ATtiny48-MMH

Features • High Performance, Low Power AVR® 8-Bit Microcontroller • Advanced RISC Architecture – 123 Powerful Instructions – Most Single Clock Cycle Execution – 32 x 8 General Purpose Working Registers – Fully Static Operation High Endurance Non-volatile Memory Segments – 4K/8K Bytes of In-System Self-Programmable Flash program memory(ATtiny48/88) – 64/64 Bytes EEPROM (ATtiny48/88) – 256/512 Bytes Internal SRAM (ATtiny48/88) – Write/Erase Cycles: 10,000 Flash/100,000 EEPROM – Data retention: 20 years at 85°C / 100 years at 25°C – Programming Lock for Software Security Peripheral Features – One 8-bit Timer/Counter with Separate Prescaler and Compare Mode – One 16-bit Timer/Counter with Prescaler, and Compare and Capture Modes – 8-channel 10-bit ADC in 32-lead TQFP and 32-pad QFN/MLF package – 6-channel 10-bit ADC in 28-pin PDIP and 28-pad QFN/MLF package – Master/Slave SPI Serial Interface – Byte-oriented 2-wire Serial Interface (Philips I2C Compatible) – Programmable Watchdog Timer with Separate On-chip Oscillator – On-chip Analog Comparator – Interrupt and Wake-up on Pin Change Special Microcontroller Features – debugWIRE On-chip Debug System – In-System Programmable via SPI Port – Power-on Reset and Programmable Brown-out Detection – Internal Calibrated Oscillator – External and Internal Interrupt Sources – Three Sleep Modes: Idle, ADC Noise Reduction and Power-down I/O and Packages – 28 Programmable I/O Lines in 32-lead TQFP and 32-pad QFN/MLF package – 24 Programmable I/O Lines in 28-pin PDIP and 28-pad QFN/MLF package – 28-pin PDIP, 32-lead TQFP, 28-pad QFN/MLF and 32-pad QFN/MLF Operating Voltage: – 1.8 – 5.5V Temperature Range: – -40°C to +85°C Speed Grade: – 0 – 4 MHz @ 1.8 – 5.5V – 0 – 8 MHz @ 2.7 – 5.5V – 0 – 12 MHz @ 4.5 – 5.5V Low Power Consumption – Active Mode: 1 MHz, 1.8V: 240µA – Power-down Mode: 0.1µA at 1.8V • • 8-bit Microcontroller with 4/8K Bytes In-System Programmable Flash ATtiny48/88 Preliminary • • • • • • Rev. 8008C–AVR–03/09 1. Pin Configurations Figure 1-1. Pinout of ATtiny48/88 TQFP Top View PD2 (INT0/PCINT18) PD1 (PCINT17) PD0 (PCINT16) PC6 (RESET/PCINT14) PC5 (ADC5/SCL/PCINT13) PC4 (ADC4/SDA/PCINT12) PC3 (ADC3/PCINT11) PC2 (ADC2/PCINT10) PDIP (PCINT14/RESET) PC6 (PCINT16) PD0 (PCINT17) PD1 (PCINT18/INT0) PD2 (PCINT19/INT1) PD3 (PCINT20/T0) PD4 VCC GND (PCINT6/CLKI) PB6 (PCINT7) PB7 (PCINT21/T1) PD5 (PCINT22/AIN0) PD6 (PCINT23/AIN1) PD7 (PCINT0/CLKO/ICP1) PB0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 28 27 26 25 24 23 22 21 20 19 18 17 16 15 PC5 (ADC5/SCL/PCINT13) PC4 (ADC4/SDA/PCINT12) PC3 (ADC3/PCINT11) PC2 (ADC2/PCINT10) PC1 (ADC1/PCINT9) PC0 (ADC0/PCINT8) GND PC7 (PCINT15) AVCC PB5 (SCK/PCINT5) PB4 (MISO/PCINT4) PB3 (MOSI/PCINT3) PB2 (SS/OC1B/PCINT2) PB1 (OC1A/PCINT1) 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 (PCINT19/INT1) PD3 (PCINT20/T0) PD4 (PCINT26) PA2 VCC GND (PCINT27) PA3 (PCINT6/CLKI) PB6 (PCINT7) PB7 1 2 3 4 5 6 7 8 PC1 (ADC1/PCINT9) PC0 (ADC0/PCINT8) PA1 (ADC7/PCINT25) GND PC7 (PCINT15) PA0 (ADC6/PCINT24) AVCC PB5 (SCK/PCINT5) (PCINT21/T1) PD5 (PCINT22/AIN0) PD6 (PCINT23/AIN1) PD7 (PCINT0/CLKO/ICP1) PB0 (PCINT1/OC1A) PB1 (PCINT2/SS/OC1B) PB2 (PCINT3/MOSI) PB3 (PCINT4/MISO) PB4 9 10 11 12 13 14 15 16 32 MLF Top View PD2 (INT0/PCINT18) PD1 (PCINT17) PD0 (PCINT16) PC6 (RESET/PCINT14) PC5 (ADC5/SCL/PCINT13) PC4 (ADC4/SDA/PCINT12) PC3 (ADC3/PCINT11) 28 27 26 25 24 23 22 32 31 30 29 28 27 26 25 PD2 (INT0/PCINT18) PD1 (PCINT17) PD0 (PCINT16) PC6 (RESET/PCINT14) PC5 (ADC5/SCL/PCINT13) PC4 (ADC4/SDA/PCINT12) PC3 (ADC3/PCINT11) PC2 (ADC2/PCINT10) 28 MLF Top View (PCINT19/INT1) PD3 (PCINT20/T0) PD4 VCC GND (PCINT6/CLKI) PB6 (PCINT7) PB7 (PCINT21/T1) PD5 1 2 3 4 5 6 7 21 20 19 18 17 16 15 PC2 (ADC2/PCINT10) PC1 (ADC1/PCINT9) PC0 (ADC0/PCINT8) GND PC7 (PCI NT15) AVCC PB5 (SCK/PCINT5) (PCINT19/INT1) PD3 (PCINT20/T0) PD4 (PCINT26) PA2 VCC GND (PCINT27) PA3 (PCINT6/CLKI) PB6 (PCINT7) PB7 1 2 3 4 5 6 7 8 24 23 22 21 20 19 18 17 PC1 (ADC1/PCINT9) PC0 (ADC0/PCINT8) PA1 (ADC7/PCINT25) GND PC7 (PCINT15) PA0 (ADC6/PCINT24) AVCC PB5 (SCK/PCINT5) 8 9 10 11 12 13 14 (PCINT22/AIN0) PD6 (PCINT23/AIN1) PD7 (PCINT0/CLKO/ICP1) PB0 (PCINT1/OC1A) PB1 (PCINT2/SS/OC1B) PB2 (PCINT3//MOSI) PB3 (PCINT4/MISO) PB4 NOTE: Bottom pad should be soldered to ground. NOTE: Bottom pad should be soldered to ground. 2 ATtiny48/88 8008C–AVR–03/09 (PCINT21/T1) PD5 (PCINT22/AIN0) PD6 (PCINT23/AIN1) PD7 (PCINT0/CLKO/ICP1) PB0 (PCINT1/OC1A) PB1 (PCINT2/SS/OC1B) PB2 (PCINT3/MOSI) PB3 (PCINT4/MISO) PB4 9 10 11 12 13 14 15 16 ATtiny48/88 1.1 1.1.1 Pin Descriptions VCC Digital supply voltage. 1.1.2 GND Ground. 1.1.3 Port A (PA3:0) (in 32-lead TQFP and 32-pad QFN/MLF packages, only) Port A is a 4-bit bi-directional I/O port with internal pull-up resistors (selected for each bit) in 32lead TQFP and 32-pad QFN/MLF package. The PA3..0 output buffers have symmetrical drive characteristics with both high sink and source capability. As inputs, Port A pins that are externally pulled low will source current if the pull-up resistors are activated. The Port A pins are tristated when a reset condition becomes active, even if the clock is not running. Port B (PB7:0) Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port B output buffers have symmetrical drive characteristics with both high sink and source capability. As inputs, Port B pins that are externally pulled low will source current if the pull-up resistors are activated. The Port B pins are tri-stated when a reset condition becomes active, even if the clock is not running. Depending on the clock selection fuse settings, PB6 can be used as input to the internal clock operating circuit. The various special features of Port B are elaborated in “Alternate Functions of Port B” on page 64 and “System Clock and Clock Options” on page 25. 1.1.4 1.1.5 Port C (PC7, PC5:0) Port C is a 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The PC7 and PC5..0 output buffers have symmetrical drive characteristics with both high sink and source capability. As inputs, Port C pins that are externally pulled low will source current if the pull-up resistors are activated. The Port C pins are tri-stated when a reset condition becomes active, even if the clock is not running. PC6/RESET If the RSTDISBL Fuse is programmed, PC6 is used as an I/O pin. Note that the electrical characteristics of PC6 differ from those of the other pins of Port C. If the RSTDISBL Fuse is unprogrammed, PC6 is used as a reset input. A low level on this pin for longer than the minimum pulse width will generate a reset, even if the clock is not running. The minimum pulse length is given in Table 21-3 on page 204. Shorter pulses are not guaranteed to generate a reset. The various special features of Port C are elaborated in “Alternate Functions of Port C” on page 67. 1.1.6 1.1.7 Port D (PD7:0) Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The PD7..4 output buffers have symmetrical drive characteristics with both high sink and source capabilities, while the PD3..0 output buffers have stronger sink capabilities. As inputs, Port D 3 8008C–AVR–03/09 pins that are externally pulled low will source current if the pull-up resistors are activated. The Port D pins are tri-stated when a reset condition becomes active, even if the clock is not running. The various special features of Port D are elaborated in “Alternate Functions of Port D” on page 70. 1.1.8 AVCC AVCC is the supply voltage pin for the A/D converter and a selection of I/O pins. This pin should be externally connected to VCC even if the ADC is not used. If the ADC is used, it is recommended this pin is connected to VCC through a low-pass filter, as described in “Analog Noise Canceling Techniques” on page 166. The following pins receive their supply voltage from AVCC: PC7, PC5:0 and (in 32-lead packages) PA1:0. All other I/O pins take their supply voltage from VCC. 4 ATtiny48/88 8008C–AVR–03/09 ATtiny48/88 2. Overview The ATtiny48/88 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced RISC architecture. By executing powerful instructions in a single clock cycle, the ATtiny48/88 achieves throughputs approaching 1 MIPS per MHz allowing the system designer to optimize power consumption versus processing speed. 2.1 Block Diagram Figure 2-1. Block Diagram GND VCC Watchdog Timer Watchdog Oscillator Power Supervision POR / BOD & RESET debugWIRE Program Logic Oscillator Circuits / Clock Generation Flash SRAM CPU EEPROM 8bit T/C 0 16bit T/C 1 A/D Conv. 2 6 DATABUS Internal Bandgap Analog Comp. SPI TWI PORT D (8) PORT B (8) PORT C (8) PORT A (4) RESET CLKI PD[0..7] PB[0..7] PC[0..7] PA[0..3] (in TQFP and MLF) The AVR core combines a rich instruction set with 32 general purpose working registers. All the 32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two independent registers to be accessed in one single instruction executed in one clock cycle. The resulting architecture is more code efficient while achieving throughputs up to ten times faster than conventional CISC microcontrollers. 5 8008C–AVR–03/09 The ATtiny48/88 provides the following features: 4/8K bytes of In-System Programmable Flash, 64/64 bytes EEPROM, 256/512 bytes SRAM, 24 general purpose I/O lines (28 I/Os in 32-lead TQFP and 32-pad QFN/MLF packages), 32 general purpose working registers, two flexible Timer/Counters with compare modes, internal and external interrupts, a byte-oriented 2-wire serial interface, an SPI serial port, a 6-channel 10-bit ADC (8 channels in 32-lead TQFP and 32pad QFN/MLF packages), a programmable Watchdog Timer with internal oscillator, and three software selectable power saving modes. Idle mode stops the CPU while allowing Timer/Counters, 2-wire serial interface, SPI port, and interrupt system to continue functioning. Power-down mode saves the register contents but freezes the oscillator, disabling all other chip functions until the next interrupt or hardware reset. ADC Noise Reduction mode stops the CPU and all I/O modules except ADC, and helps to minimize switching noise during ADC conversions. The device is manufactured using Atmel’s high density non-volatile memory technology. The On-chip ISP Flash allows the program memory to be reprogrammed In-System through an SPI serial interface, by a conventional non-volatile memory programmer, or by an on-chip boot program running on the AVR core. The boot program can use any interface to download the application program in the Flash memory. By combining an 8-bit RISC CPU with In-System SelfProgrammable Flash on a monolithic chip, the Atmel ATtiny48/88 is a powerful microcontroller that provides a highly flexible and cost effective solution to many embedded control applications. The ATtiny48/88 AVR is supported by a full suite of program and system development tools including: C compilers, macro assemblers, program debugger/simulators and evaluation kits. 2.2 Comparison Between ATtiny48 and ATtiny88 The ATtiny48 and ATtiny88 differ only in memory sizes. Table 2-1 summarizes the different memory sizes for the two devices. Table 2-1. Device ATtiny48 ATtiny88 Memory Size Summary Flash 4K Bytes 8K Bytes EEPROM 64 Bytes 64 Bytes RAM 256 Bytes 512 Bytes 6 ATtiny48/88 8008C–AVR–03/09 ATtiny48/88 3. Additional Information 3.1 Resources A comprehensive set of development tools, application notes and datasheets are available for download at http://www.atmel.com/avr. 3.2 About Code Examples This documentation contains simple code examples that briefly show how to use various parts of the device. These code examples assume that the part specific header file is included before compilation. Be aware that not all C compiler vendors include bit definitions in the header files and interrupt handling in C is compiler dependent. Please confirm with the C compiler documentation for more details. For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must be replaced with instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”. 3.3 Data Retention Reliability Qualification results show that the projected data retention failure rate is much less than 1 PPM over 20 years at 85°C or 100 years at 25°C. 3.4 Disclaimer Typical values contained in this datasheet are based on simulations and characterization of other AVR microcontrollers manufactured on the same process technology. Min and Max values will be available after the device is characterized. 7 8008C–AVR–03/09 4. AVR CPU Core 4.1 Introduction This section discusses the AVR core architecture in general. The main function of the CPU core is to ensure correct program execution. The CPU must therefore be able to access memories, perform calculations, control peripherals, and handle interrupts. 4.2 Architectural Overview Figure 4-1. Block Diagram of the AVR Architecture Data Bus 8-bit Flash Program Memory Program Counter Status and Control Instruction Register 32 x 8 General Purpose Registrers Interrupt Unit SPI Unit Watchdog Timer Indirect Addressing Instruction Decoder Direct Addressing ALU Control Lines Analog Comparator I/O Module1 Data SRAM I/O Module 2 I/O Module n EEPROM I/O Lines In order to maximize performance and parallelism, the AVR uses a Harvard architecture – with separate memories and buses for program and data. Instructions in the program memory are executed with a single level pipelining. While one instruction is being executed, the next instruction is pre-fetched from the program memory. This concept enables instructions to be executed in every clock cycle. The program memory is In-System Reprogrammable Flash memory. 8 ATtiny48/88 8008C–AVR–03/09 ATtiny48/88 The fast-access Register File contains 32 x 8-bit general purpose working registers with a single clock cycle access time. This allows single-cycle Arithmetic Logic Unit (ALU) operation. In a typical ALU operation, two operands are output from the Register File, the operation is executed, and the result is stored back in the Register File – in one clock cycle. Six of the 32 registers can be used as three 16-bit indirect address register pointers for Data Space addressing – enabling efficient address calculations. One of the these address pointers can also be used as an address pointer for look up tables in Flash program memory. These added function registers are the 16-bit X-, Y-, and Z-register, described later in this section. The ALU supports arithmetic and logic operations between registers or between a constant and a register. Single register operations can also be executed in the ALU. After an arithmetic operation, the Status Register is updated to reflect information about the result of the operation. Program flow is provided by conditional and unconditional jump and call instructions, able to directly address the whole address space. Most AVR instructions have a single 16-bit word format, but there are also 32-bit instructions. During interrupts and subroutine calls, the return address Program Counter (PC) is stored on the Stack. The Stack is effectively allocated in the general data SRAM, and consequently the Stack size is only limited by the total SRAM size and the usage of the SRAM. All user programs must initialize the SP in the Reset routine (before subroutines or interrupts are executed). The Stack Pointer (SP) is read/write accessible in the I/O space. The data SRAM can easily be accessed through the five different addressing modes supported in the AVR architecture. The memory spaces in the AVR architecture are all linear and regular memory maps. A flexible interrupt module has its control registers in the I/O space with an additional Global Interrupt Enable bit in the Status Register. All interrupts have a separate Interrupt Vector in the Interrupt Vector table. The interrupts have priority in accordance with their Interrupt Vector position. The lower the Interrupt Vector address, the higher the priority. The I/O memory space contains 64 addresses for CPU peripheral functions as Control Registers, SPI, and other I/O functions. The I/O Memory can be accessed directly, or as the Data Space locations following those of the Register File, 0x20 – 0x5F. In addition, the ATtiny48/88 has Extended I/O space from 0x60 – 0xFF in SRAM where only the ST/STS/STD and LD/LDS/LDD instructions can be used. 4.3 ALU – Arithmetic Logic Unit The high-performance AVR ALU operates in direct connection with all the 32 general purpose working registers. Within a single clock cycle, arithmetic operations between general purpose registers or between a register and an immediate are executed. The ALU operations are divided into three main categories – arithmetic, logical, and bit-functions. Some implementations of the architecture also provide a powerful multiplier supporting both signed/unsigned multiplication and fractional format. See the “Instruction Set” section for a detailed description. 4.4 Status Register The Status Register contains information about the result of the most recently executed arithmetic instruction. This information can be used for altering program flow in order to perform conditional operations. Note that the Status Register is updated after all ALU operations, as specified in the Instruction Set Reference. This will in many cases remove the need for using the dedicated compare instructions, resulting in faster and more compact code. 9 8008C–AVR–03/09 The Status Register is not automatically stored when entering an interrupt routine and restored when returning from an interrupt. This must be handled by software. The AVR Status Register – SREG – is defined as: Bit 7 I Read/Write Initial Value R/W 0 6 T R/W 0 5 H R/W 0 4 S R/W 0 3 V R/W 0 2 N R/W 0 1 Z R/W 0 0 C R/W 0 SREG • Bit 7 – I: Global Interrupt Enable The Global Interrupt Enable bit must be set for the interrupts to be enabled. The individual interrupt enable control is then performed in separate control registers. If the Global Interrupt Enable Register is cleared, none of the interrupts are enabled independent of the individual interrupt enable settings. The I-bit is cleared by hardware after an interrupt has occurred, and is set by the RETI instruction to enable subsequent interrupts. The I-bit can also be set and cleared by the application with the SEI and CLI instructions, as described in the instruction set reference. • Bit 6 – T: Bit Copy Storage The Bit Copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or destination for the operated bit. A bit from a register in the Register File can be copied into T by the BST instruction, and a bit in T can be copied into a bit in a register in the Register File by the BLD instruction. • Bit 5 – H: Half Carry Flag The Half Carry Flag H indicates a Half Carry in some arithmetic operations. Half Carry Is useful in BCD arithmetic. See the “Instruction Set Description” for detailed information. • Bit 4 – S: Sign Bit, S = N ⊕ V The S-bit is always an exclusive or between the Negative Flag N and the Two’s Complement Overflow Flag V. See the “Instruction Set Description” for detailed information. • Bit 3 – V: Two’s Complement Overflow Flag The Two’s Complement Overflow Flag V supports two’s complement arithmetics. See the “Instruction Set Description” for detailed information. • Bit 2 – N: Negative Flag The Negative Flag N indicates a negative result in an arithmetic or logic operation. See the “Instruction Set Description” for detailed information. • Bit 1 – Z: Zero Flag The Zero Flag Z indicates a zero result in an arithmetic or logic operation. See the “Instruction Set Description” for detailed information. • Bit 0 – C: Carry Flag The Carry Flag C indicates a carry in an arithmetic or logic operation. See the “Instruction Set Description” for detailed information. 10 ATtiny48/88 8008C–AVR–03/09 ATtiny48/88 4.5 General Purpose Register File The Register File is optimized for the AVR Enhanced RISC instruction set. In order to achieve the required performance and flexibility, the following input/output schemes are supported by the Register File: • One 8-bit output operand and one 8-bit result input • Two 8-bit output operands and one 8-bit result input • Two 8-bit output operands and one 16-bit result input • One 16-bit output operand and one 16-bit result input Figure 4-2 shows the structure of the 32 general purpose working registers in the CPU. Figure 4-2. AVR CPU General Purpose Working Registers 7 R0 R1 R2 … R13 General Purpose Working Registers R14 R15 R16 R17 … R26 R27 R28 R29 R30 R31 0x1A 0x1B 0x1C 0x1D 0x1E 0x1F X-register Low Byte X-register High Byte Y-register Low Byte Y-register High Byte Z-register Low Byte Z-register High Byte 0x0D 0x0E 0x0F 0x10 0x11 0 Addr. 0x00 0x01 0x02 Most of the instructions operating on the Register File have direct access to all registers, and most of them are single cycle instructions. As shown in Figure 4-2, each register is also assigned a data memory address, mapping them directly into the first 32 locations of the user Data Space. Although not being physically implemented as SRAM locations, this memory organization provides great flexibility in access of the registers, as the X-, Y- and Z-pointer registers can be set to index any register in the file. 11 8008C–AVR–03/09 4.5.1 The X-register, Y-register, and Z-register The registers R26..R31 have some added functions to their general purpose usage. These registers are 16-bit address pointers for indirect addressing of the data space. The three indirect address registers X, Y, and Z are defined as described in Figure 4-3. Figure 4-3. The X-, Y-, and Z-registers 15 X-register 7 R27 (0x1B) XH 0 7 R26 (0x1A) XL 0 0 15 Y-register 7 R29 (0x1D) 15 Z-register 7 R31 (0x1F) YH 0 7 R28 (0x1C) ZH 0 7 R30 (0x1E) YL 0 0 ZL 0 0 In the different addressing modes these address registers have functions as fixed displacement, automatic increment, and automatic decrement (see the instruction set reference for details). 4.6 Stack Pointer The Stack is mainly used for storing temporary data, for storing local variables and for storing return addresses after interrupts and subroutine calls. The Stack Pointer Register always points to the top of the Stack. Note that the Stack is implemented as growing from higher memory locations to lower memory locations. This implies that a Stack PUSH command decreases the Stack Pointer. The Stack Pointer points to the data SRAM Stack area where the Subroutine and Interrupt Stacks are located. This Stack space in the data SRAM must be defined by the program before any subroutine calls are executed or interrupts are enabled. The Stack Pointer should be set to point to RAMEND. The Stack Pointer is decremented by one when data is pushed onto the Stack with the PUSH instruction, and it is decremented by two when the return address is pushed onto the Stack with subroutine call or interrupt. The Stack Pointer is incremented by one when data is popped from the Stack with the POP instruction, and it is incremented by two when data is popped from the Stack with return from subroutine RET or return from interrupt RETI. The AVR Stack Pointer is implemented as two 8-bit registers in the I/O space. The number of bits actually used is implementation dependent. Note that the data space in some implementations of the AVR architecture is so small that only SPL is needed. In this case, the SPH Register will not be present. Bit 15 SP15 SP7 7 Read/Write R/W R/W Initial Value RAMEND RAMEND 14 SP14 SP6 6 R/W R/W RAMEND RAMEND 13 SP13 SP5 5 R/W R/W RAMEND RAMEND 12 SP12 SP4 4 R/W R/W RAMEND RAMEND 11 SP11 SP3 3 R/W R/W RAMEND RAMEND 10 SP10 SP2 2 R/W R/W RAMEND RAMEND 9 SP9 SP1 1 R/W R/W RAMEND RAMEND 8 SP8 SP0 0 R/W R/W RAMEND RAMEND SPH SPL 12 ATtiny48/88 8008C–AVR–03/09 ATtiny48/88 4.7 Instruction Execution Timing This section describes the general access timing concepts for instruction execution. The AVR CPU is driven by the CPU clock clkCPU, directly generated from the selected clock source for the chip. No internal clock division is used. Figure 4-4 shows the parallel instruction fetches and instruction executions enabled by the Harvard architecture and the fast-access Register File concept. This is the basic pipelining concept to obtain up to 1 MIPS per MHz with the corresponding unique results for functions per cost, functions per clocks, and functions per power-unit. Figure 4-4. The Parallel Instruction Fetches and Instruction Executions T1 T2 T3 T4 clkCPU 1st Instruction Fetch 1st Instruction Execute 2nd Instruction Fetch 2nd Instruction Execute 3rd Instruction Fetch 3rd Instruction Execute 4th Instruction Fetch Figure 4-5 shows the internal timing concept for the Register File. In a single clock cycle an ALU operation using two register operands is executed, and the result is stored back to the destination register. Figure 4-5. Single Cycle ALU Operation T1 T2 T3 T4 clkCPU Total Execution Time Register Operands Fetch ALU Operation Execute Result Write Back 4.8 Reset and Interrupt Handling The AVR provides several different interrupt sources. These interrupts and the separate Reset Vector each have a separate program vector in the program memory space. All interrupts are assigned individual enable bits which must be written logic one together with the Global Interrupt Enable bit in the Status Register in order to enable the interrupt. Depending on the Program Counter value, interrupts may be automatically disabled when Lock Bits LB2 or LB1 are programmed. This feature improves software security. See the section “Memory Programming” on page 184 for details. The lowest addresses in the program memory space are by default defined as the Reset and Interrupt Vectors. The complete list of vectors is shown in “Interrupts” on page 47. The list also determines the priority levels of the different interrupts. The lower the address the higher is the 13 8008C–AVR–03/09 priority level. RESET has the highest priority, and next is INT0 – the External Interrupt Request 0. Refer to “Interrupts” on page 47 for more information. When an interrupt occurs, the Global Interrupt Enable I-bit is cleared and all interrupts are disabled. The user software can write logic one to the I-bit to enable nested interrupts. All enabled interrupts can then interrupt the current interrupt routine. The I-bit is automatically set when a Return from Interrupt instruction – RETI – is executed. There are basically two types of interrupts. The first type is triggered by an event that sets the Interrupt Flag. For these interrupts, the Program Counter is vectored to the actual Interrupt Vector in order to execute the interrupt handling routine, and hardware clears the corresponding Interrupt Flag. Interrupt Flags can also be cleared by writing a logic one to the flag bit position(s) to be cleared. If an interrupt condition occurs while the corresponding interrupt enable bit is cleared, the Interrupt Flag will be set and remembered until the interrupt is enabled, or the flag is cleared by software. Similarly, if one or more interrupt conditions occur while the Global Interrupt Enable bit is cleared, the corresponding Interrupt Flag(s) will be set and remembered until the Global Interrupt Enable bit is set, and will then be executed by order of priority. The second type of interrupts will trigger as long as the interrupt condition is present. These interrupts do not necessarily have Interrupt Flags. If the interrupt condition disappears before the interrupt is enabled, the interrupt will not be triggered. When the AVR exits from an interrupt, it will always return to the main program and execute one more instruction before any pending interrupt is served. Note that the Status Register is not automatically stored when entering an interrupt routine, nor restored when returning from an interrupt routine. This must be handled by software. When using the CLI instruction to disable interrupts, the interrupts will be immediately disabled. No interrupt will be executed after the CLI instruction, even if it occurs simultaneously with the CLI instruction. The following example shows how this can be used to avoid interrupts during the timed EEPROM write sequence. Assembly Code Example in r16, SREG cli sbi EECR, EEMPE sbi EECR, EEPE out SREG, r16 ; restore SREG value (I-bit) ; store SREG value ; start EEPROM write ; disable interrupts during timed sequence C Code Example char cSREG; cSREG = SREG; /* store SREG value */ /* disable interrupts during timed sequence */ _CLI(); EECR |= (1