zl30102 Zarlink Semiconductor, zl30102 Datasheet - Page 24

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

The mode selection state machine behaves differently in Automatic mode in that when both reference REF0 and
reference REF1 are out of range (REF_OOR=1), the state machine will select the Holdover state. In Normal mode
the reference out of range (REF_OOR) status is ignored by the state machine. This is illustrated in Figure 14.
4.5.2.1
When the currently-active input reference in Automatic mode fails in a coarse manner, the REF_DIS internal signal
places the device in holdover, with the HOLDOVER pin and the REF_FAIL pin asserted. This can occur through
triggering the Single Cycle Monitor, or the Coarse Frequency Monitor, in the Reference Monitor block. If the
reference does not correct itself within the lock-disqualify duration (1 second) the LOCK pin is de-asserted. If the
reference does not correct itself within the reference-disqualify duration (2.5 seconds) the HOLDOVER pin is de-
asserted and the REF_SEL outputs indicate that the device has switched to the other reference. The LOCK pin
remains de-asserted for the full lock-time duration, regardless of the phase and frequency offset of the old and new
references. Figure 15 illustrates this process.
If the reference corrects itself within the lock-disqualify duration (< 1 second) the HOLDOVER pin is de-asserted,
and the REF_FAIL pin is de-asserted. The LOCK pin remains asserted. No reference switching takes place, and
the REF_SEL outputs indicate that the device has remained locked to the old reference.
If the reference does not correct itself within the lock-disqualify duration (1 second), but does correct itself within the
reference-disqualify duration (< 2.5 seconds) the HOLDOVER pin is de-asserted, the REF_FAIL pin is de-asserted,
and the REF_SEL outputs indicate that the device has remained locked to the old reference. However the LOCK
pin is de-asserted, the lock-qualify timer is reset, and the LOCK pin remains de-asserted for the full lock-time
duration. See 7.2, “Performance Characteristics“ on page 44 for lock-time duration.
REF_DIS=1: Current selected reference disrupted (see Figure 3). REF_DIS is an internal signal.
REF_OOR=1: Current selected reference out of range (see Figure 3). REF_OOR is an internal signal.
REF_CH= 1: Reference change, a transition in the reference selection (see Figure 13). REF_CH is an internal signal.
Automatic Reference Switching - Coarse Reference Failure
RST
REF_DIS=0 and REF_OOR=0
and REF_CH=0 and HMS=0
(HOLDOVER=1)
Figure 14 - Mode Switching in Automatic Mode
Holdover
(REF_DIS=0 and REF_OOR=0 and HMS=1)
or REF_CH=1
Zarlink Semiconductor Inc.
ZL30102
REF_DIS=1
or REF_OOR=1
(HOLDOVER=0)
24
Normal
REF_CH=1
(HOLDOVER=1)
REF_DIS=0
and REF_OOR=0
TIE Correction
Data Sheet