zl30407qcc Zarlink Semiconductor, zl30407qcc Datasheet - Page 38

• Manufacturer Part Number: zl30407qcc
• Description: Sonet/sdh Network Element Pll
• Manufacturer: Zarlink Semiconductor

5.1.5
The NORMAL to HOLDOVER to NORMAL mode switching is usually performed when:
•
•
Two types of transitions are possible:
•
•
In both cases, the change of references provides “hitless” switching.
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 r12 ppm
beyond its nominal frequency. The ZL30407 indicates this condition by setting PRIOR or SECOR status bits
or 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 line card must be replaced.
Semi-automatic transition, which involves changing RefSel input to select a secondary reference clock
without changing the mode select inputs MS2, MS1 = 00 (Normal mode). This forces the ZL30407 to
momentarily transition through the Holdover state and automatically return to Normal mode after
synchronizing to a secondary reference clock.
Manual transition, which involves switching into Holdover mode (MS2,MS1 = 01), changing references with
RefSel, and manual return to the Normal mode (MS2, MS1 = 00).
RESET = 1
Reference Switching (RefSel): NORMAL --> HOLDOVER --> NORMAL
RESET
unconditional return from
MS2,MS1 = 10 forces
any state to Free-run
FREE-
RUN
10
MS2,MS1 = 00
MS2,MS1 = 01
OR
MS2,MS1 = 01 OR
RefSel change
Figure 13 - Manual Reference Switching
HOLD-
OVER
01
Zarlink Semiconductor Inc.
MS2,MS1 = 00
Ref: OK AND
ZL30407
{AUTO}
38
RefSel Change
NORMAL
MS2,MS1 = 01
00
OR
Ref: OK-->FAIL AND
MS2,MS1 = 00
{AUTO}
HOLD-
OVER
AUTO
Ref: FAIL-->OK AND
MS2,MS1 = 00 AND
AHRD = 0
{AUTO}
Ref: FAIL-->OK AND
MS2,MS1 = 00 AND
AHRD = 1 AND MHR = 1
{MANUAL}
AHRD = 1 AND
MHR = 0
OR
Data Sheet