zl30105 Zarlink Semiconductor, zl30105 Datasheet - Page 23

• Manufacturer Part Number: zl30105
• Description: Stratum 3 Redundant System Clock Synchronizer For T1/e1/sdh, Advanced Tca And H.110
• Manufacturer: Zarlink Semiconductor

4.4.4
The Automatic mode combines the functionality of the Normal mode (automatic Holdover) with automatic reference
switching. The automatic reference switching is described in more detail in section 4.5.2, “Automatic Reference
Switching“.
4.5
4.5.1
In the manual modes of operation (MODE_SEL1:0 ≠ 11) the active reference input (REF0, REF1 or REF2) is
selected by the REF_SEL1 and REF_SEL0 pins as shown in Table 5. When the logic value of the REF_SEL pins is
changed when the DPLL is in Normal mode, the ZL30105 will perform a hitless reference switch.
When the REF_SEL inputs are used in Normal mode to force a change from the currently selected reference to
another reference, the action of the LOCK output will depend on the relative frequency and phase offset of the old
and new references. 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. 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.
REF_DIS=1: Current selected reference disrupted (see Figure 3). REF_DIS is an internal signal.
REF_CH= 1: Reference change, a transition in the reference selection (see Figure 14) or a change in the
REF_SEL pins. REF_CH is an internal signal.
Reference Switching
Automatic Mode
Manual Reference Switching
RST
REF_SEL1
0
0
1
1
(HOLDOVER=1)
REF_CH=0 and
HMS=0
REF_DIS=0 and
Figure 12 - Mode Switching in Normal Mode
Holdover
Table 5 - Manual Reference Selection
REF_SEL0
Zarlink Semiconductor Inc.
0
1
0
1
(REF_DIS=0 and HMS=1) or
ZL30105
REF_DIS=1
(HOLDOVER=0)
23
REF_DIS=1
REF_DIS=0
REF_CH=1
Normal
Input Reference Selected
REF0
REF1
REF2
REF2
REF_CH=1
(HOLDOVER=1)
TIE Correction
Data Sheet