zl30102 Zarlink Semiconductor, zl30102 Datasheet - Page 25

• Manufacturer Part Number: zl30102
• Description: T1/e1 Stratum 4/4e Redundant System Clock Synchronizer For Ds1/e1 And H.110
• Manufacturer: Zarlink Semiconductor

4.5.2.2
When the currently-active input reference in Automatic mode fails through a subtle frequency offset, the REF_FAIL
output is asserted as soon as the Precise Frequency Monitor indicates an out-of-range reference (10 to 20
seconds). The HOLDOVER output is briefly asserted (approximately three reference input cycles) and the
REF_SEL outputs indicate that the device has switched to the other reference. Where the new reference is close
enough in frequency and TIE-corrected phase for the output to stay within the phase-lock-window, the LOCK output
will remain asserted through the reference-switch process. Where the new reference has enough frequency offset
and/or TIE-corrected phase offset to force the output outside the phase-lock-window, the LOCK output will de-
assert, the lock-qualify timer is reset, and LOCK will stay de-asserted for the full lock-time duration. Figure 16
illustrates this process.
Automatic Reference Switching - Reference Frequency Out-of-Range
REF0
REF_DIS0
(internal signal)
REF_OOR0
(internal signal)
REF_FAIL0
HOLDOVER
REF_SEL
LOCK
Note: this scenario is based on REF1 remaining good throughout the duration.
Figure 15 - Automatic Reference Switching - Coarse Reference Failure
REF0
SCM or CFM failure
1 s
2.5 s
REF1
Zarlink Semiconductor Inc.
ZL30102
Lock Time
10 s
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Data Sheet