ZL50022
Data Sheet
12.1.3.1 Automatic Reference Switching Without Preferences
When the DPLL is programmed to operate in Automatic mode without Preference (RCCR Register, PMS2-0 bits =
000), all references, REF0-3, will have equal importance. A circulating Round Robin selection sequence
determines the reference to be used as shown in Figure 21. The state machine basically searches for valid
reference in a circular order of REF0 -> REF1 -> REF2 -> REF3 -> REF0, etc.
Free run
Ref 1
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Start
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1
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Ref 0 failed
Ref 0 valid
Ref 0 and 1 failed
and (Ref 2 or Ref 3 valid)
Holdover 1
Holdover 0
Ref 0
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0
All Ref failed
All Ref failed
All Ref failed
All Ref failed
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Ref 2 and 3 failed
and (Ref 0 or Ref 1 valid)
Ref 2 valid
Ref 2 failed
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ile
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Holdover 2
Ref 2
Holdover 3
Ref 3
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Figure 21 - Automatic Reference Switching State Diagram with No Preferred Reference
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