3.7.1 Input Selection

Input selection for each of the DSPLLs can be made manually through register control or automatically using an internal state machine.

Note that inputs IN3-IN4 can only be manually selected by DSPLL D.

3.7.2 Manual Input Selection

In manual mode the input selection is made by writing to a register. IN0-IN2 is available to DSPLL A and C, IN0-IN4 is available to

DSPLL D. If there is no clock signal on the selected input, the DSPLL will automatically enter holdover mode.

3.7.3 Automatic Input Selection

When configured in this mode, the DSPLLs automatically selects a valid input that has the highest configured priority. The priority

scheme is independently configurable for each DSPLL and supports revertive or non-revertive selection. All inputs are continuously

monitored for loss of signal (LOS) and/or invalid frequency range (OOF). Only inputs that do not assert both the LOS and OOF monitors

can be selected for synchronization by the automatic state machine. The DSPLL(s) will enter either holdover or freerun mode if there

are no valid inputs available. Note that automatic input selection only applies to IN0-IN2. If the Si5348 is locked to either IN3 or IN4 and

the input clock fails, the Si5348 will not go into holdover.

Si5348 Rev D Data Sheet

Functional Description

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