STC5455 Datasheet, PDF (21/56 Pages) Connor-Winfield Corporation – Synchronous Clock for SETS

STC5455
Synchronous Clock for SETS
Data sheet
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
register 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 register Disqualification Range.
The qualification range must be set less than the dis-
qualification range. Additionally, qualification soaking
time may be programmed from 0 to 63 seconds by
writing to register Qualification Soaking Time. The
pull-in range is the same as the disqualification range.
Activity Alarm
Asserted
Activity
Not Good
Activity Alarm
De-Asserted
Activity Alarm
Asserted
Continuously
Within Offset Qualification
Range for more than
Qualification soaking Time
The frequency offset of each reference is relative to
the internal freerun FcluocnkctmioaynableSrepaedcbifyicsaetleioctning
the reference in the Ref Info Selector register and
then reading the offset value from 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 more
than the qualification soaking time. An activity alarm
or frequency offset beyond the disqualification range
will disqualify the reference. It may then be re-quali-
fied if the activity alarm is off and the reference is
within the qualification range for more than the qualifi-
cation time.
The reference qualification status of each reference
may be read from register Ref Qual.
Automatic Reference Election Mechanism
The STC5455 has an auto reference elector always
elect the best candidate from the reference inputs
according to the revertivity status, each reference’s
priority and qualification. This mechanism operates
independent of reference selection mode. In other
word, regardless what the current reference selection
mode is, the auto reference elector always work in
this mechanism. The detail description of the refer-
ence selection mode is in following sections.
The reference priority is indicated in the reference pri-
ority table which is shown in register Ref Priority
Table individually for each timing generator. Each ref-
erence has one entry in the table, which may be set to
value from 0 to 15. ‘0’ revokes the reference from the
election, while 1 to 15 set the priority, where ‘1’ has
the highest, and ‘15’ has the lowest priority. The high-
est priority pre-qualified reference then is a candidate
selected by the automatic reference elector. If multi-
ple references share the same priority, the one that
has been qualified for the longest time will be recom-
mended to be the candidate. If the current highest pri-
ority reference input fails, the next-highest priority
reference is selected as the candidate.
Activity
Good
Qualified
Out of Disqualification Range
Figure 3: Reference Qualification Scheme
In order to avoid disturbance of the clock output, the
candidate reference selected by automatic reference
elector should be handled in two different mode.
Revertive mode and non-revertive mode. The mode
is determined by either enabling or disabling the
“revertive” bit of the Control Mode to “1” for revertive
or to “0” for non-revertive operation.
Preliminary
Page 21 of 56 TM121 Rev: P1.3
© Copyright the Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
Date: October 24, 2011