DS90CR288A: DS90CR288A: about input clock

Hi all,

The DS90CR287/DS90CR288A datasheet described the INPUT CLOCK as follows;

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INPUT CLOCK: The input clock should be present at all times when the part in enabled. If the clock is stopped,
the PWR DOWN pin should be asserted to disable the PLL.
====================================================================================

Is the INPUT CLOCK for receiver or for transmitter?

If it is for the receiver, how do you know that the input clock is active during PWR DOWN mode?  

Regards,
Toshi