zl30407qcc Zarlink Semiconductor, zl30407qcc Datasheet - Page 37

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

5.1.4
The NORMAL to AUTO-HOLDOVER to HOLDOVER to NORMAL sequence represents the most likely operation of
ZL30407 in Network Equipment.
The sequence starts from the Normal state and transitions to Auto Holdover state due to an unforeseen loss of
reference. The failure conditions triggering this transition were described in section 4.1.2. When in the Auto
Holdover state, the ZL30407 can return to Normal mode automatically if the lost reference is restored and the
ADHR bit is set to 0. This transition from Auto Holdover to Normal mode is performed as “hit-less” recovery for
1.544 MHz, 2.048 MHz and 19.44 MHz references. For the 8 kHz input reference, the recovery from Auto
Holdover state must transition through the Holdover state to preserve “hit-less” recovery (for details see
Section 5.1.3 on page 36). 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
ZL30407 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.
RESET = 1
Dual Reference Operation: NORMAL --> AUTO HOLDOVER--> HOLDOVER --> NORMAL
RESET
Figure 12 - Entry into Auto Holdover State and Recovery into Normal Mode by Switching
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
HOLD-
OVER
01
Zarlink Semiconductor Inc.
MS2,MS1 = 00
Ref: OK AND
ZL30407
{AUTO}
References
37
RefSel Change
MS2,MS1 = 01
NORMAL
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