zl30410 Zarlink Semiconductor, zl30410 Datasheet - Page 21

• Manufacturer Part Number: zl30410
• Description: Multi-service Line Card Pll
• Manufacturer: Zarlink Semiconductor

19.44 MHz references. For the 8 kHz input reference, the recovery from Auto Holdover state must transition
through the Holdover state to guarantee “hit-less” recovery (for details see section 5.1.3 on page 20). If the
reference clock failure persists for a period of time that exceeds the system design limit, the system control
processor may initiate a reference switch. If the secondary reference is available the ZL30410 will briefly switch into
Holdover mode and then transition to Normal mode.
The new reference clock will most likely have a different phase but it may also have a different fractional frequency
offset. In order to lock to a new reference with a different frequency, the Core PLL may be stepped gradually
towards the new frequency.
5.1.5
The NORMAL to HOLDOVER to NORMAL mode switching is usually performed when:
•
•
A reference clock is available but its frequency drifts beyond some specified limit. In a Network Element with
stratum 3 internal clocks, the reference failure is declared when its frequency drifts more than ±12 ppm
beyond its nominal frequency. The ZL30410 indicates this condition by setting PRIOR or SECOR status pins
to logic high.
During routine maintenance of equipment when orderly switching of reference clocks is possible. This may
happen when synchronization references must be rearranged or when a faulty timing card must be replaced.
RESET=1
Reference Switching (RefSel): NORMAL --> HOLDOVER --> NORMAL
RESET
Figure 11 - Entry into Auto Holdover State and Recovery into Normal Mode by Switching
unconditional return from
any state to Free-run
MS2,MS1=10 forces
FREE-
RUN
10
MS2,MS1=00
MS2,MS1=01
OR
MS2,MS1=01 OR
RefSel change
HOLD-
OVER
01
Zarlink Semiconductor Inc.
Ref: OK AND
MS2,MS1=00
ZL30410
{AUTO}
References
21
RefSel Change
NORMAL
MS2,MS1=01
00
OR
Ref: OK-->FAIL AND
MS2,MS1=00
{AUTO}
HOLD-
AUTO
OVER
{AUTO}
Ref: FAIL-->OK AND
MS2,MS1=00
Data Sheet