ACS8530 SETS
Synchronous Equipment Timing Source for
Stratum 2/3E Systems
ADVANCED COMMUNICATIONS
Description
FINAL
Features
The ACS8530 is a highly integrated, single-chip solution
for the Synchronous Equipment Timing Source (SETS)
function in a SONET or SDH Network Element. The device
generates SONET or SDH Equipment Clocks (SEC) and
Frame Synchronization clocks. The ACS8530 is fully
compliant with the required international specifications
and standards.
The device supports Free-run, Locked and Holdover
modes. It also supports all three types of reference clock
source: recovered line clock, PDH network, and node
synchronization. The ACS8530 generates independent
SEC and BITS clocks, an 8 kHz Frame Synchronization
clock and a 2 kHz Multi-Frame Synchronization clock.
Two ACS8530 devices can be used together in a Master/
Slave configuration mode allowing system protection
against a single ACS8530 failure.
A microprocessor port is incorporated, providing access to
the configuration and status registers for device setup
and monitoring. The ACS8530 supports IEEE 1149.1[5]
JTAG boundary scan.
Block Diagram
DATASHEET
Suitable for Stratum 2, 3E, 3, 4E and 4 and SONET
Minimum Clock (SMC) or SONET/SDH Equipment
Clock (SEC) applications (to Telcordia 1244-CORE[19]
Stratum 3E, and GR-253[17], and ITU-T G.812[10]
Type III and G.813[11] specifications)
Accepts 14 individual input reference clocks, all with
robust input clock source quality monitoring
Simultaneously generates nine output clocks, plus
two sync pulse outputs
Absolute Holdover accuracy better than 3 x 10-10
(manual), 7.5 x 10-14 (instantaneous); Holdover
stability defined by choice of external XO
Programmable PLL bandwidth, for wander and jitter
tracking/attenuation, 0.5 mHz to 70 Hz in 18 steps
Automatic hit-less source switchover on loss of input
Phase Transient Protection and Phase Build-out on
locked to reference and on reference switching
Microprocessor interface - Intel, Motorola, Serial,
Multiplexed, or boot from EPROM
Output phase adjustment in 6 ps steps up to ±200 ns
IEEE 1149.1 JTAG[5] Boundary Scan
Single 3.3 V operation. 5 V tolerant
Available in LQFP 100 package
Lead (Pb) - free version available (ACS8530T), RoHS
and WEEE compliant.
Figure 1 Block Diagram of the ACS8530 SETS
T4 DPLL/Freq. Synthesis
2 x AMI
10 x TTL
2 x PECL/LVDS
Programmable;
64/8 kHz (AMI)
2 kHz
4 kHz
N x 8 kHz
1.544/2.048 MHz
6.48 MHz
19.44 MHz
25.92 MHz
38.88 MHz
51.84 MHz
77.76 MHz
155.52 MHz
TCK
TDI
TMS
TRST
TDO
T4
Selector
Optional
Divider, 1/n
n = 1 to 214
PFD
Digital
Loop
Filter
T4 APLL
DTO
Frequency
Dividers
Input
Port
Monitors
and
Selection
Control
T0 DPLL/Freq. Synthesis
T0 APLL
(output)
14 x SEC
T0
Selector
IEEE
1149.1
JTAG
Chip
Clock
Generator
Optional
Divider, 1/n
n = 1 to 214
PFD
Priority Register Set
Table
Digital
Loop
Filter
Microprocessor
Port
OCXO
Frequency
Dividers
DTO
Output
Ports
TO1
to
TO7
Outputs
T01-TO7:
E1/DS1 (2.048/
1.544 MHz)
and frequency
multiples:
1.5 x, 2 x, 3 x
4 x, 6 x, 12 x
16 x and 24 x
E3/DS3
2 kHz
8 kHz
and OC-N* rates
TO8
&
TO9
T08: AMI
TO9: E1/DS1
TO10
&
TO11
TO10: 8 kHz
(FrSync)
TO11: 2 kHz
(MFrSync)
TO APLL
(feedback)
OC-N* rates =
OC-1 51.84 MHz
OC-3 155.52 MHz
and derivatives:
6.48 MHz
19.44 MHz
25.92 MHz
38.88 MHz
51.84 MHz
77.76 MHz
155.52 MHz
311.04 MHz
F8530D_001BLOCKDIA_09
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Table of Contents
ADVANCED COMMUNICATIONS
Table of Contents
FINAL
Section
ACS8530 SETS
DATASHEET
Page
Description ................................................................................................................................................................................................. 1
Block Diagram............................................................................................................................................................................................ 1
Features ..................................................................................................................................................................................................... 1
Table of Contents ...................................................................................................................................................................................... 2
Pin Diagram ............................................................................................................................................................................................... 4
Pin Description........................................................................................................................................................................................... 5
Introduction................................................................................................................................................................................................ 8
General Description................................................................................................................................................................................... 8
Overview .............................................................................................................................................................................................8
Input Reference Clock Ports .......................................................................................................................................................... 10
Locking Frequency Modes .................................................................................................................................................... 10
PECL/LVDS/AMI Input Port Selection .................................................................................................................................. 11
Clock Quality Monitoring................................................................................................................................................................. 12
Activity Monitoring ................................................................................................................................................................. 12
Frequency Monitoring ........................................................................................................................................................... 14
Selection of Input Reference Clock Source................................................................................................................................... 14
Forced Control Selection....................................................................................................................................................... 15
Automatic Control Selection ................................................................................................................................................. 15
Ultra Fast Switching .............................................................................................................................................................. 15
Fast External Switching Mode-SCRSW Pin .......................................................................................................................... 16
Output Clock Phase Continuity on Source Switchover ....................................................................................................... 16
Modes of Operation ........................................................................................................................................................................ 16
Free-run Mode ....................................................................................................................................................................... 16
Pre-locked Mode ................................................................................................................................................................... 16
Locked Mode ......................................................................................................................................................................... 17
Lost-phase Mode................................................................................................................................................................... 17
Holdover Mode ...................................................................................................................................................................... 17
Pre-locked2 Mode ................................................................................................................................................................. 19
DPLL Architecture and Configuration ............................................................................................................................................ 20
TO DPLL Main Features ........................................................................................................................................................ 20
T4 DPLL Main Features ........................................................................................................................................................ 20
TO DPLL Automatic Bandwidth Controls.............................................................................................................................. 21
Phase Detectors .................................................................................................................................................................... 21
Phase Lock/Loss Detection.................................................................................................................................................. 21
Damping Factor Programmability......................................................................................................................................... 22
Local Oscillator Clock ............................................................................................................................................................ 22
Output Wander ...................................................................................................................................................................... 23
Jitter and Wander Transfer ................................................................................................................................................... 25
Phase Build-out ..................................................................................................................................................................... 25
Input to Output Phase Adjustment....................................................................................................................................... 26
Input Wander and Jitter Tolerance....................................................................................................................................... 26
Using the DPLLs for Accurate Frequency and Phase Reporting ........................................................................................ 28
Configuration for Redundancy Protection ..................................................................................................................................... 29
Alignment of Priority Tables in Master and Slave ACS8530 .............................................................................................. 30
T4 Generation in Master and Slave ACS8530 .................................................................................................................... 30
Alignment of the Output Clock Phases in Master and Slave ACS8530............................................................................. 30
MFrSync and FrSync Alignment-SYNC2K............................................................................................................................. 31
Output Clock Ports .......................................................................................................................................................................... 32
PECL/LVDS/AMI Output Port Selection ............................................................................................................................... 32
Output Frequency Selection and Configuration .................................................................................................................. 32
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ACS8530 SETS
ADVANCED COMMUNICATIONS
FINAL
DATASHEET
Section
Page
Microprocessor Interface ....................................................................................................................................................................... 43
Introduction to Microprocessor Modes ......................................................................................................................................... 43
Motorola Mode ...................................................................................................................................................................... 44
Intel Mode.............................................................................................................................................................................. 46
Multiplexed Mode.................................................................................................................................................................. 48
Serial Mode............................................................................................................................................................................ 50
EPROM Mode......................................................................................................................................................................... 52
Power-On Reset............................................................................................................................................................................... 52
Register Map........................................................................................................................................................................................... 53
Register Organization ..................................................................................................................................................................... 53
Multi-word Registers ............................................................................................................................................................. 53
Register Access ..................................................................................................................................................................... 53
Interrupt Enable and Clear ................................................................................................................................................... 53
Defaults.................................................................................................................................................................................. 53
Register Descriptions ............................................................................................................................................................................. 57
Electrical Specifications ....................................................................................................................................................................... 134
JTAG ............................................................................................................................................................................................... 134
Over-voltage Protection ................................................................................................................................................................ 134
ESD Protection .............................................................................................................................................................................. 134
Latchup Protection........................................................................................................................................................................ 134
Maximum Ratings ......................................................................................................................................................................... 135
Operating Conditions .................................................................................................................................................................... 135
DC Characteristics ........................................................................................................................................................................ 135
DC Characteristics: AMI Input/Output Port ....................................................................................................................... 139
Jitter Performance ........................................................................................................................................................................ 141
Input/Output Timing ..................................................................................................................................................................... 144
Package Information ............................................................................................................................................................................ 145
Thermal Conditions....................................................................................................................................................................... 146
Application Information ........................................................................................................................................................................ 147
References ............................................................................................................................................................................................ 148
Abbreviations ........................................................................................................................................................................................ 148
Trademark Acknowledgements ........................................................................................................................................................... 149
Revision Status/History ....................................................................................................................................................................... 150
Notes ..................................................................................................................................................................................................... 151
Ordering Information ............................................................................................................................................................................ 152
Disclaimers.................................................................................................................................................................................... 152
Contacts......................................................................................................................................................................................... 152
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ACS8530 SETS
ADVANCED COMMUNICATIONS
Pin Diagram
FINAL
DATASHEET
100
99
98
97
96
95
94
93
92
91
90
89
88
87
86
85
84
83
82
81
80
79
78
77
76
SONSDHB
MSTSLVB
IC7
IC6
IC5
TO9
TO5
TO4
AGND3
VA3+
TO3
TO2
TO1
DGNDb
VDDb
VDDc
DGNDc
AD0
AD1
AD2
AD3
AD4
AD5
AD6
AD7
Figure 2 ACS8530 Pin Diagram Synchronous Equipment Timing Source for Stratum 2/3E Systems
AGND
TRST
IC1
IC2
AGND1
VA1+
TMS
INTREQ
TCK
REFCLK
DGND1
VD1+
VD3+
DGND3
DGND2
VD2+
IC3
SRCSW
VA2+
AGND2
TDO
IC4
TDI
I1
I2
ACS8530
SONET/SDH SETS
75
74
73
72
71
70
69
68
67
66
65
64
63
62
61
60
59
58
57
56
55
54
53
52
51
RDY
PORB
ALE
RDB
WRB
CSB
A0
A1
A2
A3
A4
A5
A6
DGNDd
VDDd
UPSEL0
UPSEL1
UPSEL2
I14
I13
I12
I11
I10
I9
I8
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
VAMI+
TO8NEG
TO8POS
GND_AMI
FrSync
MFrSync
GND_DIFFa
VDD_DIFFa
TO6POS
TO6NEG
TO7POS
TO7NEG
GND_DIFFb
VDD_DIFFb
I5POS
I5NEG
I6POS
I6NEG
VDD5
SYNC2K
I3
I4
I7
DGNDa
VDDa
1
2
3
4
5
6
7
8
9
10
11
1
12
13
14
15
16
17
18
19
20
21
22
23
24
25
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F8530D_002PINDIAG_04
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ACS8530 SETS
ADVANCED COMMUNICATIONS
Pin Description
FINAL
DATASHEET
Table 1 Power Pins
Pin Number
Symbol
I/O
Type
Description
12, 13,
16
VD1+, VD3+,
VD2+
P
-
Supply Voltage: Digital supply to gates in analog section, +3.3 Volts
±10%.
26
VAMI+
P
-
Supply Voltage: Digital supply to AMI output, +3.3 Volts ±10%.
33,
39
VDD_DIFFa,
VDD_DIFFb
P
-
Supply Voltage: Digital supply for differential ports, +3.3 Volts ±10%.
44
VDD5
P
-
Digital Supply for +5 Volts Tolerance to Input Pins. Connect to +5 Volts
(±10%) for clamping to +5 Volts. Connect to VDD for clamping to
+3.3 Volts. Leave floating for no clamping, input pins tolerant up to
+5.5 Volts.
50, 61,
85, 86
VDDa, VDDd,
VDDc, VDDb
P
-
Supply Voltage: Digital supply to logic, +3.3 Volts ±10%.
6
VA1+
P
-
Supply Voltage: Analog supply to clock multiplying PLL, +3.3 Volts ±10%.
19, 91
VA2+, VA3+
P
-
Supply Voltage: Analog supply to output PLLs, +3.3 Volts ±10%.
11, 14,
15,
DGND1, DGND3,
DGND2,
P
-
Supply Ground: Digital ground for components in PLLs.
49, 62,
84, 87
DGNDa, DGNDd,
DGNDc, DGNDb
P
-
Supply Ground: Digital ground for logic.
29
GND_AMI
P
-
Supply Ground: Digital ground for AMI output.
32,
38
GND_DIFFa,
GND_DIFFb
P
-
Supply Ground: Digital ground for differential ports.
1, 5,
20, 92
AGND, AGND1,
AGND2, AGND3
P
-
Supply Ground: Analog grounds.
Note...I = Input, O = Output, P = Power, TTLU = TTL input with pull-up resistor, TTLD = TTL input with pull-down resistor.
Table 2 Internally Connected
Pin Number
3, 4, 17, 22,
96, 97, 98
Symbol
I/O
Type
IC1, IC2, IC3, IC4,
IC5, IC6, IC7
-
-
Revision 3.02/November 2005 © Semtech Corp.
Description
Internally Connected: Leave to Float.
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ADVANCED COMMUNICATIONS
FINAL
DATASHEET
Table 3 Other Pins
Pin Number
Symbol
I/O
Type
Description
2
TRST
I
TTLD
JTAG Control Reset Input: TRST = 1 to enable JTAG Boundary Scan
mode. TRST = 0 for Boundary Scan stand-by mode, still allowing correct
device operation. If not used connect to GND or leave floating.
7
TMS
I
TTLU
JTAG Test Mode Select: Boundary Scan enable. Sampled on rising edge
of TCK. If not used connect to VDD or leave floating.
8
INTREQ
O
TTL/CMOS
9
TCK
I
TTLD
JTAG Clock: Boundary Scan clock input. If not used connect to GND or
leave floating.
10
REFCLK
I
TTL
Reference Clock: 12.800 MHz (refer to section headed Local Oscillator
Clock).
18
SRCSW
I
TTLD
Source Switching: Force Fast Source Switching. See “Fast External
Switching Mode-SCRSW Pin” on page 16.
21
TDO
O
TTL/CMOS
JTAG Output: Serial test data output. Updated on falling edge of TCK. If
not used leave floating.
23
TDI
I
TTLU
JTAG Input: Serial test data Input. Sampled on rising edge of TCK. If not
used connect to VDD or leave floating.
24
I1
I
AMI
Input Reference 1: Composite clock 64 kHz + 8 kHz.
25
I2
I
AMI
Input Reference 2: Composite clock 64 kHz + 8 kHz.
27
TO8NEG
O
AMI
Output Reference 8: Composite clock, 64 kHz + 8 kHz negative pulse.
28
TO8POS
O
AMI
Output Reference 8: Composite clock, 64 kHz + 8 kHz positive pulse.
30
FrSync
O
TTL/CMOS
Output Reference 10: 8 kHz Frame Sync output.
31
MFrSync
O
TTL/CMOS
Output Reference 11: 2 kHz Multi-Frame Sync output.
34,
35
TO6POS,
TO6NEG
O
LVDS/PECL
Output Reference 6: Programmable, default 38.88 MHz, default type
LVDS.
36,
37
TO7POS,
TO7NEG
O
PECL/LVDS
Output Reference 7: Programmable, default 19.44 MHz, default type
PECL.
40,
41
I5POS,
I5NEG
I
LVDS/PECL
Input Reference 5: Programmable, default 19.44 MHz, default type
LVDS.
42,
43
I6POS,
I6NEG
I
PECL/LVDS
Input Reference 6: Programmable, default 19.44 MHz, default type
PECL.
45
SYNC2K
I
TTLD
External Sync input: 2 kHz, 4 kHz or 8 kHz for frame alignment.
46
I3
I
TTLD
Input Reference 3: Programmable, default 8 kHz.
47
I4
I
TTLD
Input Reference 4: Programmable, default 8 kHz.
48
I7
I
TTLD
Input Reference 7: Programmable, default 19.44 MHz.
51
I8
I
TTLD
Input Reference 8: Programmable, default 19.44 MHz.
52
I9
I
TTLD
Input Reference 9: Programmable, default 19.44 MHz.
53
I10
I
TTLD
Input Reference 10: Programmable, default 19.44 MHz.
Revision 3.02/November 2005 © Semtech Corp.
Interrupt Request: Active High/Low software Interrupt output.
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ADVANCED COMMUNICATIONS
FINAL
DATASHEET
Table 3 Other Pins (cont...)
Pin Number
Symbol
I/O
Type
Description
54
I11
I
TTLD
Input Reference 11: Programmable, default (Master mode)
1.544/2.048 MHz, default (Slave mode) 6.48 MHz.
55
I12
I
TTLD
Input Reference 12: Programmable, default 1.544/2.048 MHz.
56
I13
I
TTLD
Input Reference 13: Programmable, default 1.544/2.048 MHz.
57
I14
I
TTLD
Input Reference 14: Programmable, default 1.544/2.048 MHz.
58 - 60
UPSEL(2:0)
I
TTLD
Microprocessor select: Configures the interface for a particular
microprocessor type at reset.
63 - 69
A(6:0)
I
TTLD
Microprocessor Interface Address: Address bus for the microprocessor
interface registers. A(0) is SDI in Serial mode - output in EPROM mode
only. A(1) is CLKE in serial mode.
70
CSB
I
TTLU
Chip Select (Active Low): This pin is asserted Low by the microprocessor
to enable the microprocessor interface - output in EPROM mode only.
71
WRB
I
TTLU
Write (Active Low): This pin is asserted Low by the microprocessor to
initiate a write cycle. In Motorola mode, WRB = 1 for Read.
72
RDB
I
TTLU
Read (Active Low): This pin is asserted Low by the microprocessor to
initiate a read cycle.
73
ALE
I
TTLD
Address Latch Enable: This pin becomes the address latch enable from
the microprocessor. When this pin transitions from High to Low, the
address bus inputs are latched into the internal registers. ALE = SCLK in
Serial mode.
74
PORB
I
TTLU
Power-On Reset: Master reset. If PORB is forced Low, all internal states
are reset back to default values.
75
RDY
O
TTL/CMOS
76 - 83
AD(7:0)
IO
TTLD
88
TO1
O
TTL/CMOS
Output Reference 1: Programmable, default 6.48 MHz.
89
TO2
O
TTL/CMOS
Output Reference 2: Programmable, default 38.88 MHz.
90
TO3
O
TTL/CMOS
Output Reference 3: Programmable, default 19.44 MHz.
93
TO4
O
TTL/CMOS
Output Reference 4: Programmable, default 38.88 MHz.
94
TO5
O
TTL/CMOS
Output Reference 5: Programmable, default 77.76 MHz.
95
TO9
O
TTL/CMOS
Output Reference 9: 1.544/2.048 MHz, as per ITU G.783 BITS
requirements.
99
MSTSLVB
I
TTLU
Master/Slave Select: sets the state of the Master/Slave selection
register, Reg. 34, Bit 1.
100
SONSDHB
I
TTLD
SONET or SDH Frequency Select: sets the initial power up state (or state
after a PORB) of the SONET/SDH frequency selection registers, Reg. 34,
Bit 2 and Reg. 38, Bit 5, Bit 6 and Reg. 64 Bit 4. When set Low, SDH
rates are selected (2.048 MHz etc.) and when set High, SONET rates
are selected (1.544 MHz etc.) The register states can be changed after
power-up by software.
Revision 3.02/November 2005 © Semtech Corp.
Ready/Data Acknowledge: This pin is asserted High to indicate the
device has completed a read or write operation.
Address/Data: Multiplexed data/address bus depending on the
microprocessor mode selection. AD(0) is SDO in Serial mode.
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ACS8530 SETS
ADVANCED COMMUNICATIONS
Introduction
FINAL
The ACS8530 is a highly integrated, single-chip solution
for the SETS function in a SONET/SDH Network Element,
for the generation of SEC and Frame/MultiFrame
Synchronization pulses. Digital Phase Locked Loop (DPLL)
and direct digital synthesis methods are used in the
device so that the overall PLL characteristics are very
stable and consistent compared to traditional analog
PLLs.
In Free-run mode, the ACS8530 generates a stable, lownoise clock signal at a frequency to the same accuracy as
the external oscillator, or it can be made more accurate
via software calibration to within ±0.02 ppm. In Locked
mode, the ACS8530 selects the most appropriate input
reference source and generates a stable, low-noise clock
signal locked to the selected reference. In Holdover mode,
the ACS8530 generates a stable, low-noise clock signal,
adjusted to match the last known good frequency of the
last selected reference source. A high level of phase and
frequency accuracy is made possible by an internal
resolution of up to 54 bits and internal Holdover accuracy
of up to 7.5 x 10-14 (instantaneous). In all modes, the
frequency accuracy, jitter and drift performance of the
clock meet the requirements of ITU G.736[7], G.742[8],
G783[9], G.812[10], G.813[11], G.823[13], G.824[14] and
Telcordia GR-253-CORE[17] and GR-1244-CORE[19].
The ACS8530 supports all three types of reference clock
source: recovered line clock, PDH network
synchronization timing and node synchronization. The
ACS8530 generates independent T0 and T4 clocks, an
8 kHz Frame Synchronization clock and a 2 kHz MultiFrame Synchronization clock.
One key architectural advantage that the ACS8530 has
over traditional solutions is in the use of DPLL technology
for precise and repeatable performance over temperature
or voltage variations and between parts. The overall PLL
bandwidth, loop damping, pull-in range and frequency
accuracy are all determined by digital parameters that
provide a consistent level of performance. An Analog PLL
(APLL) takes the signal from the DPLL output and provides
a lower jitter output. The APLL bandwidth is set four orders
of magnitude higher than the DPLL bandwidth. This
ensures that the overall system performance still
maintains the advantage of consistent behavior provided
by the digital approach.
The DPLLs are clocked by the external Oscillator module
(OCXO) so that the Free-run or Holdover frequency
stability is only determined by the stability of the external
Revision 3.02/November 2005 © Semtech Corp.
DATASHEET
oscillator module. This second key advantage confines all
temperature critical components to one well defined and
pre-calibrated module, whose performance can be
chosen to match the application; for example an OCXO for
Stratum 3E applications.
All performance parameters of the DPLLs are
programmable without the need to understand detailed
PLL equations. Bandwidth, damping factor and lock range
can all be set directly, for example. The PLL bandwidth
can be set over a wide range, 0.5 mHz to 70 Hz in 18
steps, to cover all SONET/SDH clock synchronization
applications.
The ACS8530 supports protection. Two ACS8530 devices
can be configured to provide protection against a single
ACS8530 failure. The protection maintains alignment of
the two ACS8530 devices (Master and Slave) and
ensures that both ACS8530 devices maintain the same
priority table, choose the same reference input and
generate the T0 clock, the 8 kHz Frame Synchronization
clock and the 2 kHz Multi-Frame Synchronization clock
with the same phase. The ACS8530 includes a multistandard microprocessor port, providing access to the
configuration and status registers for device setup and
monitoring.
General Description
Overview
The following description refers to the Block Diagram
(Figure 1 on page 1).
The ACS8530 SETS device has 14 input clocks, generates
11 output clocks, and has a total of 55 possible output
frequencies. There are two main paths through the
device: T0 and T4. Each path has an independent DPLL
and APLL pair.
The T0 path is a high quality, highly configurable path
designed to provide features necessary for node timing
synchronization within a SONET/SDH network. The T4
path is a simpler and less configurable path designed to
give a totally independent path for internal equipment
synchronization. The device supports use of either or both
paths, either locked together or independent.
Of the 14 input references, two are AMI composite clock,
two are LVDS/PECL and the remaining ten are TTL/CMOS
compatible inputs. All the TTL/CMOS are 3 V and 5 V
compatible (with clamping if required by connecting the
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ACS8530 SETS
ADVANCED COMMUNICATIONS
FINAL
VDD5 pin). The AMI inputs are ±1 V typically A.C. coupled.
Refer to the electrical characteristics section for more
information on the electrical compatibility and details.
Input frequencies supported range from 2 kHz to
155.52 MHz.
Common E1, DS1, OC-3 and sub-divisions are supported
as spot frequencies that the DPLLs will directly lock to.
Any input frequency, up to 100 MHz, that is a multiple of
8 kHz can also be locked to via an inbuilt programmable
divider.
An input reference monitor is assigned to each of the 14
inputs. The monitors operate continuously such that at all
times the status of all of the inputs to the device are
known. Each input can be monitored for both frequency
and activity, activity alone, or the monitors can be
disabled.
The frequency monitors have a “hard” (rejection) alarm
limit and a “soft” (flag only) alarm limit for monitoring
frequency, whilst the reference is still within its allowed
frequency band. Each input reference can be
programmed with a priority number allowing references to
be chosen according to the highest priority valid input. The
two paths (T0 and T4) have independent priorities to allow
completely independent operation of the two paths. Both
paths operate either automatic or external source
selection.
For automatic input reference selection, the T0 path has
a more complex state machine than the T4 path.
The T0 and T4 PLL paths support the following common
features:
z
z
z
z
z
z
z
z
Automatic source selection according to input
priorities and quality level
Different quality levels (activity alarm thresholds) for
each input
Variable bandwidth, lock range and damping factor.
Direct PLL locking to common SONET/SDH input
frequencies or any multiple of 8 kHz
Automatic mode switching between Free-run, Locked
and Holdover states
Fast detection on input failure and entry into Holdover
mode (holds at the last good frequency value)
Frequency translation between input and output rates
via direct digital synthesis
High accuracy digital architecture for stable PLL
dynamics combined with an APLL for low jitter final
output clocks.
Revision 3.02/November 2005 © Semtech Corp.
DATASHEET
There are a number of features supported by the T0 path
that are not supported by the T4 path, although these can
also all be externally controlled by software.
The additional T0 features supported are:
z
z
z
z
z
z
z
z
z
Non-revertive mode
Phase Build-out on source switch (hit-less source
switching)
Phase Build-out following phase hit on locked-to
source
I/O phase offset control
Greater programmable bandwidth from 0.5 mHz to
70 Hz in 18 steps (T4 path programmable bandwidth
in 3 steps, 18, 35 and 70 Hz)
Noise rejection on low frequency input
Manual Holdover frequency control
Controllable automatic Holdover frequency filtering
Frame Sync pulse alignment.
Either the software or an internal state machine controls
the operation of the DPLL in the T0 path. The state
machine for the T4 path is very simple and cannot be
manually/externally controlled, however the overall
operation can be controlled by manual reference source
selection. One additional feature of the T4 path is the
ability to measure a phase difference between two inputs.
The T0 path DPLL always produces an output at
77.76 MHz to feed the APLL, regardless of the frequency
selected at the output pins. The T4 path can be operated
at a number of frequencies. This is to enable the
generation of extra output frequencies, which cannot be
easily related to 77.76 MHz. When the T4 path is selected
to lock to the T0 path, the T4 DPLL locks to the 8 kHz from
the T0 DPLL. This is because all of the frequencies of
operation of the T4 path can be divided to 8 kHz and this
will ensure synchronization of all the frequencies within
the two paths.
Both of the DPLLs’ outputs are connected to multiplying
and filtering APLLs. The outputs of these APLLs are
divided making a number of frequencies simultaneously
available for selection at the output clock ports. The
various combinations of DPLL, APLL and divider
configurations allow for generation of a comprehensive
set of frequencies, as listed in Table 13.
To synchronize the lower output frequencies when the T0
PLL is locked to a high frequency reference input, an
additional input is provided. The SYNC2K pin (pin 45) is
used to reset the dividers that generate the 2kHz and
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8 kHz outputs such that the output 2/8 kHz clocks are
lined up with the input 2 kHz. This synchronization
method allows for example, a master and a slave device
to be in precise alignment.
The ACS8530 also supports Sync pulse references of
4 kHz or 8 kHz although in these cases frequencies lower
than the Sync pulse reference may not necessarily be in
phase.
Input Reference Clock Ports
Table 4 gives details of the input reference ports, showing
the input technologies and the range of frequencies
supported on each port; the default spot frequencies and
default priorities assigned to each port on power-up or by
reset are also shown. Note that SDH and SONET networks
use different default frequencies; the network type is pinselectable (using either the SONSDHB pin or via
software). Specific frequencies and priorities are set by
configuration.
SDH and SONET networks use different default
frequencies; the network type is selectable using the
cnfg_input_mode Reg. 34 Bit 2, ip_sonsdhb.
z
For SONET, ip_sonsdhb = 1
z
For SDH, ip_sonsdhb = 0.
DATASHEET
Lock8k Mode
Lock8k mode automatically sets the divider parameters
to divide the input frequency down to 8 kHz. Lock8k can
only be used on the supported spot frequencies (see
Table 4 Note(i)). Lock8k mode is enabled by setting the
lock8k bit (Bit 6) in the appropriate
cnfg_ref_source_frequency register location. Using lower
frequencies for phase comparisons in the DPLL results in
a greater tolerance to input jitter. It is possible to choose
which edge of the input reference clock to lock to, by
setting 8K edge polarity (Bit 2 of Reg. 03, test_register1).
DivN Mode
In DivN mode, the divider parameters are set manually by
configuration (Bit 7 of the cnfg_ref_source_frequency
register), but must be set so that the frequency after
division is 8 kHz.
The DivN function is defined as:
DivN = “Divide by N+1”, i.e. it is the dividing factor used
for the division of the input frequency, and has a value of
(N+1) where N is an integer from 1 to 12499 inclusive.
Therefore, in DivN mode the input frequency can be
divided by any integer value between 2 to 12500.
Consequently, any input frequency which is a multiple of
8 kHz, between 8 kHz to 100 MHz, can be supported by
using DivN mode.
On power-up or by reset, the default will be set by the state
of the SONSDHB pin (pin 100). Specific frequencies and
priorities are set by configuration.
The frequency selection is programmed via the
cnfg_ref_source_frequency register (Reg. 20 - Reg. 2D).
Note...Any reference input can be set to use DivN
independently of the frequencies and configurations of the
other inputs. However only one value of N is allowed, so all
inputs with DivN selected must be running at the same
frequency.
DivN Examples
(a) To lock to 2.000 MHz:
Locking Frequency Modes
(i)
There are three locking frequency modes that can be
configured: Direct Lock, Lock8k and DivN.
Direct Lock Mode
(ii) To achieve 8 kHz, the 2 MHz input must be
divided by 250. So, if DivN = 250 = (N + 1)
then N must be set to 249. This is done by writing
F9 hex (249 dec) to the DivN register pair
Reg. 46/47.
In Direct Lock Mode, the internal DPLL can lock to the
selected input at the spot frequency of the input, for
example 19.44 MHz performs the DPLL phase
comparisons at 19.44 MHz.
In Lock8k and DivN modes (and for special case of
155 MHz), an internal divider is used prior to the DPLL to
divide the input frequency before it is used for phase
comparisons in the DPLL.
Revision 3.02/November 2005 © Semtech Corp.
Set the cnfg_ref_source_frequency register to
10XX0000 (binary) to enable DivN, and set the
frequency to 8 kHz - the frequency required after
division. (XX = “Leaky Bucket” ID for this input).
(b) To lock to 10.000 MHz:
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(i)
The cnfg_ref_source_frequency register is set to
10XX0000 (binary) to set the DivN and the
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frequency to 8 kHz, the post-division frequency.
(XX = “Leaky Bucket” ID for this input).
(ii) To achieve 8 kHz, the 10 MHz input must be
divided by 1,250. So, if DivN, = 250 = (N+1)
then N must be set to 1,249. This is done by
writing 4E1 hex (1,249 dec to the DivN register
pair Reg. 46/47.
Direct Lock Mode 155 MHz.
The max frequency allowed for phase comparison is
77.76 MHz, so for the special case of a 155 MHz input set
to Direct Lock Mode, there is a divide-by-two function
automatically selected to bring the frequency down to
within the limits of operation.
DATASHEET
PECL/LVDS/AMI Input Port Selection
The choice of PECL or LVDS compatibility is programmed
via the cnfg_differential_inputs register, Reg. 36. Unused
PECL differential inputs should be fixed with one input
High (VDD) and the other input Low (GND), or set in LVDS
mode and left floating, in which case one input is
internally pulled High and the other Low.
An AMI port supports a composite clock, consisting of a
64 kHz AMI clock with 8 kHz boundaries marked by
deliberate violations of the AMI coding rules, as specified
in ITU recommendation G.703[6]. Departures from the
nominal pattern are detected within the ACS8530, and
may cause reference-switching if too frequent. See
section DC Characteristics: AMI Input/Output Port, for
more details. If the AMI port is unused, the pins (I1 and I2)
should be tied to GND.
Table 4 Input Reference Source Selection and Priority Table
Port Number
Channel
Number (Bin)
Input Port
Technology
Frequencies Supported
Default
Priority
I1
0001
AMI
64/8 kHz (composite clock, 64 kHz + 8 kHz)
Default (SONET): 64/8 kHz Default (SDH): 64/8 kHz
2
I2
0010
AMI
64/8 kHz (composite clock, 64 kHz + 8 kHz)
Default (SONET): 64/8 kHz Default (SDH): 64/8 kHz
3
I3
0011
TTL/CMOS
Up to 100 MHz (see Note (i))
Default (SONET): 8 kHz Default (SDH): 8 kHz
4
I4
0100
TTL/CMOS
Up to 100 MHz (see Note (i))
Default (SONET): 8 kHz Default (SDH): 8 kHz
5
I5
0101
LVDS/PECL LVDS Up to 155.52 MHz (see Note (ii))
default
Default (SONET): 19.44 MHz Default (SDH): 19.44 MHz
6
I6
0110
PECL/LVDS PECL Up to 155.52 MHz (see Note (ii))
default
Default (SONET): 19.44 MHz Default (SDH): 19.44 MHz
7
I7
0111
TTL/CMOS
Up to 100 MHz (see Note (i))
Default (SONET): 19.44 MHz Default (SDH): 19.44 MHz
8
I8
1000
TTL/CMOS
Up to 100 MHz (see Note (i))
Default (SONET): 19.44 MHz Default (SDH): 19.44 MHz
9
I9
1001
TTL/CMOS
Up to 100 MHz (see Note (i))
Default (SONET): 19.44 MHz Default (SDH): 19.44 MHz
10
I10
1010
TTL/CMOS
Up to 100 MHz (see Note (i))
Default (SONET): 19.44 MHz Default (SDH): 19.44 MHz
11
I11
1011
TTL/CMOS
Up to 100 MHz (see Note (i)) Default (Master) (SONET): 1.544 MHz Default
(Master) (SDH): 2.048 MHz Default (Slave) 6.48 MHz
12/1
(Note (iii))
I12
1100
TTL/CMOS
Up to 100 MHz (see Note (i))
Default (SONET): 1.544 MHz Default (SDH): 2.048 MHz
13
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DATASHEET
Table 4 Input Reference Source Selection and Priority Table (cont...)
Port Number
Channel
Number (Bin)
Input Port
Technology
Frequencies Supported
Default
Priority
I13
1101
TTL/CMOS
Up to 100 MHz (see Note (i))
Default (SONET): 1.544 MHz Default (SDH): 2.048 MHz
14
I14
1110
TTL/CMOS
Up to 100 MHz (see Note (i))
Default (SONET): 1.544 MHz Default (SDH): 2.048 MHz
15
Notes: (i) TTL ports (compatible also with CMOS signals) support clock speeds up to 100 MHz, with the highest spot frequency being
77.76 MHz. The actual spot frequencies are: 2 kHz, 4 kHz, 8 kHz (and N x 8 kHz), 1.544 MHz (SONET)/2.048 MHz (SDH), 6.48 MHz,
19.44 MHz, 25.92 MHz, 38.88 MHz, 51.84 MHz, 77.76 MHz. SONET or SDH input rate is selected via Reg. 34 Bit 2, ip_sonsdhb).
(ii) PECL and LVDS ports support the spot clock frequencies listed above plus 155.52 MHz (and 311.04 MHz for TO6 only).
(iii) Input port I11 is set at priority 12 on the Master SETS IC and priority 1 on the Slave SETS IC, as default on power up (or PORB). The
default setup of Master or Slave I11 priority is determined by the MSTSLVB pin.
Clock Quality Monitoring
Clock quality is monitored and used to modify the priority
tables of the local and remote ACS8530 devices. For each
input, the following parameters are monitored:
1. Activity (toggling).
2. Frequency (this monitoring is only performed when
there is no irregular operation of the clock or loss of
clock condition).
In addition, input ports I1 and I2 carry AMI-encoded
composite clocks which are monitored by the AMIdecoder blocks. Loss of signal is declared by the decoders
when either the signal amplitude falls below +0.3 V or
there is no activity for 1 ms.
Any reference source that suffers a loss-of-activity or
clock-out-of-band condition will be declared as
unavailable.
Clock quality monitoring is a continuous process which is
used to identify clock problems. There is a difference in
dynamics between the selected clock and the other
reference clocks. Anomalies occurring on non-selected
reference sources affect only that source's suitability for
selection, whereas anomalies occurring on the selected
clock could have a detrimental impact on the accuracy of
the output clock.
Anomalies detected by the activity detector are integrated
in a Leaky Bucket Accumulator (one per input channel).
Occasional anomalies do not cause the Accumulator to
cross the alarm setting threshold, so the selected
reference source is retained. Persistent anomalies cause
the alarm setting threshold to be crossed and result in the
selected reference source being rejected.
Revision 3.02/November 2005 © Semtech Corp.
Anomalies on the currently locked-to input reference
clock, whether affecting signal purity or signal frequency,
could induce jitter or frequency offsets in the output clock,
leading to anomalous behavior. Anomalies on the
selected clock, therefore, have to be detected as they
occur and the phase locked loop must be temporarily
isolated until the clock is once again pure. The clock
monitoring process cannot be used for this because the
high degree of accuracy required dictates that the
process be slow. To achieve the immediacy required by
the phase locked loop requires an alternative
mechanism. The phase locked loop itself contains a fast
activity detector such that within approximately two
missing input clock cycles, a no-activity flag is raised and
the DPLL is frozen in Holdover mode. This flag can also be
read as the main_ref_failed bit (from Reg. 06, Bit 6) and
can be set to indicate a phase lost state by enabling
Reg. 73, Bit 6. With the DPLL in Holdover mode it is
isolated from further disturbances. If the input becomes
available again before the activity or frequency monitor
rejection alarms have been raised, then the DPLL will
continue to lock to the input, with little disturbance. In this
scenario, with the DPLL in the “locked” state, the DPLL
uses “nearest edge locking” mode (±180° capture)
avoiding cycle slips or glitches caused by trying to lock to
an edge 360° away, as would happen with traditional
PLLs.
Activity Monitoring
The ACS8530 has a combined inactivity and irregularity
monitor. The ACS8530 uses a Leaky Bucket Accumulator,
which is a digital circuit which mimics the operation of an
analog integrator, in which input pulses increase the
output amplitude but die away over time. Such integrators
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are used when alarms have to be triggered either by fairly
regular defect events, which occur sufficiently close
together, or by defect events which occur in bursts. Events
which are sufficiently spread out should not trigger the
alarm. By adjusting the alarm setting threshold, the point
at which the alarm is triggered can be controlled. The
point at which the alarm is cleared depends upon the
decay rate and the alarm clearing threshold.
On the alarm setting side, if several events occur close
together, each event adds to the amplitude and the alarm
will be triggered quickly; if events occur a little more
spread out, but still sufficiently close together to
overcome the decay, the alarm will be triggered
eventually. If events occur at a rate which is not sufficient
to overcome the decay, the alarm will not be triggered. On
the alarm clearing side, if no defect events occur for a
sufficient time, the amplitude will decay gradually and the
alarm will be cleared when the amplitude falls below the
alarm clearing threshold. The ability to decay the
amplitude over time allows the importance of defect
events to be reduced as time passes by. This means that,
in the case of isolated events, the alarm will not be set,
whereas, once the alarm becomes set, it will be held on
until normal operation has persisted for a suitable time
(but if the operation is still erratic, the alarm will remain
set). See Figure 3.
DATASHEET
There is one Leaky Bucket Accumulator per input channel.
Each Leaky Bucket can select from four configurations
(Leaky Bucket Configuration 0 to 3). Each Leaky Bucket
Configuration is programmable for size, alarm set and
reset thresholds, and decay rate.
Each source is monitored over a 128 ms period. If, within
a 128 ms period, an irregularity occurs that is not deemed
to be due to allowable jitter/wander, then the
Accumulator is incremented.
The Accumulator will continue to increment up to the
point that it reaches the programmed Bucket size. The “fill
rate” of the Leaky Bucket is, therefore, 8 units/second.
The “leak rate” of the Leaky Bucket is programmable to
be in multiples of the fill rate (x 1, x 0.5, x 0.25 and
x 0.125) to give a programmable leak rate from
8 units/sec down to 1 unit/sec. A conflict between trying
to “leak” at the same time as a “fill” is avoided by
preventing a leak when a fill event occurs.
Disqualification of a non-selected reference source is
based on inactivity, or on an out-of-band result from the
frequency monitors. The currently selected reference
source can be disqualified for phase, frequency, inactivity
or if the source is outside the DPLL lock range. If the
currently selected reference source is disqualified, the
next highest priority, qualified reference source is
selected.
Figure 3 Inactivity and Irregularity Monitoring
Inactivities/Irregularities
Reference
Source
bucket_size
Leaky
Bucket
Response
upper_threshold
lower_threshold
Programmable Fall Slopes
(all programmable)
Alarm
F8530D_026Inact_Irreg_Mon_02
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Interrupts for Activity Monitors
DATASHEET
Leaky Bucket Timing
The loss of the currently selected reference source will
eventually cause the input to be considered invalid,
triggering an interrupt, if not masked. The time taken to
raise this interrupt is dependant on the Leaky Bucket
Configuration of the activity monitors. The fastest Leaky
Bucket setting will still take up to 128 ms to trigger the
interrupt. The interrupt caused by the brief loss of the
currently selected reference source is provided to
facilitate very fast source failure detection if desired. It is
triggered after missing just a couple of cycles of the
reference source. Some applications require the facility to
switch downstream devices based on the status of the
reference sources. In order to provide extra flexibility, it is
possible to flag the main_ref_failed interrupt (Reg. 06
Bit 6) on the pin TDO. This is simply a copy of the status
bit in the interrupt register and is independent of the
mask register settings. The bit is reset by writing to the
interrupt status register in the normal way. This feature
can be enabled and disabled by writing to Reg. 48 Bit 6.
The time taken (in seconds) to raise an inactivity alarm on
a reference source that has previously been fully active
(Leaky Bucket empty) will be:
(cnfg_upper_threshold_n) / 8
where n is the number (0 to 3) of the Leaky Bucket
Configuration. If an input is intermittently inactive then
this time can be longer. The default setting of
cnfg_upper_threshold_n is 6, therefore the default time is
0.75 s.
The time taken (in seconds) to cancel the activity alarm on
a previously completely inactive reference source is
calculated, for a particular Leaky Bucket, as:
[2 (a) x (b - c)]/ 8
where:
a = cnfg_decay_rate_n
b = cnfg_bucket_size_n
c = cnfg_lower_threshold_n
(where n = the number (0 to 3) of the relevant
Leaky Bucket Configuration in each case).
The default setting is shown in the following:
[21 x (8 - 4)] /8 = 1.0 secs
Frequency Monitoring
The ACS8530 performs frequency monitoring to identify
reference sources which have drifted outside the
acceptable frequency range measured with respect either
to the output clock or to the XO clock.
The sts_reference_sources out-of-band alarm for a
particular reference source is raised when the reference
source is outside the acceptable frequency range. With
the default register settings a soft alarm is raised if the
drift is outside ±11.43 ppm and a hard alarm is raised if
the drift is outside ±15.24 ppm. Both of these limits are
programmable from 3.8 ppm up to 61 ppm.
The ACS8530 DPLL has a programmable lock and
capture range frequency limit up to ±80 ppm (default is
±9.2 ppm).
Selection of Input Reference Clock Source
Under normal operation, the input reference sources are
selected automatically by an order of priority. But, for
special circumstances, such as chip or board testing, the
selection may be forced by configuration.
Revision 3.02/November 2005 © Semtech Corp.
Automatic operation selects a reference source based on
its pre-defined priority and its current availability. A table
is maintained which lists all reference sources in the order
of priority. This is initially defined by the default
configuration and can be changed via the microprocessor
interface by the Network Manager. In this way, when all
the defined sources are active and valid, the source with
the highest programmed priority is selected but, if this
source fails, the next-highest source is selected, and so
on.
Restoration of repaired reference sources is handled
carefully to avoid inadvertent disturbance of the output
clock. For this, the ACS8530 has two modes of operation;
Revertive and Non-revertive.
In Revertive mode, if a re-validated (or newly validated)
source has a higher priority than the reference source
which is currently selected, a switch over will take place.
Many applications prefer to minimize the clock switching
events and choose Non-revertive mode.
In Non-revertive mode, when a re-validated (or newly
validated) source has a higher priority then the selected
source will be maintained. The re-validation of the
reference source will be flagged in the sts_sources_valid
register and, if not masked, will generate an interrupt.
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Selection of the re-validated source can take place under
software control or if the currently selected source fails.
To enable software control, the software should briefly
enable Revertive mode to effect a switch-over to the
higher priority source. When there is a reference available
with higher priority than the selected reference, there will
be NO change of reference source as long as the
Non-revertive mode remains on, and the currently
selected source is valid. A failure of the selected
reference will always trigger a switch-over regardless of
whether Revertive or Non-revertive mode has been
chosen.
Also, in a Master/Slave redundancy-protection scheme,
the Slave device(s) must follow the Master device. The
alignment of the Master and Slave devices is part of the
protection mechanism. The availability of each source is
determined by a combination of local and remote
monitoring of each source. Each input reference source
supplied to each ACS8530 device is monitored locally and
the results are made available to other devices.
DATASHEET
are 1 to 15 (dec). A value of 0 disables the reference
source. However if two or more inputs are given the same
priority number those inputs will be selected on a first in,
first out basis. If the first of two same priority number
sources goes invalid the second will be switched in. If the
first then becomes valid again, it becomes the second
source on the first in, first out basis, and there will not be
a switch. If a third source with the same priority number
as the other two becomes valid, it joins the priority list on
the same first in, first out basis. There is no implied priority
based on the channel numbers. Revertive/Non-revertive
mode has no effect on sources with the same priority
value.
The input port I11 is also for the connection of the
synchronous clock of the T0 output of the Master device
(or the active-Slave device), to be used to align the T0
output with the Master (or active-Slave) device if this
device is acting in a subordinate-Slave or subordinateMaster role.
Forced Control Selection
Ultra Fast Switching
A configuration register, force_select_reference_source
Reg. 33, controls both the choice of automatic or forced
selection and the selection itself (when forced selection is
required). For Automatic choice of source selection, the 4
LSB bit value is set to all zeros or all ones (default). To
force a particular input (In), the Bit value is set to n (bin).
Forced selection is not the normal mode of operation, and
the force_select_reference_source variable is defaulted
to the all-one value on reset, thereby adopting the
automatic selection of the reference source.
A reference source is normally disqualified after the Leaky
Bucket monitor thresholds have been crossed. An option
for a faster disqualification has been implemented,
whereby if Reg. 48 Bit 5 (ultra_fast_switch) is set, then a
loss of activity of just a few reference clock cycles will set
the main_ref_failed alarm and cause a reference switch.
This can be configured (see Reg. 06, Bit 6) to cause an
interrupt to occur instead of, or as well as, causing the
reference switch.
Automatic Control Selection
When an automatic selection is required, the
force_select_reference_source register LSB 4 bits must
be set to all zeros or all ones. The configuration registers,
cnfg_ref_selection_priority, held in the µP port block,
consist of seven, 8-bit registers organized as one 4-bit
register per input reference port. Each register holds a
4-bit value which represents the desired priority of that
particular port. Unused ports should be given the value,
0000, in the relevant register to indicate they are not to
be included in the priority table. On power-up, or following
a reset, the whole of the configuration file will be
defaulted to the values defined by Table 4. The selection
priority values are all relative to each other, with lowervalued numbers taking higher priorities. Each reference
source should be given a unique number; the valid values
Revision 3.02/November 2005 © Semtech Corp.
The sts_interrupts register Reg. 06 Bit 6 (main_ref_failed)
is used to flag inactivity on the reference that the device
is locked to much faster than the activity monitors can
support. If Reg. 48 Bit 6 of the cnfg_monitors register
(los_flag_on_TDO) is set, then the state of this bit is driven
onto the TDO pin of the device.
Note...The flagging of the loss of the main reference failure on
TDO is simply allowing the status of the sts_interrupts bit
main_ref_failed Reg. 06 Bit 6, to be reflected in the state of
the TDO output pin. The pin will, therefore, remain High until
the interrupt is cleared. This functionality is not enabled by
default so the usual JTAG functions can be used. When the
TDO output from the ACS8530 is connected to the TDI pin of
the next device in the JTAG scan chain, the implementation
should be such that a logic change caused by the action of the
interrupt on the TDI input should not effect the operation when
JTAG is not active.
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Fast External Switching Mode-SCRSW Pin
Fast external switching mode, for fast switching between
inputs I3 or I5 and I4 or I6, can also be triggered directly
from a dedicated pin SRCSW (Figure 4), once the mode
has been initialized.
The mode is initialized by either holding SRCSW pin High
during reset (SRCSW must remain High for at least a
further 251 ms after PORB has gone High - see following
Note), or by writing to Reg. 48 Bit 4. After External
Protection Switching mode has been initialized, the value
on this pin directly selects either I3/I5 (SRCSW High) or
I4/I6 (SRCSW Low). If this mode is initialized at reset by
pulling the SRCSW pin High, then it configures the default
frequency tolerance of I3/I5 and I4/I6 to ±80 ppm
(Reg. 41 and Reg. 42) as opposed to the normal
frequency tolerance of ±9.2 ppm. Any of these registers
can be subsequently set by external software, if required.
Note...The 251 ms comprises 250 ms allowance for the
internal reset to be removed plus 1 ms allowance for APLLs to
start-up and become stable.
Selection of either input I3 or I5 is determined by the
Priority value of I3; if the programmed priority of I3 is 0,
then I5 is selected. Similarly, I6 is selected if the
programmed priority of I4 is 0.
Figure 4 I3/I5 and I4/I6 Switching
I3 Priority >0
SRCSW
I3
1
I5
0
1
T0 DPLL
I4
1
0
I6
0
I4 Priority >0
F8530D_006IPSWI3I4I5I6_01
When external protection switching is enabled, the device
will operate as a simple switch. All clock monitoring is
disabled and the DPLL will simply be forced to try to lock
on to the indicated reference source. Consequently the
device will always indicate “locked” state in the
sts_operating register (Reg. 09, Bits 2:0).
Revision 3.02/November 2005 © Semtech Corp.
DATASHEET
Output Clock Phase Continuity on Source
Switchover
If either PBO is selected on (default), or, if DPLL frequency
limit is set to less than ±30 ppm or (±9.2 ppm default), the
device will always comply with GR-1244-CORE[19]
specification for Stratum 3 (maximum rate of phase
change of 81 ns/1.326 ms), for all input frequencies.
Modes of Operation
The ACS8530 has three primary modes of operation
(Free-run, Locked and Holdover) supported by three
secondary, temporary modes (Pre-Locked, Lost-Phase
and Pre-Locked2). These are shown in the State
Transition Diagram for the T0 DPLL, Figure 5.
The ACS8530 can operate in Forced or Automatic control.
On reset, the ACS8530 reverts to Automatic Control,
where transitions between states are controlled
completely automatically. Forced Control can be invoked
by configuration, allowing transitions to be performed
under external control. This is not the normal mode of
operation, but is provided for special occasions such as
testing, or where a high degree of hands-on control is
required.
Free-run Mode
The Free-run mode is typically used following a power-on
reset or a device reset before network synchronization
has been achieved. In the Free-run mode, the timing and
synchronization signals generated from the ACS8530 are
based on the 12.800 MHz clock frequency provided from
the external oscillator and are not synchronized to an
input reference source. By default, the frequency of the
output clock is a fixed multiple of the frequency of the
external oscillator, and the accuracy of the output clock is
equal to the accuracy of the oscillator. However the
external oscillator frequency can be calibrated to improve
its accuracy by a software calibration routine using
register cnfg_nominal_frequency (Reg. 3C and 3D). For
example a 500 ppm offset crystal could be made to look
like one accurate to within ±0.02 ppm.
The transition from Free-run to Pre-locked occurs when
the ACS8530 selects a reference source.
Pre-locked Mode
The ACS8530 will spend a maximum of 100 seconds in
the Pre-locked mode. If the device is required to spend up
to 700 seconds acquiring lock (e.g. in a Stratum3E
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application) external software will be required to force the
device into Locked mode until phase lock has been
achieved. Without software control, if the device cannot
achieve lock within 100 seconds, the reference is
disqualified and a phase alarm is raised on it. The device
will then revert to Free-run mode and another reference
source, if available, will be selected.
Holdover can be configured to operate in either:
z
Automatic Mode
(Reg. 34 Bit 4, cnfg_input_mode: man_holdover set
Low), or
z
Manual Mode
(Reg. 34 Bit 4, cnfg_input_mode: man_holdover set
High).
Locked Mode
The Locked mode is entered from Pre-locked, Pre-locked2
or Phase-lost mode when an input reference source has
been selected and the DPLL has locked. The DPLL is
considered to be locked when the phase loss/lock
detectors (See“Phase Lock/Loss Detection” on page 21)
indicate that the DPLL has remained in phase lock
continuously for at least one second. When the ACS8530
is in Locked mode, the output frequency and phase tracks
that of the selected input reference source.
Automatic Mode
In Automatic mode, the device can be configured to
operate using either:
z
Averaged
(Reg. 40 Bit 7, cnfg_holdover_modes,
auto_averaging: set High) or
z
Instantaneous
(Reg. 40 Bit 7, cnfg_holdover_modes,
auto_averaging: set Low).
Lost-phase Mode
Lost-phase mode is used whenever the phase loss/lock
detectors (See“Phase Lock/Loss Detection” on page 21)
indicate that the DPLL has lost phase lock. The DPLL will
still be trying to lock to the input clock reference, if it
exists. If the Leaky Bucket Accumulator calculates that
the anomaly is serious, the device disqualifies the
reference source. If the device spends more than 100
seconds in Lost-phase mode, the reference is disqualified
and a phase alarm is raised on it. If the reference is
disqualified, one of the following transitions takes place:
1. Go to Pre-locked2;
- If a known good stand-by source is available.
Averaged
In the Averaged mode, the frequency (as reported by
sts_current_DPLL_frequency, see Reg. 0C, Reg. 0D and
Reg. 07) is filtered internally using an Infinite Impulse
Response filter, which can be set to either:
z
Fast
(Reg. 40 Bit 6, cnfg_holdover_modes, fast_averaging:
set High),
giving a -3 dB filter response point corresponding to a
period of approx. eight minutes, or
z
Slow
(Reg. 40 Bit 6, cnfg_holdover_modes, fast_averaging:
set Low)
giving a -3 dB filter response point corresponding to a
period of approx. 110 minutes.
2. Go to Holdover;
- If no stand-by sources are available.
Holdover Mode
Holdover mode is the operating condition the device
enters when its currently selected input source becomes
invalid, and no other valid replacement source is
available. In this mode, the device resorts to using stored
frequency data, acquired when the input reference source
was still valid, to control its output frequency.
In Holdover mode, the ACS8530 provides the timing and
synchronization signals to maintain the Network Element
but is not phase locked to any input reference source. Its
output frequency is determined by an averaged version of
the DPLL frequency when last in the Locked Mode.
Revision 3.02/November 2005 © Semtech Corp.
DATASHEET
Instantaneous
In Instantaneous mode, the DPLL freezes at the frequency
it was operating at the time of entering Holdover mode. It
does this by using only its internal DPLL integral path
value (as reported in Reg. 0C, 0D, and 07) to determine
output frequency. The DPLL proportional path is not used
so that any recent phase disturbances have a minimal
effect on the Holdover frequency. The integral value used
can be viewed as a filtered version of the locked output
frequency over a short period of time. The period being in
inverse proportion to the DPLL bandwidth setting.
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DATASHEET
Figure 5 Automatic Mode Control State Diagram (T0 DPLL)
(1) Reset
Free-run
select ref
(state 001)
(2) all refs evaluated
&
at least one ref valid
(3) no valid standby ref
&
(main ref invalid
or out of lock > 100s
Reference sources are flagged as valid when
active, in-band and have no phase alarm set.
(4) valid standby ref
&
[main ref invalid or
(higher-priority ref valid
& in revertive mode) or
out of lock > 100s]
All sources are continuously checked for
activity and frequency
Pre-locked
wait for up to 100s
(state 110)
Only the main source is checked for phase.
A phase lock alarm is only raised on a
reference when that reference has lost phase
whilst being used as the main reference. The
micro-processor can reset the phase lock
alarm.
(5) selected ref
phase locked
A source is considered to have phase locked
when it has been continuously in phase lock
for between 1 and 2 seconds.
Locked
keep ref
(state 100)
(6) no valid standby ref
&
main ref invalid
(10) selected source
phase locked
(9) valid standby ref
&
[main ref invalid or
(higher priority ref valid
& in revertive mode)]
Pre-locked2
wait for up to 100s
(state 101)
(12) valid standby ref
&
(main ref invalid
or out of lock >100s)
(15) valid standby ref
&
[main ref invalid or
(higher-priority ref valid
& in revertive mode) or
out of lock >100s]
(8) phase
regained
within 100s
(7) phase lost
on main ref
(11) no valid standby ref
&
Lost-phase
(main ref invalid
wait for up to 100s
or out of lock >100s)
(state 111)
Holdover
select ref
(state 010)
(13) no valid standby ref
&
(main ref invalid
or out of lock >100s)
(14) all refs evaluated
&
at least one ref valid
F8530D_018AutoModeContStateDia_02
Note...The state diagram above is for T0 DPLL only, and the 3-bit state value refers to the register sts_operating Reg. 09 Bits
[2:0] T0_DPLL_operating _mode. By contrast, the T4 DPLL has only automatic operation and can be in one of only two
possible states: “Instantaneous Automatic Holdover” with zero frequency offset (its start-up state), or “Locked”. The T4 DPLL
states are not configurable by the User and there is no “Free-run” state.
Revision 3.02/November 2005 © Semtech Corp.
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Manual Mode
(Reg. 34 Bit 4, cnfg_input_mode, man_holdover set
High.) The Holdover frequency is determined by the value
in register cnfg_holdover_frequency (Reg. 3E, Reg. 3F,
and part of Reg. 40). This is a 19-bit signed number, with
a LSB resolution of 0.0003068 ppm, which gives an
adjustment range of ±80 ppm. This value can be derived
from a reading of the register
sts_current_DPLL_frequency (Reg. 0D, Reg. 0C and
Reg. 07), which gives, in the same format, an indication of
the current output frequency deviation, which would be
read when the device is locked. If required, this value
could be read by external software and averaged over
time. The averaged value could then be fed to the
cnfg_holdover_frequency register, ready for setting the
averaged frequency value when the device enters
Holdover mode. The sts_current_DPLL_frequency value
is internally derived from the Digital Phase Locked Loop
(DPLL) integral path, which represents a short-term
average measure of the current frequency, depending on
the locked loop bandwidth (Reg. 67) selected.
It is also possible to combine the internal averaging filters
with some additional software filtering. For example the
internal fast filter could be used as an anti-aliasing filter
and the software could further filter this before
determining the actual Holdover frequency. To support
this feature, a facility to read out the internally averaged
frequency has been provided. By setting Reg. 40, Bit 5,
cnfg_holdover_modes, read_average, the value read
back from the cnfg_holdover_frequency register will be
the filtered value. The filtered value is available
regardless of what actual Holdover mode is selected.
Clearly this results in the register not reading back the
data that was written to it.
Example: Software averaging to eliminate temperature drift.
Select Manual Holdover mode by setting Reg. 34 Bit 4,
cnfg_input_mode, man_holdover High.
Select Fast Holdover Averaging mode by setting Reg. 40
Bit 6, cnfg_holdover_modes, auto_averaging High and
Reg. 40 Bit 7 High.
Select to be able to read back filtered output by setting
Reg. 40 Bit 5, cnfg_holdover_modes, read_average High.
Software periodically reads averaged value from the
cnfg_holdover_frequency register and the temperature
(not supplied from ACS8530). Software processes
frequency and temperature and places data in software
look-up table or other algorithm. Software writes back
Revision 3.02/November 2005 © Semtech Corp.
DATASHEET
appropriate averaged value into the
cnfg_holdover_frequency register.
Once Holdover mode is entered, software periodically
updates the cnfg_holdover_frequency register using the
temperature information (not supplied from ACS8530).
Mini-holdover Mode
Holdover mode so far described refers to a state to which
the internal state machine switches as a result of activity
or frequency alarms, and this state is reported in Reg. 09.
To avoid the DPLL’s frequency being pulled off as a result
of a failed input, then the DPLL has a fast mechanism to
freeze its current frequency within one or two cycles of the
input clock source stopping. Under these circumstances
the DPLL enters Mini-holdover mode; the Mini-holdover
frequency used being determined by Reg. 40, Bits [4:3],
cnfg_holdover_modes, mini_holdover_mode.
Mini-holdover mode only lasts until one of the following
happens:
z
z
z
A new source has been selected, or
The state machine enters Holdover mode, or
The original fault on the input recovers.
External Factors Affecting Holdover Mode
If the external OCXO frequency is varying due to
temperature fluctuations in the room, then the
instantaneous value can be different from the average
value, and then it may be possible to exceed the
0.05 ppm limit (depending on how extreme the
temperature fluctuations are). It is advantageous to
shield the OCXO to slow down frequency changes due to
drift and external temperature fluctuations.
The frequency accuracy of Holdover mode has to meet the
ITU-T, ETSI and Telcordia performance requirements. The
performance of the external oscillator clock is critical in
this mode, although only the frequency stability is
important - the stability of the output clock in Holdover is
directly related to the stability of the external oscillator.
Pre-locked2 Mode
This state is very similar to the Pre-Locked state. It is
entered from the Holdover state when a reference source
has been selected and applied to the phase locked loop.
It is also entered if the device is operating in Revertive
mode and a higher-priority reference source is restored.
The ACS8530 will spend a maximum of 100 seconds in
the Pre-locked2 mode. If the device is required to spend
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DATASHEET
up to 700 seconds acquiring lock (e.g. in a Stratum3E
application) external software will be required to force the
device into Locked mode until phase lock has been
achieved. Without software control, if the device cannot
achieve lock within 100 seconds, the reference is
disqualified and a phase alarm is raised on it. It will then
revert to Holdover mode and another reference source, if
available, will be selected.
TO DPLL Main Features
DPLL Architecture and Configuration
z
A Digital PLL gives a stable and consistent level of
performance that can be easily programmed for different
dynamic behavior or operating range. It is not affected by
operating conditions or silicon process variations. Digital
synthesis is used to generate all required SONET/SDH
output frequencies. The digital logic operates at
204.8 MHz that is multiplied up from the external
12.800 MHz oscillator module. Hence the best resolution
of the output signals from the DPLL is one 204.8 MHz
cycle or 4.9 ns.
z
Additional resolution and lower final output jitter is
provided by a de-jittering Analog PLL that reduces the
4.9 ns p-p jitter from the digital down to 500 ps p-p and
60 ps RMS as typical final outputs measured broadband
(from 10 Hz to 1 GHz).
This arrangement combines the advantages of the
flexibility and repeatability of a DPLL with the low jitter of
an APLL. The DPLLs in the ACS8530 are uniquely very
programmable for all PLL parameters of bandwidth (from
0.5 mHz up to 70 Hz), damping factor (from 1.2 to 20),
frequency acceptance and output range (from 0 to
80 ppm, typically 9.2 ppm), input frequency (12 common
SONET/SDH spot frequencies) and input-to-output phase
offset (in 6 ps steps up to 200 ns). There is no
requirement to understand the loop filter equations or
detailed gain parameters since all high level factors such
as overall bandwidth can be set directly via registers in
the microprocessor interface. No external critical
components are required for either the internal DPLLs or
APLLs, providing another key advantage over traditional
discrete designs.
The T4 DPLL is similar in structure to the T0 DPLL, but
since the T4 is only providing a clock synthesis and input
to output frequency translation function, with no defined
requirement for jitter attenuation or input phase jump
absorption, then its bandwidth is limited to the high end
and the T4 does not incorporate many of the Phase Buildout and adjustment facilities of the T0 DPLL.
Revision 3.02/November 2005 © Semtech Corp.
z
z
z
z
z
z
z
z
z
z
Two programmable DPLL bandwidth controls (Locked
and Acquisition bandwidth), each with 18 steps from
0.5 mHz to 70 Hz
Programmable damping factor for optional faster
locking and peaking control. Factors = 1.2, 2.5, 5, 10
or 20
Multiple phase lock detectors
Input to output phase offset adjustment
(Master/Slave), ±200 ns, 6 ps resolution step size
PBO phase offset on source switching - disturbance
down to ±5 ns
Detection of phase jump on the current source:
programmable limit from 1 - 3.5 us in 100 ms
Optional automatic Phase Build-out event on a
detected input phase jump
Multi-cycle phase detection and locking,
programmable up to ±8192 UI - improves jitter
tolerance in direct lock mode
Holdover frequency averaging with a choice of
averaging times: 8 minutes or 110 minutes and value
can be read out
Multiple E1 and DS1 outputs supported
Low jitter MFrSync (2 kHz) and FrSync (8 kHz) outputs
2 kHz and 8 kHz on TO1 to TO7 with programmable
pulse width and polarity.
T4 DPLL Main Features
z
z
z
z
z
z
z
z
z
z
Page 20
A single programmable DPLL bandwidth control:
18 Hz, 35 Hz, or 70 Hz
Programmable damping factor for optional faster
locking and peaking control. Factors = 1.2, 2.5, 5, 10
or 20
Multiple phase lock detectors
Multi-cycle phase detection and locking,
programmable up to ±8192 UI - improves jitter
tolerance in direct lock mode
DS3/E3 support (44.736 MHz / 34.368 MHz) at same
time as OC-N rates from T0
Low jitter E1/DS1 options at same time as OC-N rates
from T0
Frequencies of n x E1/DS1 including 16 and 12 x E1,
and 16 and 24 x DS1 supported
Low jitter 2 kHz and 8 kHz outputs on TO1 to TO7
Can use the T4 DPLL as an Independent FrSync DPLL
Can use the phase detector in T4 DPLL to measure
the input phase difference between two inputs.
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The structure of the T0 and T4 PLLs are shown later in
Figure 11 in the section on output clock ports. That
section also details how the DPLLs and particular output
frequencies are configured. The following sections detail
some component parts of the DPLL.
TO DPLL Automatic Bandwidth Controls
In Automatic Bandwidth Selection mode (Reg. 3B Bit 7),
the T0 DPLL bandwidth setting is selected automatically
from the Acquisition Bandwidth or Locked Bandwidth
configurations programmed in cnfg_T0_DPLL_acq_bw
Reg. 69 and cnfg_T0_DPLL_locked_bw Reg. 67
respectively. If this mode is not selected, the DPLL
acquires and locks using only the bandwidth set by
Reg. 67.
Phase Detectors
A Phase and Frequency detector is used to compare input
and feedback clocks. This operates at input frequencies
up to 77.76 MHz. The whole DPLL can operate at spot
frequencies from 2 kHz up to 77.76 MHz (155.52 MHz is
internally divided down to 77.76 MHz). A common
arrangement however is to use Lock8k mode (See
Reg. 22 to 2D, Bit 6) where all input frequencies are
divided down to 8 kHz internally. Marginally better MTIE
figures may be possible in direct lock mode due to more
regular phase updates. This direct locking capability is
one of the unique features of the ACS8530.
A patented multi-phase detector is used in order to give
an infinitesimally small input phase resolution combined
with large jitter tolerance. The following phase detectors
are used:
z
z
z
The balance between the first two types of phase detector
employed can be adjusted via registers 6A to 6D. The
default settings should be sufficient for all modes.
Adjustment of these settings affects only small signal
overshoot and bandwidth.
The multi-cycle phase detector is enabled via Reg. 74, Bit
6 set to 1 and the range is set in exponentially increasing
steps from ±1 UI, 3 UI, 7 UI, 15 UI … up to 8191 UI via
Reg. 74, Bits [3:0]. When this detector is enabled it keeps
a track of the correct phase position over many cycles of
phase difference to give excellent jitter tolerance. This
provides an alternative to switching to Lock8k mode as a
method of achieving high jitter tolerance.
An additional control (Reg. 74 Bit 5) enables the multiphase detector value to be used in the final phase value
as part of the DPLL loop. When enabled by setting High,
the multi cycle phase value will be used in the loop and
gives faster pull in (but more overshoot). The
characteristics of the loop will be similar to Lock8k mode
where again large input phase differences contribute to
the loop dynamics. Setting the bit Low only uses a max
figure of 360 degrees in the loop and will give slower pullin but gives less overshoot. The final phase position that
the loop has to pull in to is still tracked and remembered
by the multi-cycle phase detector in either case.
Phase Lock/Loss Detection
Phase lock/loss detection is handled in several ways.
Phase loss can be triggered from:
z
z
z
The phase detectors can be configured to be immune to
occasional missing input clock pulses by using nearest
edge detection (±180 deg capture) or the normal
± 360 deg phase capture range which gives frequency
locking. The device will automatically switch to nearest
edge locking when the multi-UI phase detector is not
enabled, and the other phase detectors have detected
that phase lock has been achieved. It is possible to
disable the selection of nearest edge locking via Reg. 03
Revision 3.02/November 2005 © Semtech Corp.
Bit 6 set to 1. In this setting, frequency locking will always
be enabled.
z
Phase and frequency detector (±360 deg or
± 180 deg range)
An Early/ Late Phase detector for fine resolution
A multi-cycle phase detector for large input jitter
tolerance (up to 8191 UI), which captures and
remembers phase differences of many cycles
between input and feedback clocks.
DATASHEET
The fine phase lock detector, which measures the
phase between input and feedback clock
The coarse phase lock detector, which monitors whole
cycle slips
Detection that the DPLL is at min or max frequency
Detection of no activity on the input.
Each of these sources of phase loss indication is
individually enabled via register bits (see Reg. 73, 74 and
4D). Phase lock or lost is used to determine whether to
switch to nearest edge locking and whether to use
Acquisition or Locked bandwidth settings for the DPLL.
Acquisition bandwidth is used for faster pull in from an
unlocked state.
The coarse phase lock detector detects phase differences
of n cycles between input and feedback clocks, where n is
set by Reg. 74, Bits 3:0; the same register that is used for
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the coarse phase detector range, since these functions go
hand in hand. This detector may be used in the case
where it is required that a phase loss indication is not
given for reasonable amounts of input jitter and so the
fine phase loss detector is disabled and the coarse
detector is used instead.
Damping Factor Programmability
The DPLL damping factor is set by default to provide a
maximum wander gain peak of around 0.1 dB. Many of
the specifications (e.g. GR-1244-CORE[19], G.812[10] and
G.813[11]) specify a wander transfer gain of less than
0.2 dB. GR-253[17] specifies jitter (not wander) transfer of
less than 0.1 dB. To accommodate the required levels of
transfer gain, the ACS8530 provides a choice of damping
factors, with more choice given as the bandwidth setting
increases into the frequency regions classified as jitter.
Table 5 shows which damping factors are available for
selection at the different bandwidth settings, and what
the corresponding jitter transfer approximate gain peak
will be.
Table 5 Available Damping Factors for different DPLL
Bandwidths, and associated Jitter Peak Values
DATASHEET
Local Oscillator Clock
The Master system clock on the ACS8530 should be
provided by an external clock oscillator of frequency
12.800 MHz. The clock specification is important for
meeting the AT&T, ITU/ETSI and Telcordia performance
requirements for Holdover mode. Telcordia specifications
require a non-temperature-related drift of less than 1 ppb
per day and a drift of 10 ppb over the temperature range
0 to +50°C.
Telcordia GR-1244 Specification
Table 6 Stratum 3E Specification
Parameter
Value
Initial Offset
±1 x 10-9
Offset Over Temperature (Note i)
±10 x 10-9 (Note ii)
Drift Rate Due to Ageing
±1.16 x 10-14/second (Note ii)
(= 1 x 10-9/day)
Notes: (i) Figure quoted is for long-term drift over the range
0°C to +40°C, but for short-term ( 1 to 3.5 µs could be absorbed
automatically or just flagged by the device with an
interrupt raised, the external processor can then decide
when and whether to perform a PBO event to absorb the
phase disturbance. The monitoring block for detecting
Figure 8 TO DPLL Wander and Jitter Measured Transfer Characteristics (Jitter = 0.2 UI p-p)
Revision 3.02/November 2005 © Semtech Corp.
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DATASHEET
phase shifts within the 0.1 second period operates in the
following manner: When the input phase changes by more
than 156 ns with respect to an internal version of the
DPLL output then the internal 0.1 second interval counter
is started. This internal DPLL output can be considered as
representing the previous phase of the input. If the phase
change is greater than the preset threshold
(programmable from 1 to 3.5 µs) during any time up to the
0.1 second limit, then a PBO event will be triggered
automatically (with Reg. 76, Bits 5 and 4 = 1), hence
absorbing the phase disturbance. The disturbance to the
DPLL is minimal with low DPLL bandwidth and when the
input phase change occurs within a small time interval.
be used to compensate for circuit and board wiring
delays. The output phase can be adjusted in 6 ps steps up
to 200 ns in a positive or negative direction. The phase
adjustment actually changes the phase position of the
feedback clock so that the DPLL adjusts the output clock
phases to compensate. The rate of change of phase is
therefore related to the DPLL bandwidth. For the DPLL to
track large instant changes in phase, either Lock8k mode
should be on, or the coarse phase detector should be
enabled. Register cnfg_phase_offset at Reg. 70 and 71
controls the output phase, which is only used when PBO is
off (Reg. 48, Bit 2 = 0 and Reg. 76, Bit 4 = 0).
When a PBO event is triggered, the device enters a
temporary Holdover state. When in this temporary state,
the phase of the input reference is measured, relative to
the output. The device then automatically accounts for
any measured phase difference and adds the appropriate
phase offset into the DPLL to compensate. Following a
PBO event, whatever the phase difference on change of
input, the output phase transient is minimized to be no
greater than 5 ns.
Input Wander and Jitter Tolerance
On the ACS8530, PBO can be enabled, disabled or frozen
using the microprocessor interface. By default, it is
enabled. When PBO is enabled, PBO can also be frozen (at
the current offset setting). The device will then ignore any
further PBO events occurring on any subsequent
reference switch, and maintain the current phase offset.
If PBO is disabled while the device is in the Locked mode,
there may be a phase shift on the output SEC clocks as
the DPLL locks back to 0 degrees phase error. The rate of
phase shift will depend on the programmed bandwidth.
Enabling PBO whilst in the Locked stated will also trigger
a PBO event.
PBO Phase Offset
In order to minimize the systematic (average) phase error
for PBO, a PBO Phase Offset can be programmed in
0.101 ns steps in the cnfg_PBO_phase_offset register,
Reg.72. The range of the programmable PBO phase offset
is restricted to ±1.4 ns. This can be used to eliminate an
accumulation of phase shifts in one direction.
Input to Output Phase Adjustment
When PBO is off (including Auto-PBO on phase transients),
such that the system always tries to align the outputs to
the inputs at the 0° position, there is a mechanism
provided in the ACS8530 for precise fine tuning of the
output phase position with respect to the input. This can
Revision 3.02/November 2005 © Semtech Corp.
The ACS8530 is compliant to the requirements of all
relevant standards, principally ITU Recommendation
G.825[15], ANSI DS1.101-1999[1], Telcordia GR1244[19],
GR253[17], G812[10], G813[11] and ETS 300 462-5
(1996)[4].
All reference clock inputs have a tight frequency tolerance
but a generous jitter tolerance. Pull-in, hold-in and pull-out
ranges are specified in Table 7. Minimum jitter tolerance
masks are specified in Figures 9 and 10, and Tables 7
and 9, respectively. The ACS8530 will tolerate wander
and jitter components greater than those shown in
Figure 9 and Figure 10, up to a limit determined by a
combination of the apparent long-term frequency offset
caused by wander and the eye-closure caused by jitter
(the input source will be rejected if the offset pushes the
frequency outside the hold-in range for long enough to be
detected, whilst the signal will also be rejected if the eye
closes sufficiently to affect the signal purity). Either the
Lock8k mode, or one of the extended phase capture
ranges should be engaged for high jitter tolerance
according to these masks.
All reference clock ports are monitored for quality,
including frequency offset and general activity. Single
short-term interruptions in selected reference clocks may
not cause re- arrangements, whilst longer interruptions,
or multiple, short-term interruptions, will cause rearrangements, as will frequency offsets which are
sufficiently large or sufficiently long to cause loss-of-lock
in the phase-locked loop. The failed reference source will
be removed from the priority table and declared as
unserviceable, until its perceived quality has been
restored to an acceptable level.
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Table 7 Input Reference Source Jitter Tolerance
Jitter Tolerance
Frequency
Monitor
Acceptance
Range
Frequency Acceptance Range
(Pull-in)
Frequency Acceptance Range
(Hold-in)
Frequency Acceptance Range
(Pull-out)
±4.6 ppm (see Note (i))
±9.2 ppm (see Note (ii))
±4.6 ppm (see Note (i))
±9.2 ppm (see Note (ii))
±4.6 ppm (see Note (i))
±9.2 ppm (see Note (ii))
G.703[6]
G.783[9]
±16.6 ppm
G.823[13]
GR-1244-CORE[19]
Notes: (i) The frequency acceptance and generation range will be ±4.6 ppm around the required frequency when the external crystal
frequency accuracy is within a tolerance of ±4.6 ppm.
(ii) The fundamental acceptance range and generation range is ±9.2 ppm with an exact external crystal frequency of 12.800 MHz. This
is the default DPLL range, the range is also programmable from 0 to 80 ppm in 0.08 ppm steps.
Figure 9 Minimum Input Jitter Tolerance (OC-3/STM-1)
A0
A1
A2
A3
A4
Jitter and Wander Frequency (log scale)
f0
f1
f2
f3
f4
f5
f6
f7
f8
f9
F8530_003MINIPJITTOLOC3STM1_02
Note...For inputs supporting G.783[9] compliant sources.)
Table 8 Amplitude and Frequency Values for Jitter Tolerance (OC-3/STM-1)
STM
level
Peak to peak amplitude (unit
Interval)
A0
STM-1
2800
A1
A2
A3
A4
311 39 1.5 0.15
Revision 3.02/November 2005 © Semtech Corp.
Frequency (Hz)
F0
F1
F2
F3
F4
12 u 178 u 1.6 m 15.6 m 0.125
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F5
19.3
F6
F7
F8
F9
500 6.5 k 65 k 1.3
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Figure 10 Minimum Input Jitter Tolerance (DS1/E1)
Peak-to-peak Jitter and Wander Amplitude
(log scale)
A1
A2
Jitter and Wander Frequency (log scale)
f1
f2
f3
F8530D_004MINIPJITTOLDS1E1_02
f4
Table 9 Amplitude and Frequency Values for Jitter Tolerance (DS1/E1)
Type
Spec.
Amplitude (UI p-p)
A1
Frequency (Hz)
A2
F1
F2
F3
F4
DS1
GR-1244-CORE[19]
5
0.1
10
500
8k
40 k
E1
ITU G.823[13]
1.5
0.2
20
2.4 k
18 k
100
Using the DPLLs for Accurate Frequency and Phase
Reporting
The frequency monitors in the ACS8530 perform
frequency monitoring with a programmable acceptable
limit of up to ±60.96 ppm. The resolution of the
measurement is 3.8 ppm and the measured frequency
can be read back from Reg. 4C, with channel selection at
Reg. 4B. For more accurate measurement of both
frequency and phase, the T0 and T4 DPLLs and their
phase detectors, can be used to monitor both input
frequency and phase. The T0 DPLL is always monitoring
the currently locked to source, but if the T4 path is not
used then the T4 DPLL can be used as a roving phase and
frequency meter. Via software control it could be switched
to monitor each input in turn and both the phase and
frequency can be reported with a very fine resolution.
The registers sts_current_DPLL_frequency (Reg. 0C,
Reg. 0D and Reg. 07) report the frequency of either the
T0 or T4 DPLL with respect to the external crystal XO
frequency (after calibration via Reg. 3C, 3D if used). The
selection of T4 or T0 DPLL reporting is made via Reg. 4B,
Bit 4. The value is a 19-bit signed number with one LSB
representing 0.0003068 ppm (range of ±80 ppm). This
value is actually the integral path value in the DPLL, and
as such corresponds to an averaged measurement of the
Revision 3.02/November 2005 © Semtech Corp.
input frequency, with an averaging time inversely
proportional to the DPLL bandwidth setting. Reading this
regularly can show how the currently locked source is
varying in value e.g. due to frequency wander on its input.
The input phase, as seen at the DPLL phase detector, can
be read back from register sts_current_phase, Reg. 77
and 78. T0 or T4 DPLL phase detector reporting is again
controlled by Reg. 4B, Bit 4. One LSB corresponds to
approximately 0.7 degrees phase difference. For the T0
DPLL this will be reporting the phase difference between
the input and the internal feedback clock. The phase
result is internally averaged or filtered with a -3 dB
attenuation point at approximately 100 Hz. For low DPLL
bandwidths, 1 mHz for example, this measured phase
information from the T0 DPLL gives input phase wander in
the frequency band from for example 1 mHz to 100 Hz.
This could be used to give a crude input MTIE
measurement up to an observation period of
approximately 1000 seconds using external software.
In addition, the T4 DPLL phase detector can be used to
make a phase measurement between two inputs.
Reg. 65, Bit 7 is used to switch one input to the T4 phase
detector over to the current T0 input. The other phase
detector input remains connected to the selected T4 input
source, the selected source can be forced via Reg. 35,
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Bits [3:0], or changed via the T4 priority (Reg. 18 to 1E,
when Reg. 4B, Bit 4 = 1).
Consequently the phase detector from the T4 DPLL could
be used to measure the phase difference between the
currently selected source and the stand-by source, or it
could be used to measure the phase wander of all standby sources with respect to the current source by selecting
each input in sequence. An MTIE and TDEV calculation
could be made for each input via external processing.
Configuration for Redundancy Protection
When two ACS8530 devices are to be used in a
redundancy-protection scheme within a Network Element
(NE), one will be designated as Master, one as Slave.
Table 10 How to Align the Outputs of Two ACS8530s
Action
Result
If possible, one device (the
nominated Slave) should lock to
the other device (the nominated
Master).
With the Slave locked to the
Master, their output frequencies
will be guaranteed to be the
same.
All programmed priorities within
the two devices should be the
same, except for the fact that:
(1) the Master output is
designated the highest priority
input on the Slave,
(2) the Slave output is
designated zero priority
(disabled) on the Master (Reg. 18
to 1E).
These two actions ensure that if
the Master device fails, the Slave
device will switch to lock to the
same source that the Master was
locked to before it failed.
It is expected that an NE will use the T0 output for its
internal operations. The phase of the outputs from the T4
path (TO8 & TO9) will not be aligned, unless the T4
outputs are locked to the T0 outputs.
In many applications, the clocks supplied into the system
are required to be aligned not only in frequency, but also
in phase between the Master and Slave devices. This
ensures minimal disturbance when any clock sink
switches between Master and Slave.
In order to ensure that the outputs of the two ACS8530s
are always aligned in frequency and phase, the
procedures in Table 10 should be followed.
In order to maintain the conditions outlined in Table 10 it
is necessary for software systems to maintain monitoring
and control functions. These monitoring functions should
either poll the device or respond to interrupts in order to
maintain the correct settings within the two devices.
Please refer to the descriptions or registers mentioned in
Table 10 and also Regs 34, 3B, 48, 67 and 69, for more
details on these associated settings. See also Application
Note AN-SETS-7.
Table 11 MSTSLVB Pin Operation
MSTSLVB
1=
Master
Any input detected as invalid in
one device should be disabled
within the other device
(Reg. 0E/0F & 30/31).
Phase Build-out should be
disabled on the Slave whilst it is
locked to the Master.
This will ensure that the phase of
the Slave is locked to the phase
of the Master. It also enables the
use of the Phase offset control
register to compensate for delays
between the Master and Slave.
Revertive mode should be
enabled.
This will ensure that the Slave
locks to the Master although it
may have been locked to another
source previously.
The bandwidth of the Slave
should be set higher than that of
the Master (it is recommended to
configure the slave with the
highest supported bandwidth).
This ensures that any transient
occurring on the output of the
Master is followed as closely as
possible on the Slave.
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DATASHEET
Page 29
Feature
Setting
Reason
Priority of
input I11
As programmed
(program 0 to
ensure it gets
disabled)
Make sure that the
designated Master
device cannot lock to
the output of the
Slave device.
Phase
Build-out
As programmed in
register
If the system
requires PBO, then
this being enabled
on the Master will
give the overall
system performance
with PBO. The slave
only needs to track
the Master (no PBO).
Revertive
mode
As programmed in
register
Revertive behavior of
the Master in a
Master/Slave
system will define
the overall Revertive
behavior of the
system.
T0 DPLL
bandwidth
As programmed in
register (automatic
or manual)
Device selects
locked or acquisition
bandwidth.
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Table 11 MSTSLVB Pin Operation (cont...)
MSTSLVB
0=
Slave
Feature
Setting
Reason
Priority of
input I11
1 (highest priority)
When a Slave, this
input is designated
as that connected to
the output of the
Master.
Phase
Build-out
Disabled
This ensures that the
Slave locks to the
Master with the
minimum phase
offset possible.
Revertive
mode
Enabled
This ensures that the
Slave always locks to
the Master when it is
available.
T0 DPLL
bandwidth
Forced to the
acquisition
bandwidth setting
A higher bandwidth
on the Slave ensures
closer phase
tracking.
For direct hardware control of Master or Slave operation
the Master/Slave control pin (MSTSLVB) can be used to
externally control some of these functions according to
Table 11. These functions can also be controlled via
software.
Whilst the Master and Slave outputs could be crossconnected and connected to any input on the alternative
device, input I11 has been chosen as the input controlled
by the MSTSLVB pin.
Alignment of Priority Tables in Master and Slave
ACS8530
In a redundant system where the Slave is normally locked
to the Master device, if the Master device fails the Slave
device must revert to locking to the same external
reference that the Master was locked to. This will ensure
that minimum disturbance, both in frequency and phase,
is created on the output of the Slave device due to the
failure of the Master device. As stated previously
(Table 10), it is recommended that the programmed
priorities of the reference sources are the same in both
devices, apart from the Master/Slave cross-connect
inputs.
Both devices can also monitor all their reference sources
and determine the validity of each source. It is
recommended that the availability of valid sources are
also aligned between the two devices. This is achieved by
writing the value, as reported by sts_sources_valid
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DATASHEET
Reg. 0E & 0F), from one device into the
cnfg_sts_remote_sources_valid register (Reg. 30 & 31)
of the other. This will ensure that any source considered
invalid by one device is also considered invalid by the
other. If a failure of the Master does occur, this will ensure
that the Slave will always select the reference that the
Master was locked to.
T4 Generation in Master and Slave ACS8530
As specified by the I.T.U., there is no need to align the
phases of the T4 outputs in Master and Slave devices. For
a fully redundant system, there is a need, however, to
ensure that all devices select the same reference source.
As there is no need to guarantee the alignment of phase
of the T4 outputs, the Slave devices T4 input does not
need to lock to the Masters T4 output, but only needs to
ensure that it locks to the same external reference
source. The actions of aligning the priority tables and
available reference sources performed for the T0 outputs
will be equally valid for the T4 outputs. The only difference
being that the input connected to the Master's output is
disabled for the T4 path (allowing it only to lock to external
references). This can be easily achieved as the T4 and T0
paths have separate programmed priorities. There is no
defined Holdover requirement for the T4 path.
Alignment of the Output Clock Phases in Master
and Slave ACS8530
When the ACS8530 is locked to a reference source of
frequency f, the output clocks of frequency f will be inphase with the reference source (with Phase Build-out
disabled). As all T0 output clocks from the ACS8530 are
derived from the same T0 frequency, any frequency
greater than f at the output will be “falling edge aligned”
with the output at frequency f. Any frequency less than f
will be effectively a division of f, if possible. Similarly for
T4, all T4 output clocks will be phase-related to the T4
input.
The effect of this relationship is that if the Master and
Slave devices are cross-connected with 19.44 MHz
clocks, their output clocks at 19.44 MHz, 38.88 MHz,
77.76 MHz, 155.52 MHz & 311.04 MHz will be aligned
between the two devices. However, their outputs of
6.48 MHZ, 1.544 MHz, 2.048 MHz, 2 kHz and 8 kHz etc.
would not necessarily be aligned. Whilst most
applications would not be affected by the non-alignment
of most of these clocks, the non-alignment of the 2 kHz
and/or the 8 kHz may cause framing errors.
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There are two ways to align the 2 kHz and/or 8 kHz
outputs:
1. the use of the External syncing function, or
2. directly locking the Slave to 2 kHz or 8 kHz from the
Master.
By directly locking the Slave to the 2 kHz (MFrSync) output
of the Master, all frequencies output from the Slave will
be in phase alignment with the same frequency
generated from the Master. If the Slave is directly locked
to the 8 kHz (FrSync) output from the Master, then all
frequencies except for 2 kHz MFrSync outputs will be in
alignment.
If using the external syncing function then the clock and
sync signals need to be interconnected between the
Master and Slave.
This requires some configuration enhancements. The
Sync signal is not locked to, it is sampled using the
reference clock and used to realign the generated
outputs. The generated outputs are still always locked to
the reference clock and related to each other. Details on
the Master and Slave interconnection wiring and software
configuration can be found in refer to the application note
AN-SETS-2. The following section describes the
resynchronization operation of the MFrSync via the
SYNC2K input.
MFrSync and FrSync Alignment-SYNC2K
The SYNC2K input (pin 45) is monitored by the ACS8530
for consistent phase and correct frequency and if it does
not pass these quality checks, an alarm flag is raised
(Reg. 08, Bit 7 and Reg. 09, Bit 7). The check for
consistent phase involves checking that each input edge
is within an expected timing window. The window size is
set by Reg. 7C, Bits [6:4]. An internal detector senses that
a correct SYNC2K signal is present and only then allows
the signal to resynchronize the internal dividers that
generate the 8 kHz FrSync and 2 kHz MFrSync outputs.
This sequence avoids spurious resynchronizations that
may otherwise occur with connections and
disconnections of the SYNC2K input.
The SYNC2K input will normally be a 2 kHz frequency, only
its falling edge is used. It can however be at a frequencies
of 4 kHz or 8 kHz without any change to the register
setups. Only alignment of the 8 kHz will be achieved in
this case.
Safe sampling of the SYNC2K input is achieved by using
the currently selected clock reference source to do the
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DATASHEET
input sampling. This is based on the principle that FrSync
alignment is being used on a Slave device that is locked
to the clock reference of a Master device that is also
providing the 2 kHz SYNC2K input. Phase Build-out mode
should be off (Reg. 48, Bit 2 = 0). The 2 kHz MFrSync
output from the Master device has its falling edge aligned
with the falling edge of the other output clocks, hence the
SYNC2K input is normally sampled on the rising edge of
the current input reference clock, in order to provide the
most margin. Some modification of the expected timing of
the SYNC2K with respect to the reference clock can be
achieved via Reg. 7B, Bits [1:0]. This allows for the
SYNC2K input to arrive either half a reference clock cycle
early or up to one and a half cycle late, hence allowing a
safe sampling margin to be maintained.
A different sampling resolution is used depending on the
input reference frequency and the setting of Reg. 7B Bit 6,
cnfg_sync_phase. With this bit Low, the SYNC2K input
sampling has a 6.48 MHz resolution, this being the
preferred reference frequency to lock to from the Master,
in conjunction with the SYNC2K 2 kHz, since it gives the
most timing margin on the sampling and aligns all of the
higher rate OC-3 derived clocks. When Bit 6 is High the
SYNC2K can have a sampling resolution of either
19.44 MHz (when the current locked to reference is
19.44 MHz) or 38.88 MHz (all other frequencies). This
would allow for instance a 19.44 MHz and 2 kHz pair to
be used for Slave synchronization or for Line Card
synchronization. Reg. 7B Bit 7, indep_Fr/MFrSync
controls whether the 2 kHz MFrSync and 8 kHz FrSync
outputs keep their precise alignment with the other
output clocks.
When indep_FrSync/MFrSync Reg. 7B Bit 7 is Low the
FrSyncs and the other higher rate clocks are not
independent and their alignment on the falling 8kHz edge
is maintained. This means that when bit Sync_OC-N_rates
is High, the OC-N rate dividers and clocks are also
synchronized by the SYNC2K input. On a change of phase
position of the SYNC2K, this could result in a shift in
phase of the 6.48 MHz output clock when a 19.44 MHz
precision is used for the SYNC2K input. To avoid
disturbing any of the output clocks and only align the
MFrSync and FrSync outputs, at the chosen level of
precision, then independent Frame Sync mode can be
used (Reg. 7B, Bit 7 = 1). Edge alignment of the FrSync
output with other clocks outputs may then change
depending on the SYNC2K sampling precision used. For
example, with a 19.44 MHz reference input clock and
Reg. 7B, Bits 6 & 7 both High (Independent mode and
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Sync OC-N rates), then the FrSync output will still align
with the 19.44 MHz output but not with the 6.48 MHz
output clock.
The FrSync and MFrSync outputs always come from the
T0 DPLL path. 2kHz and 8kHz outputs can also be
produced at the TO1 to TO7 outputs. These can come
from either the T0 DPLL or from the T4 DPLL, controlled
by Reg. 7A, Bit 7.
If required, this allows the T4 DPLL to be used as a
separate PLL for the FrSync and MFrSync path with a
2 kHz input and 2 kHz and 8 kHz Frame Sync outputs.
Output Clock Ports
The device supports a set of main output clocks, T0 and
T4, and a pair of secondary Sync outputs, FrSync and
MFrSync. The two main output clocks, T0 and T4, are
independent of each other and are individually selectable.
The two secondary output clocks, FrSync and MFrSync,
are derived from either T0 or T4. The frequencies of the
main output clocks are selectable from a range of predefined spot frequencies and a variety of output
technologies are supported, as defined in Table 12.
PECL/LVDS/AMI Output Port Selection
The choice of PECL or LVDS compatibility is programmed
via the cnfg_differential_outputs register, Reg. 3A.
AMI port, TO8, supports a composite clock, consisting of a
64 kHz AMI clock with 8 kHz boundaries marked by
deliberate violations of the AMI coding rules, as specified
in ITU recommendation G.703[6]. Departures from the
nominal pattern are detected within the ACS8530, and
may cause reference-switching if too frequent. See “DC
Characteristics: AMI Input/Output Port” on page 139., for
more details.
Output Frequency Selection and Configuration
The output frequency at many of the outputs is controlled
by a number of inter-dependent parameters. These
parameters control the selections within the various
blocks shown in Figure 11.
The ACS8530 contains two main DPLL/APLL paths. Whilst
they are largely independent, there are a number of ways
in which these two structures can interact. Figure 11
shows an expansion of the original Block Diagram
(Figure 1) for the PLL paths.
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DATASHEET
T0 DPLL and APLLs
The T0 DPLL always produces 77.76 MHz regardless of
either the reference frequency (frequency at the input pin
of the device) or the locking frequency (frequency at the
input of the DPLL Phase and Frequency Detector (PFD)).
The input reference is either passed directly to the PFD or
via a pre-divider (not shown) to produce the reference
input. The feedback 77.76 MHz is either divided or
synthesized to generate the locking frequency.
Digital Frequency Synthesis (DFS) is a technique for
generating an output frequency using a higher frequency
system clock (204.8 MHz in the case of the 77.76 MHz
synthesis). However, the edges of the output clock are not
ideally placed in time, since all edges of the output clock
will be aligned to the active edge of the system clock. This
will mean that the generated clock will inherently have
jitter on it equivalent to one period of the system clock.
The T0 77M forward DFS block uses DFS clocked by the
204.8 MHz system clock to synthesize the 77.76 MHz
and, therefore, has an inherent 4.9 ns of p-p jitter. There
is an option to use an APLL, the T0 feedback APLL, to filter
out this jitter before the 77.76 MHz is used to generate
the feedback locking frequency in the T0 feedback DFS
block. This analog feedback option allows a lower jitter
(