STC5423 Datasheet, PDF (20/60 Pages) Connor-Winfield Corporation – Synchronous Clock for SETS

STC5423
Synchronous Clock for SETS
Data sheet
erence inputs are LVCMOS and monitored continu-
ously for frequency, activity and quality. Each timing
generator may select any of the reference inputs
when the device is in external timing mode. T4 may
accept T0’s output as its input via internal feedback
path.
Input Frequency and Frequency Offset Detection
Input frequencies are detected automatically in
STC5423. The detector operates to detect the fre-
quency of reference inputs continuously. Any carrier
frequency change will be detected within 1ms. Each
input is also monitored for frequency offset between
input and the internal freerun clock. The frequency
offset is a key element to determine qualification of
the reference inputs. See register Ref Info Selector
and Ref Info.
Activity Monitoring
Activity monitoring is also a consecutive process
which is used to identify if the reference input is in
normal. It is accomplished with a leaky bucket accu-
mulation algorithm, as shown in Figure 2. The “leaky
bucket” accumulator has a fill observation window
that may be set from 1 to 16ms, where any hit of sig-
nal abnormality (or multiple hits) during the window
increments the bucket count by one. The leak obser-
vation window is 1 to 16 times the fill observation win-
dow. The leaky bucket accumulator decrements by
one for each leak observation window that passes
with no signal abnormality. Both windows operate in a
consecutive, non-overlapping manner. The bucket
accumulator has alarm assert and alarm de-assert
thresholds that can each be programmed from 1 to
64.
Frequency
Ref
Detector
Fill Observa-
tion Window,
1ms ~ 16ms
Pulse
Monitor
Leaky
Bucket
Accumulator
Alarm Assert
Alarm De-Assert
Leak Observation
Window, 1~16 x Fill
Observation Window
Figure 2: Activity Monitor
Applications can write to the following registers to
configure the activity monitor: Fill Obs Window,
Leak Obs Window, Bucket Size, Assert Threshold,
and De Assert ThreFshuonldc.tional Specification
Setting the bucket size to 0 will bypass the leak
bucket accumulator and assert or de-assert the activ-
ity alarm based on results of frequency detector and
pulse monitor only. A non-zero bucket size must be
greater than or equal to the alarm assert threshold
value. The alarm assert threshold value must be
greater than the alarm de-assert threshold value and
less than or equal to the bucket size value. Attempted
writes of invalid values will be ignored. Therefore,
user must carefully plan an appropriate sequence of
writes when re-configure the activity monitor. See the
registers Bucket Size, Assert Threshold and De
Assert Threshold for details.
Alarms appear in the Refs Activity register. A “1”
indicates activity, and a “0” indicates an alarm, no
activity. Note that if a reference is detected as a differ-
ent frequency, the leaky bucket accumulator is set to
the bucket size value and the reference will become
inactive immediately.
Input Qualification
A selected reference is “qualified” if it passes the
activity evaluation and its frequency offset is within
the programmed qualification range for over a pre-
programmed soaking time.
A reference qualification range may be programmed
up to 102.3 ppm by writing to register Qualification
Range, and a disqualification range set up to 102.3
ppm, by writing to the register Disqualification
Range. The qualification range must be set less than
the disqualification range. Additionally, qualification
soaking time may be programmed from 0 to 63 sec-
onds by writing to the register Qualification Soaking
Time. The pull-in range is the same as the disqualifi-
cation range.
The frequency offset of each reference is relative to
the internal freerun clock may be read by selecting
the reference in the register Ref Info Selector and
then reading the offset value from the register Ref
Info.
Figure 3 shows the reference qualification scheme. A
reference is qualified if it has no activity alarm and is
continuous within the qualification range for over the
qualification soaking time. An activity alarm or fre-
quency offset beyond the disqualification range will
Page 20 of 60 TM114 Rev: 1.4
© Copyright the Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
Date: October 24, 2011