ACS8520T Semtech, ACS8520T Datasheet - Page 13

• Manufacturer Part Number: ACS8520T
• Description: Synchronous Equipment Timing Source (SETS) for Stratum 3/4E/4 and SMC Systems
• Manufacturer: Semtech

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.
Figure 3 Inactivity and Irregularity Monitoring
Revision 3.02/October 2005 © Semtech Corp.
ADVANCED COMMUNICATIONS
Alarm
Reference
Source
Leaky
Bucket
Response
Inactivities/Irregularities
Programmable Fall Slopes
FINAL
Page 13
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.
ACS8520 SETS
(all programmable)
F8530D_026Inact_Irreg_Mon_02
bucket_size
upper_threshold
lower_threshold
DATASHEET
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