zl50021 Zarlink Semiconductor, zl50021 Datasheet - Page 41

• Manufacturer Part Number: zl50021
• Description: Enhanced 4 K Digital Switch With Stratum 3 Dpll
• Manufacturer: Zarlink Semiconductor

12.1.3.2
If a particular reference needs to have higher priority than the others, the device can be programmed in Automatic
mode with a preferred reference (RCCR Register, PMS2-0 bits = 001). When a preferred reference is selected, the
device can only switch automatically between two references, as shown in Table 8. The preferred reference will be
used as the primary reference and, by default, only its next consecutive reference will be used as the secondary
reference. No more than two references can be used in Automatic mode when a preferred reference is selected.
Figure 22 shows the state diagram for the four valid options of automatic reference switching with a preferred
reference.
Ref 0
Option 1
Option 2
Option 3
Option 4
Figure 21 - Automatic Reference Switching State Diagram with No Preferred Reference
Automatic Reference Switching With Preference
Ref 0 valid
Ref 0 failed
Holdover 0
Holdover 3
Free run
Table 8 - Preferred Reference Selection Options
Primary Reference (Preferred)
Ref 3
Start
All Ref failed
All Ref failed
Ref 0
Ref 1
Ref 2
Ref 3
Zarlink Semiconductor Inc.
Ref 2 and 3 failed
and (Ref 0 or Ref 1 valid)
and (Ref 2 or Ref 3 valid)
ZL50021
Ref 0 and 1 failed
41
All Ref failed
All Ref failed
Holdover 1
Holdover 2
Ref 1
Secondary Reference
Ref 2 failed
Ref 2 valid
Ref 1
Ref 2
Ref 3
Ref 0
Data Sheet
Ref 2