ACS8526P SEMTECH [Semtech Corporation], ACS8526P Datasheet - Page 9

• Manufacturer Part Number: ACS8526P
• Description: Line Card Protection Switch for PDH, SONET or SDH Systems
• Manufacturer: SEMTECH [Semtech Corporation]

input phase change, DPLL bandwidth, DPLL frequency
limit, and phase detector capture range. The ACS8526
always complies with GR-1244-CORE
3 (max rate of phase change of 81 ns/1.326 ms), for
input frequencies at 6.48 MHz or higher, with the default
1UI phase detector capture range.
For inputs at a lower frequency than 6.48 MHz (e.g. 8 kHz)
with the DPLL frequency limit set to greater than ±30 ppm
(note default is ±80 ppm), then to ensure compliance with
GR-1244-CORE
or 70 Hz, the input phase difference between the Master
and Slave inputs to the line card PLL should be limited to
less than 600, 330 ns or 190 ns respectively.
Alternatively, the DPLL frequency range should be set
<±30 ppm. A well designed system would have Master
and Slave clock from the clock sync cards aligned to
within a few nanoseconds. In which case a complete
system using the Semtech SETS clock card parts
(ACS8530, ACS8520 or ACS8510) and this line card part
would be fully compliant to GR-1244-CORE
specifications under all conditions due to the lower
frequency range and bandwidth set at the clock card end.
Activity Monitors
Two types of Activity monitors are incorporated in the
ACS8526:
SEC Activity Monitors
There is a SEC activity monitor assigned to each SEC
input. Each has a programmable Leaky Bucket
Accumulator which is used to determine at what point the
period of inactivity is deemed sufficient to raise or clear an
alarm. Each SEC has its own no activity alarm bit in
Reg. 11, sts_reference_sources,. The monitors operate
continuously such that at all times the activity status of
each SEC input is known.
Leaky Bucket Accumulator
Anomalies detected by the Activity Monitor are integrated
in a Leaky Bucket Accumulator. There is one Leaky Bucket
Revision 4.01/June 2006 © Semtech Corp.
ADVANCED COMMUNICATIONS
SEC Activity Monitors, which raise flags in Reg. 11,
sts_reference_sources for each SEC in event of no
input activity, as defined by the configuration of Leaky
Bucket accumulator.
Fast Activity Monitor (part of DPLL), which raises LOS
alarm on pin LOS_ALARM in event of two missing
cycles of input activity on the selected source.
[13]
at DPLL bandwidth settings of 18, 35
[13]
spec for Stratum
[13]
FINAL
Page 9
Accumulator per SEC input. The accumulators share a set
of configuration parameters which can be programmed
via Reg. 50 to Reg. 53. They are:
There are occasional anomalies that do not cause the
Accumulator to cross the alarm setting threshold, but if
the Bucket fills faster than it leaks it will eventually cross
the alarm setting threshold and the associated SEC Input
Activity Alarm bit in Reg. 11, sts_reference_sources, will
change to 1 (Alarm active).
Each Leaky Bucket Accumulator is a digital circuit which
mimics the operation of an analog integrator. If several
events occur close together, each event adds to the
amplitude and the alarm will be triggered quickly; if events
occur over a greater time period 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. Similarly, 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). Figure 3 illustrates the behavior of the Leaky Bucket
Accumulator.
Each SEC input 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 continues 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.
Bucket size
Alarm trigger (set threshold)
Alarm clear (reset threshold)
Leak rate (decay rate)
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