5
6
DDRC6
PTC6
0
DDRD0
PTD0/SS
1
DDRD1
2
DDRD2
3
DDRD3
4
DDRD4
5
DDRD5
6
DDRD6
7
DDRD7
0
DDRE0
1
DDRE1
2
DDRE2
3
DDRE3
4
DDRE4
ADC
SPI
ADCH4–ADCH0
SPE
PTB3/AD3
PTB4/AD4
PTD1/MISO
PTD2/MOSI
PTD3/SPSCK
TIM1
TIM2
ELS0B:ELS0A
PTD4/T1CH0
ELS1B:ELS1A
PTD5/T1CH1
ELS0B:ELS0A
PTD6/T2CH0
ELS1B:ELS1A
PTD7/T2CH1
PTE0/TxD
SCI
ENSCI
ICG
ECGON:
EXTXTALEN
PTE3/OSC2
ECGON
PTE4/OSC1
PTE1/RxD
PTE2
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
125
Input/Output (I/O) Ports (PORTS)
12.2 Port A
Port A is an 8-bit special-function port that shares all eight of its pins with the keyboard interrupt (KBI)
module. Port A also has software configurable pullup devices if configured as an input port.
12.2.1 Port A Data Register
The port A data register (PTA) contains a data latch for each of the eight port A pins.
Address:
Read:
Write:
$0000
Bit 7
6
5
4
3
2
1
Bit 0
PTA7
PTA6
PTA5
PTA4
PTA3
PTA2
PTA1
PTA0
KBD2
KBD1
KBD0
Reset:
Alternative
Function:
Unaffected by reset
KBD7
KBD6
KBD5
KBD4
KBD3
Figure 12-2. Port A Data Register (PTA)
PTA7–PTA0 — Port A Data Bits
These read/write bits are software programmable. Data direction of each port A pin is under the control
of the corresponding bit in data direction register A. Reset has no effect on port A data.
KBD7–KBD0 — Keyboard Inputs
The keyboard interrupt enable bits, KBIE7–KBIE0, in the keyboard interrupt control register (KBICR)
enable the port A pins as external interrupt pins. See Chapter 9 Keyboard Interrupt Module (KBI).
12.2.2 Data Direction Register A
Data direction register A (DDRA) determines whether each port A pin is an input or an output. Writing a 1
to a DDRA bit enables the output buffer for the corresponding port A pin; a 0 disables the output buffer.
Address:
Read:
Write:
Reset:
$0004
Bit 7
6
5
4
3
2
1
Bit 0
DDRA7
DDRA6
DDRA5
DDRA4
DDRA3
DDRA2
DDRA1
DDRA0
0
0
0
0
0
0
0
0
Figure 12-3. Data Direction Register A (DDRA)
DDRA7–DDRA0 — Data Direction Register A Bits
These read/write bits control port A data direction. Reset clears DDRA7–DDRA0, configuring all port
A pins as inputs.
1 = Corresponding port A pin configured as output
0 = Corresponding port A pin configured as input
NOTE
Avoid glitches on port A pins by writing to the port A data register before
changing data direction register A bits from 0 to 1.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
126
Freescale Semiconductor
Port A
Figure 12-4 shows the port A I/O logic.
VDD
READ DDRA ($0004)
PTAPUEx
WRITE DDRA ($0004)
DDRAx
INTERNAL DATA BUS
RESET
WRITE PTA ($0000)
45 k
PTAx
PTAx
READ PTA ($0000)
Figure 12-4. Port A I/O Circuit
When bit DDRAx is a 1, reading address $0000 reads the PTAx data latch. When bit DDRAx is a 0,
reading address $0000 reads the voltage level on the pin. The data latch can always be written,
regardless of the state of its data direction bit. Table 12-2 summarizes the operation of the port A pins.
Table 12-2. Port A Pin Functions
PTAPUE
Bit
DDRA
Bit
PTA
Bit
I/O Pin
Mode
Accesses to DDRA
Accesses to PTA
Read/Write
Read
Write
1
0
X(1)
Input, VDD(2)
DDRA7–DDRA0
Pin
PTA7–PTA0(3)
0
0
X
Input, Hi-Z(4)
DDRA7–DDRA0
Pin
PTA7–PTA0(3)
X
1
X
Output
DDRA7–DDRA0
PTA7–PTA0
PTA7–PTA0
1. X = Don’t care
2. I/O pin pulled up to VDD by internal pullup device
3. Writing affects data register, but does not affect input.
4. Hi-Z = High impedance
12.2.3 Port A Input Pullup Enable Register
The port A input pullup enable register (PTAPUE) contains a software configurable pullup device for each
of the eight port A pins. Each bit is individually configurable and requires that the data direction register,
DDRA, bit be configured as an input. Each pullup is automatically and dynamically disabled when a port
bit’s DDRA is configured for output mode
.
Address:
$0004
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
PTAPUE7
PTAPUE6
PTAPUE5
PTAPUE4
PTAPUE3
PTAPUE2
PTAPUE1
PTAPUE0
0
0
0
0
0
0
0
0
Figure 12-5. Port A Input Pullup Enable Register (PTAPUE)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
127
Input/Output (I/O) Ports (PORTS)
PTAPUE7–PTAPUE0 — Port A Input Pullup Enable Bits
These writable bits are software programmable to enable pullup devices on an input port bit.
1 = Corresponding port A pin configured to have internal pullup
0 = Corresponding port A pin has internal pullup disconnected
12.3 Port B
Port B is an 8-bit special-function port that shares all eight of its pins with the analog-to-digital converter
(ADC) module.
12.3.1 Port B Data Register
The port B data register (PTB) contains a data latch for each of the eight port pins.
Address:
$0001
Read:
Write:
Bit 7
6
5
4
3
2
1
Bit 0
PTB7
PTB6
PTB5
PTB4
PTB3
PTB2
PTB1
PTB0
AD2
AD1
AD0
Reset:
Unaffected by reset
Alternative Function:
AD7
AD6
AD5
AD4
AD3
Figure 12-6. Port B Data Register (PTB)
PTB7–PTB0 — Port B Data Bits
These read/write bits are software-programmable. Data direction of each port B pin is under the control
of the corresponding bit in data direction register B. Reset has no effect on port B data.
AD7–AD0 — Analog-to-Digital Input Bits
AD7–AD0 are pins used for the input channels to the analog-to-digital converter module. The channel
select bits in the ADC status and control register define which port B pin will be used as an ADC input
and overrides any control from the port I/O logic by forcing that pin as the input to the analog circuitry.
NOTE
Care must be taken when reading port B while applying analog voltages to
AD7–AD0 pins. If the appropriate ADC channel is not enabled, excessive
current drain may occur if analog voltages are applied to the PTBx/ADx pin,
while PTB is read as a digital input. Those ports not selected as analog
input channels are considered digital I/O ports.
12.3.2 Data Direction Register B
Data direction register B (DDRB) determines whether each port B pin is an input or an output. Writing a 1
to a DDRB bit enables the output buffer for the corresponding port B pin; a 0 disables the output buffer.
Address:
Read:
Write:
Reset:
$0005
Bit 7
6
5
4
3
2
1
Bit 0
DDRB7
DDRB6
DDRB5
DDRB4
DDRB3
DDRB2
DDRB1
DDRB0
0
0
0
0
0
0
0
0
Figure 12-7. Data Direction Register B (DDRB)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
128
Freescale Semiconductor
Port C
DDRB7–DDRB0 — Data Direction Register B Bits
These read/write bits control port B data direction. Reset clears DDRB7–DDRB0], configuring all port
B pins as inputs.
1 = Corresponding port B pin configured as output
0 = Corresponding port B pin configured as input
NOTE
Avoid glitches on port B pins by writing to the port B data register before
changing data direction register B bits from 0 to 1.
Figure 12-8 shows the port B I/O logic.
READ DDRB ($0005)
INTERNAL DATA BUS
WRITE DDRB ($0005)
DDRBx
RESET
WRITE PTB ($0001)
PTBx
PTBx
READ PTB ($0001)
Figure 12-8. Port B I/O Circuit
When bit DDRBx is a 1, reading address $0001 reads the PTBx data latch. When bit DDRBx is a 0,
reading address $0001 reads the voltage level on the pin. The data latch can always be written,
regardless of the state of its data direction bit. Table 12-3 summarizes the operation of the port B pins.
Table 12-3. Port B Pin Functions
DDRB
Bit
PTB
Bit
I/O Pin
Mode
Accesses to DDRB
Accesses to PTB
Read/Write
Read
Write
0
X(1)
Input, Hi-Z(2)
DDRB7–DDRB0
Pin
PTB7–PTB0(3)
1
X
Output
DDRB7–DDRB0
PTB7–PTB0
PTB7–PTB0
1. X = Don’t care
2. Hi-Z = High impedance
3. Writing affects data register, but does not affect input.
12.4 Port C
Port C is a 7-bit, general-purpose bidirectional I/O port. Port C also has software configurable pullup
devices if configured as an input port.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
129
Input/Output (I/O) Ports (PORTS)
12.4.1 Port C Data Register
The port C data register (PTC) contains a data latch for each of the seven port C pins.
NOTE
Bit 6 and bit 5 of PTC are not available in the 42-pin shrink dual in-line
package.
Address:
$0002
Bit 7
Read:
0
Write:
6
5
4
3
2
1
Bit 0
PTC6
PTC5
PTC4
PTC3
PTC2
PTC1
PTC0
Reset:
Unaffected by reset
= Unimplemented
Figure 12-9. Port C Data Register (PTC)
PTC6–PTC0 — Port C Data Bits
These read/write bits are software-programmable. Data direction of each port C pin is under the control
of the corresponding bit in data direction register C. Reset has no effect on port C data.
12.4.2 Data Direction Register C
Data direction register C (DDRC) determines whether each port C pin is an input or an output. Writing a 1
to a DDRC bit enables the output buffer for the corresponding port C pin; a 0 disables the output buffer.
Address:
$0006
Bit 7
Read:
0
Write:
Reset:
0
6
5
4
3
2
1
Bit 0
DDRC6
DDRC5
DDRC4
DDRC3
DDRC2
DDRC1
DDRC0
0
0
0
0
0
0
0
= Unimplemented
Figure 12-10. Data Direction Register C (DDRC)
DDRC6–DDRC0 — Data Direction Register C Bits
These read/write bits control port C data direction. Reset clears DDRC6–DDRC0, configuring all port C
pins as inputs.
1 = Corresponding port C pin configured as output
0 = Corresponding port C pin configured as input
NOTE
Avoid glitches on port C pins by writing to the port C data register before
changing data direction register C bits from 0 to 1.
Figure 12-11 shows the port C I/O logic.
NOTE
For those devices packaged in a 42-pin shrink dual in-line package, PTC5
and PTC6 are connected to ground internally. DDRC5 and DDRC6 should
be set to a 0 to configure PTC5 and PTC6 as inputs.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
130
Freescale Semiconductor
Port C
VDD
READ DDRC ($0006)
PTCPUEx
INTERNAL DATA BUS
WRITE DDRC ($0006)
DDRCx
RESET
WRITE PTC ($0002)
45 k
PTCx
PTCx
READ PTC ($0002)
Figure 12-11. Port C I/O Circuit
When bit DDRCx is a 1, reading address $0002 reads the PTCx data latch. When bit DDRCx is a 0,
reading address $0002 reads the voltage level on the pin. The data latch can always be written,
regardless of the state of its data direction bit. Table 12-4 summarizes the operation of the port C pins.
Table 12-4. Port C Pin Functions
PTCPUE
Bit
DDRC
Bit
PTC
Bit
Accesses to DDRC
I/O Pin
Mode
Accesses to PTC
Read/Write
Read
Write
(1)
Input, VDD
(2)
DDRC6–DDRC0
Pin
PTC6–PTC0(3)
1
0
X
0
0
X
Input, Hi-Z(4)
DDRC6–DDRC0
Pin
PTC6–PTC0(3)
X
1
X
Output
DDRC6–DDRC0
PTC6–PTC0
PTC6–PTC0
1. X = Don’t care
2. I/O pin pulled up to VDD by internal pullup device.
3. Writing affects data register, but does not affect input.
4. Hi-Z = High impedance
12.4.3 Port C Input Pullup Enable Register
The port C input pullup enable register (PTCPUE) contains a software configurable pullup device for each
of the seven port C pins. Each bit is individually configurable and requires that the data direction register,
DDRC, bit be configured as an input. Each pullup is automatically and dynamically disabled when a port
bit’s DDRC is configured for output mode.
Address:
$000E
Bit 7
Read:
0
Write:
Reset:
0
6
5
4
3
2
1
Bit 0
PTCPUE6
PTCPUE5
PTCPUE4
PTCPUE3
PTCPUE2
PTCPUE1
PTCPUE0
0
0
0
0
0
0
0
= Unimplemented
Figure 12-12. Port C Input Pullup Enable Register (PTCPUE)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
131
Input/Output (I/O) Ports (PORTS)
PTCPUE6–PTCPUE0 — Port C Input Pullup Enable Bits
These writable bits are software programmable to enable pullup devices on an input port bit.
1 = Corresponding port C pin configured to have internal pullup
0 = Corresponding port C pin internal pullup disconnected
12.5 Port D
Port D is an 8-bit special-function port that shares four of its pins with the serial peripheral interface (SPI)
module and four of its pins with two timer interface (TIM1 and TIM2) modules. Port D also has software
configurable pullup devices if configured as an input port.
12.5.1 Port D Data Register
The port D data register (PTD) contains a data latch for each of the eight port D pins.
Address:
Read:
Write:
$0003
Bit 7
6
5
4
3
2
1
Bit 0
PTD7
PTD6
PTD5
PTD4
PTD3
PTD2
PTD1
PTD0
MOSI
MISO
SS
Reset:
Alternative Function:
Unaffected by reset
T2CH1
T2CH0
T1CH1
T1CH0
SPSCK
Figure 12-13. Port D Data Register (PTD)
PTD7–PTD0 — Port D Data Bits
These read/write bits are software-programmable. Data direction of each port D pin is under the control
of the corresponding bit in data direction register D. Reset has no effect on port D data.
T2CH1 and T2CH0 — Timer 2 Channel I/O Bits
The PTD7/T2CH1–PTD6/T2CH0 pins are the TIM2 input capture/output compare pins. The edge/level
select bits, ELSxB:ELSxA, determine whether the PTD7/T2CH1–PTD6/T2CH0 pins are timer channel
I/O pins or general-purpose I/O pins. See Chapter 18 Timer Interface Module (TIM).
T1CH1 and T1CH0 — Timer 1 Channel I/O Bits
The PTD7/T1CH1–PTD6/T1CH0 pins are the TIM1 input capture/output compare pins. The edge/level
select bits, ELSxB and ELSxA, determine whether the PTD7/T1CH1–PTD6/T1CH0 pins are timer
channel I/O pins or general-purpose I/O pins. See Chapter 18 Timer Interface Module (TIM).
SPSCK — SPI Serial Clock
The PTD3/SPSCK pin is the serial clock input of the SPI module. When the SPE bit is clear, the
PTD3/SPSCK pin is available for general-purpose I/O.
MOSI — Master Out/Slave In
The PTD2/MOSI pin is the master out/slave in terminal of the SPI module. When the SPE bit is clear,
the PTD2/MOSI pin is available for general-purpose I/O.
MISO — Master In/Slave Out
The PTD1/MISO pin is the master in/slave out terminal of the SPI module. When the SPI enable bit,
SPE, is clear, the SPI module is disabled, and the PTD0/SS pin is available for general-purpose I/O.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
Port D
Data direction register D (DDRD) does not affect the data direction of port D pins that are being used
by the SPI module. However, the DDRD bits always determine whether reading port D returns the
states of the latches or the states of the pins. See Table 12-5.
SS — Slave Select
The PTD0/SS pin is the slave select input of the SPI module. When the SPE bit is clear, or when the
SPI master bit, SPMSTR, is set, the PTD0/SS pin is available for general-purpose I/O. When the SPI
is enabled, the DDRB0 bit in data direction register B (DDRB) has no effect on the PTD0/SS pin.
12.5.2 Data Direction Register D
Data direction register D (DDRD) determines whether each port D pin is an input or an output. Writing a
1 to a DDRD bit enables the output buffer for the corresponding port D pin; a 0 disables the output buffer.
Address:
Read:
Write:
Reset:
$0007
Bit 7
6
5
4
3
2
1
Bit 0
DDRD7
DDRD6
DDRD5
DDRD4
DDRD3
DDRD2
DDRD1
DDRD0
0
0
0
0
0
0
0
0
Figure 12-14. Data Direction Register D (DDRD)
DDRD7–DDRD0 — Data Direction Register D Bits
These read/write bits control port D data direction. Reset clears DDRD7–DDRD0, configuring all port D
pins as inputs.
1 = Corresponding port D pin configured as output
0 = Corresponding port D pin configured as input
NOTE
Avoid glitches on port D pins by writing to the port D data register before
changing data direction register D bits from 0 to 1.
Figure 12-15 shows the port D I/O logic.
VDD
READ DDRD ($0007)
PTDPUEx
WRITE DDRD ($0007)
INTERNAL DATA BUS
RESET
WRITE PTD ($0003)
DDRDx
30 k
PTDx
PTDx
READ PTD ($0003)
Figure 12-15. Port D I/O Circuit
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
133
Input/Output (I/O) Ports (PORTS)
When bit DDRDx is a 1, reading address $0003 reads the PTDx data latch. When bit DDRDx is a 0,
reading address $0003 reads the voltage level on the pin. The data latch can always be written,
regardless of the state of its data direction bit. Table 12-5 summarizes the operation of the port D pins.
Table 12-5. Port D Pin Functions
PTDPUE
Bit
DDRD
Bit
PTD
Bit
I/O Pin
Mode
Accesses to DDRD
Accesses to PTD
Read/Write
Read
Write
1
0
X(1)
Input, VDD(2)
DDRD7–DDRD0
Pin
PTD7–PTD0(3)
0
0
X
Input, Hi-Z(4)
DDRD7–DDRD0
Pin
PTD7–PTD0(3)
X
1
X
Output
DDRD7–DDRD0
PTD7–PTD0
PTD7–PTD0
1. X = Don’t care
2. I/O pin pulled up to VDD by internal pullup device.
3. Writing affects data register, but does not affect input.
4. Hi-Z = High imp[edance
12.5.3 Port D Input Pullup Enable Register
The port D input pullup enable register (PTDPUE) contains a software configurable pullup device for each
of the eight port D pins. Each bit is individually configurable and requires that the data direction register,
DDRD, bit be configured as an input. Each pullup is automatically and dynamically disabled when a port
bit’s DDRD is configured for output mode.
Address:
Read:
Write:
Reset:
$000F
Bit 7
6
5
4
3
2
1
Bit 0
PTDPUE7
PTDPUE6
PTDPUE5
PTDPUE4
PTDPUE3
PTDPUE2
PTDPUE1
PTDPUE0
0
0
0
0
0
0
0
0
Figure 12-16. Port D Input Pullup Enable Register (PTDPUE)
PTDPUE7–PTDPUE0 — Port D Input Pullup Enable Bits
These writable bits are software programmable to enable pullup devices on an input port bit.
1 = Corresponding port D pin configured to have internal pullup
0 = Corresponding port D pin has internal pullup disconnected
12.6 Port E
Port E is a 5-bit special-function port that shares two of its pins with the serial communications interface
(SCI) module and two of its pins with the internal clock generator (ICG).
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
134
Freescale Semiconductor
Port E
12.6.1 Port E Data Register
The port E data register contains a data latch for each of the five port E pins.
Address:
Read:
$0008
Bit 7
6
5
0
0
0
Write:
Reset:
4
3
2
1
Bit 0
PTE4
PTE3
PTE2
PTE1
PTE0
RxD
TxD
Unaffected by reset
OSC1
Alternative Function:
OSC2
= Unimplemented
Figure 12-17. Port E Data Register (PTE)
PTE4-PTE0 — Port E Data Bits
These read/write bits are software-programmable. Data direction of each port E pin is under the control
of the corresponding bit in data direction register E. Reset has no effect on port Edata.
NOTE
Data direction register E (DDRE) does not affect the data direction of port
E pins that are being used by the SCI module. However, the DDRE bits
always determine whether reading port E returns the states of the latches
or the states of the pins. See Table 12-6.
OSC2 and OSC1 — OSC2 and OSC1 Bits
Under software control, PTE4 and PTE3 can be configured as external clock inputs and outputs. PTE3
will become an output clock, OSC2, if selected in the configuration registers and enabled in the ICG
registers. PTE4 will become an external input clock source, OSC1, if selected in the configuration
registers and enabled in the ICG registers. See Chapter 7 Internal Clock Generator (ICG) Module) and
Chapter 5 Computer Operating Properly (COP) Module. While configured as oscillator pins, writes
have no effect and reads return undefined values.
RxD — SCI Receive Data Input
The PTE1/RxD pin is the receive data input for the SCI module. When the enable SCI bit, ENSCI, is
clear, the SCI module is disabled, and the PTE1/RxD pin is available for general-purpose I/O. See
Chapter 14 Enhanced Serial Communications Interface (ESCI) Module.
TxD — SCI Transmit Data Output
The PTE0/TxD pin is the transmit data output for the SCI module. When the enable SCI bit, ENSCI, is
clear, the SCI module is disabled, and the PTE0/TxD pin is available for general-purpose I/O. See
Chapter 14 Enhanced Serial Communications Interface (ESCI) Module.
12.6.2 Data Direction Register E
Data direction register E (DDRE) determines whether each port E pin is an input or an output. Writing a 1
to a DDRE bit enables the output buffer for the corresponding port E pin; a 0 disables the output buffer.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
135
Input/Output (I/O) Ports (PORTS)
Address:
Read:
$000C
Bit 7
6
5
0
0
0
0
0
Write:
Reset:
0
4
3
2
1
Bit 0
DDRE4
DDRE3
DDRE2
DDRE1
DDRE0
0
0
0
0
0
= Unimplemented
Figure 12-18. Data Direction Register E (DDRE)
DDRE4–DDRE0 — Data Direction Register E Bits
These read/write bits control port E data direction. Reset clears DDRE4–DDRE0, configuring all port
E pins as inputs.
1 = Corresponding port E pin configured as output
0 = Corresponding port E pin configured as input
NOTE
Avoid glitches on port E pins by writing to the port E data register before
changing data direction register E bits from 0 to 1.
Figure 12-19 shows the port E I/O logic.
READ DDRE ($000C)
INTERNAL DATA BUS
WRITE DDRE ($000C)
DDREx
RESET
WRITE PTE ($0008)
PTEx
PTEx
READ PTE ($0008)
Figure 12-19. Port E I/O Circuit
When bit DDREx is a 1, reading address $0008 reads the PTEx data latch. When bit DDREx is a 0,
reading address $0008 reads the voltage level on the pin. The data latch can always be written,
regardless of the state of its data direction bit. Table 12-6 summarizes the operation of the port E pins.
Table 12-6. Port E Pin Functions
DDRE
Bit
PTE
Bit
I/O Pin
Mode
Accesses to DDRE
Accesses to PTE
Read/Write
Read
Write
0
X(1)
Input, Hi-Z(2)
DDRE4–DDRE0
Pin
PTE4–PTE0(3)
1
X
Output
DDRE4–DDRE0
PTE4–PTE0
PTE4–PTE0
1. X = Don’t care
2. Hi-Z = High impedance
3. Writing affects data register, but does not affect input.
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Chapter 13
Resets and Interrupts
13.1 Introduction
Resets and interrupts are responses to exceptional events during program execution. A reset re-initializes
the MCU to its startup condition. An interrupt vectors the program counter to a service routine.
13.2 Resets
A reset immediately returns the MCU to a known startup condition and begins program execution from a
user-defined memory location.
13.2.1 Effects
A reset:
• Immediately stops the operation of the instruction being executed
• Initializes certain control and status bits
• Loads the program counter with a user-defined reset vector address from locations $FFFE and
$FFFF
• Selects CGMXCLK divided by four as the bus clock
13.2.2 External Reset
A logic 0 applied to the RST pin for a time, tIRL, generates an external reset. An external reset sets the
PIN bit in the SIM reset status register.
13.2.3 Internal Reset
Sources:
• Power-on reset (POR)
• Computer operating properly (COP)
• Low-power reset circuits
• Illegal opcode
• Illegal address
All internal reset sources pull the RST pin low for 32 CGMXCLK cycles to allow resetting of external
devices. The MCU is held in reset for an additional 32 CGMXCLK cycles after releasing the RST pin. See
Figure 13-1.
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137
Resets and Interrupts
PULLED LOW BY MCU
RST PIN
32 CYCLES
32 CYCLES
CGMXCLK
INTERNAL
RESET
Figure 13-1. Internal Reset Timing
13.2.3.1 Power-On Reset (POR)
A power-on reset (POR) is an internal reset caused by a positive transition on the VDD pin. VDD at the
POR must go completely to 0 V to reset the MCU. This distinguishes between a reset and a POR. The
POR is not a brown-out detector, low-voltage detector, or glitch detector.
A power-on reset:
• Holds the clocks to the CPU and modules inactive for an oscillator stabilization delay of 4096
CGMXCLK cycles
• Drives the RST pin low during the oscillator stabilization delay
• Releases the RST pin 32 CGMXCLK cycles after the oscillator stabilization delay
• Releases the CPU to begin the reset vector sequence 64 CGMXCLK cycles after the oscillator
stabilization delay
• Sets the POR bit in the SIM reset status register and clears all other bits in the register
OSC1
PORRST(1)
4096
CYCLES
32
CYCLES
32
CYCLES
CGMXCLK
CGMOUT
RST PIN
INTERNAL
RESET
1. PORRST is an internally generated power-on reset pulse.
Figure 13-2. Power-On Reset Recovery
13.2.3.2 Computer Operating Properly (COP) Reset
A COP reset is an internal reset caused by an overflow of the COP counter. A COP reset sets the COP
bit in the system integration module (SIM) reset status register.
To clear the COP counter and prevent a COP reset, write any value to the COP control register at location
$FFFF.
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Resets
13.2.3.3 Low-Voltage Inhibit Reset
A low-voltage inhibit (LVI) reset is an internal reset caused by a drop in the power supply voltage to the
LVITRIPF voltage.
An LVI reset:
• Holds the clocks to the CPU and modules inactive for an oscillator stabilization delay of 4096
CGMXCLK cycles after the power supply voltage rises to the LVITRIPR voltage
• Drives the RST pin low for as long as VDD is below the LVITRIPR voltage and during the oscillator
stabilization delay
• Releases the RST pin 32 CGMXCLK cycles after the oscillator stabilization delay
• Releases the CPU to begin the reset vector sequence 64 CGMXCLK cycles after the oscillator
stabilization delay
• Sets the LVI bit in the SIM reset status register
13.2.3.4 Illegal Opcode Reset
An illegal opcode reset is an internal reset caused by an opcode that is not in the instruction set. An illegal
opcode reset sets the ILOP bit in the SIM reset status register.
If the stop enable bit, STOP, in the CONFIG1 register is a 0, the STOP instruction causes an illegal
opcode reset.
13.2.3.5 Illegal Address Reset
An illegal address reset is an internal reset caused by opcode fetch from an unmapped address. An illegal
address reset sets the ILAD bit in the SIM reset status register.
A data fetch from an unmapped address does not generate a reset.
13.2.4 SIM Reset Status Register
This read-only register contains flags to show reset sources. All flag bits are automatically cleared
following a read of the register. Reset service can read the SIM reset status register to clear the register
after power-on reset and to determine the source of any subsequent reset.
The register is initialized on power-up as shown with the POR bit set and all other bits cleared. During a
POR or any other internal reset, the RST pin is pulled low. After the pin is released, it will be sampled 32
CGMXCLK cycles later. If the pin is not above a VIH at that time, then the PIN bit in the SRSR may be set
in addition to whatever other bits are set.
NOTE
Only a read of the SIM reset status register clears all reset flags. After
multiple resets from different sources without reading the register, multiple
flags remain set.
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139
Resets and Interrupts
Address:
Read:
$FE01
Bit 7
6
5
4
3
2
1
Bit 0
POR
PIN
COP
ILOP
ILAD
MODRST
LVI
0
1
0
0
0
0
0
0
0
Write:
POR:
= Unimplemented
Figure 13-3. SIM Reset Status Register (SRSR)
POR — Power-On Reset Flag
1 = Power-on reset since last read of SRSR
0 = Read of SRSR since last power-on reset
PIN — External Reset Flag
1 = External reset via RST pin since last read of SRSR
0 = POR or read of SRSR since last external reset
COP — Computer Operating Properly Reset Bit
1 = Last reset caused by timeout of COP counter
0 = POR or read of SRSR since any reset
ILOP — Illegal Opcode Reset Bit
1 = Last reset caused by an illegal opcode
0 = POR or read of SRSR since any reset
ILAD — Illegal Address Reset Bit
1 = Last reset caused by an opcode fetch from an illegal address
0 = POR or read of SRSR since any reset
MODRST — Monitor Mode Entry Module Reset Bit
1 = Last reset caused by forced monitor mode entry.
0 = POR or read of SRSR since any reset
LVI — Low-Voltage Inhibit Reset Bit
1 = Last reset caused by low-power supply voltage
0 = POR or read of SRSR since any reset
13.3 Interrupts
An interrupt temporarily changes the sequence of program execution to respond to a particular event. An
interrupt does not stop the operation of the instruction being executed, but begins when the current
instruction completes its operation.
13.3.1 Effects
An interrupt:
• Saves the CPU registers on the stack. At the end of the interrupt, the RTI instruction recovers the
CPU registers from the stack so that normal processing can resume.
• Sets the interrupt mask (I bit) to prevent additional interrupts. Once an interrupt is latched, no other
interrupt can take precedence, regardless of its priority.
• Loads the program counter with a user-defined vector address
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Interrupts
•
•
•
STACKING
ORDER
5
CONDITION CODE REGISTER
1
4
ACCUMULATOR
2
(1)
INDEX REGISTER (LOW BYTE)
3
3
2
PROGRAM COUNTER (HIGH BYTE)
4
1
PROGRAM COUNTER (LOW BYTE)
5
UNSTACKING
ORDER
•
•
•
$00FF DEFAULT ADDRESS ON RESET
1. High byte of index register is not stacked.
Figure 13-4. Interrupt Stacking Order
After every instruction, the CPU checks all pending interrupts if the I bit is not set. If more than one
interrupt is pending when an instruction is done, the highest priority interrupt is serviced first. In the
example shown in Figure 13-5, if an interrupt is pending upon exit from the interrupt service routine, the
pending interrupt is serviced before the LDA instruction is executed.
CLI
BACKGROUND
ROUTINE
LDA #$FF
INT1
PSHH
INT1 INTERRUPT SERVICE ROUTINE
PULH
RTI
INT2
PSHH
INT2 INTERRUPT SERVICE ROUTINE
PULH
RTI
Figure 13-5. Interrupt Recognition Example
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141
Resets and Interrupts
FROM RESET
BREAK
INTERRUPT
?
NO
YES
YES
BITSET?
SET?
IIBIT
NO
IRQ
INTERRUPT
?
NO
YES
ICG
INTERRUPT
?
NO
YES
OTHER
INTERRUPTS
?
YES
NO
STACK CPU REGISTERS
SET I BIT
LOAD PC WITH INTERRUPT VECTOR
FETCH NEXT
INSTRUCTION
SWI
INSTRUCTION
?
YES
NO
RTI
INSTRUCTION
?
YES
UNSTACK CPU REGISTERS
NO
EXECUTE INSTRUCTION
Figure 13-6. Interrupt Processing
The LDA opcode is prefetched by both the INT1 and INT2 RTI instructions. However, in the case of the
INT1 RTI prefetch, this is a redundant operation.
NOTE
To maintain compatibility with the M6805 Family, the H register is not
pushed on the stack during interrupt entry. If the interrupt service routine
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Freescale Semiconductor
Interrupts
modifies the H register or uses the indexed addressing mode, save the H
register and then restore it prior to exiting the routine.
13.3.2 Sources
The sources in Table 13-1 can generate CPU interrupt requests.
13.3.2.1 Software Interrupt (SWI) Instruction
The software interrupt instruction (SWI) causes a non-maskable interrupt.
NOTE
A software interrupt pushes PC onto the stack. An SWI does not push PC
– 1, as a hardware interrupt does.
Table 13-1. Interrupt Sources
Flag
Mask(1)
INT Register
Flag
Priority(2)
Vector Address
Reset
None
None
None
0
$FFFE–$FFFF
SWI instruction
None
None
None
0
$FFFC–$FFFD
IRQ pin
IRQF
IMASK1
IF1
1
$FFFA–$FFFB
ICG clock monitor
CMF
CMIE
IF2
2
$FFF8–$FFF9
TIM1 channel 0
CH0F
CH0IE
IF3
3
$FFF6–$FFF7
TIM1 channel 1
CH1F
CH1IE
IF4
4
$FFF4–$FFF5
Source
TIM1 overflow
TOF
TOIE
IF5
5
$FFF2–$FFF3
TIM2 channel 0
CH0F
CH0IE
IF6
6
$FFF0–$FFF1
TIM2 channel 1
CH1F
CH1IE
IF7
7
$FFEE–$FFEF
TOF
TOIE
IF8
8
$FFEC–$FFED
IF9
9
$FFEA–$FFEB
IF10
10
$FFE8–$FFE9
IF11
11
$FFE6–$FFE7
IF12
12
$FFE4–$FFE5
IF13
13
$FFE2–$FFE3
TIM2 overflow
SPI receiver full
SPRF
SPRIE
SPI overflow
OVRF
ERRIE
SPI mode fault
MODF
ERRIE
SPI transmitter empty
SPTE
SPTIE
SCI receiver overrun
OR
ORIE
SCI noise fag
NF
NEIE
SCI framing error
FE
FEIE
SCI parity error
PE
PEIE
SCI receiver full
SCRF
SCRIE
SCI input idle
IDLE
ILIE
SCI transmitter empty
SCTE
SCTIE
TC
TCIE
Keyboard pin
KEYF
IMASKK
IF14
14
$FFE0–$FFE1
ADC conversion complete
COCO
AIEN
IF15
15
$FFDE–$FFDF
TBIF
TBIE
IF16
16
$FFDC–$FFDD
SCI transmission complete
Timebase
1. The I bit in the condition code register is a global mask for all interrupt sources except the SWI instruction.
2. 0 = highest priority
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Resets and Interrupts
13.3.2.2 Break Interrupt
The break module causes the CPU to execute an SWI instruction at a software-programmable break
point.
13.3.2.3 IRQ Pin
A logic 0 on the IRQ1 pin latches an external interrupt request.
13.3.2.4 Internal Clock Generator (ICG)
The ICG can generate a CPU interrupt request every time the selected internal or external clock becomes
inactive. When the clock monitor CMON bit is set and the currently selected clock becomes inactive, the
clock monitor interrupt flag CMF is set. The clock monitor interrupt enable bit (CMIE) enables ICG CPU
interrupt requests. CMIE, CMF, and CMON are in the ICGCR control register.
13.3.2.5 Timer Interface Module 1 (TIM1)
TIM1 CPU interrupt sources:
• TIM1 overflow flag (TOF) — The TOF bit is set when the TIM1 counter value rolls over to $0000
after matching the value in the TIM1 counter modulo registers. The TIM1 overflow interrupt enable
bit, TOIE, enables TIM1 overflow CPU interrupt requests. TOF and TOIE are in the TIM1 status
and control register.
• TIM1 channel flags (CH1F–CH0F) — The CHxF bit is set when an input capture or output compare
occurs on channel x. The channel x interrupt enable bit, CHxIE, enables channel x TIM1 CPU
interrupt requests. CHxF and CHxIE are in the TIM1 channel x status and control register.
13.3.2.6 Timer Interface Module 2 (TIM2)
TIM2 CPU interrupt sources:
• TIM2 overflow flag (TOF) — The TOF bit is set when the TIM2 counter value rolls over to $0000
after matching the value in the TIM2 counter modulo registers. The TIM2 overflow interrupt enable
bit, TOIE, enables TIM2 overflow CPU interrupt requests. TOF and TOIE are in the TIM2 status
and control register.
• TIM2 channel flags (CH1F–CH0F) — The CHxF bit is set when an input capture or output compare
occurs on channel x. The channel x interrupt enable bit, CHxIE, enables channel x TIM2 CPU
interrupt requests. CHxF and CHxIE are in the TIM2 channel x status and control register.
13.3.2.7 Serial Peripheral Interface (SPI)
SPI CPU interrupt sources:
• SPI receiver full bit (SPRF) — The SPRF bit is set every time a byte transfers from the shift register
to the receive data register. The SPI receiver interrupt enable bit, SPRIE, enables SPRF CPU
interrupt requests. SPRF is in the SPI status and control register and SPRIE is in the SPI control
register.
• SPI transmitter empty (SPTE) — The SPTE bit is set every time a byte transfers from the transmit
data register to the shift register. The SPI transmit interrupt enable bit, SPTIE, enables SPTE CPU
interrupt requests. SPTE is in the SPI status and control register and SPTIE is in the SPI control
register.
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Interrupts
•
•
Mode fault bit (MODF) — The MODF bit is set in a slave SPI if the SS pin goes high during a
transmission with the mode fault enable bit (MODFEN) set. In a master SPI, the MODF bit is set if
the SS pin goes low at any time with the MODFEN bit set. The error interrupt enable bit, ERRIE,
enables MODF CPU interrupt requests. MODF, MODFEN, and ERRIE are in the SPI status and
control register.
Overflow bit (OVRF) — The OVRF bit is set if software does not read the byte in the receive data
register before the next full byte enters the shift register. The error interrupt enable bit, ERRIE,
enables OVRF CPU interrupt requests. OVRF and ERRIE are in the SPI status and control
register.
13.3.2.8 Serial Communications Interface (SCI)
SCI CPU interrupt sources:
• SCI transmitter empty bit (SCTE) — SCTE is set when the SCI data register transfers a character
to the transmit shift register. The SCI transmit interrupt enable bit, SCTIE, enables transmitter CPU
interrupt requests. SCTE is in SCI status register 1. SCTIE is in SCI control register 2.
• Transmission complete bit (TC) — TC is set when the transmit shift register and the SCI data
register are empty and no break or idle character has been generated. The transmission complete
interrupt enable bit, TCIE, enables transmitter CPU interrupt requests. TC is in SCI status
register 1. TCIE is in SCI control register 2.
• SCI receiver full bit (SCRF) — SCRF is set when the receive shift register transfers a character to
the SCI data register. The SCI receive interrupt enable bit, SCRIE, enables receiver CPU
interrupts. SCRF is in SCI status register 1. SCRIE is in SCI control register 2.
• Idle input bit (IDLE) — IDLE is set when 10 or 11 consecutive 1s shift in from the RxD pin. The idle
line interrupt enable bit, ILIE, enables IDLE CPU interrupt requests. IDLE is in SCI status register 1.
ILIE is in SCI control register 2.
• Receiver overrun bit (OR) — OR is set when the receive shift register shifts in a new character
before the previous character was read from the SCI data register. The overrun interrupt enable
bit, ORIE, enables OR to generate SCI error CPU interrupt requests. OR is in SCI status register 1.
ORIE is in SCI control register 3.
• Noise flag (NF) — NF is set when the SCI detects noise on incoming data or break characters,
including start, data, and stop bits. The noise error interrupt enable bit, NEIE, enables NF to
generate SCI error CPU interrupt requests. NF is in SCI status register 1. NEIE is in SCI control
register 3.
• Framing error bit (FE) — FE is set when a 0 occurs where the receiver expects a stop bit. The
framing error interrupt enable bit, FEIE, enables FE to generate SCI error CPU interrupt requests.
FE is in SCI status register 1. FEIE is in SCI control register 3.
• Parity error bit (PE) — PE is set when the SCI detects a parity error in incoming data. The parity
error interrupt enable bit, PEIE, enables PE to generate SCI error CPU interrupt requests. PE is in
SCI status register 1. PEIE is in SCI control register 3.
13.3.2.9 KBD0–KBD7 Pins
A logic 0 on a keyboard interrupt pin latches an external interrupt request.
13.3.2.10 Analog-to-Digital Converter (ADC)
When the AIEN bit is set, the ADC module is capable of generating a CPU interrupt after each ADC
conversion. The COCO bit is not used as a conversion complete flag when interrupts are enabled.
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Resets and Interrupts
13.3.2.11 Timebase Module (TBM)
The timebase module can interrupt the CPU on a regular basis with a rate defined by TBR2–TBR0. When
the timebase counter chain rolls over, the TBIF flag is set. If the TBIE bit is set, enabling the timebase
interrupt, the counter chain overflow will generate a CPU interrupt request.
Interrupts must be acknowledged by writing a 1 to the TACK bit.
13.3.3 Interrupt Status Registers
The flags in the interrupt status registers identify maskable interrupt sources. Table 13-2 summarizes the
interrupt sources and the interrupt status register flags that they set. The interrupt status registers can be
useful for debugging.
Table 13-2. Interrupt Source Flags
Interrupt Source
Interrupt Status
Register Flag
Reset
—
SWI instruction
—
IRQ pin
IF1
ICG clock monitor
IF2
TIM1 channel 0
IF3
TIM1 channel 1
IF4
TIM1 overflow
IF5
TIM2 channel 0
IF6
TIM2 channel 1
IF7
TIM2 overflow
IF8
SPI receive
IF9
SPI transmit
IF10
SCI error
IF11
SCI receive
IF12
SCI transmit
IF13
Keyboard
IF14
ADC conversion complete
IF15
Timebase
IF16
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Freescale Semiconductor
Interrupts
13.3.3.1 Interrupt Status Register 1
Address:
$FE04
Bit 7
6
5
4
3
2
1
Bit 0
Read:
IF6
IF5
IF4
IF3
IF2
IF1
0
0
Write:
R
R
R
R
R
R
R
R
Reset:
0
0
0
0
0
0
0
0
R
= Reserved
Figure 13-7. Interrupt Status Register 1 (INT1)
IF6–IF1 — Interrupt Flags 6–1
These flags indicate the presence of interrupt requests from the sources shown in Table 13-2.
1 = Interrupt request present
0 = No interrupt request present
Bit 1 and Bit 0 — Always read 0
13.3.3.2 Interrupt Status Register 2
Address:
$FE05
Bit 7
6
5
4
3
2
1
Bit 0
Read:
IF14
IF13
IF12
IF11
IF10
IF9
IF8
IF7
Write:
R
R
R
R
R
R
R
R
0
0
0
0
0
0
0
0
R
= Reserved
Reset:
Figure 13-8. Interrupt Status Register 2 (INT2)
IF14–IF7 — Interrupt Flags 14–7
These flags indicate the presence of interrupt requests from the sources shown in Table 13-2.
1 = Interrupt request present
0 = No interrupt request present
13.3.3.3 Interrupt Status Register 3
Address:
$FE06
Bit 7
6
5
4
3
2
1
Bit 0
Read:
0
0
0
0
0
0
IF16
IF15
Write:
R
R
R
R
R
R
R
R
Reset:
0
0
0
0
0
0
0
0
R
= Reserved
Figure 13-9. Interrupt Status Register 3 (INT3)
IF16–IF15 — Interrupt Flags 16–15
This flag indicates the presence of an interrupt request from the source shown in Table 13-2.
1 = Interrupt request present
0 = No interrupt request present
Bits 7–2 — Always read 0
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Resets and Interrupts
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Freescale Semiconductor
Chapter 14
Enhanced Serial Communications Interface (ESCI) Module
14.1 Introduction
The enhanced serial communications interface (ESCI) module allows asynchronous communications
with peripheral devices and other microcontroller units (MCU).
14.2 Features
Features include:
• Full-duplex operation
• Standard mark/space non-return-to-zero (NRZ) format
• Programmable baud rates
• Programmable 8-bit or 9-bit character length
• Separately enabled transmitter and receiver
• Separate receiver and transmitter central processor unit (CPU) interrupt requests
• Programmable transmitter output polarity
• Two receiver wakeup methods:
– Idle line wakeup
– address mark wakeup
• Interrupt-driven operation with eight interrupt flags:
– Transmitter empty
– Transmission complete
– Receiver full
– Idle receiver input
– Receiver overrun
– Noise error
– Framing error
– Parity error
• Receiver framing error detection
• Hardware parity checking
• 1/16 bit-time noise detection
14.3 Pin Name Conventions
The generic names of the ESCI input/output (I/O) pins are:
• RxD (receive data)
• TxD (transmit data)
ESCI I/O lines are implemented by sharing parallel I/O port pins. The full name of an ESCI input or output
reflects the name of the shared port pin. Table 14-1 shows the full names and the generic names of the
ESCI I/O pins. The generic pin names appear in the text of this section.
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149
Enhanced Serial Communications Interface (ESCI) Module
USER RAM — 512 BYTES
8-BIT KEYBOARD
INTERRUPT MODULE
MONITOR ROM — 304 BYTES
2-CHANNEL TIMER INTERFACE
MODULE 1
FLASH PROGRAMMING ROUTINES
ROM — 720 BYTES
USER FLASH VECTOR SPACE — 36 BYTES
PTE4/OSC1
PTE3/OSC2
INTERNAL CLOCK
GENERATOR MODULE
RST(3)
SYSTEM INTEGRATION
MODULE
IRQ(3)
SINGLE EXTERNAL
INTERRUPT MODULE
VREFL
VDD
VSS
VDDA
VSSA
PTD7/T2CH1(1)
PTD6/T2CH0(1)
PTD5/T1CH1(1)
PTD4/T1CH0(1)
PTD3/SPSCK(1)
PTD2/MOSI(1)
PTD1/MISO(1)
PTD0/SS(1)
PTE2
PTE1/RxD
PTE0/TxD
SERIAL PERIPHERAL
INTERFACE MODULE
MONITOR MODULE
8-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
DDRD
COMPUTER OPERATING
PROPERLY MODULE
POWER-ON RESET
MODULE
PTC6(1)
PTC5(1)
PTC4(1)(2)
PTC3(1)(2)
PTC2(1)(2)
PTC1(1)(2)
PTC0(1)(2)
SERIAL COMMUNICATIONS
INTERFACE MODULE
DDRE
VREFH
2-CHANNEL TIMER INTERFACE
MODULE 2
PORTA
DUAL VOLTAGE
LOW-VOLTAGE INHIBIT MODULE
PORTB
USER FLASH
MC68HC908GT16 — 15,872 BYTES
MC68HC908GT8 — 7,680 BYTES
PTB7/AD7
PTB6/AD6
PTB5/AD5
PTB4/AD4
PTB3/AD3
PTB2/AD2
PTB1/AD1
PTB0/AD0
PORTC
SINGLE BREAKPOINT BREAK
MODULE
PTA7/KBD7–
PTA0/KBD0(1)
PORTD
DDRA
CONTROL AND STATUS
REGISTERS — 64 BYTES
DDRB
PROGRAMMABLE TIMEBASE
MODULE
ARITHMETIC/LOGIC
UNIT (ALU)
DDRC
CPU
REGISTERS
PORTE
INTERNAL BUS
M68HC08 CPU
MEMORY MAP
MODULE
SECURITY
MODULE
CONFIGURATION REGISTER 1
MODULE
CONFIGURATION REGISTER 2
MODULE
MONITOR MODE ENTRY
MODULE
1. Ports are software configurable with pullup device if input port.
2. Higher current drive port pins
3. Pin contains integrated pullup device
Figure 14-1. Block Diagram Highlighting ESCI Block and Pins
Table 14-1. Pin Name Conventions
Generic Pin Names
Full Pin Names
RxD
TxD
PTE1/RxD
PTE0/TxD
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Freescale Semiconductor
Functional Description
14.4 Functional Description
Figure 14-2 shows the structure of the ESCI module. The ESCI allows full-duplex, asynchronous, NRZ
serial communication between the MCU and remote devices, including other MCUs. The transmitter and
receiver of the ESCI operate independently, although they use the same baud rate generator. During
normal operation, the CPU monitors the status of the ESCI, writes the data to be transmitted, and
processes received data.
For reference, a summary of the ESCI module input/output registers is provided in Figure 14-4.
INTERNAL BUS
ERROR
INTERRUPT
CONTROL
RECEIVE
SHIFT REGISTER
RxD
ESCI DATA
REGISTER
RECEIVER
INTERRUPT
CONTROL
TRANSMITTER
INTERRUPT
CONTROL
ESCI DATA
REGISTER
RxD
TRANSMIT
SHIFT REGISTER
ARBITER-
TxD
SCI_TxD
TXINV
LINR
SCTIE
R8
TCIE
T8
SCRIE
ILIE
TE
SCTE
RE
TC
RWU
SBK
SCRF
OR
ORIE
IDLE
NF
NEIE
FE
FEIE
PE
PEIE
LOOPS
LOOPS
RECEIVE
CONTROL
WAKEUP
CONTROL
ENSCI
ENSCI
TRANSMIT
CONTROL
FLAG
CONTROL
BKF
M
RPF
WAKE
LINT
ILTY
PRESCALER
÷4
BUS CLOCK
PRESCALER
BAUD RATE
GENERATOR
÷ 16
PEN
PTY
DATA SELECTION
CONTROL
Figure 14-2. ESCI Module Block Diagram
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
151
Enhanced Serial Communications Interface (ESCI) Module
14.4.1 Data Format
The SCI uses the standard non-return-to-zero mark/space data format illustrated in Figure 14-3.
START
BIT
START
BIT
8-BIT DATA FORMAT
(BIT M IN SCC1 CLEAR)
BIT 0
BIT 1
BIT 2
BIT 3
BIT 4
BIT 5
BIT 6
PARITY
OR DATA
BIT
BIT 7
BIT 1
BIT 2
BIT 3
BIT 4
BIT 5
STOP
BIT
PARITY
OR DATA
BIT
9-BIT DATA FORMAT
(BIT M IN SCC1 SET)
BIT 0
NEXT
START
BIT
BIT 6
BIT 7
BIT 8
NEXT
START
BIT
STOP
BIT
Figure 14-3. SCI Data Formats
Addr.
$0009
$000A
$000B
$0013
$0014
$0015
$0016
$0017
$0018
$0019
Register Name
ESCI Prescaler Register Read:
(SCPSC) Write:
See page 172. Reset:
ESCI Arbiter Control Read:
Register (SCIACTL) Write:
See page 176. Reset:
ESCI Arbiter Data Read:
Register (SCIADAT) Write:
See page 177. Reset:
ESCI Control Register 1 Read:
(SCC1) Write:
See page 163. Reset:
ESCI Control Register 2 Read:
(SCC2) Write:
See page 165. Reset:
ESCI Control Register 3 Read:
(SCC3) Write:
See page 167. Reset:
ESCI Status Register 1 Read:
(SCS1) Write:
See page 168. Reset:
ESCI Status Register 2 Read:
(SCS2) Write:
See page 170. Reset:
ESCI Data Register Read:
(SCDR) Write:
See page 171. Reset:
ESCI Baud Rate Register Read:
(SCBR) Write:
See page 171. Reset:
Bit 7
6
5
4
3
2
1
Bit 0
PDS2
PDS1
PDS0
PSSB4
PSSB3
PSSB2
PSSB1
PSSB0
0
0
ALOST
0
0
AM0
ACLK
0
AFIN
0
ARUN
0
AROVFL
0
ARD8
AM1
0
ARD7
0
ARD6
0
ARD5
0
ARD4
0
ARD3
0
ARD2
0
ARD1
0
ARD0
0
0
0
0
0
0
0
0
LOOPS
ENSCI
TXINV
M
WAKE
ILTY
PEN
PTY
0
0
0
0
0
0
0
0
SCTIE
TCIE
SCRIE
ILIE
TE
RE
RWU
SBK
0
R8
0
0
0
0
0
0
0
T8
R
R
ORIE
NEIE
FEIE
PEIE
U
SCTE
0
TC
0
SCRF
0
IDLE
0
OR
0
NF
0
FE
0
PE
1
0
1
0
0
0
0
0
0
0
0
0
0
BKF
0
RPF
0
R7
T7
0
R6
T6
0
R5
T5
0
R2
T2
0
R1
T1
0
R0
T0
R
LINR
SCP1
SCR2
SCR1
SCR0
0
0
0
= Unimplemented
0
0
R4
R3
T4
T3
Unaffected by reset
SCP0
R
0
R
0
= Reserved
0
0
U = Unaffected
0
Figure 14-4. ESCI I/O Register Summary
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
152
Freescale Semiconductor
Functional Description
14.4.2 Transmitter
Figure 14-5 shows the structure of the SCI transmitter and the registers are summarized in Figure 14-4.
INTERNAL BUS
BAUD
DIVIDER
÷ 16
ESCI DATA REGISTER
SCP1
11-BIT
TRANSMIT
SHIFT REGISTER
STOP
SCP0
SCR1
H
SCR2
8
7
6
5
4
3
2
START
PRESCALER
÷4
1
0
L
SCI_TxD
PSSB3
PSSB2
PTY
MSB
PARITY
GENERATION
T8
BREAK
(ALL ZEROS)
PSSB4
PEN
PREAMBLE
(ALL ONES)
PDS0
M
SHIFT ENABLE
PDS1
TXINV
LOAD FROM SCDR
PDS2
TRANSMITTER CPU INTERRUPT REQUEST
BUS CLOCK
PRESCALER
SCR0
TRANSMITTER
CONTROL LOGIC
PSSB1
PSSB0
SCTE
SCTE
SCTIE
TC
TCIE
SBK
LOOPS
SCTIE
ENSCI
TC
TE
TCIE
LINT
Figure 14-5. ESCI Transmitter
14.4.2.1 Character Length
The transmitter can accommodate either 8-bit or 9-bit data. The state of the M bit in ESCI control
register 1 (SCC1) determines character length. When transmitting 9-bit data, bit T8 in ESCI control
register 3 (SCC3) is the ninth bit (bit 8).
14.4.2.2 Character Transmission
During an ESCI transmission, the transmit shift register shifts a character out to the TxD pin. The ESCI
data register (SCDR) is the write-only buffer between the internal data bus and the transmit shift register.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
153
Enhanced Serial Communications Interface (ESCI) Module
To initiate an ESCI transmission:
1. Enable the ESCI by writing a 1 to the enable ESCI bit (ENSCI) in ESCI control register 1 (SCC1).
2. Enable the transmitter by writing a 1 to the transmitter enable bit (TE) in ESCI control register 2
(SCC2).
3. Clear the ESCI transmitter empty bit (SCTE) by first reading ESCI status register 1 (SCS1) and
then writing to the SCDR. For 9-bit data, also write the T8 bit in SCC3.
4. Repeat step 3 for each subsequent transmission.
At the start of a transmission, transmitter control logic automatically loads the transmit shift register with
a preamble of 1s. After the preamble shifts out, control logic transfers the SCDR data into the transmit
shift register. A 0 start bit automatically goes into the least significant bit (LSB) position of the transmit shift
register. A 1 stop bit goes into the most significant bit (MSB) position.
The ESCI transmitter empty bit, SCTE, in SCS1 becomes set when the SCDR transfers a byte to the
transmit shift register. The SCTE bit indicates that the SCDR can accept new data from the internal data
bus. If the ESCI transmit interrupt enable bit, SCTIE, in SCC2 is also set, the SCTE bit generates a
transmitter CPU interrupt request.
When the transmit shift register is not transmitting a character, the TxD pin goes to the idle condition,
logic 1. If at any time software clears the ENSCI bit in ESCI control register 1 (SCC1), the transmitter and
receiver relinquish control of the port E pins.
14.4.2.3 Break Characters
Writing a 1 to the send break bit, SBK, in SCC2 loads the transmit shift register with a break character.
For TXINV = 0 (output not inverted), a transmitted break character contains all 0s and has no start, stop,
or parity bit. Break character length depends on the M bit in SCC1 and the LINR bits in SCBR. As long as
SBK is at 1, transmitter logic continuously loads break characters into the transmit shift register. After
software clears the SBK bit, the shift register finishes transmitting the last break character and then
transmits at least one 1. The automatic 1 at the end of a break character guarantees the recognition of
the start bit of the next character.
When LINR is cleared in SCBR, the ESCI recognizes a break character when a start bit is followed by
eight or nine 0 data bits and a 0 where the stop bit should be, resulting in a total of 10 or 11 consecutive
0 data bits. When LINR is set in SCBR, the ESCI recognizes a break character when a start bit is followed
by 9 or 10 0 data bits and a 0 where the stop bit should be, resulting in a total of 11 or 12 consecutive 0
data bits.
Receiving a break character has these effects on ESCI registers:
• Sets the framing error bit (FE) in SCS1
• Sets the ESCI receiver full bit (SCRF) in SCS1
• Clears the ESCI data register (SCDR)
• Clears the R8 bit in SCC3
• Sets the break flag bit (BKF) in SCS2
• May set the overrun (OR), noise flag (NF), parity error (PE),
or reception in progress flag (RPF) bits
14.4.2.4 Idle Characters
For TXINV = 0 (output not inverted), a transmitted idle character contains all 1s and has no start, stop, or
parity bit. Idle character length depends on the M bit in SCC1. The preamble is a synchronizing idle
character that begins every transmission.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
154
Freescale Semiconductor
Functional Description
If the TE bit is cleared during a transmission, the TxD pin becomes idle after completion of the
transmission in progress. Clearing and then setting the TE bit during a transmission queues an idle
character to be sent after the character currently being transmitted.
NOTE
When queueing an idle character, return the TE bit to 1 before the stop bit
of the current character shifts out to the TxD pin. Setting TE after the stop
bit appears on TxD causes data previously written to the SCDR to be lost.
A good time to toggle the TE bit for a queued idle character is when the
SCTE bit becomes set and just before writing the next byte to the SCDR.
14.4.2.5 Inversion of Transmitted Output
The transmit inversion bit (TXINV) in ESCI control register 1 (SCC1) reverses the polarity of transmitted
data. All transmitted values including idle, break, start, and stop bits, are inverted when TXINV is at 1. See
14.8.1 ESCI Control Register 1.
14.4.2.6 Transmitter Interrupts
These conditions can generate CPU interrupt requests from the ESCI transmitter:
• ESCI transmitter empty (SCTE) — The SCTE bit in SCS1 indicates that the SCDR has transferred
a character to the transmit shift register. SCTE can generate a transmitter CPU interrupt request.
Setting the ESCI transmit interrupt enable bit, SCTIE, in SCC2 enables the SCTE bit to generate
transmitter CPU interrupt requests.
• Transmission complete (TC) — The TC bit in SCS1 indicates that the transmit shift register and the
SCDR are empty and that no break or idle character has been generated. The transmission
complete interrupt enable bit, TCIE, in SCC2 enables the TC bit to generate transmitter CPU
interrupt requests.
14.4.3 Receiver
Figure 14-6 shows the structure of the ESCI receiver. The receiver I/O registers are summarized in
Figure 14-4.
14.4.3.1 Character Length
The receiver can accommodate either 8-bit or 9-bit data. The state of the M bit in ESCI control register 1
(SCC1) determines character length. When receiving 9-bit data, bit R8 in ESCI control register 3 (SCC3)
is the ninth bit (bit 8). When receiving 8-bit data, bit R8 is a copy of the eighth bit (bit 7).
14.4.3.2 Character Reception
During an ESCI reception, the receive shift register shifts characters in from the RxD pin. The ESCI data
register (SCDR) is the read-only buffer between the internal data bus and the receive shift register.
After a complete character shifts into the receive shift register, the data portion of the character transfers
to the SCDR. The ESCI receiver full bit, SCRF, in ESCI status register 1 (SCS1) becomes set, indicating
that the received byte can be read. If the ESCI receive interrupt enable bit, SCRIE, in SCC2 is also set,
the SCRF bit generates a receiver CPU interrupt request.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
155
Enhanced Serial Communications Interface (ESCI) Module
INTERNAL BUS
SCP1
SCR2
SCP0
SCR0
BUS CLOCK
BAUD
DIVIDER
DATA
RECOVERY
RxD
BKF
PDS2
ALL ZEROS
RPF
PDS1
PDS0
PSSB4
PSSB3
PSSB2
M
WAKE
ILTY
PSSB1
PEN
PSSB0
PTY
11-BIT
RECEIVE SHIFT REGISTER
STOP
÷ 16
H
ALL ONES
PRESCALER
PRESCALER
÷4
ESCI DATA REGISTER
8
7
6
5
4
WAKEUP
LOGIC
2
1
L
RWU
R8
PARITY
CHECKING
CPU INTERRUPT
REQUEST
0
IDLE
IDLE
ILIE
ILIE
SCRIE
OR
ORIE
ERROR CPU
INTERRUPT REQUEST
3
SCRF
SCRF
SCRIE
START
SCR1
MSB
LINR
NF
NEIE
FE
FEIE
PE
PEIE
OR
ORIE
NF
NEIE
FE
FEIE
PE
PEIE
Figure 14-6. ESCI Receiver Block Diagram
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
156
Freescale Semiconductor
Functional Description
14.4.3.3 Data Sampling
The receiver samples the RxD pin at the RT clock rate. The RT clock is an internal signal with a frequency
16 times the baud rate. To adjust for baud rate mismatch, the RT clock is resynchronized at these times
(see Figure 14-7):
• After every start bit
• After the receiver detects a data bit change from 1 to 0 (after the majority of data bit samples at
RT8, RT9, and RT10 returns a valid 1 and the majority of the next RT8, RT9, and RT10 samples
returns a valid 0)
To locate the start bit, data recovery logic does an asynchronous search for a 0 preceded by three 1s.
When the falling edge of a possible start bit occurs, the RT clock begins to count to 16.
START BIT
RxD
SAMPLES
START BIT
QUALIFICATION
LSB
START BIT
DATA
VERIFICATION SAMPLING
RT CLOCK
STATE
RT1
RT1
RT1
RT1
RT1
RT1
RT1
RT1
RT1
RT2
RT3
RT4
RT5
RT6
RT7
RT8
RT9
RT10
RT11
RT12
RT13
RT14
RT15
RT16
RT1
RT2
RT3
RT4
RT
CLOCK
RT CLOCK
RESET
Figure 14-7. Receiver Data Sampling
To verify the start bit and to detect noise, data recovery logic takes samples at RT3, RT5, and RT7.
Table 14-2 summarizes the results of the start bit verification samples.
Table 14-2. Start Bit Verification
RT3, RT5, and RT7 Samples
Start Bit Verification
Noise Flag
000
Yes
0
001
Yes
1
010
Yes
1
011
No
0
100
Yes
1
101
No
0
110
No
0
111
No
0
If start bit verification is not successful, the RT clock is reset and a new search for a start bit begins.
To determine the value of a data bit and to detect noise, recovery logic takes samples at RT8, RT9, and
RT10. Table 14-3 summarizes the results of the data bit samples.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
157
Enhanced Serial Communications Interface (ESCI) Module
Table 14-3. Data Bit Recovery
RT8, RT9, and RT10 Samples
Data Bit Determination
Noise Flag
000
0
0
001
0
1
010
0
1
011
1
1
100
0
1
101
1
1
110
1
1
111
1
0
NOTE
The RT8, RT9, and RT10 samples do not affect start bit verification. If any
or all of the RT8, RT9, and RT10 start bit samples are 1s following a
successful start bit verification, the noise flag (NF) is set and the receiver
assumes that the bit is a start bit.
To verify a stop bit and to detect noise, recovery logic takes samples at RT8, RT9, and RT10. Table 14-4
summarizes the results of the stop bit samples.
Table 14-4. Stop Bit Recovery
RT8, RT9, and RT10 Samples
Framing Error Flag
Noise Flag
000
1
0
001
1
1
010
1
1
011
0
1
100
1
1
101
0
1
110
0
1
111
0
0
14.4.3.4 Framing Errors
If the data recovery logic does not detect a 1 where the stop bit should be in an incoming character, it sets
the framing error bit, FE, in SCS1. A break character also sets the FE bit because a break character has
no stop bit. The FE bit is set at the same time that the SCRF bit is set.
14.4.3.5 Baud Rate Tolerance
A transmitting device may be operating at a baud rate below or above the receiver baud rate.
Accumulated bit time misalignment can cause one of the three stop bit data samples to fall outside the
actual stop bit. Then a noise error occurs. If more than one of the samples is outside the stop bit, a framing
error occurs. In most applications, the baud rate tolerance is much more than the degree of misalignment
that is likely to occur.
As the receiver samples an incoming character, it resynchronizes the RT clock on any valid falling edge
within the character. Resynchronization within characters corrects misalignments between transmitter bit
times and receiver bit times.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
158
Freescale Semiconductor
Functional Description
Slow Data Tolerance
Figure 14-8 shows how much a slow received character can be misaligned without causing a noise error
or a framing error. The slow stop bit begins at RT8 instead of RT1 but arrives in time for the stop bit data
samples at RT8, RT9, and RT10.
MSB
STOP
RT16
RT15
RT14
RT13
RT12
RT11
RT10
RT9
RT8
RT7
RT6
RT5
RT4
RT3
RT2
RT1
RECEIVER
RT CLOCK
DATA SAMPLES
Figure 14-8. Slow Data
For an 8-bit character, data sampling of the stop bit takes the receiver 9 bit times × 16 RT cycles
+ 10 RT cycles = 154 RT cycles.
With the misaligned character shown in Figure 14-8, the receiver counts 154 RT cycles at the point when
the count of the transmitting device is 9 bit times × 16 RT cycles + 3 RT cycles = 147 RT cycles.
The maximum percent difference between the receiver count and the transmitter count of a slow 8-bit
character with no errors is:
154 – 147 × 100 = 4.54%
-------------------------154
For a 9-bit character, data sampling of the stop bit takes the receiver 10 bit times × 16 RT cycles
+ 10 RT cycles = 170 RT cycles.
With the misaligned character shown in Figure 14-8, the receiver counts 170 RT cycles at the point when
the count of the transmitting device is 10 bit times × 16 RT cycles + 3 RT cycles = 163 RT cycles.
The maximum percent difference between the receiver count and the transmitter count of a slow 9-bit
character with no errors is:
170 – 163 × 100 = 4.12%
-------------------------170
Fast Data Tolerance
Figure 14-9 shows how much a fast received character can be misaligned without causing a noise error
or a framing error. The fast stop bit ends at RT10 instead of RT16 but is still there for the stop bit data
samples at RT8, RT9, and RT10.
STOP
IDLE OR NEXT CHARACTER
RT16
RT15
RT14
RT13
RT12
RT11
RT10
RT9
RT8
RT7
RT6
RT5
RT4
RT3
RT2
RT1
RECEIVER
RT CLOCK
DATA SAMPLE
Figure 14-9. Fast Data
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
159
Enhanced Serial Communications Interface (ESCI) Module
For an 8-bit character, data sampling of the stop bit takes the receiver 9 bit times × 16 RT cycles
+ 10 RT cycles = 154 RT cycles.
With the misaligned character shown in Figure 14-9, the receiver counts 154 RT cycles at the point when
the count of the transmitting device is 10 bit times × 16 RT cycles = 160 RT cycles.
The maximum percent difference between the receiver count and the transmitter count of a fast 8-bit
character with no errors is
154 – 160 × 100 = 3.90%.
-------------------------154
For a 9-bit character, data sampling of the stop bit takes the receiver 10 bit times × 16 RT cycles
+ 10 RT cycles = 170 RT cycles.
With the misaligned character shown in Figure 14-9, the receiver counts 170 RT cycles at the point when
the count of the transmitting device is 11 bit times × 16 RT cycles = 176 RT cycles.
The maximum percent difference between the receiver count and the transmitter count of a fast 9-bit
character with no errors is:
170 – 176 × 100 = 3.53%.
-------------------------170
14.4.3.6 Receiver Wakeup
So that the MCU can ignore transmissions intended only for other receivers in multiple-receiver systems,
the receiver can be put into a standby state. Setting the receiver wakeup bit, RWU, in SCC2 puts the
receiver into a standby state during which receiver interrupts are disabled.
Depending on the state of the WAKE bit in SCC1, either of two conditions on the RxD pin can bring the
receiver out of the standby state:
1. Address mark — An address mark is a 1 in the MSB position of a received character. When the
WAKE bit is set, an address mark wakes the receiver from the standby state by clearing the RWU
bit. The address mark also sets the ESCI receiver full bit, SCRF. Software can then compare the
character containing the address mark to the user-defined address of the receiver. If they are the
same, the receiver remains awake and processes the characters that follow. If they are not the
same, software can set the RWU bit and put the receiver back into the standby state.
2. Idle input line condition — When the WAKE bit is clear, an idle character on the RxD pin wakes the
receiver from the standby state by clearing the RWU bit. The idle character that wakes the receiver
does not set the receiver idle bit, IDLE, or the ESCI receiver full bit, SCRF. The idle line type bit,
ILTY, determines whether the receiver begins counting 1s as idle character bits after the start bit
or after the stop bit.
NOTE
With the WAKE bit clear, setting the RWU bit after the RxD pin has been
idle will cause the receiver to wake up.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
160
Freescale Semiconductor
Low-Power Modes
14.4.3.7 Receiver Interrupts
These sources can generate CPU interrupt requests from the ESCI receiver:
• ESCI receiver full (SCRF) — The SCRF bit in SCS1 indicates that the receive shift register has
transferred a character to the SCDR. SCRF can generate a receiver CPU interrupt request. Setting
the ESCI receive interrupt enable bit, SCRIE, in SCC2 enables the SCRF bit to generate receiver
CPU interrupts.
• Idle input (IDLE) — The IDLE bit in SCS1 indicates that 10 or 11 consecutive 1s shifted in from the
RxD pin. The idle line interrupt enable bit, ILIE, in SCC2 enables the IDLE bit to generate CPU
interrupt requests.
14.4.3.8 Error Interrupts
These receiver error flags in SCS1 can generate CPU interrupt requests:
• Receiver overrun (OR) — The OR bit indicates that the receive shift register shifted in a new
character before the previous character was read from the SCDR. The previous character remains
in the SCDR, and the new character is lost. The overrun interrupt enable bit, ORIE, in SCC3
enables OR to generate ESCI error CPU interrupt requests.
• Noise flag (NF) — The NF bit is set when the ESCI detects noise on incoming data or break
characters, including start, data, and stop bits. The noise error interrupt enable bit, NEIE, in SCC3
enables NF to generate ESCI error CPU interrupt requests.
• Framing error (FE) — The FE bit in SCS1 is set when a 0 occurs where the receiver expects a stop
bit. The framing error interrupt enable bit, FEIE, in SCC3 enables FE to generate ESCI error CPU
interrupt requests.
• Parity error (PE) — The PE bit in SCS1 is set when the ESCI detects a parity error in incoming
data. The parity error interrupt enable bit, PEIE, in SCC3 enables PE to generate ESCI error CPU
interrupt requests.
14.5 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
14.5.1 Wait Mode
The ESCI module remains active in wait mode. Any enabled CPU interrupt request from the ESCI module
can bring the MCU out of wait mode.
If ESCI module functions are not required during wait mode, reduce power consumption by disabling the
module before executing the WAIT instruction.
14.5.2 Stop Mode
The ESCI module is inactive in stop mode. The STOP instruction does not affect ESCI register states.
ESCI module operation resumes after the MCU exits stop mode.
Because the internal clock is inactive during stop mode, entering stop mode during an ESCI transmission
or reception results in invalid data.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
161
Enhanced Serial Communications Interface (ESCI) Module
14.6 ESCI During Break Module Interrupts
The BCFE bit in the break flag control register (SBFCR) enables software to clear status bits during the
break state. See Chapter 19 Development Support.
To allow software to clear status bits during a break interrupt, write a 1 to the BCFE bit. If a status bit is
cleared during the break state, it remains cleared when the MCU exits the break state.
To protect status bits during the break state, write a 0 to the BCFE bit. With BCFE at 0 (its default state),
software can read and write I/O registers during the break state without affecting status bits. Some status
bits have a two-step read/write clearing procedure. If software does the first step on such a bit before the
break, the bit cannot change during the break state as long as BCFE is at 0. After the break, doing the
second step clears the status bit.
14.7 I/O Signals
Port E shares two of its pins with the ESCI module. The two ESCI I/O pins are:
• PTE0/TxD — transmit data
• PTE1/RxD — receive data
14.7.1 PTE0/TxD (Transmit Data)
The PTE0/TxD pin is the serial data output from the ESCI transmitter. The ESCI shares the PTE0/TxD
pin with port E. When the ESCI is enabled, the PTE0/TxD pin is an output regardless of the state of the
DDRE0 bit in data direction register E (DDRE).
14.7.2 PTE1/RxD (Receive Data)
The PTE1/RxD pin is the serial data input to the ESCI receiver. The ESCI shares the PTE1/RxD pin with
port E. When the ESCI is enabled, the PTE1/RxD pin is an input regardless of the state of the DDRE1 bit
in data direction register E (DDRE).
14.8 I/O Registers
These I/O registers control and monitor ESCI operation:
• ESCI control register 1, SCC1
• ESCI control register 2, SCC2
• ESCI control register 3, SCC3
• ESCI status register 1, SCS1
• ESCI status register 2, SCS2
• ESCI data register, SCDR
• ESCI baud rate register, SCBR
• ESCI prescaler register, SCPSC
• ESCI arbiter control register, SCIACTL
• ESCI arbiter data register, SCIADAT
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
I/O Registers
14.8.1 ESCI Control Register 1
ESCI control register 1 (SCC1):
• Enables loop mode operation
• Enables the ESCI
• Controls output polarity
• Controls character length
• Controls ESCI wakeup method
• Controls idle character detection
• Enables parity function
• Controls parity type
Address: $0013
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
LOOPS
ENSCI
TXINV
M
WAKE
ILTY
PEN
PTY
0
0
0
0
0
0
0
0
Figure 14-10. ESCI Control Register 1 (SCC1)
LOOPS — Loop Mode Select Bit
This read/write bit enables loop mode operation. In loop mode the RxD pin is disconnected from the
ESCI, and the transmitter output goes into the receiver input. Both the transmitter and the receiver
must be enabled to use loop mode. Reset clears the LOOPS bit.
1 = Loop mode enabled
0 = Normal operation enabled
ENSCI — Enable ESCI Bit
This read/write bit enables the ESCI and the ESCI baud rate generator. Clearing ENSCI sets the SCTE
and TC bits in ESCI status register 1 and disables transmitter interrupts. Reset clears the ENSCI bit.
1 = ESCI enabled
0 = ESCI disabled
TXINV — Transmit Inversion Bit
This read/write bit reverses the polarity of transmitted data. Reset clears the TXINV bit.
1 = Transmitter output inverted
0 = Transmitter output not inverted
NOTE
Setting the TXINV bit inverts all transmitted values including idle, break,
start, and stop bits.
M — Mode (Character Length) Bit
This read/write bit determines whether ESCI characters are eight or nine bits long (See
Table 14-5).The ninth bit can serve as a receiver wakeup signal or as a parity bit. Reset clears the M
bit.
1 = 9-bit ESCI characters
0 = 8-bit ESCI characters
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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163
Enhanced Serial Communications Interface (ESCI) Module
WAKE — Wakeup Condition Bit
This read/write bit determines which condition wakes up the ESCI: a 1 (address mark) in the MSB
position of a received character or an idle condition on the RxD pin. Reset clears the WAKE bit.
1 = Address mark wakeup
0 = Idle line wakeup
Table 14-5. Character Format Selection
Control Bits
Character Format
M
PEN:PTY
Start Bits
Data Bits
Parity
Stop Bits
Character Length
0
0 X
1
8
None
1
10 bits
1
0 X
1
9
None
1
11 bits
0
1 0
1
7
Even
1
10 bits
0
1 1
1
7
Odd
1
10 bits
1
1 0
1
8
Even
1
11 bits
1
1 1
1
8
Odd
1
11 bits
ILTY — Idle Line Type Bit
This read/write bit determines when the ESCI starts counting 1s as idle character bits. The counting
begins either after the start bit or after the stop bit. If the count begins after the start bit, then a string
of 1s preceding the stop bit may cause false recognition of an idle character. Beginning the count after
the stop bit avoids false idle character recognition, but requires properly synchronized transmissions.
Reset clears the ILTY bit.
1 = Idle character bit count begins after stop bit
0 = Idle character bit count begins after start bit
PEN — Parity Enable Bit
This read/write bit enables the ESCI parity function (see Table 14-5). When enabled, the parity
function inserts a parity bit in the MSB position (see Table 14-3). Reset clears the PEN bit.
1 = Parity function enabled
0 = Parity function disabled
PTY — Parity Bit
This read/write bit determines whether the ESCI generates and checks for odd parity or even parity
(see Table 14-5). Reset clears the PTY bit.
1 = Odd parity
0 = Even parity
NOTE
Changing the PTY bit in the middle of a transmission or reception can
generate a parity error.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
I/O Registers
14.8.2 ESCI Control Register 2
ESCI control register 2 (SCC2):
• Enables these CPU interrupt requests:
– SCTE bit to generate transmitter CPU interrupt requests
– TC bit to generate transmitter CPU interrupt requests
– SCRF bit to generate receiver CPU interrupt requests
– IDLE bit to generate receiver CPU interrupt requests
• Enables the transmitter
• Enables the receiver
• Enables ESCI wakeup
• Transmits ESCI break characters
Address: $0014
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
SCTIE
TCIE
SCRIE
ILIE
TE
RE
RWU
SBK
0
0
0
0
0
0
0
0
Figure 14-11. ESCI Control Register 2 (SCC2)
SCTIE — ESCI Transmit Interrupt Enable Bit
This read/write bit enables the SCTE bit to generate ESCI transmitter CPU interrupt requests. Setting
the SCTIE bit in SCC2 enables the SCTE bit to generate CPU interrupt requests. Reset clears the
SCTIE bit.
1 = SCTE enabled to generate CPU interrupt
0 = SCTE not enabled to generate CPU interrupt
TCIE — Transmission Complete Interrupt Enable Bit
:
This read/write bit enables the TC bit to generate ESCI transmitter CPU interrupt requests. Reset
clears the TCIE bit.
1 = TC enabled to generate CPU interrupt requests
0 = TC not enabled to generate CPU interrupt requests
SCRIE — ESCI Receive Interrupt Enable Bit
This read/write bit enables the SCRF bit to generate ESCI receiver CPU interrupt requests. Setting the
SCRIE bit in SCC2 enables the SCRF bit to generate CPU interrupt requests. Reset clears the
SCRIE bit.
1 = SCRF enabled to generate CPU interrupt
0 = SCRF not enabled to generate CPU interrupt
ILIE — Idle Line Interrupt Enable Bit
This read/write bit enables the IDLE bit to generate ESCI receiver CPU interrupt requests. Reset clears
the ILIE bit.
1 = IDLE enabled to generate CPU interrupt requests
0 = IDLE not enabled to generate CPU interrupt requests
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
165
Enhanced Serial Communications Interface (ESCI) Module
TE — Transmitter Enable Bit
Setting this read/write bit begins the transmission by sending a preamble of 10 or 11 1s from the
transmit shift register to the TxD pin. If software clears the TE bit, the transmitter completes any
transmission in progress before the TxD returns to the idle condition (1). Clearing and then setting TE
during a transmission queues an idle character to be sent after the character currently being
transmitted. Reset clears the TE bit.
1 = Transmitter enabled
0 = Transmitter disabled
NOTE
Writing to the TE bit is not allowed when the enable ESCI bit (ENSCI) is
clear. ENSCI is in ESCI control register 1.
RE — Receiver Enable Bit
Setting this read/write bit enables the receiver. Clearing the RE bit disables the receiver but does not
affect receiver interrupt flag bits. Reset clears the RE bit.
1 = Receiver enabled
0 = Receiver disabled
NOTE
Writing to the RE bit is not allowed when the enable ESCI bit (ENSCI) is
clear. ENSCI is in ESCI control register 1.
RWU — Receiver Wakeup Bit
This read/write bit puts the receiver in a standby state during which receiver interrupts are disabled.
The WAKE bit in SCC1 determines whether an idle input or an address mark brings the receiver out
of the standby state and clears the RWU bit. Reset clears the RWU bit.
1 = Standby state
0 = Normal operation
SBK — Send Break Bit
Setting and then clearing this read/write bit transmits a break character followed by a 1. The 1 after the
break character guarantees recognition of a valid start bit. If SBK remains set, the transmitter
continuously transmits break characters with no 1s between them. Reset clears the SBK bit.
1 = Transmit break characters
0 = No break characters being transmitted
NOTE
Do not toggle the SBK bit immediately after setting the SCTE bit. Toggling
SBK before the preamble begins causes the ESCI to send a break
character instead of a preamble.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
I/O Registers
14.8.3 ESCI Control Register 3
ESCI control register 3 (SCC3):
• Stores the ninth ESCI data bit received and the ninth ESCI data bit to be transmitted.
• Enables these interrupts:
– Receiver overrun
– Noise error
– Framing error
– Parity error
Address:
Read:
Write:
Reset:
$0015
Bit 7
R8
U
6
5
4
3
2
1
Bit 0
T8
R
R
ORIE
NEIE
FEIE
PEIE
0
0
= Unimplemented
0
R
0
= Reserved
0
0
U = Unaffected
0
Figure 14-12. ESCI Control Register 3 (SCC3)
R8 — Received Bit 8
When the ESCI is receiving 9-bit characters, R8 is the read-only ninth bit (bit 8) of the received
character. R8 is received at the same time that the SCDR receives the other 8 bits.
When the ESCI is receiving 8-bit characters, R8 is a copy of the eighth bit (bit 7). Reset has no effect
on the R8 bit.
T8 — Transmitted Bit 8
When the ESCI is transmitting 9-bit characters, T8 is the read/write ninth bit (bit 8) of the transmitted
character. T8 is loaded into the transmit shift register at the same time that the SCDR is loaded into
the transmit shift register. Reset clears the T8 bit.
ORIE — Receiver Overrun Interrupt Enable Bit
This read/write bit enables ESCI error CPU interrupt requests generated by the receiver overrun bit,
OR. Reset clears ORIE.
1 = ESCI error CPU interrupt requests from OR bit enabled
0 = ESCI error CPU interrupt requests from OR bit disabled
NEIE — Receiver Noise Error Interrupt Enable Bit
This read/write bit enables ESCI error CPU interrupt requests generated by the noise error bit, NE.
Reset clears NEIE.
1 = ESCI error CPU interrupt requests from NE bit enabled
0 = ESCI error CPU interrupt requests from NE bit disabled
FEIE — Receiver Framing Error Interrupt Enable Bit
This read/write bit enables ESCI error CPU interrupt requests generated by the framing error bit, FE.
Reset clears FEIE.
1 = ESCI error CPU interrupt requests from FE bit enabled
0 = ESCI error CPU interrupt requests from FE bit disabled
PEIE — Receiver Parity Error Interrupt Enable Bit
This read/write bit enables ESCI receiver CPU interrupt requests generated by the parity error bit, PE.
Reset clears PEIE.
1 = ESCI error CPU interrupt requests from PE bit enabled
0 = ESCI error CPU interrupt requests from PE bit disabled
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
167
Enhanced Serial Communications Interface (ESCI) Module
14.8.4 ESCI Status Register 1
ESCI status register 1 (SCS1) contains flags to signal these conditions:
• Transfer of SCDR data to transmit shift register complete
• Transmission complete
• Transfer of receive shift register data to SCDR complete
• Receiver input idle
• Receiver overrun
• Noisy data
• Framing error
• Parity error
Address:
$0016
Bit 7
6
5
4
3
2
1
Bit 0
Read:
SCTE
TC
SCRF
IDLE
OR
NF
FE
PE
1
1
0
0
0
0
0
0
Write:
Reset:
= Unimplemented
Figure 14-13. ESCI Status Register 1 (SCS1)
SCTE — ESCI Transmitter Empty Bit
This clearable, read-only bit is set when the SCDR transfers a character to the transmit shift register.
SCTE can generate an ESCI transmitter CPU interrupt request. When the SCTIE bit in SCC2 is set,
SCTE generates an ESCI transmitter CPU interrupt request. In normal operation, clear the SCTE bit
by reading SCS1 with SCTE set and then writing to SCDR. Reset sets the SCTE bit.
1 = SCDR data transferred to transmit shift register
0 = SCDR data not transferred to transmit shift register
TC — Transmission Complete Bit
This read-only bit is set when the SCTE bit is set, and no data, preamble, or break character is being
transmitted. TC generates an ESCI transmitter CPU interrupt request if the TCIE bit in SCC2 is also
set. TC is cleared automatically when data, preamble, or break is queued and ready to be sent. There
may be up to 1.5 transmitter clocks of latency between queueing data, preamble, and break and the
transmission actually starting. Reset sets the TC bit.
1 = No transmission in progress
0 = Transmission in progress
SCRF — ESCI Receiver Full Bit
This clearable, read-only bit is set when the data in the receive shift register transfers to the ESCI data
register. SCRF can generate an ESCI receiver CPU interrupt request. When the SCRIE bit in SCC2 is
set the SCRF generates a CPU interrupt request. In normal operation, clear the SCRF bit by reading
SCS1 with SCRF set and then reading the SCDR. Reset clears SCRF.
1 = Received data available in SCDR
0 = Data not available in SCDR
IDLE — Receiver Idle Bit
This clearable, read-only bit is set when 10 or 11 consecutive 1s appear on the receiver input. IDLE
generates an ESCI error CPU interrupt request if the ILIE bit in SCC2 is also set. Clear the IDLE bit by
reading SCS1 with IDLE set and then reading the SCDR. After the receiver is enabled, it must receive
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
I/O Registers
a valid character that sets the SCRF bit before an idle condition can set the IDLE bit. Also, after the
IDLE bit has been cleared, a valid character must again set the SCRF bit before an idle condition can
set the IDLE bit. Reset clears the IDLE bit.
1 = Receiver input idle
0 = Receiver input active (or idle since the IDLE bit was cleared)
OR — Receiver Overrun Bit
This clearable, read-only bit is set when software fails to read the SCDR before the receive shift
register receives the next character. The OR bit generates an ESCI error CPU interrupt request if the
ORIE bit in SCC3 is also set. The data in the shift register is lost, but the data already in the SCDR is
not affected. Clear the OR bit by reading SCS1 with OR set and then reading the SCDR. Reset clears
the OR bit.
1 = Receive shift register full and SCRF = 1
0 = No receiver overrun
Software latency may allow an overrun to occur between reads of SCS1 and SCDR in the flag-clearing
sequence. Figure 14-14 shows the normal flag-clearing sequence and an example of an overrun
caused by a delayed flag-clearing sequence. The delayed read of SCDR does not clear the OR bit
because OR was not set when SCS1 was read. Byte 2 caused the overrun and is lost. The next
flag-clearing sequence reads byte 3 in the SCDR instead of byte 2.
In applications that are subject to software latency or in which it is important to know which byte is lost
due to an overrun, the flag-clearing routine can check the OR bit in a second read of SCS1 after
reading the data register.
BYTE 1
BYTE 2
BYTE 3
SCRF = 0
SCRF = 1
SCRF = 0
SCRF = 1
SCRF = 0
SCRF = 1
NORMAL FLAG CLEARING SEQUENCE
BYTE 4
READ SCS1
SCRF = 1
OR = 0
READ SCS1
SCRF = 1
OR = 0
READ SCS1
SCRF = 1
OR = 0
READ SCDR
BYTE 1
READ SCDR
BYTE 2
READ SCDR
BYTE 3
BYTE 1
BYTE 2
BYTE 3
SCRF = 0
OR = 0
SCRF = 1
OR = 1
SCRF = 0
OR = 1
SCRF = 1
SCRF = 1
OR = 1
DELAYED FLAG CLEARING SEQUENCE
BYTE 4
READ SCS1
SCRF = 1
OR = 0
READ SCS1
SCRF = 1
OR = 1
READ SCDR
BYTE 1
READ SCDR
BYTE 3
Figure 14-14. Flag Clearing Sequence
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
169
Enhanced Serial Communications Interface (ESCI) Module
NF — Receiver Noise Flag Bit
This clearable, read-only bit is set when the ESCI detects noise on the RxD pin. NF generates an NF
CPU interrupt request if the NEIE bit in SCC3 is also set. Clear the NF bit by reading SCS1 and then
reading the SCDR. Reset clears the NF bit.
1 = Noise detected
0 = No noise detected
FE — Receiver Framing Error Bit
This clearable, read-only bit is set when a 0 is accepted as the stop bit. FE generates an ESCI error
CPU interrupt request if the FEIE bit in SCC3 also is set. Clear the FE bit by reading SCS1 with FE set
and then reading the SCDR. Reset clears the FE bit.
1 = Framing error detected
0 = No framing error detected
PE — Receiver Parity Error Bit
This clearable, read-only bit is set when the ESCI detects a parity error in incoming data. PE generates
a PE CPU interrupt request if the PEIE bit in SCC3 is also set. Clear the PE bit by reading SCS1 with
PE set and then reading the SCDR. Reset clears the PE bit.
1 = Parity error detected
0 = No parity error detected
14.8.5 ESCI Status Register 2
ESCI status register 2 (SCS2) contains flags to signal these conditions:
• Break character detected
• Incoming data
Address:
Read:
Write:
Reset:
$0017
Bit 7
0
0
6
0
5
0
4
0
3
0
2
0
1
BKF
Bit 0
RPF
0
0
= Unimplemented
0
0
0
0
0
Figure 14-15. ESCI Status Register 2 (SCS2)
BKF — Break Flag Bit
This clearable, read-only bit is set when the ESCI detects a break character on the RxD pin. In SCS1,
the FE and SCRF bits are also set. In 9-bit character transmissions, the R8 bit in SCC3 is cleared. BKF
does not generate a CPU interrupt request. Clear BKF by reading SCS2 with BKF set and then reading
the SCDR. Once cleared, BKF can become set again only after 1s again appear on the RxD pin
followed by another break character. Reset clears the BKF bit.
1 = Break character detected
0 = No break character detected
RPF — Reception in Progress Flag Bit
This read-only bit is set when the receiver detects a 0 during the RT1 time period of the start bit search.
RPF does not generate an interrupt request. RPF is reset after the receiver detects false start bits
(usually from noise or a baud rate mismatch), or when the receiver detects an idle character. Polling
RPF before disabling the ESCI module or entering stop mode can show whether a reception is in
progress.
1 = Reception in progress
0 = No reception in progress
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
I/O Registers
14.8.6 ESCI Data Register
The ESCI data register (SCDR) is the buffer between the internal data bus and the receive and transmit
shift registers. Reset has no effect on data in the ESCI data register.
Address:
$0018
Bit 7
6
5
4
3
2
1
Bit 0
Read:
R7
R6
R5
R4
R3
R2
R1
R0
Write:
T7
T6
T5
T4
T3
T2
T1
T0
Reset:
Unaffected by reset
Figure 14-16. ESCI Data Register (SCDR)
R7/T7:R0/T0 — Receive/Transmit Data Bits
Reading address $0018 accesses the read-only received data bits, R7:R0. Writing to address $0018
writes the data to be transmitted, T7:T0. Reset has no effect on the ESCI data register.
NOTE
Do not use read-modify-write instructions on the ESCI data register.
14.8.7 ESCI Baud Rate Register
The ESCI baud rate register (SCBR) together with the ESCI prescaler register selects the baud rate for
both the receiver and the transmitter.
NOTE
There are two prescalers available to adjust the baud rate. One in the ESCI
baud rate register and one in the ESCI prescaler register.
Address:
Read:
Write:
Reset:
$0019
Bit 7
6
5
4
3
2
1
Bit 0
R
LINR
SCP1
SCP0
R
SCR2
SCR1
SCR0
0
0
0
0
0
0
0
0
R
= Reserved
= Unimplemented
Figure 14-17. ESCI Baud Rate Register (SCBR)
LINR — LIN Receiver Bits
This read/write bit selects the enhanced ESCI features for the local interconnect network (LIN) protocol
as shown in Table 14-6. Reset clears LINR.
Table 14-6. ESCI LIN Control Bits
LINR
M
0
X
Normal ESCI functionality
Functionality
1
0
11-bit break detect enabled for LIN receiver
1
1
12-bit break detect enabled for LIN receiver
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
171
Enhanced Serial Communications Interface (ESCI) Module
SCP1 and SCP0 — ESCI Baud Rate Register Prescaler Bits
These read/write bits select the baud rate register prescaler divisor as shown in Table 14-7. Reset
clears SCP1 and SCP0.
Table 14-7. ESCI Baud Rate Prescaling
SCP[1:0]
Baud Rate Register
Prescaler Divisor (BPD)
0 0
1
0 1
3
1 0
4
1 1
13
SCR2–SCR0 — ESCI Baud Rate Select Bits
These read/write bits select the ESCI baud rate divisor as shown in Table 14-8. Reset clears
SCR2–SCR0.
Table 14-8. ESCI Baud Rate Selection
SCR[2:1:0]
Baud Rate Divisor (BD)
0 0 0
1
0 0 1
2
0 1 0
4
0 1 1
8
1 0 0
16
1 0 1
32
1 1 0
64
1 1 1
128
14.8.8 ESCI Prescaler Register
The ESCI prescaler register (SCPSC) together with the ESCI baud rate register selects the baud rate for
both the receiver and the transmitter.
NOTE
There are two prescalers available to adjust the baud rate. One in the ESCI
baud rate register and one in the ESCI prescaler register.
Address:
Read:
Write:
Reset:
$0009
Bit 7
6
5
4
3
2
1
Bit 0
PDS2
PDS1
PDS0
PSSB4
PSSB3
PSSB2
PSSB1
PSSB0
0
0
0
0
0
0
0
0
Figure 14-18. ESCI Prescaler Register (SCPSC)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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I/O Registers
PDS2–PDS0 — Prescaler Divisor Select Bits
These read/write bits select the prescaler divisor as shown in Table 14-9. Reset clears PDS2–PDS0.
NOTE
The setting of ‘000’ will bypass this prescaler. It is not recommended to
bypass the prescaler while ENSCI is set, because the switching is not glitch
free.
Table 14-9. ESCI Prescaler Division Ratio
PS[2:1:0]
Prescaler Divisor (PD)
0 0 0
Bypass this prescaler
0 0 1
2
0 1 0
3
0 1 1
4
1 0 0
5
1 0 1
6
1 1 0
7
1 1 1
8
PSSB4–PSSB0 — Clock Insertion Select Bits
These read/write bits select the number of clocks inserted in each 32 output cycle frame to achieve
more timing resolution on the average prescaler frequency as shown in Table 14-10. Reset clears
PSSB4–PSSB0.
Table 14-10. ESCI Prescaler Divisor Fine Adjust
PSSB[4:3:2:1:0]
Prescaler Divisor Fine Adjust (PDFA)
0 0 0 0 0
0/32 = 0
0 0 0 0 1
1/32 = 0.03125
0 0 0 1 0
2/32 = 0.0625
0 0 0 1 1
3/32 = 0.09375
0 0 1 0 0
4/32 = 0.125
0 0 1 0 1
5/32 = 0.15625
0 0 1 1 0
6/32 = 0.1875
0 0 1 1 1
7/32 = 0.21875
0 1 0 0 0
8/32 = 0.25
0 1 0 0 1
9/32 = 0.28125
0 1 0 1 0
10/32 = 0.3125
0 1 0 1 1
11/32 = 0.34375
0 1 1 0 0
12/32 = 0.375
0 1 1 0 1
13/32 = 0.40625
0 1 1 1 0
14/32 = 0.4375
Table continued on next page
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
173
Enhanced Serial Communications Interface (ESCI) Module
Table 14-10. ESCI Prescaler Divisor Fine Adjust (Continued)
PSSB[4:3:2:1:0]
Prescaler Divisor Fine Adjust (PDFA)
0 1 1 1 1
15/32 = 0.46875
1 0 0 0 0
16/32 = 0.5
1 0 0 0 1
17/32 = 0.53125
1 0 0 1 0
18/32 = 0.5625
1 0 0 1 1
19/32 = 0.59375
1 0 1 0 0
20/32 = 0.625
1 0 1 0 1
21/32 = 0.65625
1 0 1 1 0
22/32 = 0.6875
1 0 1 1 1
23/32 = 0.71875
1 1 0 0 0
24/32 = 0.75
1 1 0 0 1
25/32 = 0.78125
1 1 0 1 0
26/32 = 0.8125
1 1 0 1 1
27/32 = 0.84375
1 1 1 0 0
28/32 = 0.875
1 1 1 0 1
29/32 = 0.90625
1 1 1 1 0
30/32 = 0.9375
1 1 1 1 1
31/32 = 0.96875
Use the following formula to calculate the ESCI baud rate:
f Bus
Baud rate = -----------------------------------------------------------------------------------64 × BPD × BD × ( PD + PDFA )
where:
fBus =
BPD =
BD
=
PD
=
PDFA =
Bus frequency
Baud rate register prescaler divisor
Baud rate divisor
Prescaler divisor
Prescaler divisor fine adjust
Table 14-11 shows the ESCI baud rates that can be generated with a 4.9152-MHz bus frequency.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
I/O Registers
Table 14-11. ESCI Baud Rate Selection Examples
PS[2:1:0]
PSSB[4:3:2:1:0]
SCP[1:0]
Prescaler
Divisor
(BPD)
SCR[2:1:0]
Baud Rate
Divisor
(BD)
0 0 0
X X X X X
0 0
1
0 0 0
1
76,800
1 1 1
0 0 0 0 0
0 0
1
0 0 0
1
9600
1 1 1
0 0 0 0 1
0 0
1
0 0 0
1
9562.65
1 1 1
0 0 0 1 0
0 0
1
0 0 0
1
9525.58
1 1 1
1 1 1 1 1
0 0
1
0 0 0
1
8563.07
0 0 0
X X X X X
0 0
1
0 0 1
2
38,400
0 0 0
X X X X X
0 0
1
0 1 0
4
19,200
0 0 0
X X X X X
0 0
1
0 1 1
8
9600
0 0 0
X X X X X
0 0
1
1 0 0
16
4800
0 0 0
X X X X X
0 0
1
1 0 1
32
2400
0 0 0
X X X X X
0 0
1
1 1 0
64
1200
0 0 0
X X X X X
0 0
1
1 1 1
128
600
0 0 0
X X X X X
0 1
3
0 0 0
1
25,600
0 0 0
X X X X X
0 1
3
0 0 1
2
12,800
0 0 0
X X X X X
0 1
3
0 1 0
4
6400
0 0 0
X X X X X
0 1
3
0 1 1
8
3200
0 0 0
X X X X X
0 1
3
1 0 0
16
1600
0 0 0
X X X X X
0 1
3
1 0 1
32
800
0 0 0
X X X X X
0 1
3
1 1 0
64
400
0 0 0
X X X X X
0 1
3
1 1 1
128
200
0 0 0
X X X X X
1 0
4
0 0 0
1
19,200
0 0 0
X X X X X
1 0
4
0 0 1
2
9600
0 0 0
X X X X X
1 0
4
0 1 0
4
4800
0 0 0
X X X X X
1 0
4
0 1 1
8
2400
0 0 0
X X X X X
1 0
4
1 0 0
16
1200
0 0 0
X X X X X
1 0
4
1 0 1
32
600
0 0 0
X X X X X
1 0
4
1 1 0
64
300
0 0 0
X X X X X
1 0
4
1 1 1
128
150
0 0 0
X X X X X
1 1
13
0 0 0
1
5908
0 0 0
X X X X X
1 1
13
0 0 1
2
2954
0 0 0
X X X X X
1 1
13
0 1 0
4
1477
0 0 0
X X X X X
1 1
13
0 1 1
8
739
0 0 0
X X X X X
1 1
13
1 0 0
16
369
0 0 0
X X X X X
1 1
13
1 0 1
32
185
0 0 0
X X X X X
1 1
13
1 1 0
64
92
0 0 0
X X X X X
1 1
13
1 1 1
128
46
Baud Rate
(fBus= 4.9152 MHz)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
175
Enhanced Serial Communications Interface (ESCI) Module
14.9 ESCI Arbiter
The ESCI module comprises an arbiter module designed to support software for communication tasks as
bus arbitration, baud rate recovery and break time detection. The arbiter module consists of an 9-bit
counter with 1-bit overflow and control logic. The CPU can control operation mode via the ESCI arbiter
control register (SCIACTL).
14.9.1 ESCI Arbiter Control Register
Address:
$000A
Bit 7
Read:
Write:
Reset:
AM1
6
ALOST
0
0
5
4
AM0
ACLK
0
0
3
2
1
Bit 0
AFIN
ARUN
AROVFL
ARD8
0
0
0
0
= Unimplemented
Figure 14-19. ESCI Arbiter Control Register (SCIACTL)
AM1 and AM0 — Arbiter Mode Select Bits
These read/write bits select the mode of the arbiter module as shown in Table 14-12. Reset clears
AM1 and AM0.
Table 14-12. ESCI Arbiter Selectable Modes
AM[1:0]
ESCI Arbiter Mode
0 0
Idle / counter reset
0 1
Bit time measurement
1 0
Bus arbitration
1 1
Reserved / do not use
ALOST — Arbitration Lost Flag
This read-only bit indicates loss of arbitration. Clear ALOST by writing a 0 to AM1. Reset clears
ALOST.
ACLK — Arbiter Counter Clock Select Bit
This read/write bit selects the arbiter counter clock source. Reset clears ACLK.
1 = Arbiter counter is clocked with one half of the ESCI input clock generated by the ESCI prescaler
0 = Arbiter counter is clocked with one quarter of the bus clock
AFIN— Arbiter Bit Time Measurement Finish Flag
This read-only bit indicates bit time measurement has finished. Clear AFIN by writing any value to
SCIACTL. Reset clears AFIN.
1 = Bit time measurement has finished
0 = Bit time measurement not yet finished
ARUN— Arbiter Counter Running Flag
This read-only bit indicates the arbiter counter is running. Reset clears ARUN.
1 = Arbiter counter running
0 = Arbiter counter stopped
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
176
Freescale Semiconductor
ESCI Arbiter
AROVFL— Arbiter Counter Overflow Bit
This read-only bit indicates an arbiter counter overflow. Clear AROVFL by writing any value to
SCIACTL. Writing 0s to AM1 and AM0 resets the counter keeps it in this idle state. Reset clears
AROVFL.
1 = Arbiter counter overflow has occurred
0 = No arbiter counter overflow has occurred
ARD8— Arbiter Counter MSB
This read-only bit is the MSB of the 9-bit arbiter counter. Clear ARD8 by writing any value to SCIACTL.
Reset clears ARD8.
14.9.2 ESCI Arbiter Data Register
Address: $000B
Read:
Bit 7
6
5
4
3
2
1
Bit 0
ARD7
ARD6
ARD5
ARD4
ARD3
ARD2
ARD1
ARD0
0
0
0
0
0
0
0
0
Write:
Reset:
= Unimplemented
Figure 14-20. ESCI Arbiter Data Register (SCIADAT)
ARD7–ARD0 — Arbiter Least Significant Counter Bits
These read-only bits are the eight LSBs of the 9-bit arbiter counter. Clear ARD7–ARD0 by writing any
value to SCIACTL. Writing 0s to AM1 and AM0 permanently resets the counter and keeps it in this idle
state. Reset clears ARD7–ARD0.
14.9.3 Bit Time Measurement
Two bit time measurement modes, described here, are available according to the state of ACLK.
1. ACLK = 0 — The counter is clocked with one quarter of the bus clock. The counter is started when
a falling edge on the RxD pin is detected. The counter will be stopped on the next falling edge.
ARUN is set while the counter is running, AFIN is set on the second falling edge on RxD (for
instance, the counter is stopped). This mode is used to recover the received baud rate. See
Figure 14-21.
2. ACLK = 1 — The counter is clocked with one half of the ESCI input clock generated by the ESCI
prescaler. The counter is started when a 0 is detected on RxD (see Figure 14-22). A 0 on RxD on
enabling the bit time measurement with ACLK = 1 leads to immediate start of the counter (see
Figure 14-23). The counter will be stopped on the next rising edge of RxD. This mode is used to
measure the length of a received break.
14.9.4 Arbitration Mode
If AM[1:0] is set to 10, the arbiter module operates in arbitration mode. On every rising edge of SCI_TxD
(output of the ESCI module, internal chip signal), the counter is started. When the counter reaches $38
(ACLK = 0) or $08 (ACLK = 1), RxD is statically sensed. If in this case, RxD is sensed low (for example,
another bus is driving the bus dominant) ALOST is set. As long as ALOST is set, the TxD pin is forced
to 1, resulting in a seized transmission.
If SCI_TxD is sensed 0 without having sensed a 0 before on RxD, the counter will be reset, arbitration
operation will be restarted after the next rising edge of SCI_TxD.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
177
Enhanced Serial Communications Interface (ESCI) Module
MEASURED TIME
CPU READS RESULT
OUT OF SCIADAT
COUNTER STOPS,
AFIN = 1
COUNTER STARTS,
ARUN = 1
CPU WRITES SCIACTL
WITH $20
RXD
Figure 14-21. Bit Time Measurement with ACLK = 0
MEASURED TIME
CPU READS RESULT OUT
OF SCIADAT
COUNTER STOPS, AFIN = 1
CPU WRITES SCIACTL WITH $30
COUNTER STARTS, ARUN = 1
RXD
Figure 14-22. Bit Time Measurement with ACLK = 1, Scenario A
MEASURED TIME
CPU READS RESULT
OUT OF SCIADAT
COUNTER STOPS,
AFIN = 1
COUNTER STARTS,
ARUN = 1
CPU WRITES SCIACTL
WITH $30
RXD
Figure 14-23. Bit Time Measurement with ACLK = 1, Scenario B
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
Chapter 15
System Integration Module (SIM)
15.1 Introduction
This section describes the system integration module (SIM). Together with the central processor unit
(CPU), the SIM controls all microconroller unit (MCU) activities. A block diagram of the SIM is shown in
Figure 15-1. Table 15-1 is a summary of the SIM input/output (I/O) registers. The SIM is a system state
controller that coordinates CPU and exception timing.
The SIM is responsible for:
• Bus clock generation and control for CPU and peripherals:
– Stop/wait/reset/break entry and recovery
– Internal clock control
• Master reset control, including power-on reset (POR) and computer operating properly (COP)
timeout
• Interrupt arbitration
Table 15-1 shows the internal signal names used in this section.
Table 15-1. Signal Name Conventions
Signal Name
Description
CGMXCLK
Selected clock source from internal clock generator module (ICG)
CGMOUT
Clock output from ICG module
(Bus clock = CGMOUT divided by two)
IAB
Internal address bus
IDB
Internal data bus
PORRST
Signal from the power-on reset module to the SIM
IRST
Internal reset signal
R/W
Read/write signal
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
179
System Integration Module (SIM)
MODULE STOP
MODULE WAIT
CPU STOP (FROM CPU)
CPU WAIT (FROM CPU)
STOP/WAIT
CONTROL
SIMOSCEN (TO ICG)
SIM
COUNTER
CGMXCLK (FROM ICG)
CGMOUT (FROM ICG)
÷2
CLOCK
CONTROL
VDD
INTERNAL CLOCKS
CLOCK GENERATORS
INTERNAL
PULLUP
DEVICE
FORCED MONITOR MODE ENTRY
RESET
PIN LOGIC
LVI (FROM LVI MODULE)
POR CONTROL
MASTER
RESET
CONTROL
RESET PIN CONTROL
SIM RESET STATUS REGISTER
ILLEGAL OPCODE (FROM CPU)
ILLEGAL ADDRESS (FROM ADDRESS
MAP DECODERS)
COP (FROM COP MODULE)
RESET
INTERRUPT SOURCES
INTERRUPT CONTROL
AND PRIORITY DECODE
CPU INTERFACE
Figure 15-1. SIM Block Diagram
Addr.
$FE00
Register Name
SIM Break Status Register Read:
(SBSR) Write:
See page 193. Reset:
Bit 7
6
5
4
3
2
1
R
R
R
R
R
R
0
0
0
0
0
0
0
0
POR
PIN
COP
ILOP
ILAD
MODRST
LVI
0
1
0
0
0
0
0
0
0
R
R
R
R
R
R
R
R
SBSW
NOTE
Bit 0
R
Note: Writing a 0 clears SBSW.
$FE01
$FE02
SIM Reset Status Register Read:
(SRSR) Write:
See page 194. POR:
Read:
SIM Upper Byte Address
Write:
Register (SUBAR)
Reset:
Figure 15-2. SIM I/O Register Summary
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
SIM Bus Clock Control and Generation
Addr.
$FE03
$FE04
$FE05
$FE06
Register Name
SIM Break Flag Control Read:
Register (SBFCR) Write:
See page 195. Reset:
Bit 7
6
5
4
3
2
1
Bit 0
BCFE
R
R
R
R
R
R
R
0
Interrupt Status Read:
Register 1 (INT1) Write:
See page 189. Reset:
IF6
IF5
IF4
IF3
IF2
IF1
0
0
R
R
R
R
R
R
R
R
0
0
0
0
0
0
0
0
Interrupt Status Read:
Register 2 (INT2) Write:
See page 190. Reset:
IF14
IF13
IF12
IF11
IF10
IF9
IF8
IF7
R
R
R
R
R
R
R
R
0
0
0
0
0
0
0
0
Interrupt Status Read:
Register 3 (INT3) Write:
See page 190. Reset:
0
0
0
0
0
0
IF16
IF15
R
R
R
R
R
R
R
R
0
0
0
0
0
0
0
R
= Reserved
0
= Unimplemented
Figure 15-2. SIM I/O Register Summary (Continued)
15.2 SIM Bus Clock Control and Generation
The bus clock generator provides system clock signals for the CPU and peripherals on the MCU. The
system clocks are generated from an incoming clock, CGMOUT, as shown in Figure 15-3. This clock
originates from either an external oscillator or from the internal clock generator.
COPCLK
TBMCLK
ECLK
CLOCK
SELECT
CIRCUIT
CGMXCLK
ICLK
÷2
ICG
GENERATOR
A
CGMOUT
B S*
*WHEN S = 1,
CGMOUT = B
CS
COP PRESCALER
TBM PRESCALER
SIM COUNTER
BUS CLOCK
GENERATORS
÷2
SIM
MONITOR MODE
USER MODE
ICG
Figure 15-3. System Clock Signals
15.2.1 Bus Timing
In user mode, the internal bus frequency is the internal clock generator output (CGMXCLK) divided by
four.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
181
System Integration Module (SIM)
15.2.2 Clock Startup from POR or LVI Reset
When the power-on reset module or the low-voltage inhibit module generates a reset, the clocks to the
CPU and peripherals are inactive and held in an inactive phase until after the 4096 CGMXCLK cycle POR
timeout has completed. The RST pin is driven low by the SIM during this entire period. The IBUS clocks
start upon completion of the timeout.
15.2.3 Clocks in Stop Mode and Wait Mode
Upon exit from stop mode by an interrupt, break, or reset, the SIM allows CGMXCLK to clock the SIM
counter. The CPU and peripheral clocks do not become active until after the stop delay timeout. This
timeout is selectable as 4096 or 32 CGMXCLK cycles. See 15.6.2 Stop Mode.
In wait mode, the CPU clocks are inactive. The SIM also produces two sets of clocks for other modules.
Refer to the wait mode subsection of each module to see if the module is active or inactive in wait mode.
Some modules can be programmed to be active in wait mode.
15.3 Reset and System Initialization
The MCU has these reset sources:
• Power-on reset module (POR)
• External reset pin (RST)
• Computer operating properly module (COP)
• Low-voltage inhibit module (LVI)
• Illegal opcode
• Illegal address
• Forced monitor mode entry reset (MODRST)
All of these resets produce the vector $FFFE:$FFFF ($FEFE:$FEFF in monitor mode) and assert the
internal reset signal (IRST). IRST causes all registers to be returned to their default values and all
modules to be returned to their reset states.
An internal reset clears the SIM counter (see 15.4 SIM Counter), but an external reset does not. Each of
the resets sets a corresponding bit in the SIM reset status register (SRSR). See 15.7 SIM Registers.
15.3.1 External Pin Reset
The RST pin circuit includes an internal pullup device. Pulling the asynchronous RST pin low halts all
processing. The PIN bit of the SIM reset status register (SRSR) is set as long as RST is held low for a
minimum of 67 CGMXCLK cycles, assuming that neither the POR nor the LVI was the source of the reset.
See Table 15-2 for details. Figure 15-4 shows the relative timing.
CGMOUT
RST
IAB
PC
VECT H VECT L
Figure 15-4. External Reset Timing
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
182
Freescale Semiconductor
Reset and System Initialization
15.3.2 Active Resets from Internal Sources
All internal reset sources actively pull the RST pin low for 32 CGMXCLK cycles to allow resetting of
external peripherals. The internal reset signal IRST continues to be asserted for an additional 32 cycles.
See Figure 15-5. An internal reset can be caused by an illegal address, illegal opcode, COP timeout, LVI,
or POR. See Figure 15-6.
NOTE
For LVI or POR resets, the SIM cycles through 4096 CGMXCLK cycles
during which the SIM forces the RST pin low. The internal reset signal then
follows the sequence from the falling edge of RST shown in Figure 15-5.
The COP reset is asynchronous to the bus clock.
The active reset feature allows the part to issue a reset to peripherals and other chips within a system
built around the MCU.
IRST
RST PULLED LOW BY MCU
RST
32 CYCLES
32 CYCLES
CGMXCLK
IAB
VECTOR HIGH
Figure 15-5. Internal Reset Timing
ILLEGAL ADDRESS RST
ILLEGAL OPCODE RST
COPRST
LVI
POR
MODRST
INTERNAL RESET
Figure 15-6. Sources of Internal Reset
Table 15-2. PIN Bit Set Timing
Reset Recovery Type
Actual Number of Cycles
POR/LVI
4163 (4096 + 64 + 3)
All others
67 (64 + 3)
15.3.2.1 Power-On Reset
When power is first applied to the MCU, the power-on reset module (POR) generates a pulse to indicate
that power-on has occurred. The external reset pin (RST) is held low while the SIM counter counts out
4096 + 32 CGMXCLK cycles. Thirty-two CGMXCLK cycles later, the CPU and memories are released
from reset to allow the reset vector sequence to occur.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
183
System Integration Module (SIM)
At power-on, these events occur:
• A POR pulse is generated.
• The internal reset signal is asserted.
• The SIM enables CGMOUT.
• Internal clocks to the CPU and modules are held inactive for 4096 CGMXCLK cycles to allow
stabilization of the oscillator.
• The RST pin is driven low during the oscillator stabilization time.
• The POR bit of the SIM reset status register (SRSR) is set and all other bits in the register are
cleared.
OSC1
PORRST
4096
CYCLES
32
CYCLES
32
CYCLES
CGMXCLK
CGMOUT
RST
IRST
IAB
$FFFE
$FFFF
Figure 15-7. POR Recovery
15.3.2.2 Computer Operating Properly (COP) Reset
An input to the SIM is reserved for the COP reset signal. The overflow of the COP counter causes an
internal reset and sets the COP bit in the SIM reset status register (SRSR). The SIM actively pulls down
the RST pin for all internal reset sources.
The COP module is disabled if the RST pin or the IRQ pin is held at VTST while the MCU is in monitor
mode. The COP module can be disabled only through combinational logic conditioned with the high
voltage signal on the RST or the IRQ pin. This prevents the COP from becoming disabled as a result of
external noise. During a break state, VTST on the RST pin disables the COP module.
15.3.2.3 Illegal Opcode Reset
The SIM decodes signals from the CPU to detect illegal instructions. An illegal instruction sets the ILOP
bit in the SIM reset status register (SRSR) and causes a reset.
If the stop enable bit, STOP, in the CONFIG1 register is 0, the SIM treats the STOP instruction as an
illegal opcode and causes an illegal opcode reset. The SIM actively pulls down the RST pin for all internal
reset sources.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
184
Freescale Semiconductor
SIM Counter
15.3.2.4 Illegal Address Reset
An opcode fetch from an unmapped address generates an illegal address reset. The SIM verifies that the
CPU is fetching an opcode prior to asserting the ILAD bit in the SIM reset status register (SRSR) and
resetting the MCU. A data fetch from an unmapped address does not generate a reset. The SIM actively
pulls down the RST pin for all internal reset sources.
15.3.2.5 Low-Voltage Inhibit (LVI) Reset
The low-voltage inhibit module (LVI) asserts its output to the SIM when the VDD voltage falls to the
LVITRIPF voltage. The LVI bit in the SIM reset status register (SRSR) is set, and the external reset pin
(RST) is held low while the SIM counter counts out 4096 + 32 CGMXCLK cycles. Thirty-two CGMXCLK
cycles later, the CPU is released from reset to allow the reset vector sequence to occur. The SIM actively
pulls down the RST pin for all internal reset sources.
15.3.2.6 Monitor Mode Entry Module Reset (MODRST)
The monitor mode entry module reset (MODRST) asserts its output to the SIM when monitor mode is
entered in the condition where the reset vectors are erased ($FF). (See 19.3.1 Functional Description.)
When MODRST gets asserted, an internal reset occurs. The SIM actively pulls down the RST pin for all
internal reset sources.
15.4 SIM Counter
The SIM counter is used by the power-on reset module (POR) and in stop mode recovery to allow the
oscillator time to stabilize before enabling the internal bus (IBUS) clocks. The SIM counter is 13 bits long.
15.4.1 SIM Counter During Power-On Reset
The power-on reset module (POR) detects power applied to the MCU. At power-on, the POR circuit
asserts the signal PORRST. Once the SIM is initialized, it enables the clock generation module (CGM) to
drive the bus clock state machine.
15.4.2 SIM Counter During Stop Mode Recovery
The SIM counter also is used for stop mode recovery. The STOP instruction clears the SIM counter. After
an interrupt, break, or reset, the SIM senses the state of the short stop recovery bit, SSREC, in the
CONFIG1 register. If the SSREC bit is a 1, then the stop recovery is reduced from the normal delay of
4096 CGMXCLK cycles down to 32 CGMXCLK cycles. This is ideal for applications using canned
oscillators that do not require long startup times from stop mode. External crystal applications should use
the full stop recovery time, that is, with SSREC cleared.
15.4.3 SIM Counter and Reset States
External reset has no effect on the SIM counter. See 15.6.2 Stop Mode for details. The SIM counter is
free-running after all reset states. See 15.3.2 Active Resets from Internal Sources for counter control and
internal reset recovery sequences.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
185
System Integration Module (SIM)
15.5 Exception Control
Normal, sequential program execution can be changed in three different ways:
• Interrupts:
– Maskable hardware CPU interrupts
– Non-maskable software interrupt instruction (SWI)
• Reset
• Break interrupts
15.5.1 Interrupts
At the beginning of an interrupt, the CPU saves the CPU register contents on the stack and sets the
interrupt mask (I bit) to prevent additional interrupts. At the end of an interrupt, the RTI instruction recovers
the CPU register contents from the stack so that normal processing can resume. Figure 15-8 shows
interrupt entry timing. Figure 15-9 shows interrupt recovery timing.
MODULE
INTERRUPT
I BIT
IAB
IDB
DUMMY
SP
DUMMY
SP – 1
SP – 2
PC – 1[7:0] PC – 1[15:8]
SP – 3
X
SP – 4
A
VECT H
CCR
VECT L
V DATA H
START ADDR
V DATA L
OPCODE
R/W
Figure 15-8. Interrupt Entry Timing
MODULE
INTERRUPT
I BIT
IAB
IDB
SP – 4
SP – 3
CCR
SP – 2
A
SP – 1
X
SP
PC
PC + 1
PC – 1 [7:0] PC – 1 [15:8] OPCODE
OPERAND
R/W
Figure 15-9. Interrupt Recovery Timing
Interrupts are latched, and arbitration is performed in the SIM at the start of interrupt processing. The
arbitration result is a constant that the CPU uses to determine which vector to fetch. Once an interrupt is
latched by the SIM, no other interrupt can take precedence, regardless of priority, until the latched
interrupt is serviced (or the I bit is cleared). See Figure 15-10.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
186
Freescale Semiconductor
Exception Control
FROM RESET
BREAK
I BIT
SET?
INTERRUPT?
YES
NO
YES
I BIT SET?
NO
IRQ
INTERRUPT?
YES
NO
AS MANY INTERRUPTS
AS EXIST ON CHIP
STACK CPU REGISTERS
SET I BIT
LOAD PC WITH INTERRUPT VECTOR
FETCH NEXT
INSTRUCTION
SWI
INSTRUCTION?
YES
NO
RTI
INSTRUCTION?
YES
UNSTACK CPU REGISTERS
NO
EXECUTE INSTRUCTION
Figure 15-10. Interrupt Processing
15.5.1.1 Hardware Interrupts
A hardware interrupt does not stop the current instruction. Processing of a hardware interrupt begins after
completion of the current instruction. When the current instruction is complete, the SIM checks all pending
hardware interrupts. If interrupts are not masked (I bit clear in the condition code register) and if the
corresponding interrupt enable bit is set, the SIM proceeds with interrupt processing; otherwise, the next
instruction is fetched and executed.
If more than one interrupt is pending at the end of an instruction execution, the highest priority interrupt is
serviced first. Figure 15-11 demonstrates what happens when two interrupts are pending. If an interrupt
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
187
System Integration Module (SIM)
is pending upon exit from the original interrupt service routine, the pending interrupt is serviced before the
LDA instruction is executed.
The LDA opcode is prefetched by both the INT1 and INT2 RTI instructions. However, in the case of the
INT1 RTI prefetch, this is a redundant operation.
NOTE
To maintain compatibility with the M6805 Family, the H register is not
pushed on the stack during interrupt entry. If the interrupt service routine
modifies the H register or uses the indexed addressing mode, software
should save the H register and then restore it prior to exiting the routine.
CLI
LDA #$FF
INT1
BACKGROUND
ROUTINE
PSHH
INT1 INTERRUPT SERVICE ROUTINE
PULH
RTI
INT2
PSHH
INT2 INTERRUPT SERVICE ROUTINE
PULH
RTI
Figure 15-11. Interrupt Recognition Example
15.5.1.2 SWI Instruction
The SWI instruction is a non-maskable instruction that causes an interrupt regardless of the state of the
interrupt mask (I bit) in the condition code register.
NOTE
A software interrupt pushes PC onto the stack. A software interrupt does
not push PC – 1, as a hardware interrupt does.
15.5.1.3 Interrupt Status Registers
The flags in the interrupt status registers identify maskable interrupt sources. Table 15-3 summarizes the
interrupt sources and the interrupt status register flags that they set. The interrupt status registers can be
useful for debugging.
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Freescale Semiconductor
Exception Control
Table 15-3. Interrupt Sources
Priority
Interrupt Source
Interrupt Status
Register Flag
Highest
Reset
—
SWI instruction
—
IRQ pin
I1
ICG clock monitor
I2
TIM1 channel 0
I3
TIM1 channel 1
I4
TIM1 overflow
I5
TIM2 channel 0
I6
TIM2 channel 1
I7
TIM2 overflow
I8
SPI receiver full
I9
SPI transmitter empty
I10
SCI receive error
I11
SCI receive
I12
SCI transmit
I13
Keyboard
I14
ADC conversion complete
I15
Timebase module
I16
Lowest
Interrupt Status Register 1
Address:
$FE04
Bit 7
6
5
4
3
2
1
Bit 0
Read:
I6
I5
I4
I3
I2
I1
0
0
Write:
R
R
R
R
R
R
R
R
Reset:
0
0
0
0
0
0
0
0
R
= Reserved
Figure 15-12. Interrupt Status Register 1 (INT1)
I6–I1 — Interrupt Flags 1–6
These flags indicate the presence of interrupt requests from the sources shown in Table 15-3.
1 = Interrupt request present
0 = No interrupt request present
Bit 0 and Bit 1 — Always read 0
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
189
System Integration Module (SIM)
Interrupt Status Register 2
Address:
$FE05
Bit 7
6
5
4
3
2
1
Bit 0
Read:
I14
I13
I12
I11
I10
I9
I8
I7
Write:
R
R
R
R
R
R
R
R
Reset:
0
0
0
0
0
0
0
0
R
= Reserved
Figure 15-13. Interrupt Status Register 2 (INT2)
I14–I7 — Interrupt Flags 14–7
These flags indicate the presence of interrupt requests from the sources shown in Table 15-3.
1 = Interrupt request present
0 = No interrupt request present
Interrupt Status Register 3
Address:
$FE06
Bit 7
6
5
4
3
2
1
Bit 0
Read:
0
0
0
0
0
0
I16
I15
Write:
R
R
R
R
R
R
R
R
Reset:
0
0
0
0
0
0
0
0
R
= Reserved
Figure 15-14. Interrupt Status Register 3 (INT3)
Bits 7–2 — Always read 0
I16–I15 — Interrupt Flags 16–15
These flags indicate the presence of an interrupt request from the source shown in Table 15-3.
1 = Interrupt request present
0 = No interrupt request present
15.5.2 Reset
All reset sources always have equal and highest priority and cannot be arbitrated.
15.5.3 Break Interrupts
The break module can stop normal program flow at a software-programmable break point by asserting its
break interrupt output (see Chapter 18 Timer Interface Module (TIM)). The SIM puts the CPU into the
break state by forcing it to the SWI vector location. Refer to the break interrupt subsection of each module
to see how each module is affected by the break state.
15.5.4 Status Flag Protection in Break Mode
The SIM controls whether status flags contained in other modules can be cleared during break mode. The
user can select whether flags are protected from being cleared by properly initializing the break clear flag
enable bit (BCFE) in the SIM break flag control register (SBFCR).
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Freescale Semiconductor
Low-Power Modes
Protecting flags in break mode ensures that set flags will not be cleared while in break mode. This
protection allows registers to be freely read and written during break mode without losing status flag
information.
Setting the BCFE bit enables the clearing mechanisms. Once cleared in break mode, a flag remains
cleared even when break mode is exited. Status flags with a 2-step clearing mechanism — for example,
a read of one register followed by the read or write of another — are protected, even when the first step
is accomplished prior to entering break mode. Upon leaving break mode, execution of the second step
will clear the flag as normal.
15.6 Low-Power Modes
Executing the WAIT or STOP instruction puts the MCU in a low power-consumption mode for standby
situations. The SIM holds the CPU in a non-clocked state. The operation of each of these modes is
described in the following subsections. Both STOP and WAIT clear the interrupt mask (I) in the condition
code register, allowing interrupts to occur.
15.6.1 Wait Mode
In wait mode, the CPU clocks are inactive while the peripheral clocks continue to run. Figure 15-15 shows
the timing for wait mode entry.
IAB
IDB
WAIT ADDR
WAIT ADDR + 1
PREVIOUS DATA
NEXT OPCODE
SAME
SAME
SAME
SAME
R/W
Note:
Previous data can be operand data or the WAIT opcode, depending on the
last instruction.
Figure 15-15. Wait Mode Entry Timing
A module that is active during wait mode can wake up the CPU with an interrupt if the interrupt is enabled.
Stacking for the interrupt begins one cycle after the WAIT instruction during which the interrupt occurred.
In wait mode, the CPU clocks are inactive. Refer to the wait mode subsection of each module to see if the
module is active or inactive in wait mode. Some modules can be programmed to be active in wait mode.
Wait mode also can be exited by a reset or break. A break interrupt during wait mode sets the SIM break
stop/wait bit, SBSW, in the SIM break status register (SBSR). If the COP disable bit, COPD, in the
CONFIG1 register is 0, then the computer operating properly module (COP) is enabled and remains
active in wait mode.
Figure 15-16 and Figure 15-17 show the timing for WAIT recovery.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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System Integration Module (SIM)
IAB
$6E0B
IDB
$A6
$A6
$6E0C
$A6
$01
$00FF
$0B
$00FE
$00FD
$00FC
$6E
EXITSTOPWAIT
Note: EXITSTOPWAIT = RST pin, CPU interrupt or break interrupt interrupt
Figure 15-16. Wait Recovery from Interrupt or Break
32
CYCLES
IAB
IDB
$6E0B
$A6
$A6
32
CYCLES
RSTVCTH
RST VCTL
$A6
RST
CGMXCLK
Figure 15-17. Wait Recovery from Internal Reset
15.6.2 Stop Mode
In stop mode, the SIM counter is reset and the system clocks are disabled. An interrupt request from a
module can cause an exit from stop mode. Stacking for interrupts begins after the selected stop recovery
time has elapsed. Reset or break also causes an exit from stop mode.
The SIM disables the clock generator module outputs (CGMOUT and CGMXCLK) in stop mode, stopping
the CPU and peripherals. Stop recovery time is selectable using the SSREC bit in CONFIG1. If SSREC
is set, stop recovery is reduced from the normal delay of 4096 CGMXCLK cycles down to 32. This is ideal
for applications using canned oscillators that do not require long startup times from stop mode.
NOTE
All applications should use the full stop recovery time by clearing the
SSREC bit unless OSCENINSTOP is set in CONFIG2.
The SIM counter is held in reset from the execution of the STOP instruction until the beginning of stop
recovery. It is then used to time the recovery period. Figure 15-18 shows stop mode entry timing.
NOTE
To minimize stop current, all pins configured as inputs should be driven to
a 1 or 0.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
SIM Registers
CPUSTOP
IAB
STOP ADDR + 1
STOP ADDR
IDB
PREVIOUS DATA
SAME
SAME
NEXT OPCODE
SAME
SAME
R/W
Note: Previous data can be operand data or the STOP opcode, depending on the last instruction.
Figure 15-18. Stop Mode Entry Timing
STOP RECOVERY PERIOD
CGMXCLK
INT/BREAK
IAB
STOP + 2
STOP +1
STOP + 2
SP
SP – 1
SP – 2
SP – 3
Figure 15-19. Stop Mode Recovery from Interrupt
15.7 SIM Registers
The SIM has three memory-mapped registers. Table 15-4 shows the mapping of these registers.
Table 15-4. SIM Registers
Address
Register
Access Mode
$FE00
SBSR
User
$FE01
SRSR
User
$FE03
SBFCR
User
15.7.1 SIM Break Status Register
The SIM break status register (SBSR) contains a flag to indicate that a break caused an exit from wait
mode. This register is only used in emulation mode.
Address:
$FE00
Bit 7
Read:
Write:
Reset:
6
5
4
3
2
R
R
R
R
R
R
0
0
0
0
0
0
R
= Reserved
1
SBSW
Note(1)
0
Bit 0
R
0
Note: 1. Writing a 0 clears SBSW.
Figure 15-20. SIM Break Status Register (SBSR)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
193
System Integration Module (SIM)
SBSW — SIM Break Stop/Wait
SBSW can be read within the break state SWI routine. The user can modify the return address on the
stack by subtracting one from it.
1 = Wait mode was exited by break interrupt.
0 = Wait mode was not exited by break interrupt.
15.7.2 SIM Reset Status Register
The SRSR register contains flags that show the source of the latest reset. The status register will
automatically clear after reading it. A power-on reset sets the POR bit and clears all other bits in the
register. All other reset sources set the individual flag bits but do not clear the register. More than one
reset source can be flagged at any time depending on the conditions at the time of the internal or external
reset. For example, the POR and LVI bits can both be set if the power supply has a slow rise time.
Address:
Read:
$FE01
Bit 7
6
5
4
3
2
1
Bit 0
POR
PIN
COP
ILOP
ILAD
MODRST
LVI
0
1
0
0
0
0
0
0
0
Write:
Reset:
= Unimplemented
Figure 15-21. SIM Reset Status Register (SRSR)
POR — Power-On Reset Bit
1 = Last reset caused by POR circuit
0 = Read of SRSR
PIN — External Reset Bit
1 = Last reset caused by external reset pin (RST)
0 = POR or read of SRSR
COP — Computer Operating Properly Reset Bit
1 = Last reset caused by COP counter
0 = POR or read of SRSR
ILOP — Illegal Opcode Reset Bit
1 = Last reset caused by an illegal opcode
0 = POR or read of SRSR
ILAD — Illegal Address Reset Bit (opcode fetches only)
1 = Last reset caused by an opcode fetch from an illegal address
0 = POR or read of SRSR
MODRST — Monitor Mode Entry Module Reset Bit
1 = Last reset caused by monitor mode entry when vector locations $FFFE and $FFFF are $FF after
POR while IRQ ≠ VTST
0 = POR or read of SRSR
LVI — Low-Voltage Inhibit Reset Bit
1 = Last reset caused by the LVI circuit
0 = POR or read of SRSR
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Freescale Semiconductor
SIM Registers
15.7.3 SIM Break Flag Control Register
The SIM break control register contains a bit that enables software to clear status bits while the MCU is
in a break state.
Address:
Read:
Write:
Reset:
$FE03
Bit 7
6
5
4
3
2
1
Bit 0
BCFE
R
R
R
R
R
R
R
0
R
= Reserved
Figure 15-22. SIM Break Flag Control Register (SBFCR)
BCFE — Break Clear Flag Enable Bit
This read/write bit enables software to clear status bits by accessing status registers while the MCU is
in a break state. To clear status bits during the break state, the BCFE bit must be set.
1 = Status bits clearable during break
0 = Status bits not clearable during break
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System Integration Module (SIM)
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Freescale Semiconductor
Chapter 16
Serial Peripheral Interface (SPI) Module
16.1 Introduction
This section describes the serial peripheral interface (SPI) module, which allows full-duplex, synchronous,
serial communications with peripheral devices.
The text that follows describes the SPI. The SPI I/O pin names are SS (slave select), SPSCK (SPI serial
clock), MOSI (master out slave in), and MISO (master in/slave out). The SPI shares four I/O pins with four
parallel I/O ports.
16.2 Features
Features of the SPI module include:
• Full-duplex operation
• Master and slave modes
• Double-buffered operation with separate transmit and receive registers
• Four master mode frequencies (maximum = bus frequency ÷ 2)
• Maximum slave mode frequency = bus frequency
• Serial clock with programmable polarity and phase
• Two separately enabled interrupts:
– SPRF (SPI receiver full)
– SPTE (SPI transmitter empty)
• Mode fault error flag with CPU interrupt capability
• Overflow error flag with CPU interrupt capability
• Programmable wired-OR mode
• I/O (input/output) port bit(s) software configurable with pullup device(s) if configured as input port
bit(s)
16.3 Functional Description
The SPI module allows full-duplex, synchronous, serial communication between the MCU and peripheral
devices, including other MCUs. Software can poll the SPI status flags or SPI operation can be interrupt
driven.
If a port bit is configured for input, then an internal pullup device may be enabled for that port bit.
The following paragraphs describe the operation of the SPI module. Refer to Figure 16-2 for a summary
of the SPI I/O registers.
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Freescale Semiconductor
197
Serial Peripheral Interface (SPI) Module
8-BIT KEYBOARD
INTERRUPT MODULE
FLASH PROGRAMMING ROUTINES
ROM — 720 BYTES
USER FLASH VECTOR SPACE — 36 BYTES
PTE4/OSC1
PTE3/OSC2
INTERNAL CLOCK
GENERATOR MODULE
RST(3)
SYSTEM INTEGRATION
MODULE
IRQ(3)
SINGLE EXTERNAL
INTERRUPT MODULE
VREFH
VREFL
2-CHANNEL TIMER INTERFACE
MODULE 2
DDRA
PTD7/T2CH1(1)
PTD6/T2CH0(1)
PTD5/T1CH1(1)
PTD4/T1CH0(1)
PTD3/SPSCK(1)
PTD2/MOSI(1)
PTD1/MISO(1)
PTD0/SS(1)
PTE2
PTE1/RxD
PTE0/TxD
SERIAL PERIPHERAL
INTERFACE MODULE
MONITOR MODULE
8-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
PTC6(1)
PTC5(1)
PTC4(1)(2)
PTC3(1)(2)
PTC2(1)(2)
PTC1(1)(2)
PTC0(1)(2)
SERIAL COMMUNICATIONS
INTERFACE MODULE
COMPUTER OPERATING
PROPERLY MODULE
POWER-ON RESET
MODULE
VDD
VSS
VDDA
VSSA
2-CHANNEL TIMER INTERFACE
MODULE 1
DDRD
MONITOR ROM — 304 BYTES
PORTA
USER RAM — 512 BYTES
PORTB
DUAL VOLTAGE
LOW-VOLTAGE INHIBIT MODULE
PTB7/AD7
PTB6/AD6
PTB5/AD5
PTB4/AD4
PTB3/AD3
PTB2/AD2
PTB1/AD1
PTB0/AD0
PORTC
USER FLASH
MC68HC908GT16 — 15,872 BYTES
MC68HC908GT8 — 7,680 BYTES
PTA7/KBD7–
PTA0/KBD0(1)
PORTD
SINGLE BREAKPOINT BREAK
MODULE
DDRB
CONTROL AND STATUS
REGISTERS — 64 BYTES
DDRC
PROGRAMMABLE TIMEBASE
MODULE
ARITHMETIC/LOGIC
UNIT (ALU)
MEMORY MAP
MODULE
DDRE
CPU
REGISTERS
PORTE
INTERNAL BUS
M68HC08 CPU
SECURITY
MODULE
CONFIGURATION REGISTER 1
MODULE
CONFIGURATION REGISTER 2
MODULE
MONITOR MODE ENTRY
MODULE
1. Ports are software configurable with pullup device if input port.
2. Higher current drive port pins
3. Pin contains integrated pullup device
Figure 16-1. Block Diagram Highlighting SPI Block and Pins
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Freescale Semiconductor
Functional Description
INTERNAL BUS
TRANSMIT DATA REGISTER
SHIFT REGISTER
BUSCLK
7
6
5
4
3
2
1
MISO
0
÷2
MOSI
÷8
CLOCK
DIVIDER
RECEIVE DATA REGISTER
÷ 32
PIN
CONTROL
LOGIC
÷ 128
SPMSTR
SPE
CLOCK
SELECT
SPR1
SPSCK
M
CLOCK
LOGIC
S
SS
SPR0
SPMSTR
TRANSMITTER CPU INTERRUPT REQUEST
RECEIVER/ERROR CPU INTERRUPT REQUEST
CPHA
MODFEN
CPOL
SPWOM
ERRIE
SPI
CONTROL
SPTIE
SPRIE
SPE
SPRF
SPTE
OVRF
MODF
Figure 16-2. SPI Module Block Diagram
Addr.
$0010
$0011
$0012
Register Name
SPI Control Register Read:
(SPCR) Write:
See page 213. Reset:
SPI Status and Control Read:
Register (SPSCR) Write:
See page 214. Reset:
SPI Data Register Read:
(SPDR) Write:
See page 216. Reset:
Bit 7
6
5
4
3
2
1
Bit 0
SPRIE
R
SPMSTR
CPOL
CPHA
SPWOM
SPE
SPTIE
0
SPRF
0
1
OVRF
0
MODF
1
SPTE
0
0
0
MODFEN
SPR1
SPR0
0
R1
T1
0
R0
T0
ERRIE
0
R7
T7
0
R6
T6
R
= Reserved
0
R5
T5
0
1
0
R4
R3
R2
T4
T3
T2
Unaffected by reset
= Unimplemented
Figure 16-3. SPI I/O Register Summary
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Serial Peripheral Interface (SPI) Module
16.3.1 Master Mode
The SPI operates in master mode when the SPI master bit, SPMSTR, is set.
NOTE
In a multi-SPI system, configure the SPI modules as master or slave before
enabling them. Enable the master SPI before enabling the slave SPI.
Disable the slave SPI before disabling the master SPI. See 16.12.1 SPI
Control Register.
Only a master SPI module can initiate transmissions. Software begins the transmission from a master SPI
module by writing to the transmit data register. If the shift register is empty, the byte immediately transfers
to the shift register, setting the SPI transmitter empty bit, SPTE. The byte begins shifting out on the MOSI
pin under the control of the serial clock. See Figure 16-4.
MASTER MCU
SHIFT REGISTER
SLAVE MCU
MISO
MISO
MOSI
MOSI
SPSCK
BAUD RATE
GENERATOR
SS
SHIFT REGISTER
SPSCK
VDD
SS
Figure 16-4. Full-Duplex Master-Slave Connections
The SPR1 and SPR0 bits control the baud rate generator and determine the speed of the shift register.
(See 16.12.2 SPI Status and Control Register.) Through the SPSCK pin, the baud rate generator of the
master also controls the shift register of the slave peripheral.
As the byte shifts out on the MOSI pin of the master, another byte shifts in from the slave on the master’s
MISO pin. The transmission ends when the receiver full bit, SPRF, becomes set. At the same time that
SPRF becomes set, the byte from the slave transfers to the receive data register. In normal operation,
SPRF signals the end of a transmission. Software clears SPRF by reading the SPI status and control
register with SPRF set and then reading the SPI data register. Writing to the SPI data register (SPDR)
clears SPTE.
16.3.2 Slave Mode
The SPI operates in slave mode when SPMSTR is clear. In slave mode, the SPSCK pin is the input for
the serial clock from the master MCU. Before a data transmission occurs, the SS pin of the slave SPI must
be low. SS must remain low until the transmission is complete. See 16.6.2 Mode Fault Error.
In a slave SPI module, data enters the shift register under the control of the serial clock from the master
SPI module. After a byte enters the shift register of a slave SPI, it transfers to the receive data register,
and the SPRF bit is set. To prevent an overflow condition, slave software then must read the receive data
register before another full byte enters the shift register.
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Freescale Semiconductor
Transmission Formats
The maximum frequency of the SPSCK for an SPI configured as a slave is the bus clock speed (which is
twice as fast as the fastest master SPSCK clock that can be generated). The frequency of the SPSCK for
an SPI configured as a slave does not have to correspond to any SPI baud rate. The baud rate only
controls the speed of the SPSCK generated by an SPI configured as a master. Therefore, the frequency
of the SPSCK for an SPI configured as a slave can be any frequency less than or equal to the bus speed.
When the master SPI starts a transmission, the data in the slave shift register begins shifting out on the
MISO pin. The slave can load its shift register with a new byte for the next transmission by writing to its
transmit data register. The slave must write to its transmit data register at least one bus cycle before the
master starts the next transmission. Otherwise, the byte already in the slave shift register shifts out on the
MISO pin. Data written to the slave shift register during a transmission remains in a buffer until the end of
the transmission.
When the clock phase bit (CPHA) is set, the first edge of SPSCK starts a transmission. When CPHA is
clear, the falling edge of SS starts a transmission. See 16.4 Transmission Formats.
NOTE
SPSCK must be in the proper idle state before the slave is enabled to
prevent SPSCK from appearing as a clock edge.
16.4 Transmission Formats
During an SPI transmission, data is simultaneously transmitted (shifted out serially) and received (shifted
in serially). A serial clock synchronizes shifting and sampling on the two serial data lines. A slave select
line allows selection of an individual slave SPI device; slave devices that are not selected do not interfere
with SPI bus activities. On a master SPI device, the slave select line can optionally be used to indicate
multiple-master bus contention.
16.4.1 Clock Phase and Polarity Controls
Software can select any of four combinations of serial clock (SPSCK) phase and polarity using two bits
in the SPI control register (SPCR). The clock polarity is specified by the CPOL control bit, which selects
an active high or low clock and has no significant effect on the transmission format.
The clock phase (CPHA) control bit selects one of two fundamentally different transmission formats. The
clock phase and polarity should be identical for the master SPI device and the communicating slave
device. In some cases, the phase and polarity are changed between transmissions to allow a master
device to communicate with peripheral slaves having different requirements.
NOTE
Before writing to the CPOL bit or the CPHA bit, disable the SPI by clearing
the SPI enable bit (SPE).
16.4.2 Transmission Format When CPHA = 0
Figure 16-5 shows an SPI transmission in which CPHA = 0. The figure should not be used as a
replacement for data sheet parametric information.
Two waveforms are shown for SPSCK: one for CPOL = 0 and another for CPOL = 1. The diagram may
be interpreted as a master or slave timing diagram since the serial clock (SPSCK), master in/slave out
(MISO), and master out/slave in (MOSI) pins are directly connected between the master and the slave.
The MISO signal is the output from the slave, and the MOSI signal is the output from the master. The SS
line is the slave select input to the slave. The slave SPI drives its MISO output only when its slave select
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
201
Serial Peripheral Interface (SPI) Module
input (SS) is low, so that only the selected slave drives to the master. The SS pin of the master is not
shown but is assumed to be inactive. The SS pin of the master must be high or must be reconfigured as
general-purpose I/O not affecting the SPI. (See 16.6.2 Mode Fault Error.) When CPHA = 0, the first
SPSCK edge is the MSB capture strobe. Therefore, the slave must begin driving its data before the first
SPSCK edge, and a falling edge on the SS pin is used to start the slave data transmission. The slave’s
SS pin must be toggled back to high and then low again between each byte transmitted as shown in
Figure 16-6.
When CPHA = 0 for a slave, the falling edge of SS indicates the beginning of the transmission. This
causes the SPI to leave its idle state and begin driving the MISO pin with the MSB of its data. Once the
transmission begins, no new data is allowed into the shift register from the transmit data register.
Therefore, the SPI data register of the slave must be loaded with transmit data before the falling edge of
SS. Any data written after the falling edge is stored in the transmit data register and transferred to the shift
register after the current transmission.
SPSCK CYCLE #
FOR REFERENCE
1
2
3
4
5
6
7
8
MSB
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
LSB
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
LSB
SPSCK; CPOL = 0
SPSCK; CPOL =1
MOSI
FROM MASTER
MISO
FROM SLAVE
MSB
SS; TO SLAVE
CAPTURE STROBE
Figure 16-5. Transmission Format (CPHA = 0)
MISO/MOSI
BYTE 1
BYTE 2
BYTE 3
MASTER SS
SLAVE SS
CPHA = 0
SLAVE SS
CPHA = 1
Figure 16-6. CPHA/SS Timing
16.4.3 Transmission Format When CPHA = 1
Figure 16-7 shows an SPI transmission in which CPHA = 1. The figure should not be used as a
replacement for data sheet parametric information. Two waveforms are shown for SPSCK: one for
CPOL = 0 and another for CPOL = 1. The diagram may be interpreted as a master or slave timing
diagram since the serial clock (SPSCK), master in/slave out (MISO), and master out/slave in (MOSI) pins
are directly connected between the master and the slave. The MISO signal is the output from the slave,
and the MOSI signal is the output from the master. The SS line is the slave select input to the slave. The
slave SPI drives its MISO output only when its slave select input (SS) is low, so that only the selected
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
Transmission Formats
slave drives to the master. The SS pin of the master is not shown but is assumed to be inactive. The SS
pin of the master must be high or must be reconfigured as general-purpose I/O not affecting the SPI. (See
16.6.2 Mode Fault Error.) When CPHA = 1, the master begins driving its MOSI pin on the first SPSCK
edge. Therefore, the slave uses the first SPSCK edge as a start transmission signal. The SS pin can
remain low between transmissions. This format may be preferable in systems having only one master and
only one slave driving the MISO data line.
SPSCK CYCLE #
FOR REFERENCE
1
2
3
4
5
6
7
8
MOSI
FROM MASTER
MSB
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
LSB
MISO
FROM SLAVE
MSB
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
SPSCK; CPOL = 0
SPSCK; CPOL =1
LSB
SS; TO SLAVE
CAPTURE STROBE
Figure 16-7. Transmission Format (CPHA = 1)
When CPHA = 1 for a slave, the first edge of the SPSCK indicates the beginning of the transmission. This
causes the SPI to leave its idle state and begin driving the MISO pin with the MSB of its data. Once the
transmission begins, no new data is allowed into the shift register from the transmit data register.
Therefore, the SPI data register of the slave must be loaded with transmit data before the first edge of
SPSCK. Any data written after the first edge is stored in the transmit data register and transferred to the
shift register after the current transmission.
16.4.4 Transmission Initiation Latency
When the SPI is configured as a master (SPMSTR = 1), writing to the SPDR starts a transmission. CPHA
has no effect on the delay to the start of the transmission, but it does affect the initial state of the SPSCK
signal. When CPHA = 0, the SPSCK signal remains inactive for the first half of the first SPSCK cycle.
When CPHA = 1, the first SPSCK cycle begins with an edge on the SPSCK line from its inactive to its
active level. The SPI clock rate (selected by SPR1:SPR0) affects the delay from the write to SPDR and
the start of the SPI transmission. (See Figure 16-8.) The internal SPI clock in the master is a free-running
derivative of the internal MCU clock. To conserve power, it is enabled only when both the SPE and
SPMSTR bits are set. Since the SPI clock is free-running, it is uncertain where the write to the SPDR
occurs relative to the slower SPSCK. This uncertainty causes the variation in the initiation delay shown
in Figure 16-8. This delay is no longer than a single SPI bit time. That is, the maximum delay is two MCU
bus cycles for DIV2, eight MCU bus cycles for DIV8, 32 MCU bus cycles for DIV32, and 128 MCU bus
cycles for DIV128.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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203
Serial Peripheral Interface (SPI) Module
WRITE
TO SPDR
INITIATION DELAY
BUS
CLOCK
MOSI
MSB
BIT 6
BIT 5
SPSCK
CPHA = 1
SPSCK
CPHA = 0
SPSCK CYCLE
NUMBER
1
3
2
INITIATION DELAY FROM WRITE SPDR TO TRANSFER BEGIN
WRITE
TO SPDR
BUS
CLOCK
EARLIEST
BUS
CLOCK
WRITE
TO SPDR
EARLIEST
BUS
CLOCK
WRITE
TO SPDR
EARLIEST
BUS
CLOCK
WRITE
TO SPDR
EARLIEST
LATEST
SPSCK = BUS CLOCK ÷ 2;
2 POSSIBLE START POINTS
SPSCK = BUS CLOCK ÷ 8;
8 POSSIBLE START POINTS
LATEST
SPSCK = BUS CLOCK ÷ 32;
32 POSSIBLE START POINTS
LATEST
SPSCK = BUS CLOCK ÷ 128;
128 POSSIBLE START POINTS
LATEST
Figure 16-8. Transmission Start Delay (Master)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
Queuing Transmission Data
16.5 Queuing Transmission Data
The double-buffered transmit data register allows a data byte to be queued and transmitted. For an SPI
configured as a master, a queued data byte is transmitted immediately after the previous transmission
has completed. The SPI transmitter empty flag (SPTE) indicates when the transmit data buffer is ready
to accept new data. Write to the transmit data register only when SPTE is high. Figure 16-9 shows the
timing associated with doing back-to-back transmissions with the SPI (SPSCK has CPHA: CPOL = 1:0).
WRITE TO SPDR
SPTE
1
3
2
8
5
10
SPSCK
CPHA:CPOL = 1:0
MOSI
MSB BIT BIT BIT BIT BIT BIT LSB MSB BIT BIT BIT BIT BIT BIT LSB MSB BIT BIT BIT
6 5 4 3 2 1
6 5 4 3 2 1
6 5 4
BYTE 1
BYTE 2
BYTE 3
4
SPRF
9
6
READ SPSCR
11
7
READ SPDR
12
1 CPU WRITES BYTE 1 TO SPDR, CLEARING SPTE BIT.
7 CPU READS SPDR, CLEARING SPRF BIT.
2 BYTE 1 TRANSFERS FROM TRANSMIT DATA
REGISTER TO SHIFT REGISTER, SETTING SPTE BIT.
8 CPU WRITES BYTE 3 TO SPDR, QUEUEING BYTE
3 AND CLEARING SPTE BIT.
9 SECOND INCOMING BYTE TRANSFERS FROM SHIFT
REGISTER TO RECEIVE DATA REGISTER, SETTING
SPRF BIT.
10 BYTE 3 TRANSFERS FROM TRANSMIT DATA
REGISTER TO SHIFT REGISTER, SETTING SPTE BIT.
11 CPU READS SPSCR WITH SPRF BIT SET.
3 CPU WRITES BYTE 2 TO SPDR, QUEUEING BYTE 2
AND CLEARING SPTE BIT.
FIRST INCOMING BYTE TRANSFERS FROM SHIFT
REGISTER TO RECEIVE DATA REGISTER, SETTING
SPRF BIT.
5 BYTE 2 TRANSFERS FROM TRANSMIT DATA
REGISTER TO SHIFT REGISTER, SETTING SPTE BIT.
6 CPU READS SPSCR WITH SPRF BIT SET.
4
12 CPU READS SPDR, CLEARING SPRF BIT.
Figure 16-9. SPRF/SPTE CPU Interrupt Timing
The transmit data buffer allows back-to-back transmissions without the slave precisely timing its writes
between transmissions as in a system with a single data buffer. Also, if no new data is written to the data
buffer, the last value contained in the shift register is the next data word to be transmitted.
For an idle master or idle slave that has no data loaded into its transmit buffer, the SPTE is set again no
more than two bus cycles after the transmit buffer empties into the shift register. This allows the user to
queue up a 16-bit value to send. For an already active slave, the load of the shift register cannot occur
until the transmission is completed. This implies that a back-to-back write to the transmit data register is
not possible. SPTE indicates when the next write can occur.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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205
Serial Peripheral Interface (SPI) Module
16.6 Error Conditions
The following flags signal SPI error conditions:
• Overflow (OVRF) — Failing to read the SPI data register before the next full byte enters the shift
register sets the OVRF bit. The new byte does not transfer to the receive data register, and the
unread byte still can be read. OVRF is in the SPI status and control register.
• Mode fault error (MODF) — The MODF bit indicates that the voltage on the slave select pin (SS)
is inconsistent with the mode of the SPI. MODF is in the SPI status and control register.
16.6.1 Overflow Error
The overflow flag (OVRF) becomes set if the receive data register still has unread data from a previous
transmission when the capture strobe of bit 1 of the next transmission occurs. The bit 1 capture strobe
occurs in the middle of SPSCK cycle 7 (see Figure 16-5 and Figure 16-7.) If an overflow occurs, all data
received after the overflow and before the OVRF bit is cleared does not transfer to the receive data
register and does not set the SPI receiver full bit (SPRF). The unread data that transferred to the receive
data register before the overflow occurred can still be read. Therefore, an overflow error always indicates
the loss of data. Clear the overflow flag by reading the SPI status and control register and then reading
the SPI data register.
OVRF generates a receiver/error CPU interrupt request if the error interrupt enable bit (ERRIE) is also
set. The SPRF, MODF, and OVRF interrupts share the same CPU interrupt vector (see Figure 16-12.) It
is not possible to enable MODF or OVRF individually to generate a receiver/error CPU interrupt request.
However, leaving MODFEN low prevents MODF from being set.
If the CPU SPRF interrupt is enabled and the OVRF interrupt is not, watch for an overflow condition.
Figure 16-10 shows how it is possible to miss an overflow. The first part of Figure 16-10 shows how it is
possible to read the SPSCR and SPDR to clear the SPRF without problems. However, as illustrated by
the second transmission example, the OVRF bit can be set in between the time that SPSCR and SPDR
are read.
BYTE 1
BYTE 2
BYTE 3
BYTE 4
1
4
6
8
SPRF
OVRF
READ
SPSCR
2
READ
SPDR
5
3
1
BYTE 1 SETS SPRF BIT.
2
CPU READS SPSCR WITH SPRF BIT SET
AND OVRF BIT CLEAR.
CPU READS BYTE 1 IN SPDR,
CLEARING SPRF BIT.
BYTE 2 SETS SPRF BIT.
3
4
7
5
CPU READS SPSCR WITH SPRF BIT SET
AND OVRF BIT CLEAR.
6
BYTE 3 SETS OVRF BIT. BYTE 3 IS LOST.
7
CPU READS BYTE 2 IN SPDR, CLEARING SPRF BIT,
BUT NOT OVRF BIT.
8
BYTE 4 FAILS TO SET SPRF BIT BECAUSE
OVRF BIT IS NOT CLEARED. BYTE 4 IS LOST.
Figure 16-10. Missed Read of Overflow Condition
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Freescale Semiconductor
Error Conditions
In this case, an overflow can be missed easily. Since no more SPRF interrupts can be generated until this
OVRF is serviced, it is not obvious that bytes are being lost as more transmissions are completed. To
prevent this, either enable the OVRF interrupt or do another read of the SPSCR following the read of the
SPDR. This ensures that the OVRF was not set before the SPRF was cleared and that future
transmissions can set the SPRF bit. Figure 16-11 illustrates this process. Generally, to avoid this second
SPSCR read, enable the OVRF to the CPU by setting the ERRIE bit.
BYTE 1
SPI RECEIVE
COMPLETE
BYTE 2
5
1
BYTE 3
7
BYTE 4
11
SPRF
OVRF
READ
SPSCR
2
READ
SPDR
4
3
1
BYTE 1 SETS SPRF BIT.
2
CPU READS SPSCR WITH SPRF BIT SET
AND OVRF BIT CLEAR.
CPU READS BYTE 1 IN SPDR,
CLEARING SPRF BIT.
3
6
9
8
12
10
14
13
8
CPU READS BYTE 2 IN SPDR,
CLEARING SPRF BIT.
9
CPU READS SPSCR AGAIN
TO CHECK OVRF BIT.
10 CPU READS BYTE 2 SPDR,
CLEARING OVRF BIT.
4
CPU READS SPSCR AGAIN
TO CHECK OVRF BIT.
11 BYTE 4 SETS SPRF BIT.
5
BYTE 2 SETS SPRF BIT.
12 CPU READS SPSCR.
6
CPU READS SPSCR WITH SPRF BIT SET
AND OVRF BIT CLEAR.
13 CPU READS BYTE 4 IN SPDR,
CLEARING SPRF BIT.
7
BYTE 3 SETS OVRF BIT. BYTE 3 IS LOST.
14 CPU READS SPSCR AGAIN
TO CHECK OVRF BIT.
Figure 16-11. Clearing SPRF When OVRF Interrupt Is Not Enabled
16.6.2 Mode Fault Error
Setting SPMSTR selects master mode and configures the SPSCK and MOSI pins as outputs and the
MISO pin as an input. Clearing SPMSTR selects slave mode and configures the SPSCK and MOSI pins
as inputs and the MISO pin as an output. The mode fault bit, MODF, becomes set any time the state of
the slave select pin, SS, is inconsistent with the mode selected by SPMSTR.
To prevent SPI pin contention and damage to the MCU, a mode fault error occurs if:
• The SS pin of a slave SPI goes high during a transmission
• The SS pin of a master SPI goes low at any time
For the MODF flag to be set, the mode fault error enable bit (MODFEN) must be set. Clearing the
MODFEN bit does not clear the MODF flag but does prevent MODF from being set again after MODF is
cleared.
MODF generates a receiver/error CPU interrupt request if the error interrupt enable bit (ERRIE) is also
set. The SPRF, MODF, and OVRF interrupts share the same CPU interrupt vector. (See Figure 16-12.)
It is not possible to enable MODF or OVRF individually to generate a receiver/error CPU interrupt request.
However, leaving MODFEN low prevents MODF from being set.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Serial Peripheral Interface (SPI) Module
In a master SPI with the mode fault enable bit (MODFEN) set, the mode fault flag (MODF) is set if SS
goes low. A mode fault in a master SPI causes the following events to occur:
• If ERRIE = 1, the SPI generates an SPI receiver/error CPU interrupt request.
• The SPE bit is cleared.
• The SPTE bit is set.
• The SPI state counter is cleared.
• The data direction register of the shared I/O port regains control of port drivers.
NOTE
To prevent bus contention with another master SPI after a mode fault error,
clear all SPI bits of the data direction register of the shared I/O port before
enabling the SPI.
When configured as a slave (SPMSTR = 0), the MODF flag is set if SS goes high during a transmission.
When CPHA = 0, a transmission begins when SS goes low and ends once the incoming SPSCK goes
back to its idle level following the shift of the eighth data bit. When CPHA = 1, the transmission begins
when the SPSCK leaves its idle level and SS is already low. The transmission continues until the SPSCK
returns to its idle level following the shift of the last data bit. See
See 16.4 Transmission Formats.
NOTE
Setting the MODF flag does not clear the SPMSTR bit. SPMSTR has no
function when SPE = 0. Reading SPMSTR when MODF = 1 shows the
difference between a MODF occurring when the SPI is a master and when
it is a slave.
NOTE
When CPHA = 0, a MODF occurs if a slave is selected (SS is low) and later
unselected (SS is high) even if no SPSCK is sent to that slave. This
happens because SS low indicates the start of the transmission (MISO
driven out with the value of MSB) for CPHA = 0. When CPHA = 1, a slave
can be selected and then later unselected with no transmission occurring.
Therefore, MODF does not occur since a transmission was never begun.
In a slave SPI (MSTR = 0), MODF generates an SPI receiver/error CPU interrupt request if the ERRIE bit
is set. The MODF bit does not clear the SPE bit or reset the SPI in any way. Software can abort the SPI
transmission by clearing the SPE bit of the slave.
NOTE
A high on the SS pin of a slave SPI puts the MISO pin in a high impedance
state. Also, the slave SPI ignores all incoming SPSCK clocks, even if it was
already in the middle of a transmission.
To clear the MODF flag, read the SPSCR with the MODF bit set and then write to the SPCR register. This
entire clearing mechanism must occur with no MODF condition existing or else the flag is not cleared.
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Interrupts
16.7 Interrupts
Four SPI status flags can be enabled to generate CPU interrupt requests. See Table 16-1.
Table 16-1. SPI Interrupts
Flag
Request
SPTE — Transmitter empty
SPI transmitter CPU interrupt request (SPTIE = 1, SPE = 1)
SPRF — Receiver full
SPI receiver CPU interrupt request (SPRIE = 1)
OVRF — Overflow
SPI receiver/error interrupt request (ERRIE = 1)
MODF — Mode fault
SPI receiver/error interrupt request (ERRIE = 1)
Reading the SPI status and control register with SPRF set and then reading the receive data register
clears SPRF. The clearing mechanism for the SPTE flag is always just a write to the transmit data register.
The SPI transmitter interrupt enable bit (SPTIE) enables the SPTE flag to generate transmitter CPU
interrupt requests, provided that the SPI is enabled (SPE = 1).
The SPI receiver interrupt enable bit (SPRIE) enables SPRF to generate receiver CPU interrupt requests,
regardless of the state of SPE. See Figure 16-12.
SPTE
SPTIE
SPE
SPI TRANSMITTER
CPU INTERRUPT REQUEST
SPRIE
SPRF
SPI RECEIVER/ERROR
ERRIE
CPU INTERRUPT REQUEST
MODF
OVRF
Figure 16-12. SPI Interrupt Request Generation
The error interrupt enable bit (ERRIE) enables both the MODF and OVRF bits to generate a receiver/error
CPU interrupt request.
The mode fault enable bit (MODFEN) can prevent the MODF flag from being set so that only the OVRF
bit is enabled by the ERRIE bit to generate receiver/error CPU interrupt requests.
The following sources in the SPI status and control register can generate CPU interrupt requests:
• SPI receiver full bit (SPRF) — SPRF becomes set every time a byte transfers from the shift register
to the receive data register. If the SPI receiver interrupt enable bit, SPRIE, is also set, SPRF
generates an SPI receiver/error CPU interrupt request.
• SPI transmitter empty (SPTE) — SPTE becomes set every time a byte transfers from the transmit
data register to the shift register. If the SPI transmit interrupt enable bit, SPTIE, is also set, SPTE
generates an SPTE CPU interrupt request.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Serial Peripheral Interface (SPI) Module
16.8 Resetting the SPI
Any system reset completely resets the SPI. Partial resets occur whenever the SPI enable bit (SPE) is 0.
Whenever SPE is 0, the following occurs:
• The SPTE flag is set.
• Any transmission currently in progress is aborted.
• The shift register is cleared.
• The SPI state counter is cleared, making it ready for a new complete transmission.
• All the SPI port logic is defaulted back to being general-purpose I/O.
These items are reset only by a system reset:
• All control bits in the SPCR register
• All control bits in the SPSCR register (MODFEN, ERRIE, SPR1, and SPR0)
• The status flags SPRF, OVRF, and MODF
By not resetting the control bits when SPE is low, the user can clear SPE between transmissions without
having to set all control bits again when SPE is set back high for the next transmission.
By not resetting the SPRF, OVRF, and MODF flags, the user can still service these interrupts after the
SPI has been disabled. The user can disable the SPI by writing 0 to the SPE bit. The SPI can also be
disabled by a mode fault occurring in an SPI that was configured as a master with the MODFEN bit set.
16.9 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
16.9.1 Wait Mode
The SPI module remains active after the execution of a WAIT instruction. In wait mode the SPI module
registers are not accessible by the CPU. Any enabled CPU interrupt request from the SPI module can
bring the MCU out of wait mode.
If SPI module functions are not required during wait mode, reduce power consumption by disabling the
SPI module before executing the WAIT instruction.
To exit wait mode when an overflow condition occurs, enable the OVRF bit to generate CPU interrupt
requests by setting the error interrupt enable bit (ERRIE). See 16.7 Interrupts.
16.9.2 Stop Mode
The SPI module is inactive after the execution of a STOP instruction. The STOP instruction does not
affect register conditions. SPI operation resumes after an external interrupt. If stop mode is exited by
reset, any transfer in progress is aborted, and the SPI is reset.
16.10 SPI During Break Interrupts
The system integration module (SIM) controls whether status bits in other modules can be cleared during
the break state. BCFE in the SIM break flag control register (SBFCR) enables software to clear status bits
during the break state. See Chapter 15 System Integration Module (SIM).
To allow software to clear status bits during a break interrupt, write a 1 to BCFE. If a status bit is cleared
during the break state, it remains cleared when the MCU exits the break state.
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I/O Signals
To protect status bits during the break state, write a 0 to BCFE. With BCFE at 0 (its default state), software
can read and write I/O registers during the break state without affecting status bits. Some status bits have
a 2-step read/write clearing procedure. If software does the first step on such a bit before the break, the
bit cannot change during the break state as long as BCFE is 0. After the break, doing the second step
clears the status bit.
Since the SPTE bit cannot be cleared during a break with BCFE cleared, a write to the transmit data
register in break mode does not initiate a transmission nor is this data transferred into the shift register.
Therefore, a write to the SPDR in break mode with BCFE cleared has no effect.
16.11 I/O Signals
The SPI module has four I/O pins:
• MISO — Master input/slave output
• MOSI — Master output/slave input
• SPSCK — Serial clock
• SS — Slave select
16.11.1 MISO (Master In/Slave Out)
MISO is one of the two SPI module pins that transmits serial data. In full duplex operation, the MISO pin
of the master SPI module is connected to the MISO pin of the slave SPI module. The master SPI
simultaneously receives data on its MISO pin and transmits data from its MOSI pin.
Slave output data on the MISO pin is enabled only when the SPI is configured as a slave. The SPI is
configured as a slave when its SPMSTR bit is 0 and its SS pin is low. To support a multiple-slave system,
a high on the SS pin puts the MISO pin in a high-impedance state.
When enabled, the SPI controls data direction of the MISO pin regardless of the state of the data direction
register of the shared I/O port.
16.11.2 MOSI (Master Out/Slave In)
MOSI is one of the two SPI module pins that transmits serial data. In full-duplex operation, the MOSI pin
of the master SPI module is connected to the MOSI pin of the slave SPI module. The master SPI
simultaneously transmits data from its MOSI pin and receives data on its MISO pin.
When enabled, the SPI controls data direction of the MOSI pin regardless of the state of the data direction
register of the shared I/O port.
16.11.3 SPSCK (Serial Clock)
The serial clock synchronizes data transmission between master and slave devices. In a master MCU,
the SPSCK pin is the clock output. In a slave MCU, the SPSCK pin is the clock input. In full-duplex
operation, the master and slave MCUs exchange a byte of data in eight serial clock cycles.
When enabled, the SPI controls data direction of the SPSCK pin regardless of the state of the data
direction register of the shared I/O port.
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Serial Peripheral Interface (SPI) Module
16.11.4 SS (Slave Select)
The SS pin has various functions depending on the current state of the SPI. For an SPI configured as a
slave, the SS is used to select a slave. For CPHA = 0, the SS is used to define the start of a transmission.
(See 16.4 Transmission Formats.) Since it is used to indicate the start of a transmission, SS must be
toggled high and low between each byte transmitted for the CPHA = 0 format. However, it can remain low
between transmissions for the CPHA = 1 format. See Figure 16-13.
When an SPI is configured as a slave, the SS pin is always configured as an input. It cannot be used as
a general-purpose I/O regardless of the state of the MODFEN control bit. However, the MODFEN bit can
still prevent the state of SS from creating a MODF error. See 16.12.2 SPI Status and Control Register.
MISO/MOSI
BYTE 1
BYTE 2
BYTE 3
MASTER SS
SLAVE SS
CPHA = 0
SLAVE SS
CPHA = 1
Figure 16-13. CPHA/SS Timing
NOTE
A high on the SS pin of a slave SPI puts the MISO pin in a high-impedance
state. The slave SPI ignores all incoming SPSCK clocks, even if it was
already in the middle of a transmission.
When an SPI is configured as a master, the SS input can be used in conjunction with the MODF flag to
prevent multiple masters from driving MOSI and SPSCK. (See 16.6.2 Mode Fault Error.) For the state of
the SS pin to set the MODF flag, the MODFEN bit in the SPSCK register must be set. If MODFEN is 0 for
an SPI master, the SS pin can be used as a general-purpose I/O under the control of the data direction
register of the shared I/O port. When MODFEN is 1, SS is an input-only pin to the SPI regardless of the
state of the data direction register of the shared I/O port.
The CPU can always read the state of the SS pin by configuring the appropriate pin as an input and
reading the port data register. See Table 16-2
.
Table 16-2. SPI Configuration
SPE
SPMSTR
MODFEN
SPI Configuration
Function of SS Pin
0
X(1))
X
Not enabled
General-purpose I/O;
SS ignored by SPI
1
0
X
Slave
Input-only to SPI
1
1
0
Master without MODF
General-purpose I/O;
SS ignored by SPI
1
1
1
Master with MODF
Input-only to SPI
1. X = Don’t care
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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I/O Registers
16.12 I/O Registers
Three registers control and monitor SPI operation:
• SPI control register (SPCR)
• SPI status and control register (SPSCR)
• SPI data register (SPDR)
16.12.1 SPI Control Register
The SPI control register:
• Enables SPI module interrupt requests
• Configures the SPI module as master or slave
• Selects serial clock polarity and phase
• Configures the SPSCK, MOSI, and MISO pins as open-drain outputs
• Enables the SPI module
Address: $0010
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
SPRIE
R
SPMSTR
CPOL
CPHA
SPWOM
SPE
SPTIE
0
0
1
0
1
0
0
0
R
= Reserved
Figure 16-14. SPI Control Register (SPCR)
SPRIE — SPI Receiver Interrupt Enable Bit
This read/write bit enables CPU interrupt requests generated by the SPRF bit. The SPRF bit is set
when a byte transfers from the shift register to the receive data register. Reset clears the SPRIE bit.
1 = SPRF CPU interrupt requests enabled
0 = SPRF CPU interrupt requests disabled
SPMSTR — SPI Master Bit
This read/write bit selects master mode operation or slave mode operation. Reset sets the SPMSTR
bit.
1 = Master mode
0 = Slave mode
CPOL — Clock Polarity Bit
This read/write bit determines the logic state of the SPSCK pin between transmissions. (See Figure
16-5 and Figure 16-7.) To transmit data between SPI modules, the SPI modules must have identical
CPOL values. Reset clears the CPOL bit.
CPHA — Clock Phase Bit
This read/write bit controls the timing relationship between the serial clock and SPI data. (See Figure
16-5 and Figure 16-7.) To transmit data between SPI modules, the SPI modules must have identical
CPHA values. When CPHA = 0, the SS pin of the slave SPI module must be high between bytes. (See
Figure 16-13.) Reset sets the CPHA bit.
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Serial Peripheral Interface (SPI) Module
SPWOM — SPI Wired-OR Mode Bit
This read/write bit disables the pullup devices on pins SPSCK, MOSI, and MISO so that those pins
become open-drain outputs.
1 = Wired-OR SPSCK, MOSI, and MISO pins
0 = Normal push-pull SPSCK, MOSI, and MISO pins
SPE — SPI Enable
This read/write bit enables the SPI module. Clearing SPE causes a partial reset of the SPI. (See 16.8
Resetting the SPI.) Reset clears the SPE bit.
1 = SPI module enabled
0 = SPI module disabled
SPTIE— SPI Transmit Interrupt Enable
This read/write bit enables CPU interrupt requests generated by the SPTE bit. SPTE is set when a byte
transfers from the transmit data register to the shift register. Reset clears the SPTIE bit.
1 = SPTE CPU interrupt requests enabled
0 = SPTE CPU interrupt requests disabled
16.12.2 SPI Status and Control Register
The SPI status and control register contains flags to signal these conditions:
• Receive data register full
• Failure to clear SPRF bit before next byte is received (overflow error)
• Inconsistent logic level on SS pin (mode fault error)
• Transmit data register empty
The SPI status and control register also contains bits that perform these functions:
• Enable error interrupts
• Enable mode fault error detection
• Select master SPI baud rate
Address: $0011
Bit 7
Read:
SPRF
Write:
Reset:
0
6
ERRIE
0
5
4
3
OVRF
MODF
SPTE
0
0
1
2
1
Bit 0
MODFEN
SPR1
SPR0
0
0
0
= Unimplemented
Figure 16-15. SPI Status and Control Register (SPSCR)
SPRF — SPI Receiver Full Bit
This clearable, read-only flag is set each time a byte transfers from the shift register to the receive data
register. SPRF generates a CPU interrupt request if the SPRIE bit in the SPI control register is set also.
During an SPRF CPU interrupt, the CPU clears SPRF by reading the SPI status and control register
with SPRF set and then reading the SPI data register.
Reset clears the SPRF bit.
1 = Receive data register full
0 = Receive data register not full
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I/O Registers
ERRIE — Error Interrupt Enable Bit
This read/write bit enables the MODF and OVRF bits to generate CPU interrupt requests. Reset clears
the ERRIE bit.
1 = MODF and OVRF can generate CPU interrupt requests
0 = MODF and OVRF cannot generate CPU interrupt requests
OVRF — Overflow Bit
This clearable, read-only flag is set if software does not read the byte in the receive data register before
the next full byte enters the shift register. In an overflow condition, the byte already in the receive data
register is unaffected, and the byte that shifted in last is lost. Clear the OVRF bit by reading the SPI
status and control register with OVRF set and then reading the receive data register. Reset clears the
OVRF bit.
1 = Overflow
0 = No overflow
MODF — Mode Fault Bit
This clearable, read-only flag is set in a slave SPI if the SS pin goes high during a transmission with
MODFEN set. In a master SPI, the MODF flag is set if the SS pin goes low at any time with the
MODFEN bit set. Clear MODF by reading the SPI status and control register (SPSCR) with MODF set
and then writing to the SPI control register (SPCR). Reset clears the MODF bit.
1 = SS pin at inappropriate logic level
0 = SS pin at appropriate logic level
SPTE — SPI Transmitter Empty Bit
This clearable, read-only flag is set each time the transmit data register transfers a byte into the shift
register. SPTE generates an SPTE CPU interrupt request if SPTIE in the SPI control register is set
also.
NOTE
Do not write to the SPI data register unless SPTE is high.
During an SPTE CPU interrupt, the CPU clears SPTE by writing to the transmit data register.
Reset sets the SPTE bit.
1 = Transmit data register empty
0 = Transmit data register not empty
MODFEN — Mode Fault Enable Bit
This read/write bit, when set, allows the MODF flag to be set. If the MODF flag is set, clearing MODFEN
does not clear the MODF flag. If the SPI is enabled as a master and the MODFEN bit is 0, then the SS
pin is available as a general-purpose I/O.
If the MODFEN bit is 1, then the SS pin is not available as a general-purpose I/O. When the SPI is
enabled as a slave, the SS pin is not available as a general-purpose I/O regardless of the value of
MODFEN. See 16.11.4 SS (Slave Select).
If the MODFEN bit is 0, the level of the SS pin does not affect the operation of an enabled SPI
configured as a master. For an enabled SPI configured as a slave, having MODFEN low only prevents
the MODF flag from being set. It does not affect any other part of SPI operation. See 16.6.2 Mode Fault
Error.
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Serial Peripheral Interface (SPI) Module
SPR1 and SPR0 — SPI Baud Rate Select Bits
In master mode, these read/write bits select one of four baud rates as shown in Table 16-3. SPR1 and
SPR0 have no effect in slave mode. Reset clears SPR1 and SPR0.
Table 16-3. SPI Master Baud Rate Selection
SPR1 and SPR0
Baud Rate Divisor (BD)
00
2
01
8
10
32
11
128
Use this formula to calculate the SPI baud rate:
Baud rate =
BUSCLK
BD
16.12.3 SPI Data Register
The SPI data register consists of the read-only receive data register and the write-only transmit data
register. Writing to the SPI data register writes data into the transmit data register. Reading the SPI data
register reads data from the receive data register. The transmit data and receive data registers are
separate registers that can contain different values. See Figure 16-2.
Address: $0012
Bit 7
6
5
4
3
2
1
Bit 0
Read:
R7
R6
R5
R4
R3
R2
R1
R0
Write:
T7
T6
T5
T4
T3
T2
T1
T0
Reset:
Unaffected by reset
Figure 16-16. SPI Data Register (SPDR)
R7–R0/T7–T0 — Receive/Transmit Data Bits
NOTE
Do not use read-modify-write instructions on the SPI data register since the
register read is not the same as the register written.
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Chapter 17
Timebase Module (TBM)
17.1 Introduction
This section describes the timebase module (TBM). The TBM will generate periodic interrupts at user
selectable rates using a counter clocked by the external crystal clock. This TBM version uses 15 divider
stages, eight of which are user selectable.
17.2 Features
Features of the TBM include:
• Software programmable 1-Hz, 4-Hz, 16-Hz, 256-Hz, 512-Hz, 1024-Hz, 2048-Hz, and 4096-Hz
periodic interrupt using external 32.768-kHz crystal
• User selectable oscillator clock source enable during stop mode to allow periodic wakeup from stop
17.3 Functional Description
NOTE
This module is designed for a 32.768-kHz oscillator.
This module can generate a periodic interrupt by dividing the clock TBMCLK. The counter is initialized to
all 0s when TBON bit is cleared. The counter, shown in Figure 17-1, starts counting when the TBON bit
is set. When the counter overflows at the tap selected by TBR2:TBR0, the TBIF bit gets set. If the TBIE
bit is set, an interrupt request is sent to the CPU. The TBIF flag is cleared by writing a 1 to the TACK bit.
The first time the TBIF flag is set after enabling the timebase module, the interrupt is generated at
approximately half of the overflow period. Subsequent events occur at the exact period.
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Timebase Module (TBM)
TBON
÷2
TBMCLK
÷2
÷2
÷2
÷8
÷2
÷2
÷ 16
÷2
÷ 32
÷ 64
÷ 128
÷2
÷2
÷2
÷2
÷ 2048
÷2
÷ 8192
TACK
÷2
TBR0
÷2
TBR1
÷2
TBR2
TBMINT
÷ 32768
TBIF
000
TBIE
R
001
010
011
100
SEL
101
110
111
Figure 17-1. Timebase Block Diagram
17.4 Timebase Register Description
The timebase has one register, the timebase control register (TBCR), which is used to enable the
timebase interrupts and set the rate.
Address:
$001C
Bit 7
Read:
TBIF
Write:
Reset:
0
6
5
4
TBR2
TBR1
TBR0
0
0
0
= Unimplemented
3
2
1
Bit 0
TBIE
TBON
R
0
0
0
0
R
= Reserved
0
TACK
Figure 17-2. Timebase Control Register (TBCR)
TBIF — Timebase Interrupt Flag
This read-only flag bit is set when the timebase counter has rolled over.
1 = Timebase interrupt pending
0 = Timebase interrupt not pending
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Interrupts
TBR2:TBR0 — Timebase Rate Selection
These read/write bits are used to select the rate of timebase interrupts as shown in Table 17-1.
Table 17-1. Timebase Rate Selection for OSC1 = 32.768 kHz
TBR2
TBR1
TBR0
Divider
0
0
0
32768
Timebase Interrupt Rate
Hz
ms
1
1000
0
0
1
8192
4
250
0
1
0
2048
16
62.5
0
1
1
128
256
~ 3.9
1
0
0
64
512
~2
1
0
1
32
1024
~1
1
1
0
16
2048
~0.5
1
1
1
8
4096
~0.24
NOTE
Do not change TBR2:TBR0 bits while the timebase is enabled (TBON = 1).
TACK — Timebase ACKnowledge
The TACK bit is a write-only bit and always reads as 0. Writing a 1 to this bit clears TBIF, the timebase
interrupt flag bit. Writing a 0 to this bit has no effect.
1 = Clear timebase interrupt flag
0 = No effect
TBIE — Timebase Interrupt Enabled
This read/write bit enables the timebase interrupt when the TBIF bit becomes set. Reset clears the
TBIE bit.
1 = Timebase interrupt enabled
0 = Timebase interrupt disabled
TBON — Timebase Enabled
This read/write bit enables the timebase. Timebase may be turned off to reduce power consumption
when its function is not necessary. The counter can be initialized by clearing and then setting this bit.
Reset clears the TBON bit.
1 = Timebase enabled
0 = Timebase disabled and the counter initialized to 0s
17.5 Interrupts
The timebase module can interrupt the CPU on a regular basis with a rate defined by TBR2:TBR0. When
the timebase counter chain rolls over, the TBIF flag is set. If the TBIE bit is set, enabling the timebase
interrupt, the counter chain overflow will generate a CPU interrupt request.
Interrupts must be acknowledged by writing a 1 to the TACK bit.
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Timebase Module (TBM)
17.6 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
17.6.1 Wait Mode
The timebase module remains active after execution of the WAIT instruction. In wait mode, the timebase
register is not accessible by the CPU.
If the timebase functions are not required during wait mode, reduce the power consumption by stopping
the timebase before enabling the WAIT instruction.
17.6.2 Stop Mode
The timebase module may remain active after execution of the STOP instruction if the oscillator has been
enabled to operate during stop mode through the OSCSTOPEN bit in the CONFIG register. The timebase
module can be used in this mode to generate a periodic wakeup from stop mode.
If the oscillator has not been enabled to operate in stop mode, the timebase module will not be active
during STOP mode. In stop mode the timebase register is not accessible by the CPU.
If the timebase functions are not required during stop mode, reduce the power consumption by stopping
the timebase before enabling the STOP instruction.
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Chapter 18
Timer Interface Module (TIM)
18.1 Introduction
This section describes the timer interface (TIM) module. The TIM is a two-channel timer that provides a
timing reference with input capture, output compare, and pulse-width-modulation functions. Figure 18-1
is a block diagram of the TIM.
This particular MCU has two timer interface modules which are denoted as TIM1 and TIM2.
PRESCALER SELECT
INTERNAL
BUS CLOCK
PRESCALER
TSTOP
PS2
TRST
PS1
PS0
16-BIT COUNTER
TOF
TOIE
16-BIT COMPARATOR
INTERRUPT
LOGIC
TMODH:TMODL
TOV0
CHANNEL 0
ELS0B
ELS0A
CH0MAX
16-BIT COMPARATOR
TCH0H:TCH0L
PORT
LOGIC
T[1,2]CH0
CH0F
16-BIT LATCH
CH0IE
MS0A
INTERRUPT
LOGIC
MS0B
INTERNAL BUS
TOV1
CHANNEL 1
ELS1B
ELS1A
CH1MAX
16-BIT COMPARATOR
TCH1H:TCH1L
PORT
LOGIC
T[1,2]CH1
CH1F
16-BIT LATCH
MS1A
CH1IE
INTERRUPT
LOGIC
Figure 18-1. TIM Block Diagram
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221
Timer Interface Module (TIM)
8-BIT KEYBOARD
INTERRUPT MODULE
FLASH PROGRAMMING ROUTINES
ROM — 720 BYTES
USER FLASH VECTOR SPACE — 36 BYTES
PTE4/OSC1
PTE3/OSC2
INTERNAL CLOCK
GENERATOR MODULE
RST(3)
SYSTEM INTEGRATION
MODULE
IRQ(3)
SINGLE EXTERNAL
INTERRUPT MODULE
VREFH
VREFL
2-CHANNEL TIMER INTERFACE
MODULE 2
DDRA
PTD7/T2CH1(1)
PTD6/T2CH0(1)
PTD5/T1CH1(1)
PTD4/T1CH0(1)
PTD3/SPSCK(1)
PTD2/MOSI(1)
PTD1/MISO(1)
PTD0/SS(1)
PTE2
PTE1/RxD
PTE0/TxD
SERIAL PERIPHERAL
INTERFACE MODULE
MONITOR MODULE
8-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
PTC6(1)
PTC5(1)
PTC4(1)(2)
PTC3(1)(2)
PTC2(1)(2)
PTC1(1)(2)
PTC0(1)(2)
SERIAL COMMUNICATIONS
INTERFACE MODULE
COMPUTER OPERATING
PROPERLY MODULE
POWER-ON RESET
MODULE
VDD
VSS
VDDA
VSSA
2-CHANNEL TIMER INTERFACE
MODULE 1
DDRD
MONITOR ROM — 304 BYTES
PORTA
USER RAM — 512 BYTES
PORTB
DUAL VOLTAGE
LOW-VOLTAGE INHIBIT MODULE
PTB7/AD7
PTB6/AD6
PTB5/AD5
PTB4/AD4
PTB3/AD3
PTB2/AD2
PTB1/AD1
PTB0/AD0
PORTC
USER FLASH
MC68HC908GT16 — 15,872 BYTES
MC68HC908GT8 — 7,680 BYTES
PTA7/KBD7–
PTA0/KBD0(1)
PORTD
SINGLE BREAKPOINT BREAK
MODULE
DDRB
CONTROL AND STATUS
REGISTERS — 64 BYTES
DDRC
PROGRAMMABLE TIMEBASE
MODULE
ARITHMETIC/LOGIC
UNIT (ALU)
MEMORY MAP
MODULE
DDRE
CPU
REGISTERS
PORTE
INTERNAL BUS
M68HC08 CPU
SECURITY
MODULE
CONFIGURATION REGISTER 1
MODULE
CONFIGURATION REGISTER 2
MODULE
MONITOR MODE ENTRY
MODULE
1. Ports are software configurable with pullup device if input port.
2. Higher current drive port pins
3. Pin contains integrated pullup device
Figure 18-2. Block Diagram Highlighting TIM Blocks and Pins
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Features
18.2 Features
Features of the TIM include:
• Two input capture/output compare channels:
– Rising-edge, falling-edge, or any-edge input capture trigger
– Set, clear, or toggle output compare action
• Buffered and unbuffered pulse-width-modulation (PWM) signal generation
• Programmable TIM clock input with 7-frequency internal bus clock prescaler selection
• Free-running or modulo up-count operation
• Toggle any channel pin on overflow
• TIM counter stop and reset bits
18.3 Pin Name Conventions
The text that follows describes both timers, TIM1 and TIM2. The TIM input/output (I/O) pin names are
T[1,2]CH0 (timer channel 0) and T[1,2]CH1 (timer channel 1), where “1” is used to indicate TIM1 and “2”
is used to indicate TIM2. The two TIMs share four I/O pins with four port D I/O port pins.
NOTE
References to either timer 1 or timer 2 may be made in the following text by
omitting the timer number. For example, TCH0 may refer generically to
T1CH0 and T2CH0, and TCH1 may refer to T1CH1 and T2CH1.
18.4 Functional Description
Figure 18-1 shows the structure of the TIM. The central component of the TIM is the 16-bit TIM counter
that can operate as a free-running counter or a modulo up-counter. The TIM counter provides the timing
reference for the input capture and output compare functions. The TIM counter modulo registers,
TMODH:TMODL, control the modulo value of the TIM counter. Software can read the TIM counter value
at any time without affecting the counting sequence.
The two TIM channels (per timer) are programmable independently as input capture or output compare
channels. If a channel is configured as input capture, then an internal pullup device may be enabled for
that channel. See 12.5.3 Port D Input Pullup Enable Register.
Figure 18-3 summarizes the timer registers.
NOTE
References to either timer 1 or timer 2 may be made in the following text by
omitting the timer number. For example, TSC may generically refer to both
T1SC and T2SC.
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Timer Interface Module (TIM)
Addr.
Register Name
Bit 7
6
5
TOIE
TSTOP
4
3
0
0
2
1
Bit 0
PS2
PS1
PS0
Timer 1 Status and Control Read:
Register (T1SC) Write:
See page 231. Reset:
TOF
0
0
1
0
0
0
0
0
Bit 15
14
13
12
11
10
9
Bit 8
$0021
Timer 1 Counter Read:
Register High (T1CNTH) Write:
See page 232. Reset:
0
0
0
0
0
0
0
0
Bit 7
6
5
4
3
2
1
Bit 0
$0022
Timer 1 Counter Read:
Register Low (T1CNTL) Write:
See page 232. Reset:
0
0
0
0
0
0
0
0
Bit 15
14
13
12
11
10
9
Bit 8
1
1
1
1
1
1
1
1
Bit 7
6
5
4
3
2
1
Bit 0
1
1
1
1
1
1
1
1
CH0IE
MS0B
MS0A
ELS0B
ELS0A
TOV0
CH0MAX
0
0
0
0
0
0
0
0
Bit 15
14
13
12
11
10
9
Bit 8
2
1
Bit 0
$0020
$0023
$0024
Timer 1 Counter Modulo Read:
Register High (T1MODH) Write:
See page 233. Reset:
Timer 1 Counter Modulo Read:
Register Low (T1MODL) Write:
See page 233. Reset:
Timer 1 Channel 0 Status and Read:
$0025
Control Register (T1SC0) Write:
See page 233. Reset:
$0026
$0027
Timer 1 Channel 0 Read:
Register High (T1CH0H) Write:
See page 236. Reset:
Timer 1 Channel 0 Read:
Register Low (T1CH0L) Write:
See page 236. Reset:
Timer 1 Channel 1 Status and Read:
$0028
Control Register (T1SC1) Write:
See page 234. Reset:
$0029
Timer 1 Channel 1 Read:
Register High (T1CH1H) Write:
See page 236. Reset:
$002A
Timer 1 Channel 1 Read:
Register Low (T1CH1L) Write:
See page 236. Reset:
$002B
Timer 2 Status and Control Read:
Register (T2SC) Write:
See page 231. Reset:
0
CH0F
0
TRST
Indeterminate after reset
Bit 7
6
5
4
3
Indeterminate after reset
CH1F
0
0
CH1IE
MS1A
ELS1B
ELS1A
TOV1
CH1MAX
0
0
0
0
0
0
0
0
Bit 15
14
13
12
11
10
9
Bit 8
2
1
Bit 0
PS2
PS1
PS0
0
0
0
Indeterminate after reset
Bit 7
6
5
4
3
Indeterminate after reset
TOF
0
0
TOIE
TSTOP
0
1
0
0
TRST
0
0
= Unimplemented
Figure 18-3. TIM I/O Register Summary (Sheet 1 of 2)
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Freescale Semiconductor
Functional Description
Addr.
$002C
$002D
$002E
$002F
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
Timer 2 Counter Read:
Register High (T2CNTH) Write:
See page 232. Reset:
Bit 15
14
13
12
11
10
9
Bit 8
0
0
0
0
0
0
0
0
Timer 2 Counter Read:
Register Low (T2CNTL) Write:
See page 232. Reset:
Bit 7
6
5
4
3
2
1
Bit 0
0
0
0
0
0
0
0
0
Bit 15
14
13
12
11
10
9
Bit 8
1
1
1
1
1
1
1
1
Bit 7
6
5
4
3
2
1
Bit 0
1
1
1
1
1
1
1
1
CH0IE
MS0B
MS0A
ELS0B
ELS0A
TOV0
CH0MAX
0
0
0
0
0
0
0
0
Bit 15
14
13
12
11
10
9
Bit 8
2
1
Bit 0
Timer 2 Counter Modulo Read:
Register High (T2MODH) Write:
See page 233. Reset:
Timer 2 Counter Modulo Read:
Register Low (T2MODL) Write:
See page 233. Reset:
Timer 2 Channel 0 Status and Read:
$0030
Control Register (T2SC0) Write:
See page 233. Reset:
$0031
$0032
Timer 2 Channel 0 Read:
Register High (T2CH0H) Write:
See page 236. Reset:
Timer 2 Channel 0 Read:
Register Low (T2CH0L) Write:
See page 236. Reset:
Timer 2 Channel 1 Status and Read:
$0033
Control Register (T2SC1) Write:
See page 234. Reset:
$0034
$0035
Timer 2 Channel 1 Read:
Register High (T2CH1H) Write:
See page 236. Reset:
Timer 2 Channel 1 Read:
Register Low (T2CH1L) Write:
See page 236. Reset:
CH0F
0
Indeterminate after reset
Bit 7
6
5
4
3
Indeterminate after reset
CH1F
0
0
CH1IE
MS1A
ELS1B
ELS1A
TOV1
CH1MAX
0
0
0
0
0
0
0
0
Bit 15
14
13
12
11
10
9
Bit 8
2
1
Bit 0
Indeterminate after reset
Bit 7
6
5
4
3
Indeterminate after reset
= Unimplemented
Figure 18-3. TIM I/O Register Summary (Sheet 2 of 2)
18.4.1 TIM Counter Prescaler
The TIM clock source can be one of the seven prescaler outputs. The prescaler generates seven clock
rates from the internal bus clock. The prescaler select bits, PS[2:0], in the TIM status and control register
select the TIM clock source.
18.4.2 Input Capture
With the input capture function, the TIM can capture the time at which an external event occurs. When an
active edge occurs on the pin of an input capture channel, the TIM latches the contents of the TIM counter
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Timer Interface Module (TIM)
into the TIM channel registers, TCHxH:TCHxL. The polarity of the active edge is programmable. Input
captures can generate TIM CPU interrupt requests.
18.4.3 Output Compare
With the output compare function, the TIM can generate a periodic pulse with a programmable polarity,
duration, and frequency. When the counter reaches the value in the registers of an output compare
channel, the TIM can set, clear, or toggle the channel pin. Output compares can generate TIM CPU
interrupt requests.
18.4.3.1 Unbuffered Output Compare
Any output compare channel can generate unbuffered output compare pulses as described in 18.4.3
Output Compare. The pulses are unbuffered because changing the output compare value requires writing
the new value over the old value currently in the TIM channel registers.
An unsynchronized write to the TIM channel registers to change an output compare value could cause
incorrect operation for up to two counter overflow periods. For example, writing a new value before the
counter reaches the old value but after the counter reaches the new value prevents any compare during
that counter overflow period. Also, using a TIM overflow interrupt routine to write a new, smaller output
compare value may cause the compare to be missed. The TIM may pass the new value before it is written.
Use the following methods to synchronize unbuffered changes in the output compare value on channel x:
• When changing to a smaller value, enable channel x output compare interrupts and write the new
value in the output compare interrupt routine. The output compare interrupt occurs at the end of
the current output compare pulse. The interrupt routine has until the end of the counter overflow
period to write the new value.
• When changing to a larger output compare value, enable TIM overflow interrupts and write the new
value in the TIM overflow interrupt routine. The TIM overflow interrupt occurs at the end of the
current counter overflow period. Writing a larger value in an output compare interrupt routine (at
the end of the current pulse) could cause two output compares to occur in the same counter
overflow period.
18.4.3.2 Buffered Output Compare
Channels 0 and 1 can be linked to form a buffered output compare channel whose output appears on the
TCH0 pin. The TIM channel registers of the linked pair alternately control the output.
Setting the MS0B bit in TIM channel 0 status and control register (TSC0) links channel 0 and channel 1.
The output compare value in the TIM channel 0 registers initially controls the output on the TCH0 pin.
Writing to the TIM channel 1 registers enables the TIM channel 1 registers to synchronously control the
output after the TIM overflows. At each subsequent overflow, the TIM channel registers (0 or 1) that
control the output are the ones written to last. TSC0 controls and monitors the buffered output compare
function, and TIM channel 1 status and control register (TSC1) is unused. While the MS0B bit is set, the
channel 1 pin, TCH1, is available as a general-purpose I/O pin.
NOTE
In buffered output compare operation, do not write new output compare
values to the currently active channel registers. User software should track
the currently active channel to prevent writing a new value to the active
channel. Writing to the active channel registers is the same as generating
unbuffered output compares.
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Functional Description
18.4.4 Pulse Width Modulation (PWM)
By using the toggle-on-overflow feature with an output compare channel, the TIM can generate a PWM
signal. The value in the TIM counter modulo registers determines the period of the PWM signal. The
channel pin toggles when the counter reaches the value in the TIM counter modulo registers. The time
between overflows is the period of the PWM signal.
As Figure 18-4 shows, the output compare value in the TIM channel registers determines the pulse width
of the PWM signal. The time between overflow and output compare is the pulse width. Program the TIM
to clear the channel pin on output compare if the state of the PWM pulse is logic 1. Program the TIM to
set the pin if the state of the PWM pulse is logic 0.
The value in the TIM counter modulo registers and the selected prescaler output determines the
frequency of the PWM output. The frequency of an 8-bit PWM signal is variable in 256 increments. Writing
$00FF (255) to the TIM counter modulo registers produces a PWM period of 256 times the internal bus
clock period if the prescaler select value is $000. See 18.9.1 TIM Status and Control Register.
The value in the TIM channel registers determines the pulse width of the PWM output. The pulse width of
an 8-bit PWM signal is variable in 256 increments. Writing $0080 (128) to the TIM channel registers
produces a duty cycle of 128/256 or 50%.
OVERFLOW
OVERFLOW
OVERFLOW
PERIOD
PULSE
WIDTH
TCHx
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
Figure 18-4. PWM Period and Pulse Width
18.4.4.1 Unbuffered PWM Signal Generation
Any output compare channel can generate unbuffered PWM pulses as described in 18.4.4 Pulse Width
Modulation (PWM). The pulses are unbuffered because changing the pulse width requires writing the new
pulse width value over the old value currently in the TIM channel registers.
An unsynchronized write to the TIM channel registers to change a pulse width value could cause incorrect
operation for up to two PWM periods. For example, writing a new value before the counter reaches the
old value but after the counter reaches the new value prevents any compare during that PWM period.
Also, using a TIM overflow interrupt routine to write a new, smaller pulse width value may cause the
compare to be missed. The TIM may pass the new value before it is written.
Use the following methods to synchronize unbuffered changes in the PWM pulse width on channel x:
• When changing to a shorter pulse width, enable channel x output compare interrupts and write the
new value in the output compare interrupt routine. The output compare interrupt occurs at the end
of the current pulse. The interrupt routine has until the end of the PWM period to write the new
value.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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227
Timer Interface Module (TIM)
•
When changing to a longer pulse width, enable TIM overflow interrupts and write the new value in
the TIM overflow interrupt routine. The TIM overflow interrupt occurs at the end of the current PWM
period. Writing a larger value in an output compare interrupt routine (at the end of the current pulse)
could cause two output compares to occur in the same PWM period.
NOTE
In PWM signal generation, do not program the PWM channel to toggle on
output compare. Toggling on output compare prevents reliable 0% duty
cycle generation and removes the ability of the channel to self-correct in the
event of software error or noise. Toggling on output compare also can
cause incorrect PWM signal generation when changing the PWM pulse
width to a new, much larger value.
18.4.4.2 Buffered PWM Signal Generation
Channels 0 and 1 can be linked to form a buffered PWM channel whose output appears on the TCH0 pin.
The TIM channel registers of the linked pair alternately control the pulse width of the output.
Setting the MS0B bit in TIM channel 0 status and control register (TSC0) links channel 0 and channel 1.
The TIM channel 0 registers initially control the pulse width on the TCH0 pin. Writing to the TIM channel 1
registers enables the TIM channel 1 registers to synchronously control the pulse width at the beginning
of the next PWM period. At each subsequent overflow, the TIM channel registers (0 or 1) that control the
pulse width are the ones written to last. TSC0 controls and monitors the buffered PWM function, and TIM
channel 1 status and control register (TSC1) is unused. While the MS0B bit is set, the channel 1 pin,
TCH1, is available as a general-purpose I/O pin.
NOTE
In buffered PWM signal generation, do not write new pulse width values to
the currently active channel registers. User software should track the
currently active channel to prevent writing a new value to the active
channel. Writing to the active channel registers is the same as generating
unbuffered PWM signals.
18.4.4.3 PWM Initialization
To ensure correct operation when generating unbuffered or buffered PWM signals, use the following
initialization procedure:
1. In the TIM status and control register (TSC):
a. Stop the TIM counter by setting the TIM stop bit, TSTOP.
b. Reset the TIM counter and prescaler by setting the TIM reset bit, TRST.
2. In the TIM counter modulo registers (TMODH:TMODL), write the value for the required PWM
period.
3. In the TIM channel x registers (TCHxH:TCHxL), write the value for the required pulse width.
4. In TIM channel x status and control register (TSCx):
a. Write 0:1 (for unbuffered output compare or PWM signals) or 1:0 (for buffered output compare
or PWM signals) to the mode select bits, MSxB:MSxA. (See Table 18-2.)
b. Write 1 to the toggle-on-overflow bit, TOVx.
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Freescale Semiconductor
Interrupts
c. Write 1:0 (to clear output on compare) or 1:1 (to set output on compare) to the edge/level
select bits, ELSxB:ELSxA. The output action on compare must force the output to the
complement of the pulse width level. (See Table 18-2.)
NOTE
In PWM signal generation, do not program the PWM channel to toggle on
output compare. Toggling on output compare prevents reliable 0% duty
cycle generation and removes the ability of the channel to self-correct in the
event of software error or noise. Toggling on output compare can also
cause incorrect PWM signal generation when changing the PWM pulse
width to a new, much larger value.
5. In the TIM status control register (TSC), clear the TIM stop bit, TSTOP.
Setting MS0B links channels 0 and 1 and configures them for buffered PWM operation. The TIM channel
0 registers (TCH0H:TCH0L) initially control the buffered PWM output. TIM status control register 0
(TSCR0) controls and monitors the PWM signal from the linked channels.
Clearing the toggle-on-overflow bit, TOVx, inhibits output toggles on TIM overflows. Subsequent output
compares try to force the output to a state it is already in and have no effect. The result is a 0% duty cycle
output.
Setting the channel x maximum duty cycle bit (CHxMAX) and setting the TOVx bit generates a 100% duty
cycle output. (See 18.9.4 TIM Channel Status and Control Registers.)
18.5 Interrupts
The following TIM sources can generate interrupt requests:
• TIM overflow flag (TOF) — The TOF bit is set when the TIM counter reaches the modulo value
programmed in the TIM counter modulo registers. The TIM overflow interrupt enable bit, TOIE,
enables TIM overflow CPU interrupt requests. TOF and TOIE are in the TIM status and control
register.
• TIM channel flags (CH1F:CH0F) — The CHxF bit is set when an input capture or output compare
occurs on channel x. Channel x TIM CPU interrupt requests are controlled by the channel x
interrupt enable bit, CHxIE. Channel x TIM CPU interrupt requests are enabled when CHxIE = 1.
CHxF and CHxIE are in the TIM channel x status and control register.
18.6 Low-Power Modes
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.
18.6.1 Wait Mode
The TIM remains active after the execution of a WAIT instruction. In wait mode, the TIM registers are not
accessible by the CPU. Any enabled CPU interrupt request from the TIM can bring the MCU out of wait
mode.
If TIM functions are not required during wait mode, reduce power consumption by stopping the TIM before
executing the WAIT instruction.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Timer Interface Module (TIM)
18.6.2 Stop Mode
The TIM is inactive after the execution of a STOP instruction. The STOP instruction does not affect
register conditions or the state of the TIM counter. TIM operation resumes when the MCU exits stop mode
after an external interrupt.
18.7 TIM During Break Interrupts
A break interrupt stops the TIM counter.
The system integration module (SIM) controls whether status bits in other modules can be cleared during
the break state. The BCFE bit in the SIM break flag control register (SBFCR) enables software to clear
status bits during the break state. See 15.7.3 SIM Break Flag Control Register.
To allow software to clear status bits during a break interrupt, write a 1 to the BCFE bit. If a status bit is
cleared during the break state, it remains cleared when the MCU exits the break state.
To protect status bits during the break state, write a 0 to the BCFE bit. With BCFE at 0 (its default state),
software can read and write I/O registers during the break state without affecting status bits. Some status
bits have a 2-step read/write clearing procedure. If software does the first step on such a bit before the
break, the bit cannot change during the break state as long as BCFE is at 0. After the break, doing the
second step clears the status bit.
18.8 I/O Signals
Port D shares four of its pins with the TIM. The four TIM channel I/O pins are T1CH0, T1CH1, T2CH0,
and T2CH1 as described in 18.3 Pin Name Conventions.
Each channel I/O pin is programmable independently as an input capture pin or an output compare pin.
T1CH0 and T2CH0 can be configured as buffered output compare or buffered PWM pins.
18.9 I/O Registers
NOTE
References to either timer 1 or timer 2 may be made in the following text by
omitting the timer number. For example, TSC may generically refer to both
T1SC AND T2SC.
These I/O registers control and monitor operation of the TIM:
• TIM status and control register (TSC)
• TIM counter registers (TCNTH:TCNTL)
• TIM counter modulo registers (TMODH:TMODL)
• TIM channel status and control registers (TSC0, TSC1)
• TIM channel registers (TCH0H:TCH0L, TCH1H:TCH1L)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
I/O Registers
18.9.1 TIM Status and Control Register
The TIM status and control register (TSC):
• Enables TIM overflow interrupts
• Flags TIM overflows
• Stops the TIM counter
• Resets the TIM counter
• Prescales the TIM counter clock
Address: T1SC, $0020 and T2SC, $002B
Bit 7
Read:
TOF
Write:
0
Reset:
0
6
5
TOIE
TSTOP
0
1
4
3
0
0
TRST
0
0
2
1
Bit 0
PS2
PS1
PS0
0
0
0
= Unimplemented
Figure 18-5. TIM Status and Control Register (TSC)
TOF — TIM Overflow Flag Bit
This read/write flag is set when the TIM counter reaches the modulo value programmed in the TIM
counter modulo registers. Clear TOF by reading the TIM status and control register when TOF is set
and then writing a 0 to TOF. If another TIM overflow occurs before the clearing sequence is complete,
then writing 0 to TOF has no effect. Therefore, a TOF interrupt request cannot be lost due to
inadvertent clearing of TOF. Reset clears the TOF bit. Writing a 1 to TOF has no effect.
1 = TIM counter has reached modulo value
0 = TIM counter has not reached modulo value
TOIE — TIM Overflow Interrupt Enable Bit
This read/write bit enables TIM overflow interrupts when the TOF bit becomes set. Reset clears the
TOIE bit.
1 = TIM overflow interrupts enabled
0 = TIM overflow interrupts disabled
TSTOP — TIM Stop Bit
This read/write bit stops the TIM counter. Counting resumes when TSTOP is cleared. Reset sets the
TSTOP bit, stopping the TIM counter until software clears the TSTOP bit.
1 = TIM counter stopped
0 = TIM counter active
NOTE
Do not set the TSTOP bit before entering wait mode if the TIM is required
to exit wait mode.
TRST — TIM Reset Bit
Setting this write-only bit resets the TIM counter and the TIM prescaler. Setting TRST has no effect on
any other registers. Counting resumes from $0000. TRST is cleared automatically after the TIM
counter is reset and always reads as 0. Reset clears the TRST bit.
1 = Prescaler and TIM counter cleared
0 = No effect
NOTE
Setting the TSTOP and TRST bits simultaneously stops the TIM counter at
a value of $0000.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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231
Timer Interface Module (TIM)
PS[2:0] — Prescaler Select Bits
These read/write bits select one of the seven prescaler outputs as the input to the TIM counter as Table
18-1 shows. Reset clears the PS[2:0] bits.
Table 18-1. Prescaler Selection
PS2
PS1
PS0
TIM Clock Source
0
0
0
Internal bus clock ÷ 1
0
0
1
Internal bus clock ÷ 2
0
1
0
Internal bus clock ÷ 4
0
1
1
Internal bus clock ÷ 8
1
0
0
Internal bus clock ÷ 16
1
0
1
Internal bus clock ÷ 32
1
1
0
Internal bus clock ÷ 64
1
1
1
Not available
18.9.2 TIM Counter Registers
The two read-only TIM counter registers contain the high and low bytes of the value in the TIM counter.
Reading the high byte (TCNTH) latches the contents of the low byte (TCNTL) into a buffer. Subsequent
reads of TCNTH do not affect the latched TCNTL value until TCNTL is read. Reset clears the TIM counter
registers. Setting the TIM reset bit (TRST) also clears the TIM counter registers.
NOTE
If you read TCNTH during a break interrupt, be sure to unlatch TCNTL by
reading TCNTL before exiting the break interrupt. Otherwise, TCNTL
retains the value latched during the break.
Address: T1CNTH, $0021 and T2CNTH, $002C
Read:
Bit 7
6
5
4
3
2
1
Bit 0
Bit 15
14
13
12
11
10
9
Bit 8
0
0
0
0
0
0
0
0
Write:
Reset:
= Unimplemented
Figure 18-6. TIM Counter Registers High (TCNTH)
Address: T1CNTL, $0022 and T2CNTL, $002D
Read:
Bit 7
6
5
4
3
2
1
Bit 0
Bit 7
6
5
4
3
2
1
Bit 0
0
0
0
0
0
0
0
Write:
Reset:
0
= Unimplemented
Figure 18-7. TIM Counter Registers Low (TCNTL)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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I/O Registers
18.9.3 TIM Counter Modulo Registers
The read/write TIM modulo registers contain the modulo value for the TIM counter. When the TIM counter
reaches the modulo value, the overflow flag (TOF) becomes set, and the TIM counter resumes counting
from $0000 at the next timer clock. Writing to the high byte (TMODH) inhibits the TOF bit and overflow
interrupts until the low byte (TMODL) is written. Reset sets the TIM counter modulo registers.
Address: T1MODH, $0023 and T2MODH, $002E
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
Bit 15
14
13
12
11
10
9
Bit 8
1
1
1
1
1
1
1
1
Figure 18-8. TIM Counter Modulo Register High (TMODH)
Address: T1MODL, $0024 and T2MODL, $002F
Read:
Write:
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
Bit 7
6
5
4
3
2
1
Bit 0
1
1
1
1
1
1
1
1
Figure 18-9. TIM Counter Modulo Register Low (TMODL)
NOTE
Reset the TIM counter before writing to the TIM counter modulo registers.
18.9.4 TIM Channel Status and Control Registers
Each of the TIM channel status and control registers:
• Flags input captures and output compares
• Enables input capture and output compare interrupts
• Selects input capture, output compare, or PWM operation
• Selects high, low, or toggling output on output compare
• Selects rising edge, falling edge, or any edge as the active input capture trigger
• Selects output toggling on TIM overflow
• Selects 0% and 100% PWM duty cycle
• Selects buffered or unbuffered output compare/PWM operation
Address: T1SC0, $0025 and T2SC0, $0030
Bit 7
Read:
CH0F
Write:
0
Reset:
0
6
5
4
3
2
1
Bit 0
CH0IE
MS0B
MS0A
ELS0B
ELS0A
TOV0
CH0MAX
0
0
0
0
0
0
0
Figure 18-10. TIM Channel 0 Status and Control Register (TSC0)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
233
Timer Interface Module (TIM)
Address: T1SC1, $0028 and T2SC1, $0033
Bit 7
Read:
CH1F
Write:
0
Reset:
0
6
CH1IE
0
5
0
0
4
3
2
1
Bit 0
MS1A
ELS1B
ELS1A
TOV1
CH1MAX
0
0
0
0
0
= Unimplemented
Figure 18-11. TIM Channel 1 Status and Control Register (TSC1)
CHxF — Channel x Flag Bit
When channel x is an input capture channel, this read/write bit is set when an active edge occurs on
the channel x pin. When channel x is an output compare channel, CHxF is set when the value in the
TIM counter registers matches the value in the TIM channel x registers.
When TIM CPU interrupt requests are enabled (CHxIE = 1), clear CHxF by reading TIM channel x
status and control register with CHxF set and then writing a 0 to CHxF. If another interrupt request
occurs before the clearing sequence is complete, then writing 0 to CHxF has no effect. Therefore, an
interrupt request cannot be lost due to inadvertent clearing of CHxF.
Reset clears the CHxF bit. Writing a 1 to CHxF has no effect.
1 = Input capture or output compare on channel x
0 = No input capture or output compare on channel x
CHxIE — Channel x Interrupt Enable Bit
This read/write bit enables TIM CPU interrupt service requests on channel x.
Reset clears the CHxIE bit.
1 = Channel x CPU interrupt requests enabled
0 = Channel x CPU interrupt requests disabled
MSxB — Mode Select Bit B
This read/write bit selects buffered output compare/PWM operation. MSxB exists only in the TIM1
channel 0 and TIM2 channel 0 status and control registers.
Setting MS0B disables the channel 1 status and control register and reverts TCH1 to general-purpose
I/O.
Reset clears the MSxB bit.
1 = Buffered output compare/PWM operation enabled
0 = Buffered output compare/PWM operation disabled
MSxA — Mode Select Bit A
When ELSxB:A ≠ 00, this read/write bit selects either input capture operation or unbuffered output
compare/PWM operation. See Table 18-2.
1 = Unbuffered output compare/PWM operation
0 = Input capture operation
When ELSxB:A = 00, this read/write bit selects the initial output level of the TCHx pin. See Table 18-2.
Reset clears the MSxA bit.
1 = Initial output level low
0 = Initial output level high
NOTE
Before changing a channel function by writing to the MSxB or MSxA bit, set
the TSTOP and TRST bits in the TIM status and control register (TSC).
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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I/O Registers
Table 18-2. Mode, Edge, and Level Selection
MSxB
MSxA
ELSxB
ELSxA
X
0
0
0
X
1
0
0
0
0
0
1
0
0
1
0
Mode
Output preset
Configuration
Pin under port control; initial output level high
Pin under port control; initial output level low
Capture on rising edge only
Input capture
Capture on falling edge only
0
0
1
1
Capture on rising or falling edge
0
1
0
0
Software compare only
0
1
0
1
0
1
1
0
0
1
1
1
1
X
0
1
1
X
1
0
1
X
1
1
Output compare or PWM
Toggle output on compare
Clear output on compare
Set output on compare
Toggle output on compare
Buffered output compare or
buffered PWM
Clear output on compare
Set output on compare
ELSxB and ELSxA — Edge/Level Select Bits
When channel x is an input capture channel, these read/write bits control the active edge-sensing logic
on channel x.
When channel x is an output compare channel, ELSxB and ELSxA control the channel x output
behavior when an output compare occurs.
When ELSxB and ELSxA are both clear, channel x is not connected to port D, and pin PTDx/TCHx is
available as a general-purpose I/O pin. Table 18-2 shows how ELSxB and ELSxA work.
Reset clears the ELSxB and ELSxA bits.
NOTE
Before enabling a TIM channel register for input capture operation, make
sure that the PTD/TCHx pin is stable for at least two bus clocks.
TOVx — Toggle On Overflow Bit
When channel x is an output compare channel, this read/write bit controls the behavior of the channel
x output when the TIM counter overflows. When channel x is an input capture channel, TOVx has no
effect.
Reset clears the TOVx bit.
1 = Channel x pin toggles on TIM counter overflow.
0 = Channel x pin does not toggle on TIM counter overflow.
NOTE
When TOVx is set, a TIM counter overflow takes precedence over a
channel x output compare if both occur at the same time.
CHxMAX — Channel x Maximum Duty Cycle Bit
When the TOVx bit is at 1, setting the CHxMAX bit forces the duty cycle of buffered and unbuffered
PWM signals to 100%. As Figure 18-12 shows, the CHxMAX bit takes effect in the cycle after it is set
or cleared. The output stays at the 100% duty cycle level until the cycle after CHxMAX is cleared.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
235
Timer Interface Module (TIM)
OVERFLOW
OVERFLOW
OVERFLOW
OVERFLOW
OVERFLOW
PERIOD
TCHx
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
OUTPUT
COMPARE
CHxMAX
Figure 18-12. CHxMAX Latency
18.9.5 TIM Channel Registers
These read/write registers contain the captured TIM counter value of the input capture function or the
output compare value of the output compare function. The state of the TIM channel registers after reset
is unknown.
In input capture mode (MSxB:MSxA = 0:0), reading the high byte of the TIM channel x registers (TCHxH)
inhibits input captures until the low byte (TCHxL) is read.
In output compare mode (MSxB:MSxA ≠ 0:0), writing to the high byte of the TIM channel x registers
(TCHxH) inhibits output compares until the low byte (TCHxL) is written.
Address: T1CH0H, $0026 and T2CH0H, $0031
Bit 7
6
5
4
3
Read:
Bit 15
14
13
12
11
Write:
Reset:
Indeterminate after reset
2
1
Bit 0
10
9
Bit 8
Figure 18-13. TIM Channel 0 Register High (TCH0H)
Address: T1CH0L, $0027 and T2CH0L $0032
Bit 7
6
5
Read:
Bit 7
6
5
Write:
Reset:
4
3
2
1
Bit 0
4
3
2
1
Bit 0
Indeterminate after reset
Figure 18-14. TIM Channel 0 Register Low (TCH0L)
Address: T1CH1H, $0029 and T2CH1H, $0034
Bit 7
6
5
4
3
Read:
Bit 15
14
13
12
11
Write:
Reset:
Indeterminate after reset
2
1
Bit 0
10
9
Bit 8
Figure 18-15. TIM Channel 1 Register High (TCH1H)
Address: T1CH1L, $002A and T2CH1L, $0035
Bit 7
6
5
4
3
Read:
Bit 7
6
5
4
3
Write:
Reset:
Indeterminate after reset
2
1
Bit 0
2
1
Bit 0
Figure 18-16. TIM Channel 1 Register Low (TCH1L)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
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Freescale Semiconductor
Chapter 19
Development Support
19.1 Introduction
This section describes the break module, the monitor module (MON), and the monitor mode entry
methods.
19.2 Break Module (BRK)
This section describes the break module (BRK). The break module can generate a break interrupt that
stops normal program flow at a defined address to enter a background program.
Features of the break module include:
• Accessible input/output (I/O) registers during the break interrupt
• Central processor unit (CPU) generated break interrupts
• Software-generated break interrupts
• Computer operating properly (COP) disabling during break interrupts
19.2.1 Functional Description
When the internal address bus matches the value written in the break address registers, the break module
issues a breakpoint signal to the system integration module (SIM). The SIM then causes the CPU to load
the instruction register with a software interrupt instruction (SWI). The program counter vectors to $FFFC
and $FFFD ($FEFC and $FEFD in monitor mode).
The following events can cause a break interrupt to occur:
• A CPU generated address (the address in the program counter) matches the contents of the break
address registers.
• Software writes a 1 to the BRKA bit in the break status and control register.
When a CPU generated address matches the contents of the break address registers, the break interrupt
is generated. A return-from-interrupt instruction (RTI) in the break routine ends the break interrupt and
returns the microcontroller unit (MCU) to normal operation. Figure 19-2 shows the structure of the break
module.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
237
Development Support
8-BIT KEYBOARD
INTERRUPT MODULE
FLASH PROGRAMMING ROUTINES
ROM — 720 BYTES
USER FLASH VECTOR SPACE — 36 BYTES
PTE4/OSC1
PTE3/OSC2
INTERNAL CLOCK
GENERATOR MODULE
RST(3)
SYSTEM INTEGRATION
MODULE
IRQ(3)
SINGLE EXTERNAL
INTERRUPT MODULE
VREFH
VREFL
2-CHANNEL TIMER INTERFACE
MODULE 2
DDRA
PTD7/T2CH1(1)
PTD6/T2CH0(1)
PTD5/T1CH1(1)
PTD4/T1CH0(1)
PTD3/SPSCK(1)
PTD2/MOSI(1)
PTD1/MISO(1)
PTD0/SS(1)
PTE2
PTE1/RxD
PTE0/TxD
SERIAL PERIPHERAL
INTERFACE MODULE
MONITOR MODULE
8-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
PTC6(1)
PTC5(1)
PTC4(1)(2)
PTC3(1)(2)
PTC2(1)(2)
PTC1(1)(2)
PTC0(1)(2)
SERIAL COMMUNICATIONS
INTERFACE MODULE
COMPUTER OPERATING
PROPERLY MODULE
POWER-ON RESET
MODULE
VDD
VSS
VDDA
VSSA
2-CHANNEL TIMER INTERFACE
MODULE 1
DDRD
MONITOR ROM — 304 BYTES
PORTA
USER RAM — 512 BYTES
PORTB
DUAL VOLTAGE
LOW-VOLTAGE INHIBIT MODULE
PTB7/AD7
PTB6/AD6
PTB5/AD5
PTB4/AD4
PTB3/AD3
PTB2/AD2
PTB1/AD1
PTB0/AD0
PORTC
USER FLASH
MC68HC908GT16 — 15,872 BYTES
MC68HC908GT8 — 7,680 BYTES
PTA7/KBD7–
PTA0/KBD0(1)
PORTD
SINGLE BREAKPOINT BREAK
MODULE
DDRB
CONTROL AND STATUS
REGISTERS — 64 BYTES
DDRC
PROGRAMMABLE TIMEBASE
MODULE
ARITHMETIC/LOGIC
UNIT (ALU)
MEMORY MAP
MODULE
DDRE
CPU
REGISTERS
PORTE
INTERNAL BUS
M68HC08 CPU
SECURITY
MODULE
CONFIGURATION REGISTER 1
MODULE
CONFIGURATION REGISTER 2
MODULE
MONITOR MODE ENTRY
MODULE
1. Ports are software configurable with pullup device if input port.
2. Higher current drive port pins
3. Pin contains integrated pullup device
Figure 19-1. Block Diagram Highlighting BRK and MON Blocks
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
238
Freescale Semiconductor
Break Module (BRK)
IAB15–IAB8
BREAK ADDRESS REGISTER HIGH
8-BIT COMPARATOR
IAB15–IAB0
CONTROL
BREAK
8-BIT COMPARATOR
BREAK ADDRESS REGISTER LOW
IAB7–IAB0
Figure 19-2. Break Module Block Diagram
Addr.
$FE00
Register Name
Read:
SIM Break Status Register
(SBSR) Write:
See page 242.
Reset:
Bit 7
6
5
4
3
2
1
Bit 0
0
0
0
1
0
0
SBSW
0
R
R
R
R
R
R
NOTE
R
0
0
0
1
0
0
0
0
BCFE
R
R
R
R
R
R
R
Bit 15
14
13
12
11
10
9
Bit 8
0
0
0
0
0
0
0
0
Bit 7
6
5
4
3
2
1
Bit 0
0
0
0
0
0
0
0
0
BRKE
BRKA
0
0
0
0
0
0
0
0
0
0
0
0
0
0
R
= Reserved
Note: Writing a 0 clear SBSW.
$FE03
Read:
SIM Break Flag Control
Register (SBFCR) Write:
See page 242.
Reset:
Read:
Break Address Register High
$FE09
(BRKH) Write:
See page 241.
Reset:
Read:
Break Address Register Low
$FE0A
(BRKL) Write:
See page 241.
Reset:
$FE0B
Read:
Break Status and Control
Register (BRKSCR) Write:
See page 241.
Reset:
0
= Unimplemented
Figure 19-3. I/O Register Summary
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
239
Development Support
When the internal address bus matches the value written in the break address registers or when software
writes a 1 to the BRKA bit in the break status and control register, the CPU starts a break interrupt by:
•
Loading the instruction register with the SWI instruction
•
Loading the program counter with $FFFC and $FFFD ($FEFC and $FEFD in monitor mode)
The break interrupt timing is:
•
When a break address is placed at the address of the instruction opcode, the instruction is not
executed until after completion of the break interrupt routine.
•
When a break address is placed at an address of an instruction operand, the instruction is executed
before the break interrupt.
•
When software writes a 1 to the BRKA bit, the break interrupt occurs just before the next instruction
is executed.
By updating a break address and clearing the BRKA bit in a break interrupt routine, a break interrupt can
be generated continuously.
CAUTION
A break address should be placed at the address of the instruction opcode.
When software does not change the break address and clears the BRKA
bit in the first break interrupt routine, the next break interrupt will not be
generated after exiting the interrupt routine even when the internal address
bus matches the value written in the break address registers.
19.2.1.1 Flag Protection During Break Interrupts
The system integration module (SIM) controls whether or not module status bits can be cleared during
the break state. The BCFE bit in the break flag control register (BFCR) enables software to clear status
bits during the break state. See 15.7.3 SIM Break Flag Control Register and the Break Interrupts
subsection for each module.
19.2.1.2 TIM1 and TIM2 During Break Interrupts
A break interrupt stops the timer counters.
19.2.1.3 COP During Break Interrupts
The COP is disabled during a break interrupt when VTST is present on the RST pin.
19.2.2 Break Module Registers
These registers control and monitor operation of the break module:
•
Break status and control register (BRKSCR)
•
Break address register high (BRKH)
•
Break address register low (BRKL)
•
SIM break status register (SBSR)
•
SIM break flag control register (SBFCR)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
240
Freescale Semiconductor
Break Module (BRK)
19.2.2.1 Break Status and Control Register
The break status and control register (BRKSCR) contains break module enable and status bits.
Address:
$FE0B
Read:
Write:
Reset:
Bit 7
6
BRKE
BRKA
0
0
5
4
3
2
1
Bit 0
0
0
0
0
0
0
0
0
0
0
0
0
= Unimplemented
Figure 19-4. Break Status and Control Register (BRKSCR)
BRKE — Break Enable Bit
This read/write bit enables breaks on break address register matches. Clear BRKE by writing a 0 to
bit 7. Reset clears the BRKE bit.
1 = Breaks enabled on 16-bit address match
0 = Breaks disabled
BRKA — Break Active Bit
This read/write status and control bit is set when a break address match occurs. Writing a 1 to BRKA
generates a break interrupt. Clear BRKA by writing a 0 to it before exiting the break routine. Reset
clears the BRKA bit.
1 = (When read) Break address match
0 = (When read) No break address match
19.2.2.2 Break Address Registers
The break address registers (BRKH and BRKL) contain the high and low bytes of the desired breakpoint
address. Reset clears the break address registers.
Address:
Read:
Write:
Reset:
$FE09
Bit 7
6
5
4
3
2
1
Bit 0
Bit 15
14
13
12
11
10
9
Bit 8
0
0
0
0
0
0
0
0
Figure 19-5. Break Address Register High (BRKH)
Address:
Read:
Write:
Reset:
$FE0A
Bit 7
6
5
4
3
2
1
Bit 0
Bit 7
6
5
4
3
2
1
Bit 0
0
0
0
0
0
0
0
0
Figure 19-6. Break Address Register Low (BRKL)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
241
Development Support
19.2.2.3 SIM Break Status Register
The SIM break status register (SBSR) contains a flag to indicate that a break caused an exit from wait
mode. This register is only used in emulation mode.
Address: $FE00
Bit 7
Read:
Write:
6
R
R
5
R
4
R
3
R
2
R
1
Bit 0
SBSW
R
Note(1)
Reset:
0
R
= Reserved
1. Writing a 0 clears SBSW.
Figure 19-7. SIM Break Status Register (SBSR)
SBSW — SIM Break Stop/Wait
SBSW can be read within the break state SWI routine. The user can modify the return address on the
stack by subtracting one from it.
1 = Wait mode was exited by break interrupt
0 = Wait mode was not exited by break interrupt
19.2.2.4 Break Flag Control Register
The SIM break flag control register (SBFCR) contains a bit that enables software to clear status bits while
the MCU is in a break state.
Address:
Read:
Write:
Reset:
$FE03
Bit 7
6
5
4
3
2
1
Bit 0
BCFE
R
R
R
R
R
R
R
0
R
= Reserved
Figure 19-8. SIM Break Flag Control Register (SBFCR)
BCFE — Break Clear Flag Enable Bit
This read/write bit enables software to clear status bits by accessing status registers while the MCU is
in a break state. To clear status bits during the break state, the BCFE bit must be set.
1 = Status bits clearable during break
0 = Status bits not clearable during break
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
242
Freescale Semiconductor
Monitor Module (MON)
19.3 Monitor Module (MON)
The monitor module allows debugging and programming of the microcontroller unit (MCU) through a
single-wire interface with a host computer. Monitor mode entry can be achieved without use of the higher
test voltage, VTST, as long as vector addresses $FFFE and $FFFF are blank, thus reducing the hardware
requirements for in-circuit programming.
Features of the monitor module include:
•
Normal user-mode pin functionality
•
One pin dedicated to serial communication between monitor read-only memory (ROM) and host
computer
•
Standard mark/space non-return-to-zero (NRZ) communication with host computer
•
Execution of code in random-access memory (RAM) or Flash
•
Flash memory security feature(1)
•
Flash memory programming interface
•
External 4.92 MHz or 9.83 MHz clock used to generate internal frequency of 2.4576 MHz
•
Optional ICG mode of operation (no external clock or high voltage)
•
Monitor mode entry without high voltage, VTST, if reset vector is blank ($FFFE and $FFFF contain
$FF)
•
Normal monitor mode entry if high voltage is applied to IRQ
19.3.1 Functional Description
Figure 19-9 shows a simplified monitor mode entry flowchart.
The monitor ROM receives and executes commands from a host computer. Figure 19-10, Figure 19-11,
and Figure 19-12 show example circuits used to enter monitor mode and communicate with a host
computer via a standard RS-232 interface.
Simple monitor commands can access any memory address. In monitor mode, the MCU can execute
code downloaded into RAM by a host computer while most MCU pins retain normal operating mode
functions. All communication between the host computer and the MCU is through the PTA0 pin. A
level-shifting and multiplexing interface is required between PTA0 and the host computer. PTA0 is used
in a wired-OR configuration and requires a pullup resistor.
The monitor code has been updated from previous versions of the monitor code to allow the ICG to
generate the internal clock. This option, which is selected when IRQ is held low out of reset, is intended
to support serial communication/ programming at 9600 baud in monitor mode by using the ICG, and the
ICG user trim value ICGTR5 (if programmed) to generate the desired internal frequency (2.4576 MHz). If
ICGTR5 is not programmed (i.e., the value is $FF) then the ICG will operate at a nominal (untrimmed)
2.45 MHz and communications will be nominally at 9600 baud but the untrimmed rate may cause
difficulties with hosts which cannot automatically adjust their data rates to match.
Since this feature is enabled only when IRQ is held low out of reset, it cannot be used when the reset
vector is programmed (i.e., the value is not $FFFF) because entry into monitor mode in this case requires
VTST on IRQ.
1. No security feature is absolutely secure. However, Freescale’s strategy is to make reading or copying the Flash difficult for
unauthorized users.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
243
Development Support
POR RESET
NO
CONDITIONS
FROM Table 19-1
PTA0 = 1,
RESET
BLANK?
IRQ = VTST?
YES
PTA0 = 1, PTC0 = 1,
PTC1 = 0, AND
PTC3 = 1?
NO
NO
YES
YES
FORCED
MONITOR MODE
NORMAL
USER MODE
NORMAL
MONITOR MODE
FACTORY
USE ONLY
SEND 8 BYTES
SECURITY
IS RESET
POR?
YES
NO
YES
ARE ALL
SECURITY BYTES
CORRECT?
ENABLE FLASH
NO
DISABLE FLASH
MONITOR MODE ENTRY
DEBUGGING
AND FLASH
PROGRAMMING
(IF FLASH
IS ENABLED)
EXECUTE
MONITOR CODE
YES
DOES RESET
OCCUR?
NO
Figure 19-9. Simplified Monitor Mode Entry Flowchart
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
244
Freescale Semiconductor
Monitor Module (MON)
VDD
VDDA
RST
VDD
0.1 μF
0.1 μF
MAX232
1
+
1 μF
VCC 16
C1+
4
+
C1–
GND
N.C.
OSC1
IRQ
VTST
1 μF
10
8
9
VDD
+
1 μF
V– 6
7
PTC0
N.C.
PTC3
N.C.
PTC1
N.C.
2 kΩ
10 kΩ
74HC125
5
6
+
DB9
3
OSC2
15
V+ 2
C2+
5 C2–
2
N.C.
0.1 μF
3
1 μF
VDD
74HC125
3
2
PTA0
4
VSS
VSSA
1
5
Figure 19-10. Forced Monitor Mode (Low)
VDD
RST
VDD
0.1 μF
0.1 μF
MAX232
1
1 μF
+
N.C.
16
9.8304 MHz CLOCK
0.1 μF
3
4
1 μF
VDD
VCC
C1+
+
C1–
GND 15
C2+
V+ 2
1 μF
1 μF
DB9
2
7
10
3
8
9
OSC2
OSC1
VDD
+
N.C.
IRQ
10 kΩ
+
74HC125
5
6
2
74HC125
3
N.C.
PTC3
N.C.
PTC1
N.C.
PTA0
4
1
5
PTC0
VTST
V– 6
5 C2–
VDDA
VSS
VSSA
Figure 19-11. Forced Monitor Mode (High)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
245
Development Support
VDD
VDDA
RST
VDD
0.1 μF
0.1 μF
N.C.
9.8304 MHz CLOCK
MAX232
1
1 μF
+
3
4
1 μF
+
VCC 16
C1–
15
5
PTC0
PTC3
0.1 μF
C2+
GND
V+ 2
V– 6
1 μF
7
10
8
9
1 μF
VDD
+
IRQ
PTC1
74HC125
5
6
74HC125
3
2
10 kΩ
PTA0
VSSA
2 kΩ
9.1 V
10 kΩ
+
10 kΩ
1 kΩ
VTST
DB9
3
VDD
OSC1
VDD
C1+
5 C2–
2
OSC2
VSS
4
1
Figure 19-12. Standard Monitor Mode
Table 19-1 shows the pin conditions for entering monitor mode. As specified in the table, monitor mode
must be entered after a power-on reset (POR) and will allow communication at 9600 baud provided one
of the following sets of conditions is met:
1. If $FFFE and $FFFF does not contain $FF (programmed state):
– The external clock is 4.9152 MHz with PTC3 low or 9.8304 MHz with PTC3 high
– IRQ = VTST
2. If $FFFE and $FFFF contain $FF (erased state):
– The external clock is 9.8304 MHz
– IRQ = VDD (this can be implemented through the internal IRQ pullup)
3. If $FFFE and $FFFF contain $FF (erased state):
– IRQ = VSS (ICG is selected, no external clock required)
Once out of reset, the MCU waits for the host to send eight security bytes (see 19.3.2 Security). After the
security bytes, the MCU sends a break signal (10 consecutive 0s) to the host, indicating that it is ready to
receive a command.
NOTE
The PTA0 pin must remain high for 24 bus cycles after the RST pin goes
high to enter monitor mode properly.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
246
Freescale Semiconductor
Monitor Module (MON)
Table 19-1. Monitor Mode Signal Requirements and Options
Mode
Normal
Monitor
Forced
Monitor
User
MON08
Function
[Pin No.]
Serial
Mode Selection Divider
Reset Comm.
ICG
Vector
PTA0
PTC0
PTC1
PTC3
Communication Speed
IRQ
RST
VTST
VDD or VSS
X
1
1
0
0
OFF Disabled
4.9152
MHz
2.4576
MHz
9600
VTST
VDD or VSS
X
1
1
0
1
OFF Disabled
9.8304
MHz
2.4576
MHz
9600
VDD
VDD
$FFFF
(blank)
1
X
X
X
OFF Disabled
9.8304
MHz
2.4576
MHz
9600
VSS
VDD
$FFFF
(blank)
1
X
X
X
ON Disabled
X
Nominal
2.4576
MHz
Nominal
9600
VDD
or VSS
VDD
or VSS
Not
$FFFF
X
X
X
X
X
Enabled
X
X
X
VTST
[6]
RST
[4]
—
COM
[8]
MOD0
[12]
MOD1
[14]
DIV4
[16]
—
—
OSC1
[13]
—
—
COP
External
Bus
Clock Frequency
Baud
Range
1. PTA0 must have a pullup resistor to VDD in monitor mode.
2. Communication speed in the table is an example to obtain a baud rate of 9600.
Baud rate using external oscillator is bus frequency / 256.
3. External clock is a 4.1952 MHz or 9.8304 MHz canned oscillator on OSC1.
4. X = don’t care.
5. MON08 pin refers to P&E Microcomputer Systems’ MONOUT-Cyclone 2 by 8-pin connector.
NC
1
2
GND
NC
3
4
RST
NC
5
6
IRQ
NC
7
8
PTA0
NC
9
10
NC
NC
11
12
PTC0
OSC1
13
14
PTC1
VDD
15
16
PTC3
19.3.1.1 Normal Monitor Mode
When VTST is applied to IRQ and PTC3 is low upon monitor mode entry, the bus frequency is a
divide-by-two of the input clock. If PTC3 is high with VTST applied to IRQ upon monitor mode entry, the
bus frequency will be a divide-by-four of the input clock. Holding the PTC3 pin low when entering monitor
mode causes a bypass of a divide-by-two stage at the oscillator only if VTST is applied to IRQ. In this
event, the CGMOUT frequency is equal to the CGMXCLK frequency, and the OSC1 input directly
generates internal bus clocks. In this case, the OSC1 signal must have a 50% duty cycle at maximum bus
frequency.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
247
Development Support
If monitor mode was entered with VTST on IRQ, then the COP is disabled as long as VTST is applied to
either IRQ or RST.
This condition states that as long as VTST is maintained on the IRQ pin after entering monitor mode, or if
VTST is applied to RST after the initial reset to get into monitor mode (when VTST was applied to IRQ),
then the COP will be disabled. In the latter situation, after VTST is applied to the RST pin, VTST can be
removed from the IRQ pin in the interest of freeing the IRQ for normal functionality in monitor mode.
19.3.1.2 Forced Monitor Mode
If entering monitor mode without high voltage on IRQ (where applied voltage is either VDD or VSS), then
all port C pin requirements and conditions, including the PTC3 frequency divisor selection, are not in
effect. This is to reduce circuit requirements when performing in-circuit programming.
If IRQ = VDD on monitor mode entry, an external oscillator of 9.8304 MHz is required for a 9600 baud rate.
If IRQ = VSS on monitor mode entry, the ICG generates a 9600 baud rate using the trimmed ICG value in
the ICGTR5 register. If the ICGTR5 register is blank, the baud rate will be a nominal 9600 baud which
may not be adequate for standard PC serial communication.
When forced monitor mode is entered, the COP is always disabled regardless of the state of IRQ or RST.
NOTE
If the reset vector is blank and monitor mode is entered, the chip will see an
additional reset cycle after the initial POR reset. Once the part has been
programmed, the traditional method of applying a voltage, VTST, to IRQ
must be used to enter monitor mode.
19.3.1.3 Monitor Vectors
In monitor mode, the MCU uses different vectors for reset, SWI (software interrupt), and break interrupt
than those for user mode. The alternate vectors are in the $FE page instead of the $FF page and allow
code execution from the internal monitor firmware instead of user code.
NOTE
Exiting monitor mode after it has been initiated by having a blank reset
vector requires a power-on reset (POR). Pulling RST low will not exit
monitor mode in this situation.
Table 19-2 summarizes the differences between user mode and monitor mode.
Table 19-2. Mode Differences
Functions
Modes
Reset
Vector High
Reset
Vector Low
Break
Vector High
Break
Vector Low
SWI
Vector High
SWI
Vector Low
User
$FFFE
$FFFF
$FFFC
$FFFD
$FFFC
$FFFD
Monitor
$FEFE
$FEFF
$FEFC
$FEFD
$FEFC
$FEFD
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
248
Freescale Semiconductor
Monitor Module (MON)
19.3.1.4 Data Format
Communication with the monitor ROM is in standard non-return-to-zero (NRZ) mark/space data format.
Transmit and receive baud rates must be identical.
START
BIT
BIT 0
BIT 1
BIT 2
BIT 3
BIT 4
BIT 5
BIT 6
BIT 7
STOP
BIT
NEXT
START
BIT
Figure 19-13. Monitor Data Format
19.3.1.5 Break Signal
A start bit (0) followed by nine 0 bits is a break signal. When the monitor receives a break signal, it drives
the PTA0 pin high for the duration of two bits and then echoes back the break signal.
MISSING STOP BIT
0
1
2
3
4
5
2-STOP BIT DELAY BEFORE ZERO ECHO
6
7
0
1
2
3
4
5
6
7
Figure 19-14. Break Transaction
19.3.1.6 Baud Rate
The communication baud rate is controlled by the external clock or ICG upon entry into monitor mode.
Table 19-1 lists external frequencies required to achieve a standard baud rate of 9600 bps. The effective
baud rate is the bus frequency divided by 256.
19.3.1.7 Commands
The monitor ROM firmware uses these commands:
•
READ (read memory)
•
WRITE (write memory)
•
IREAD (indexed read)
•
IWRITE (indexed write)
•
READSP (read stack pointer)
•
RUN (run user program)
The monitor ROM firmware echoes each received byte back to the PTA0 pin for error checking. An 11-bit
delay at the end of each command allows the host to send a break character to cancel the command. A
delay of two bit times occurs before each echo and before READ, IREAD, or READSP data is returned.
The data returned by a read command appears after the echo of the last byte of the command.
NOTE
Wait one bit time after each echo before sending the next byte.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
249
Development Support
FROM
HOST
4
ADDRESS
HIGH
READ
READ
4
1
ADDRESS
HIGH
ADDRESS
LOW
1
ADDRESS
LOW
DATA
1
4
3, 2
4
ECHO
RETURN
Notes:
1 = Echo delay, approximately 2 bit times
2 = Data return delay, approximately 2 bit times
3 = Cancel command delay, 11 bit times
4 = Wait 1 bit time before sending next byte.
Figure 19-15. Read Transaction
FROM
HOST
3
ADDRESS
HIGH
WRITE
WRITE
3
1
ADDRESS
HIGH
1
ADDRESS
LOW
3
ADDRESS
LOW
1
DATA
DATA
3
1
2, 3
ECHO
Notes:
1 = Echo delay, approximately 2 bit times
2 = Cancel command delay, 11 bit times
3 = Wait 1 bit time before sending next byte.
Figure 19-16. Write Transaction
A brief description of each monitor mode command is given in Table 19-3 through Table 19-7.
Table 19-3. READ (Read Memory) Command
Description
Read byte from memory
Operand
2-byte address in high-byte:low-byte order
Data Returned
Returns contents of specified address
Opcode
$4A
Command Sequence
SENT TO MONITOR
READ
ECHO
READ
ADDRESS
HIGH
ADDRESS
HIGH
ADDRESS
LOW
ADDRESS
LOW
DATA
RETURN
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
250
Freescale Semiconductor
Monitor Module (MON)
Table 19-4. WRITE (Write Memory) Command
Description
Operand
Data Returned
Opcode
Write byte to memory
2-byte address in high-byte:low-byte order; low byte followed by data byte
None
$49
Command Sequence
FROM HOST
ADDRESS
HIGH
WRITE
WRITE
ADDRESS
HIGH
ADDRESS
LOW
ADDRESS
LOW
DATA
DATA
ECHO
Table 19-5. IREAD (Indexed Read) Command
Description
Operand
Data Returned
Opcode
Read next 2 bytes in memory from last address accessed
None
Returns contents of next two addresses
$1A
Command Sequence
FROM HOST
IREAD
IREAD
DATA
DATA
ECHO
RETURN
A sequence of IREAD or IWRITE commands can access a block of memory sequentially over the full
64-Kbyte memory map.
Table 19-6. READSP (Read Stack Pointer) Command
Description
Operand
Data Returned
Opcode
Reads stack pointer
None
Returns incremented stack pointer value (SP + 1) in high-byte:low-byte order
$0C
Command Sequence
FROM HOST
READSP
ECHO
READSP
SP
HIGH
SP
LOW
RETURN
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
251
Development Support
Table 19-7. RUN (Run User Program) Command
Description
Executes PULH and RTI instructions
Operand
None
Data Returned
None
Opcode
$28
Command Sequence
FROM HOST
RUN
RUN
ECHO
The MCU executes the SWI and PSHH instructions when it enters monitor mode. The RUN command
tells the MCU to execute the PULH and RTI instructions. Before sending the RUN command, the host can
modify the stacked CPU registers to prepare to run the host program. The READSP command returns
the incremented stack pointer value, SP + 1. The high and low bytes of the program counter are at
addresses SP + 5 and SP + 6.
SP
HIGH BYTE OF INDEX REGISTER
SP + 1
CONDITION CODE REGISTER
SP + 2
ACCUMULATOR
SP + 3
LOW BYTE OF INDEX REGISTER
SP + 4
HIGH BYTE OF PROGRAM COUNTER
SP + 5
LOW BYTE OF PROGRAM COUNTER
SP + 6
SP + 7
Figure 19-17. Stack Pointer at Monitor Mode Entry
19.3.2 Security
A security feature discourages unauthorized reading of Flash locations while in monitor mode. The host
can bypass the security feature at monitor mode entry by sending eight security bytes that match the
bytes at locations $FFF6–$FFFD. Locations $FFF6–$FFFD contain user-defined data.
NOTE
Do not leave locations $FFF6–$FFFD blank. For security reasons, program
locations $FFF6–$FFFD even if they are not used for vectors.
During monitor mode entry, the MCU waits after the power-on reset for the host to send the eight security
bytes on pin PTA0. If the received bytes match those at locations $FFF6–$FFFD, the host bypasses the
security feature and can read all Flash locations and execute code from Flash. Security remains bypassed
until a power-on reset occurs. If the reset was not a power-on reset, security remains bypassed and
security code entry is not required. See Figure 19-18.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
252
Freescale Semiconductor
Monitor Module (MON)
Upon power-on reset, if the received bytes of the security code do not match the data at locations
$FFF6–$FFFD, the host fails to bypass the security feature. The MCU remains in monitor mode, but
reading a Flash location returns an invalid value and trying to execute code from Flash causes an illegal
address reset. After receiving the eight security bytes from the host, the MCU transmits a break character,
signifying that it is ready to receive a command.
NOTE
The MCU does not transmit a break character until after the host sends the
eight security bytes.
VDD
COMMAND
BYTE 8
FROM HOST
BYTE 2
RST
BYTE 1
4096 + 32 CGMXCLK CYCLES
PA0
4
BREAK
2
1
COMMAND ECHO
Notes:
1 = Echo delay, approximately 2 bit times
2 = Data return delay, approximately 2 bit times
4 = Wait 1 bit time before sending next byte
5 = Wait until the monitor ROM runs
1
BYTE 8 ECHO
FROM MCU
1
BYTE 2 ECHO
4
1
BYTE 1 ECHO
5
Figure 19-18. Monitor Mode Entry Timing
To determine whether the security code entered is correct, check to see if bit 6 of RAM address $40 is
set. If it is, then the correct security code has been entered and Flash can be accessed.
If the security sequence fails, the device should be reset by a power-on reset and brought up in monitor
mode to attempt another entry. After failing the security sequence, the Flash module can also be mass
erased by executing an erase routine that was downloaded into internal RAM. The mass erase operation
clears the security code locations so that all eight security bytes become $FF (blank).
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
253
Development Support
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
254
Freescale Semiconductor
Chapter 20
Electrical Specifications
20.1 Introduction
This section contains electrical and timing specifications.
20.2 Absolute Maximum Ratings
Maximum ratings are the extreme limits to which the microcontroller unit (MCU) can be exposed without
permanently damaging it.
NOTE
This device is not guaranteed to operate properly at the maximum ratings. Refer to 20.5 5.0-V DC
Electrical Characteristics for guaranteed operating conditions.
Characteristic(1)
Symbol
Value
Unit
Supply voltage
VDD
–0.3 to + 6.0
V
Input voltage
VIn
VSS – 0.3 to VDD + 0.3
V
I
± 15
mA
Maximum current for pins PTA5-PTA7, PTD4
IPTA5–PTA7
± 20
mA
Maximum current for pins PTC0–PTC4
IPTC0–PTC4
± 25
mA
Maximum current into VDD
Imvdd
150
mA
Maximum current out of VSS
Imvss
150
mA
Tstg
–55 to +150
°C
Maximum current per pin excluding those specified below
Storage temperature
1. Voltages referenced to VSS
NOTE
This device contains circuitry to protect the inputs against damage due to
high static voltages or electric fields; however, it is advised that normal
precautions be taken to avoid application of any voltage higher than
maximum-rated voltages to this high-impedance circuit. For proper
operation, it is recommended that VIn and VOut be constrained to the range
VSS ≤ (VIn or VOut) ≤ VDD. Reliability of operation is enhanced if unused
inputs are connected to an appropriate logic voltage level (for example,
either VSS or VDD).
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
255
Electrical Specifications
20.3 Functional Operating Range
Characteristic
Symbol
Value
Unit
TA
–40 to +85
°C
VDD
3.0 ±10%
5.0 ±10%
V
Symbol
Value
Unit
Thermal resistance
42-pin SDIP
44-pin QFP
θJA
60
95
°C/W
I/O pin power dissipation
PI/O
User determined
W
Power dissipation(1)
PD
PD = (IDD × VDD) + PI/O =
K/(TJ + 273 °C)
W
Constant(2)
K
PD × (TA + 273 °C)
+ PD2 × θJA
W/°C
Average junction temperature
TJ
TA + (PD × θJA)
°C
Operating temperature range
Operating voltage range
20.4 Thermal Characteristics
Characteristic
1. Power dissipation is a function of temperature.
2. K is a constant unique to the device. K can be determined for a known TA and measured PD. With this value of K,
PD and TJ can be determined for any value of TA.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
256
Freescale Semiconductor
5.0-V DC Electrical Characteristics
20.5 5.0-V DC Electrical Characteristics
Characteristic(1)
Output high voltage
(ILoad = –2.0 mA) all I/O pins
(ILoad = –10.0 mA) all I/O pins
(ILoad = –20.0 mA) pins PTC0–PTC4 only
Maximum combined IOH for port C, port E,
port PTD0–PTD3
Maximum combined IOH for port PTD4–PTD7,
port A, port B
Maximum total IOH for all port pins
Output low voltage
(ILoad = 1.6 mA) all I/O pins
(ILoad = 10 mA) all I/O pins
(ILoad = 20mA) pins PTC0–PTC4 only
Maximum combined IOL for port C, port E,
port PTD0–PTD3
Maximum combined IOL for port PTD4–PTD7,
port A, port B
Maximum total IOL for all port pins
Symbol
Min
Typ(2)
Max
Unit
VOH
VOH
VOH
IOH1
VDD – 0.8
VDD – 1.5
VDD – 1.5
—
—
—
—
—
—
—
—
50
V
V
V
mA
IOH2
—
—
50
mA
IOHT
—
—
100
mA
VOL
VOL
VOL
IOL1
—
—
—
—
—
—
—
—
0.4
1.5
1.5
50
V
V
V
mA
IOL2
—
—
50
mA
IOLT
—
—
100
mA
Input high voltage
All ports, IRQ, RST, OSC1
VIH
0.7 × VDD
—
VDD
V
Input low voltage
All ports, IRQ, RST, OSC1
VIL
VSS
—
0.2 × VDD
V
IINJ
– 2.0
—
+ 2.0
mA
DC injection current, all ports(3)
Total DC current injection (sum of all
I/O)(3)
IINJTOT
– 25
—
+25
mA
I/O ports Hi-Z leakage current(4)
IIL
—
—
±10
μA
Input current
IIn
—
—
±1
μA
Pullup resistors (as input only)
Ports PTA7/KBD7–PTA0/KBD0, PTC6–PTC0,
PTD7/T2CH1–PTD0/SS
RPU
20
45
65
kΩ
Capacitance
Ports (as input or output)
COut
CIn
—
—
—
—
12
8
pF
Monitor mode entry voltage
VTST
VDD + 2.5
—
VDD + 4.0
V
Low-voltage inhibit, trip falling voltage
VTRIPF
3.90
4.25
4.50
V
Low-voltage inhibit, trip rising voltage
VTRIPR
4.20
4.35
4.60
V
Low-voltage inhibit reset/recover hysteresis
(VTRIPF + VHYS = VTRIPR)
VHYS
—
100
—
mV
POR rearm voltage(5)
VPOR
0
—
100
mV
VPORRST
0
700
800
mV
RPOR
0.035
—
—
V/ms
POR reset
voltage(6)
POR rise time ramp
rate(7)
1. VDD = 5.0 Vdc ± 10%, VSS = 0 Vdc, TA = TA (min) to TA (max), unless otherwise noted
2. Typical values reflect average measurements at midpoint of voltage range, 25°C only.
3. Some disturbance of the ADC accuracy is possible during any injection event and is dependent on board layout and power
supply decoupling. This parameter is guaranteed by characterization.
4. Pullups and pulldowns are disabled. Port B leakage is specified in 20.16 ADC Characteristics.
5. Maximum is highest voltage that POR is guaranteed.
6. Maximum is highest voltage that POR is possible.
7. If minimum VDD is not reached before the internal POR reset is released, RST must be driven low externally until minimum
VDD is reached.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
257
Electrical Specifications
20.6 3.0-V DC Electrical Characteristics
Characteristic(1)
Output high voltage
(ILoad = –0.6 mA) all I/O pins
(ILoad = –4.0 mA) all I/O pins
(ILoad = –10.0 mA) pins PTC0–PTC4 only
Maximum combined IOH for port C, port E,
port PTD0–PTD3
Maximum combined IOH for port PTD4–PTD7,
port A, port B
Maximum total IOH for all port pins
Output low voltage
(ILoad = 0.5 mA) all I/O pins
(ILoad = 5.0 mA) all I/O pins
(ILoad = 10.0 mA) pins PTC0–PTC4 only
Maximum combined IOL for port C, port E,
port PTD0–PTD3
Maximum combined IOL for port PTD4–PTD7,
port A, port B
Maximum total IOL for all port pins
Symbol
Min
Typ(2)
Max
Unit
VOH
VOH
VOH
IOH1
VDD – 0.3
VDD – 1.0
VDD –1.0
—
—
—
—
—
—
—
—
30
V
V
V
mA
IOH2
—
—
30
mA
IOHT
—
—
60
mA
VOL
VOL
VOL
IOL1
—
—
—
—
—
—
—
—
0.3
1.0
1.0
30
V
V
V
mA
IOL2
—
—
30
mA
IOLT
—
—
60
mA
Input high voltage
All ports, IRQ, RST, OSC1
VIH
0.7 × VDD
—
VDD
V
Input low voltage
All ports, IRQ, RST, OSC1
VIL
VSS
—
0.3 × VDD
V
IINJ
– 2.0
—
+ 2.0
mA
DC injection current, all ports(3)
(3)
IINJTOT
– 25
—
+25
mA
I/O ports Hi-Z leakage current(4)
IIL
—
—
±10
μA
Input current
Total DC current injection (sum of all I/O)
IIn
—
—
±1
μA
Pullup resistors (as input only)
Ports PTA7/KBD7–PTA0/KBD0, PTC6–PTC0,
PTD7/T2CH1–PTD0/SS
RPU
20
45
65
kΩ
Capacitance
Ports (as input or output)
COut
CIn
—
—
—
—
12
8
pF
Monitor mode entry voltage
VTST
VDD + 2.5
—
VDD + 4.0
V
Low-voltage inhibit, trip falling voltage
VTRIPF
2.45
2.60
2.70
V
Low-voltage inhibit, trip rising voltage
VTRIPR
2.55
2.66
2.80
V
Low-voltage inhibit reset/recover hysteresis
(VTRIPF + VHYS = VTRIPR)
VHYS
—
60
—
mV
POR rearm voltage(5)
VPOR
0
—
100
mV
VPORRST
0
700
800
mV
RPOR
0.02
—
—
V/ms
(6)
POR reset voltage
POR rise time ramp rate(7)
1. VDD = 3.0 Vdc ± 10%, VSS = 0 Vdc, TA = TA (min) to TA (max), unless otherwise noted
2. Typical values reflect average measurements at midpoint of voltage range, 25°C only.
3. Some disturbance of the ADC accuracy is possible during any injection event and is dependent on board layout and power
supply decoupling. This parameter is guaranteed by characterization.
4. Pullups and pulldowns are disabled.
5. Maximum is highest voltage that POR is guaranteed.
6. Maximum is highest voltage that POR is possible.
7. If minimum VDD is not reached before the internal POR reset is released, RST must be driven low externally until minimum
VDD is reached.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
258
Freescale Semiconductor
Supply Current Characteristics
20.7 Supply Current Characteristics
Voltage
Bus
Frequency
(MHz)
Symbol
Typ(2)
Max
Unit
Run mode VDD supply current(3)
5.0
3.0
8
4
RIDD
15
4.5
20
8
mA
Wait mode VDD supply current(4)
5.0
3.0
8
4
WIDD
4
1.5
8
4
mA
1
20
300
50
500
5
—
—
—
—
2
12
200
30
300
3
—
—
—
—
Characteristic(1)
Stop mode VDD supply current(5)
25°C
25°C with TBM enabled(6)
25°C with LVI and TBM enabled(6)
–40°C to 85°C with TBM enabled(6)
–40°C to 85°C with LVI and TBM enabled(6)
Stop mode VDD supply current(5)
25°C
25°C with TBM enabled(6)
25°C with LVI and TBM enabled(6)
–40°C to 85°C with TBM enabled(6)
–40°C to 85°C with LVI and TBM enabled(6)
5.0
3.0
SIDD
SIDD
μA
μA
1. VDD = 5.0 Vdc ± 10%, VSS = 0 Vdc, TA = TA (min) to TA (max), unless otherwise noted
2. Typical values reflect average measurements at 25°C only.
3. Run (operating) IDD measured using external square wave clock source (fOSC = 32 MHz for 5 V and fOSC = 16 MHz for 3 V).
All inputs 0.2 V from rail. No dc loads. Less than 100 pF on all outputs. Measured with all modules enabled.
4. Wait IDD measured using external square wave clock source (fOSC = 32 MHz for 5 V and fOSC = 16 MHz for 3 V). All inputs
0.2 V from rail. No dc loads. Less than 100 pF on all outputs. All ports configured as inputs. Measured with ICG and LVI
enabled.
5. Stop IDD is measured with OSC1 = VSS.
6. Stop IDD with TBM enabled is measured using an external square wave clock source (fOSC = 32 MHz for 5 V and
fOSC = 16 MHz for 3 V).
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
259
Electrical Specifications
20.8 5-V Control Timing
Characteristic(1)
Symbol
Min
Max
Unit
Internal operating frequency
fOP (fBus)
—
8
MHz
Internal clock period (1/fOP)
tcyc
122
—
ns
RST input pulse width low
tRL
50
—
ns
IRQ interrupt pulse width low (edge-triggered)
tILIH
50
—
ns
—
tcyc
tILIL
IRQ interrupt pulse period
(2)
Note
1. VDD = 4.5 to 5.5 Vdc, VSS = 0 Vdc, TA = TL to TH; timing shown with respect to 20% VDD and 70% VSS, unless otherwise
noted.
2. The minimum period is the number of cycles it takes to execute the interrupt service routine plus 1 tcyc.
tRL
RST
tILIL
tILIH
IRQ
Figure 20-1. RST and IRQ Timing
20.9 3-V Control Timing
Characteristic(1)
Symbol
Min
Max
Unit
Internal operating frequency
fOP (fBus)
—
4
MHz
Internal clock period (1/fOP)
tcyc
244
—
ns
RST input pulse width low
tRL
125
—
ns
IRQ interrupt pulse width low (edge-triggered)
tILIH
125
—
ns
—
tcyc
tILIL
IRQ interrupt pulse period
(2)
Note
1. VDD = 2.7 to 3.3 Vdc, VSS = 0 Vdc, TA = TL to TH; timing shown with respect to 20% VDD and 70% VDD, unless otherwise
noted.
2. The minimum period is the number of cycles it takes to execute the interrupt service routine plus 1 tcyc.
tRL
RST
tILIL
tILIH
IRQ
Figure 20-2. RST and IRQ Timing
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
260
Freescale Semiconductor
Internal Oscillator Characteristics
20.10 Internal Oscillator Characteristics
Characteristic(1)
Internal oscillator base frequency(2), (3)
Internal oscillator tolerance
Internal oscillator multiplier(4)
Symbol
Min
Typ
Max
Unit
fINTOSC
230.4
307.2
384
kHz
fOSC_TOL
–25
—
+25
%
N
1
—
127
—
1. VDD = 5.5 Vdc to 2.7 Vdc, VSS = 0 Vdc, TA = TA (min) to TA (max), unless otherwise noted
2. Internal oscillator is selectable through software for a maximum frequency. Actual frequency will be
multiplier (N) x base frequency.
3. fBus = (fINTOSC / 4) x N when internal clock source selected
4. Multiplier must be chosen to limit the maximum bus frequency of 4 MHz for 2.7-V operation and 8 MHz
for 4.5-V operation.
20.11 External Oscillator Characteristics
Characteristic(1)
Symbol
Min
Typ
Max
dc(5)
—
32 M(6)
60
307.2 k
—
—
307.2 k
32 M(6)
Unit
option(2)(3)
External clock
With ICG clock disabled
With ICG clock enabled
EXTSLOW = 1(4)
EXTSLOW = 0(4)
fEXTOSC
External crystal options(7)(8)
EXTSLOW = 1(4)
EXTSLOW = 0(4)
fEXTOSC
30 k
1M
—
—
100 k
10 M
Hz
Crystal load capacitance(9)
CL
—
—
—
pF
Crystal fixed capacitance(9)
C1
—
2 x CL
—
pF
C2
—
2 x CL
—
pF
RB
—
10
—
MΩ
RS
—
—
—
MΩ
Crystal tuning
capacitance(9)
Feedback bias resistor
Series resistor
(9)
(9)(10)
Hz
1. VDD = 5.5 to 2.7 Vdc, VSS = 0 Vdc, TA = TA (min) to TA (max), unless otherwise noted
2. Setting EXTCLKEN configuration option enables OSC1 pin for external clock square-wave input.
3. No more than 10% duty cycle deviation from 50%
4. EXTSLOW configuration option configures external oscillator for a slow speed crystal and sets the clock monitor circuits of
the ICG module to expect an external clock frequency that is higher/lower than the internal oscillator base frequency,
fINTOSC.
5. Some modules may require a minimum frequency greater than dc for proper operation. See appropriate table for this
information.
6. MCU speed derates from 32 MHz at VDD = 4.5 Vdc to 16 MHz at VDD = 2.7 Vdc.
7. Setting EXTCLKEN and EXTXTALEN configuration options enables OSC1 and OSC2 pins for external crystal option.
8. fBus = (fEXTOSC / 4) when external clock source is selected.
9. Consult crystal vendor data sheet, see Figure 7-4. External Clock Generator Block Diagram.
10. Not required for high-frequency crystals
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
261
Electrical Specifications
20.12 Trimmed Accuracy of the Internal Clock Generator
The unadjusted frequency of the low-frequency base clock (IBASE), when the comparators in the
frequency comparator indicate zero error, can vary as much as ±25% due to process, temperature, and
voltage. The trimming capability exists to compensate for process effects. The remaining variation in
frequency is due to temperature, voltage, and change in target frequency (multiply register setting). These
effects are designed to be minimal, however variation does occur. Better performance is seen at 3 V and
lower settings of N.
20.12.1 2.7-Volt to 3.3-Volt Trimmed Internal Clock Generator Characteristics
Characteristic(1)
Symbol
Min
Typ
Max
Unit
Absolute trimmed internal oscillator tolerance(2), (3)
–40°C to 85°C
Fabs_tol
—
2.5
4.0
%
Variation over temperature(3), (4)
Var_temp
—
0.03
0.05
%/°C
Var_volt
—
—
0.5
0.7
2.0
2.0
%/V
Variation over voltage
25°C
–40°C to 85°C
(3), (5)
1. These specifications concern long-term frequency variation. Each measurement is taken over a 1-ms period.
2. Absolute value of variation in ICG output frequency, trimmed at nominal VDD and temperature, as temperature and VDD are
allowed to vary for a single given setting of N.
3. Specification is characterized but not tested.
4. Variation in ICG output frequency for a fixed N and voltage
5. Variation in ICG output frequency for a fixed N
20.12.2 4.5-Volt to 5.5-Volt Trimmed Internal Clock Generator Characteristics
Characteristic(1)
Symbol
Min
Typ
Max
Unit
Fabs_tol
—
4.0
4.0
%
Variation over temperature(3), (4)
Var_temp
—
0.05
0.08
%/°C
Variation over voltage(3), (5)
25°C
–40°C to 85°C
Var_volt
—
—
1.0
1.0
2.0
2.0
%/V
Absolute trimmed internal oscillator
–40°C to 85°C
tolerance(2), (3)
1. These specifications concern long-term frequency variation. Each measurement is taken over a 1-ms period.
2. Absolute value of variation in ICG output frequency, trimmed at nominal VDD and temperature, as temperature and VDD are
allowed to vary for a single given setting of N.
3. Specification is characterized but not tested.
4. Variation in ICG output frequency for a fixed N and voltage
5. Variation in ICG output frequency for a fixed N
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
262
Freescale Semiconductor
Output High-Voltage Characteristics
20.13 Output High-Voltage Characteristics
0
–5
–10
–40
0
25
85
IOH (mA)
–15
–20
–25
–30
–35
–40
3
3.2
3.4
3.6
VOH (V)
3.8
4.0
4.2
VOH > VDD –0.8 V @ IOH = –2.0 mA
VOH > VDD –1.5 V @ IOH = –10.0 mA
Figure 20-3. Typical High-Side Driver Characteristics –
Port PTA7–PTA0 (VDD = 4.5 Vdc)
0
IOH (mA)
–5
–40
0
25
85
–10
–15
–20
–25
1.3
1.5
1.7
1.9
VOH (V)
VOH > VDD –0.3 V @ IOH = –0.6 mA
VOH > VDD –1.0 V @ IOH = –10.0 mA
2.1
2.3
2.5
Figure 20-4. Typical High-Side Driver Characteristics –
Port PTA7–PTA0 (VDD = 2.7 Vdc)
0
–5
–10
–40
0
25
85
IOH (mA)
–15
–20
–25
–30
–35
–40
3
3.2
3.4
3.6
VOH (V)
3.8
4.0
4.2
VOH > VDD –1.5 V @ IOH = –20.0 mA
Figure 20-5. Typical High-Side Driver Characteristics –
Port PTC4–PTC0 (VDD = 4.5 Vdc)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
263
Electrical Specifications
0
IOH (mA)
–5
–40
0
25
85
–10
–15
–20
–25
1.3
1.5
1.7
1.9
VOH (V)
VOH > VDD –1.0 V @ IOH = –10.0 mA
2.1
2.3
2.5
Figure 20-6. Typical High-Side Driver Characteristics –
Port PTC4–PTC0 (VDD = 2.7 Vdc)
0
–10
–20
–40
0
25
85
IOH (mA)
–30
–40
–50
–60
–70
–80
–90
3
3.2
3.4
3.6
VOH > VDD –0.8 V @ IOH = –2.0 mA
VOH > VDD –1.5 V @ IOH = –10.0 mA
3.8
VOH (V)
4.0
4.2
4.4
4.6
Figure 20-7. Typical High-Side Driver Characteristics –
Ports PTB7–PTB0, PTC6–PTC5, PTD7–PTD0, and PTE1–PTE0 (VDD = 5.5 Vdc)
0
IOH (mA)
–5
–40
0
25
85
–10
–15
–20
–25
1.3
1.5
1.7
1.9
VOH (V)
VOH > VDD –0.3 V @ IOH = –0.6 mA
VOH > VDD –1.0 V @ IOH = –4.0 mA
2.1
2.3
2.5
Figure 20-8. Typical High-Side Driver Characteristics –
Ports PTB7–PTB0, PTC6–PTC5, PTD7–PTD0, and PTE1–PTE0 (VDD = 2.7 Vdc)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
264
Freescale Semiconductor
Output Low-Voltage Characteristics
20.14 Output Low-Voltage Characteristics
35
30
–40
0
25
85
IOL (mA)
25
20
15
10
5
0
0
0.2
0.4
0.6
0.8
VOL (V)
1.0
1.2
1.4
1.6
VOL < 0.4 V @ IOL = 1.6 mA
VOL < 1.5 V @ IOL = 10.0 mA
Figure 20-9. Typical Low-Side Driver Characteristics –
Port PTA7–PTA0 (VDD = 5.5 Vdc)
14
12
–40
0
25
85
IOL (mA)
10
8
6
4
2
0
0.2
0.4
0.6
0.8
1.0
VOL (V)
1.2
1.4
1.6
VOL < 0.3 V @ IOL = 0.5 mA
VOL < 1.0 V @ IOL = 6.0 mA
Figure 20-10. Typical Low-Side Driver Characteristics –
Port PTA7–PTA0 (VDD = 2.7 Vdc)
60
IOL (mA)
50
40
–40
0
25
85
30
20
10
0
0.4
0.6
0.8
1.0
1.2
1.4
1.6
VOL (V)
VOL < 1.5 V @ IOL = 20 mA
Figure 20-11. Typical Low-Side Driver Characteristics –
Port PTC4–PTC0 (VDD = 4.5 Vdc)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
265
Electrical Specifications
30
25
–40
0
25
85
IOL (mA)
20
15
10
5
0
0.2
0.4
0.6
0.8
1.0
VOL (V)
1.2
1.6
1.4
VOL < 0.8 V @ IOL = 10 mA
Figure 20-12. Typical Low-Side Driver Characteristics –
Port PTC4–PTC0 (VDD = 2.7 Vdc)
35
30
–40
0
25
85
25
IOL (mA)
20
15
10
5
0
0
0.2
0.4
0.6
0.8
VOL (V)
1.0
1.2
1.6
1.4
VOL < 0.4 V @ IOL = 1.6 mA
VOL < 1.5 V @ IOL = 10.0 mA
Figure 20-13. Typical Low-Side Driver Characteristics –
Ports PTB7–PTB0, PTC6–PTC5, PTD7–PTD0, and PTE1–PTE0 (VDD = 5.5 Vdc)
14
12
–40
0
25
85
IOL (mA)
10
8
6
4
2
0
0
0.2
0.4
0.6
0.8
VOL (V)
1.0
1.2
1.4
1.6
VOL < 0.3 V @ IOL = 0.5 mA
VOL < 1.0 V @ IOL = 6.0 mA
Figure 20-14. Typical Low-Side Driver Characteristics –
Ports PTB7–PTB0, PTC6–PTC5, PTD7–PTD0, and PTE1–PTE0 (VDD = 2.7 Vdc)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
266
Freescale Semiconductor
Typical Supply Currents
20.15 Typical Supply Currents
16
14
12
IDD (mA)
10
8
6
4
5.5 V
3.6 V
2
0
0
1
2
3
4
5
fBUS (MHz)
6
7
8
9
Figure 20-15. Typical Operating IDD, with All Modules
Turned On (–40°C to 85°C)
5.0
4.5
4.0
3.5
IDD (mA)
3.0
2.5
2.0
1.5
1.0
5.5 V
3.6 V
0.5
0
0
1
2
3
4
fBUS (MHz)
5
6
7
8
Figure 20-16. Typical Wait Mode IDD, with all Modules Disabled
(–40°C to 85°C)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
267
Electrical Specifications
20.16 ADC Characteristics
Characteristic(1)
Symbol
Min
Max
Unit
Comments
Supply voltage
VDDA
2.7
(VDD min)
5.5
(VDD max)
V
VDDA should be tied to the
same potential as VDD via
separate traces.
Input voltages
VADIN
0
VDDA
V
Resolution
BAD
8
8
Bits
Absolute accuracy
(VREFL = 0 V,
VREFH = VDDA = 5 V ± 10%)
AAD
—
±1
LSB
Includes quantization
ADC internal clock
fADIC
0.5
1.048
MHz
tAIC = 1/fADIC, tested only
at 1 MHz
Conversion range
RAD
VREFL
VREFH
V
VSSA ≤ VADIN ≤ VDDA
Power-up time
tADPU
16
ADC voltage reference high
VREFH
VSSA – 0.1
VDDA + 0.1
V
VREFL ≤ VREFH
ADC voltage reference low
VREFL
VSSA – 0.1
VDDA + 0.1
V
VREFL ≤ VREFH
tADC
16
17
tAIC cycles
tADS
5
—
tAIC cycles
Zero input reading(3)
ZADI
00
01
Hex
VIN = VREFL
reading(3)
FADI
FE
FF
Hex
VIN = VREFH
CADI
—
8
pF
Not tested
—
—
±1
μA
Conversion time
Sample time
Full-scale
(2)
Input capacitance
leakage(4)
Input
Port B
tAIC cycles
1. VDD = 5.0 Vdc ± 10%, VSS = 0 Vdc, VDDA = 5.0 Vdc ± 10%, VSSA = 0 Vdc, VREFH = 5.0 Vdc ± 10%, VREFL = 0
2. Source impedances greater than 10 kΩ adversely affect internal RC charging time during input sampling.
3. Zero-input/full-scale reading requires sufficient decoupling measures for accurate conversions.
4. The external system error caused by input leakage current is approximately equal to the product of R source and input
current.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
268
Freescale Semiconductor
5.0-V SPI Characteristics
20.17 5.0-V SPI Characteristics
Diagram
Number(1)
Characteristic(2)
Symbol
Min
Max
Unit
Operating frequency
Master
Slave
fOP(M)
fOP(S)
fOP/128
dc
fOP/2
fOP
MHz
MHz
1
Cycle time
Master
Slave
tCYC(M)
tCYC(S)
2
1
128
—
tCYC
tCYC
2
Enable lead time
tLead(S)
1
—
tCYC
3
Enable lag time
tLag(S)
1
—
tCYC
4
Clock (SPSCK) high time
Master
Slave
tSCKH(M)
tSCKH(S)
tCYC –25
1/2 tCYC –25
64 tCYC
—
ns
ns
5
Clock (SPSCK) low time
Master
Slave
tSCKL(M)
tSCKL(S)
tCYC –25
1/2 tCYC –25
64 tCYC
—
ns
ns
6
Data setup time (inputs)
Master
Slave
tSU(M)
tSU(S)
30
30
—
—
ns
ns
7
Data hold time (inputs)
Master
Slave
tH(M)
tH(S)
30
30
—
—
ns
ns
8
Access time, slave(3)
CPHA = 0
CPHA = 1
tA(CP0)
tA(CP1)
0
0
40
40
ns
ns
9
Disable time, slave(4)
tDIS(S)
—
40
ns
10
Data valid time, after enable edge
Master
Slave(5)
tV(M)
tV(S)
—
—
50
50
ns
ns
11
Data hold time, outputs, after enable edge
Master
Slave
tHO(M)
tHO(S)
0
0
—
—
ns
ns
1. Numbers refer to dimensions in Figure 20-17 and Figure 20-18.
2. All timing is shown with respect to 20% VDD and 70% VDD, unless noted; 100 pF load on all SPI pins.
3. Time to data active from high-impedance state
4. Hold time to high-impedance state
5. With 100 pF on all SPI pins
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
269
Electrical Specifications
20.18 3.0-V SPI Characteristics
Diagram
Number(1)
Characteristic(2)
Symbol
Min
Max
Unit
Operating frequency
Master
Slave
fOP(M)
fOP(S)
fOP/128
dc
fOP/2
fOP
MHz
MHz
1
Cycle time
Master
Slave
tCYC(M)
tCYC(S)
2
1
128
—
tCYC
tCYC
2
Enable lead time
tLead(s)
1
—
tCYC
3
Enable lag time
tLag(s)
1
—
tCYC
4
Clock (SPSCK) high time
Master
Slave
tSCKH(M)
tSCKH(S)
tCYC –35
1/2 tCYC –35
64 tCYC
—
ns
ns
5
Clock (SPSCK) low time
Master
Slave
tSCKL(M)
tSCKL(S)
tCYC –35
1/2 tCYC –35
64 tCYC
—
ns
ns
6
Data setup time (inputs)
Master
Slave
tSU(M)
tSU(S)
40
40
—
—
ns
ns
7
Data hold time (inputs)
Master
Slave
tH(M)
tH(S)
40
40
—
—
ns
ns
8
Access time, slave(3)
CPHA = 0
CPHA = 1
tA(CP0)
tA(CP1)
0
0
50
50
ns
ns
9
Disable time, slave(4)
tDIS(S)
—
50
ns
10
Data valid time, after enable edge
Master
Slave(5)
tV(M)
tV(S)
—
—
60
60
ns
ns
11
Data hold time, outputs, after enable edge
Master
Slave
tHO(M)
tHO(S)
0
0
—
—
ns
ns
1. Numbers refer to dimensions in Figure 20-17 and Figure 20-18.
2. All timing is shown with respect to 20% VDD and 70% VDD, unless noted; 100 pF load on all SPI pins.
3. Time to data active from high-impedance state
4. Hold time to high-impedance state
5. With 100 pF on all SPI pins
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
270
Freescale Semiconductor
3.0-V SPI Characteristics
SS
INPUT
SS PIN OF MASTER HELD HIGH
1
SPSCK OUTPUT
CPOL = 0
NOTE
SPSCK OUTPUT
CPOL = 1
NOTE
5
4
5
4
6
MISO
INPUT
MSB IN
BITS 6–1
11
MOSI
OUTPUT
MASTER MSB OUT
7
LSB IN
10
11
BITS 6–1
MASTER LSB OUT
Note: This first clock edge is generated internally, but is not seen at the SPSCK pin.
a) SPI Master Timing (CPHA = 0)
SS
INPUT
SS PIN OF MASTER HELD HIGH
1
SPSCK OUTPUT
CPOL = 0
5
NOTE
4
SPSCK OUTPUT
CPOL = 1
5
NOTE
4
6
MISO
INPUT
MSB IN
10
MOSI
OUTPUT
BITS 6–1
11
MASTER MSB OUT
7
LSB IN
10
BITS 6–1
MASTER LSB OUT
Note: This last clock edge is generated internally, but is not seen at the SPSCK pin.
b) SPI Master Timing (CPHA = 1)
Figure 20-17. SPI Master Timing
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
271
Electrical Specifications
SS
INPUT
3
1
SPSCK INPUT
CPOL = 0
5
4
2
SPSCK INPUT
CPOL = 1
5
4
9
8
MISO
INPUT
SLAVE
MSB OUT
6
MOSI
OUTPUT
BITS 6–1
7
NOTE
11
11
10
MSB IN
SLAVE LSB OUT
BITS 6–1
LSB IN
Note: Not defined but normally MSB of character just received
a) SPI Slave Timing (CPHA = 0)
SS
INPUT
1
SPSCK INPUT
CPOL = 0
5
4
2
3
SPSCK INPUT
CPOL = 1
8
MISO
OUTPUT
MOSI
INPUT
5
4
10
NOTE
9
SLAVE
MSB OUT
6
7
BITS 6–1
11
10
MSB IN
SLAVE LSB OUT
BITS 6–1
LSB IN
Note: Not defined but normally LSB of character previously transmitted
b) SPI Slave Timing (CPHA = 1)
Figure 20-18. SPI Slave Timing
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
272
Freescale Semiconductor
Timer Interface Module Characteristics
20.19 Timer Interface Module Characteristics
Characteristic
Input capture pulse width
Symbol
Min
Max
Unit
tTIH, tTIL
1
—
tCYC
20.20 Memory Characteristics
Characteristic
Symbol
Min
Typ
Max
Unit
VRDR
1.3
—
—
V
—
1
—
—
MHz
fRead(1)
8k
—
8M
Hz
Flash page erase time
1 k cycles
tErase
0.9
3.6
1
4
1.1
5.5
ms
Flash mass erase time
tMErase
4
—
—
ms
Flash PGM/ERASE to HVEN set up time
tNVS
10
—
—
μs
Flash high-voltage hold time
tNVH
5
—
—
μs
Flash high-voltage hold time (mass erase)
tNVHL
100
—
—
μs
Flash program hold time
tPGS
5
—
—
μs
Flash program time
tPROG
30
—
40
μs
Flash return to read time
tRCV(2)
1
—
—
μs
—
—
4
ms
RAM data retention voltage
Flash program bus clock frequency
Flash read bus clock frequency
Flash cumulative program HV period
(3)
tHV
Flash program endurance(4)
—
10k
100k
—
Cycles
Flash data retention time(5)
—
15
100
—
Years
1. fRead is defined as the frequency range for which the Flash memory can be read.
2. tRCV is defined as the time it needs before the Flash can be read after turning off the high voltage charge pump, by clearing
HVEN to 0.
3. tHV is defined as the cumulative high voltage programming time to the same row before next erase.
tHV must satisfy this condition: tNVS + tNVH + tPGS + (tPROG × 32) ≤ tHV maximum.
4. Typical endurance was evaluated for this product family. For additional information on how Freescale defines Typical
Endurance, please refer to Engineering Bulletin EB619.
5. Typical data retention values are based on intrinsic capability of the technology measured at high temperature and de-rated
to 25°C using the Arrhenius equation. For additional information on how Freescale defines Typical Data Retention, please
refer to Engineering Bulletin EB618.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
273
Electrical Specifications
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
274
Freescale Semiconductor
Chapter 21
Ordering Information and Mechanical Specifications
21.1 Introduction
This section contains ordering numbers for the MC68HC908GT16 and MC68HC908GT8 and gives the
dimensions for:
• 42-pin shrink dual in-line package (case 858-01)
• 44-pin plastic quad flat pack (case 824A-01)
The following figures show the latest package drawings at the time of this publication. To make sure that
you have the latest package specifications, contact your local Freescale Semiconductor sales office.
21.2 MC Order Numbers
Table 21-1. MC Order Numbers
Operating
Temperature Range
Package
MC908GT16CB
–40°C to +85°C
42-pin SDIP
MC908GT16CFB
–40°C to +85°C
44-pin QFP
MC908GT8CB
–40°C to +85°C
42-pin SDIP
MC908GT8CFB
–40°C to +85°C
44-pin QFP
MC Order Number
MC908GTXX X XX E
FAMILY
Pb FREE
PACKAGE DESIGNATOR
TEMPERATURE RANGE
Figure 21-1. Device Numbering System
21.3 Package Dimensions
Refer to the following pages for detailed package dimensions.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
275
Appendix A
MC68HC08GT16
A.1 Introduction
This section introduces the MC68HC08GT16, the ROM part equivalent to the MC68HC908GT16. The
entire data book apply to this ROM device, with exceptions outlined in this appendix.
Table A-1. Summary of MC68HC08GT16 and MC68HC908GT16 Differences
MC68HC08GT16
MC68HC908GT16
Memory ($C000–$FDFF)
15,872 bytes ROM
15,872 bytes Flash
User vectors ($FFDC–$FFFF)
36 bytes ROM
36 bytes Flash
Registers at $FE08 and $FF7E
Not used;
Locations are reserved.
Flash related registers.
$FE08 — FLCR
$FF7E — FLBPR
Registers at $FF80 and $FF81
ICG trim registers with fixed values.
ICG user trim registers.
Monitor ROM
Used for testing purposes only.
Used for testing and Flash programming/erasing.
A.2 MCU Block Diagram
Figure A-1 shows the block diagram of the MC68HC08GT16.
A.3 Memory Map
The MC68HC08GT16 has 15,872 bytes of user ROM from $C000 to $FDFF, and 36 bytes of user ROM
vectors from $FFDC to $FFFF. On the MC68HC908GT16, these memory locations are Flash memory.
Table A-2 shows the memory map of the MC68HC08GT16.
A.4 Reserved Registers
The two registers at $FE08 and $FF7E are reserved locations on the MC68HC08GT16.
On the MC68HC908GT16, these two locations are the Flash control register and the Flash block protect
register respectively.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
281
MC68HC08GT16
8-BIT KEYBOARD
INTERRUPT MODULE
USER ROM VECTOR SPACE — 36 BYTES
PTE4/OSC1
PTE3/OSC2
INTERNAL CLOCK
GENERATOR MODULE
RST(3)
SYSTEM INTEGRATION
MODULE
IRQ(3)
SINGLE EXTERNAL
INTERRUPT MODULE
VREFL
DDRA
PTD7/T2CH1(1)
PTD6/T2CH0(1)
PTD5/T1CH1(1)
PTD4/T1CH0(1)
PTD3/SPSCK(1)
PTD2/MOSI(1)
PTD1/MISO(1)
PTD0/SS(1)
PTE2
PTE1/RxD
PTE0/TxD
SERIAL PERIPHERAL
INTERFACE MODULE
MONITOR MODULE
8-BIT ANALOG-TO-DIGITAL
CONVERTER MODULE
POWER
PTC6(1)
PTC5(1)
PTC4(1)(2)
PTC3(1)(2)
PTC2(1)(2)
PTC1(1)(2)
PTC0(1)(2)
SERIAL COMMUNICATIONS
INTERFACE MODULE
COMPUTER OPERATING
PROPERLY MODULE
POWER-ON RESET
MODULE
VDD
VSS
VDDA
VSSA
2-CHANNEL TIMER INTERFACE
MODULE 2
DDRD
MONITOR ROM (ROM Block) — 649 BYTES
MONITOR ROM (Jump Table) — 24 BYTES
2-CHANNEL TIMER INTERFACE
MODULE 1
PORTA
USER RAM — 512 BYTES
PORTB
DUAL VOLTAGE
LOW-VOLTAGE INHIBIT MODULE
PTB7/AD7
PTB6/AD6
PTB5/AD5
PTB4/AD4
PTB3/AD3
PTB2/AD2
PTB1/AD1
PTB0/AD0
PORTC
15,872 BYTES
PTA7/KBD7–
PTA0/KBD0(1)
PORTD
USER ROM
DDRB
SINGLE BREAKPOINT BREAK
MODULE
DDRC
CONTROL AND STATUS
REGISTERS — 64 BYTES
MONITOR ROM (Monitor Block) — 350 BYTES
VREFH
PROGRAMMABLE TIMEBASE
MODULE
ARITHMETIC/LOGIC
UNIT (ALU)
MEMORY MAP
MODULE
DDRE
CPU
REGISTERS
PORTE
INTERNAL BUS
M68HC08 CPU
SECURITY
MODULE
CONFIGURATION REGISTER 1
MODULE
CONFIGURATION REGISTER 2
MODULE
MONITOR MODE ENTRY
MODULE
1. Ports are software configurable with pullup device if input port.
2. Higher current drive port pins
3. Pin contains integrated pullup device
Figure A-1. MC68HC08GT16 Block Diagram
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
282
Freescale Semiconductor
Reserved Registers
$0000
↓
$003F
$0040
↓
$023F
$0240
↓
$1B4F
$1B50
↓
$1DD8
$1DD9
↓
$BFFF
I/O REGISTERS
64 BYTES
RAM
512 BYTES
UNIMPLEMENTED
6416 BYTES
MONITOR ROM (ROM BLOCK)
649 BYTES
UNIMPLEMENTED
41,511 BYTES
$C000
↓
ROM
15,872 BYTES
$FDFF
$FE00
SIM BREAK STATUS REGISTER (SBSR)
$FE01
SIM RESET STATUS REGISTER (SRSR)
$FE02
RESERVED (SUBAR)
$FE03
SIM BREAK FLAG CONTROL REGISTER (SBFCR)
$FE04
INTERRUPT STATUS REGISTER 1 (INT1)
$FE05
INTERRUPT STATUS REGISTER 2 (INT2)
$FE06
INTERRUPT STATUS REGISTER 3 (INT3)
$FE07
RESERVED
$FE08
RESERVED
$FE09
BREAK ADDRESS REGISTER HIGH (BRKH)
$FE0A
BREAK ADDRESS REGISTER LOW (BRKL)
$FE0B
BREAK STATUS AND CONTROL REGISTER (BRKSCR)
$FE0C
LVI STATUS REGISTER (LVISR)
$FE0D
↓
$FE0F
$FE10
↓
$FE1F
UNIMPLEMENTED
3 BYTES
UNIMPLEMENTED
16 BYTES
RESERVED FOR COMPATIBILITY WITH MONITOR CODE
FOR A-FAMILY PART
Table A-2. MC68HC08GT16 Memory Map
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
283
MC68HC08GT16
$FE20
↓
$FF7D
$FF7E
MONITOR ROM (MONITOR BLOCK)
350 BYTES
RESERVED
$FF7F
MONITOR ROM (JUMP TABLE) 1 BYTE
$FF80
ICG TRIM REGISTER 5V (ICGTR5) FIX VALUE
$FF81
ICG TRIM REGISTER 3V (ICGTR3) FIX VALUE
$FF82
↓
$FF96
$FF97
↓
$FFDB
$FFDC
↓
$FFFF(1)
MONITOR ROM (JUMP TABLE)
21 BYTES
UNIMPLEMENTED
69 BYTES
ROM VECTORS
36 BYTES
1. $FFF6–$FFFD reserved for eight security bytes
Table A-2. MC68HC08GT16 Memory Map (Continued)
A.5 ICG Trim Registers
The two ICG trim registers at $FF80 and $FF81 are masked with fixed values on the MC68HC08GT16.
These are not trim values. These registers are available for compatibility with the MC68HC908GT16 only.
On the MC68HC908GT16, these two trim registers are used to store user trim values.
A.6 Monitor ROM
The monitor program on the MC68HC08GT16 is for device testing only.
A.7 ADC Reference Pins (VREFH and VREFL)
VREFH must be connected to the same voltage potential as the analog supply pin, VDDA. VREFL must be
connected to the same voltage potential as the analog supply pin, VSSA.
A.8 Electrical Specifications
Electrical specifications for the MC68HC908GT16 apply to the MC68HC08GT16, except for the
parameters indicated below.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
284
Freescale Semiconductor
Electrical Specifications
A.8.1 5.0-V DC Electrical Characteristics
Characteristic(1)
Symbol
Min
Typ(2)
Max
Unit
VOH
VOH
VOH
IOH1
VDD – 0.8
VDD – 1.5
VDD – 1.5
—
—
—
—
—
—
—
—
50
V
V
V
mA
IOH2
—
—
50
mA
IOHT
—
—
100
mA
VOL
VOL
VOL
IOL1
—
—
—
—
—
—
—
—
0.4
1.5
1.5
50
V
V
V
mA
IOL2
—
—
50
mA
IOLT
—
—
100
mA
Input high voltage
All ports, IRQ, RST, OSC1
VIH
0.7 × VDD
—
VDD
V
Input low voltage
All ports, IRQ, RST, OSC1
VIL
VSS
—
0.2 × VDD
V
IINJ
– 2.0
—
+ 2.0
mA
IINJTOT
– 25
—
+25
mA
Output high voltage
(ILoad = –2.0 mA) all I/O pins
(ILoad = –10.0 mA) all I/O pins
(ILoad = –20.0 mA) pins PTC0–PTC4 only
Maximum combined IOH for port C, port E,
port PTD0–PTD3
Maximum combined IOH for port PTD4–PTD7,
port A, port B
Maximum total IOH for all port pins
Output low voltage
(ILoad = 1.6 mA) all I/O pins
(ILoad = 10 mA) all I/O pins
(ILoad = 20mA) pins PTC0–PTC4 only
Maximum combined IOL for port C, port E,
port PTD0–PTD3
Maximum combined IOL for port PTD4–PTD7,
port A, port B
Maximum total IOL for all port pins
DC injection current, all ports(3)
Total DC current injection (sum of all
I/O)(3)
IIL
—
—
±10
μA
IIn
—
—
±1
μA
Pullup resistors (as input only)
Ports PTA7/KBD7–PTA0/KBD0, PTC6–PTC0,
PTD7/T2CH1–PTD0/SS
RPU
20
30
65
kΩ
Capacitance
Ports (as input or output)
COut
CIn
—
—
—
—
12
8
pF
Monitor mode entry voltage
VTST
VDD + 2.5
—
VDD + 4.0
V
Low-voltage inhibit, trip falling voltage
VTRIPF
3.90
4.25
4.50
V
Low-voltage inhibit, trip rising voltage
VTRIPR
4.00
4.35
4.60
V
VHYS
—
100
—
mV
POR rearm voltage(5)
VPOR
0
—
100
mV
POR reset voltage(6)
VPORRST
0
700
—
mV
RPOR
0.035
—
—
V/ms
I/O ports Hi-Z leakage
current(4)
Input current
Low-voltage inhibit reset/recover hysteresis
(VTRIPF + VHYS = VTRIPR)
POR rise time ramp rate(7)
1. VDD = 5.0 Vdc ± 10%, VSS = 0 Vdc, TA = TA (min) to TA (max), unless otherwise noted
2. Typical values reflect average measurements at midpoint of voltage range, 25°C only.
3. Some disturbance of the ADC accuracy is possible during any injection event and is dependent on board layout and power
supply decoupling. This parameter is guaranteed by characterization.
4. Pullups and pulldowns are disabled. Port B leakage is specified in 20.16 ADC Characteristics.
5. Maximum is highest voltage that POR is guaranteed.
6. Maximum is highest voltage that POR is possible.
7. If minimum VDD is not reached before the internal POR reset is released, RST must be driven low externally until minimum
VDD is reached.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
285
MC68HC08GT16
A.8.2 3.0-V DC Electrical Characteristics
Characteristic(1)
Symbol
Min
Typ(2)
Max
Unit
VOH
VOH
VOH
IOH1
VDD – 0.3
VDD – 1.0
VDD –1.0
—
—
—
—
—
—
—
—
30
V
V
V
mA
IOH2
—
—
30
mA
IOHT
—
—
60
mA
VOL
VOL
VOL
IOL1
—
—
—
—
—
—
—
—
0.3
1.0
1.0
30
V
V
V
mA
IOL2
—
—
30
mA
IOLT
—
—
60
mA
Input high voltage
All ports, IRQ, RST, OSC1
VIH
0.7 × VDD
—
VDD
V
Input low voltage
All ports, IRQ, RST, OSC1
VIL
VSS
—
0.3 × VDD
V
IINJ
– 2.0
—
+ 2.0
mA
IINJTOT
– 25
—
+25
mA
Output high voltage
(ILoad = –0.6 mA) all I/O pins
(ILoad = –4.0 mA) all I/O pins
(ILoad = –10.0 mA) pins PTC0–PTC4 only
Maximum combined IOH for port C, port E,
port PTD0–PTD3
Maximum combined IOH for port PTD4–PTD7,
port A, port B
Maximum total IOH for all port pins
Output low voltage
(ILoad = 0.5 mA) all I/O pins
(ILoad = 5.0 mA) all I/O pins
(ILoad = 10.0 mA) pins PTC0–PTC4 only
Maximum combined IOL for port C, port E,
port PTD0–PTD3
Maximum combined IOL for port PTD4–PTD7,
port A, port B
Maximum total IOL for all port pins
DC injection current, all ports(3)
Total DC current injection (sum of all
I/O)(3)
IIL
—
—
±10
μA
IIn
—
—
±1
μA
Pullup resistors (as input only)
Ports PTA7/KBD7–PTA0/KBD0, PTC6–PTC0,
PTD7/T2CH1–PTD0/SS
RPU
20
30
65
kΩ
Capacitance
Ports (as input or output)
COut
CIn
—
—
—
—
12
8
pF
Monitor mode entry voltage
VTST
VDD + 2.5
—
VDD + 4.0
V
Low-voltage inhibit, trip falling voltage
VTRIPF
2.40
2.55
2.70
V
Low-voltage inhibit, trip rising voltage
VTRIPR
2.50
2.65
2.80
V
VHYS
—
60
—
mV
POR rearm voltage(5)
VPOR
0
—
100
mV
POR reset voltage(6)
VPORRST
0
700
—
mV
RPOR
0.02
—
—
V/ms
I/O ports Hi-Z leakage
current(4)
Input current
Low-voltage inhibit reset/recover hysteresis
(VTRIPF + VHYS = VTRIPR)
POR rise time ramp rate(7)
1. VDD = 3.0 Vdc ± 10%, VSS = 0 Vdc, TA = TA (min) to TA (max), unless otherwise noted
2. Typical values reflect average measurements at midpoint of voltage range, 25°C only.
3. Some disturbance of the ADC accuracy is possible during any injection event and is dependent on board layout and power
supply decoupling. This parameter is guaranteed by characterization.
4. Pullups and pulldowns are disabled.
5. Maximum is highest voltage that POR is guaranteed.
6. Maximum is highest voltage that POR is possible.
7. If minimum VDD is not reached before the internal POR reset is released, RST must be driven low externally until minimum
VDD is reached.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
286
Freescale Semiconductor
Electrical Specifications
A.8.3 Supply Current Characteristics
Voltage
Bus
Frequency
(MHz)
Symbol
Typ(2)
Max
Unit
Run mode VDD supply current(3)
5.0
3.0
8
4
RIDD
15
4.5
20
8
mA
Wait mode VDD supply current(4)
5.0
3.0
8
4
WIDD
4
1.5
8
4
mA
1
20
300
50
500
5
—
—
—
—
1
12
200
30
300
3
—
—
—
—
Characteristic(1)
Stop mode VDD supply current(5)
25°C
25°C with TBM enabled(6)
25°C with LVI and TBM enabled(6)
–40°C to 85°C with TBM enabled(6)
–40°C to 85°C with LVI and TBM enabled(6)
Stop mode VDD supply current(5)
25°C
25°C with TBM enabled(6)
25°C with LVI and TBM enabled(6)
–40°C to 85°C with TBM enabled(6)
–40°C to 85°C with LVI and TBM enabled(6)
5.0
3.0
SIDD
SIDD
μA
μA
1. VDD = 5.0 Vdc ± 10%, VSS = 0 Vdc, TA = TA (min) to TA (max), unless otherwise noted.
2. Typical values reflect average measurements at 25°C only.
3. Run (operating) IDD measured using external square wave clock source (fOSC = 32 MHz for 5 V and fOSC = 16 MHz for
3 V). All inputs 0.2 V from rail. No dc loads. Less than 100 pF on all outputs. Measured with all modules enabled.
4. Wait IDD measured using external square wave clock source (fOSC = 32 MHz for 5 V and fOSC = 16 MHz for 3 V). All inputs
0.2 V from rail. No dc loads. Less than 100 pF on all outputs. All ports configured as inputs. Measured with ICG and LVI
enabled.
5. Stop IDD is measured with OSC1 = VSS.
6. Stop IDD with TBM enabled is measured using an external square wave clock source (fOSC = 32 MHz for 5 V and
fOSC = 16 MHz for 3 V).
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
287
MC68HC08GT16
A.9 ADC Characteristics
Characteristic(1)
Symbol
Min
Max
Unit
Comments
Supply voltage
VDDA
2.7
(VDD min)
5.5
(VDD max)
V
VDDA should be tied to the
same potential as VDD via
separate traces.
Input voltages
VADIN
0
VDDA
V
Resolution
BAD
8
8
Bits
Absolute accuracy
(VREFL = VSSA, VREFH = VDDA)
AAD
—
± 1.5
LSB
Includes quantization
ADC internal clock
fADIC
0.5
1.048
MHz
tAIC = 1/fADIC, tested only
at 1 MHz
Conversion range
RAD
VREFL
VREFH
V
VSSA ≤ VADIN ≤ VDDA
Power-up time
tADPU
16
ADC voltage reference high
VREFH
VSSA – 0.1
VDDA + 0.1
V
VREFL ≤ VREFH
ADC voltage reference low
VREFL
VSSA – 0.1
VDDA + 0.1
V
VREFL ≤ VREFH
Conversion time
tADC
16
17
tAIC cycles
Sample time(2)
tADS
5
—
tAIC cycles
Zero input reading(3)
ZADI
00
01
Hex
VIN = VREFL
reading(3)
FADI
FE
FF
Hex
VIN = VREFH
CADI
—
8
pF
Not tested
—
—
±1
μA
Full-scale
Input capacitance
Input leakage(4)
Port B
tAIC cycles
1. VDD = 5.0 Vdc ± 10%, VSS = 0 Vdc, VDDA = 5.0 Vdc ± 10%, VSSA = 0 Vdc, VREFH = 5.0 Vdc ± 10%, VREFL = 0
2. Source impedances greater than 10 kΩ adversely affect internal RC charging time during input sampling.
3. Zero-input/full-scale reading requires sufficient decoupling measures for accurate conversions.
4. The external system error caused by input leakage current is approximately equal to the product of R source and input
current.
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
288
Freescale Semiconductor
Order Numbers
A.9.1 Internal Oscillator Characteristics
Characteristic(1)
Internal oscillator base frequency(2), (3)
Internal oscillator tolerance
Internal oscillator multiplier
(4)
Symbol
Min
Typ
Max
Unit
fINTOSC
183.75
245
306.25
kHz
fOSC_TOL
–25
—
+25
%
N
1
—
127
—
1. VDD = 5.5 Vdc to 2.7 Vdc, VSS = 0 Vdc, TA = TA (min) to TA (max), unless otherwise noted
2. Internal oscillator is selectable through software for a maximum frequency.
Actual frequency will be multiplier (N) x base frequency.
3. fBus = (fINTOSC / 4) x N when internal clock source selected
4. Multiplier must be chosen to limit the maximum bus frequency of 4 MHz for 2.7-V operation and 8 MHz for 4.5-V operation.
A.9.2 Memory Characteristics
Characteristic
RAM data retention voltage
Symbol
Min
Max
Unit
VRDR
1.3
—
V
Note: Since MC68HC08GT16 is a ROM device, Flash memory electrical characteristics do not apply.
A.10 Order Numbers
These part numbers are generic numbers only. To place an order, ROM code must be submitted to the
ROM Processing Center (RPC).
MC Order Number
Package
Operating Temperature Range
RoHS Compliant
MC08GT16CBE
42-pin SDIP
–40 to +85°C
Yes
MC08GT16CFBE
44-pin QFP
–40 to +85°C
Yes
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
289
MC68HC08GT16
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
290
Freescale Semiconductor
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MC68HC908GT16
Rev. 5.0, 04/2007
RoHS-compliant and/or Pb-free versions of Freescale products have the functionality
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