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参数资料
| 型号： | ACS8509 |
| 元件分类： | 数字传输电路 |
| 英文描述： | ATM/SONET/SDH SUPPORT CIRCUIT, PQFP100 |
| 封装： | LQFP-100 |
| 文件页数： | 33/68页 |
| 文件大小： | 703K |
| 代理商： | ACS8509 |
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ADVANCED COMMUNICATIONS
FINAL
DATASHEET
Revision 2.00/January 2006 Semtech Corp.
Page 39
www.semtech.com
ACS8509 SETS
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 9.
The “leaky bucket” accumulators are programmable for
size, alarm set & 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 (x1, x0.5, x0.25 and x0.125) 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, active reference
source is selected.
Frequency Monitoring
The ACS8509 performs frequency monitoring to identify
reference sources which have drifted outside the
acceptable frequency range of ±16.6 ppm (measured
with respect to the output 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. The ACS8509
DPLL has a programmable frequency limit of ±80 ppm. If
the range is programmed to be > 16.6 ppm, the frequency
monitors should be disabled so the input reference
source is not automatically rejected as out of frequency
range.
Modes of Operation
The ACS8509 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, Figure 10.
The ACS8509 can operate in Forced or Automatic control.
On reset, the ACS8509 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 ACS8509 are
based on the Master clock frequency provided from the
external oscillator and are not synchronized to an input
reference source. 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 Master clock.
The transition from Free-run to Pre-locked occurs when
the ACS8509 selects a reference source.
Pre-Locked mode
The ACS8509 will enter the Locked state in a maximum of
100 seconds, as defined by GR-1244-CORE specification,
if the selected reference source is of good quality. If the
device cannot achieve lock within 100 seconds, it reverts
to Free-run mode and another reference source is
selected.
Locked mode
The Locked mode is used when an input reference source
has been selected and the PLL has had time to lock.
When the Locked mode is achieved, the output signal is in
phase and locked to the selected input reference source.
The selected input reference source is determined by the
priority table.
When the ACS8509 is in Locked mode, the output
frequency and phase follows that of the selected input
reference source. Variations of the external crystal
frequency have a minimal effect on the output frequency.
Only the minimum to maximum frequency range is
affected. Note that the term, “in phase”, is not applied in
the conventional sense when the ACS8509 is used as a
frequency translator (e.g., when the input frequency is
2.048 MHz and the output frequency is 19.44 MHz) as
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相关代理商/技术参数 |
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|---|---|
| ACS8509T | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:Synchronous Equipment Timing Source for SONET or SDH Network Elements |
| ACS8510 | 制造商:Semtech Corporation 功能描述:Timing Source 100-Pin LQFP |
| ACS8510_03 | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:Synchronous Equipment Timing Source for SONET or SDH Network Elements |
| ACS8510REV2.1 | 制造商:Semtech Corporation 功能描述:Timing Source 100-Pin LQFP |
| ACS8510REV2.1SETS | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Synchronous Equipment Timing Source for SONET or SDH Network Elements |
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