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DP83640: Using CLK_OUT as an external PTP clock reference input

reto hermann
Intellectual 720 points
Other Parts Discussed in Thread: DP83640

Dear all,

I have a question regrading the the PHYTER DP83640. According to the pin description in the DS  the "CLK_OUT" pin can be used as an input or as an output. We want to use this pin as an input for an external 25MHz PTP reference clock and we are using the following settings.

(1) Strap option CLK_OUT_EN (GPIO1) set to low (2k2 pull-down resistor)
(2) Register Settings : PTP_CLKSRC -> CLK_SRC            is set to 0x2
                                                                    -> CLK_SRC_PER is set to 0x28

                                                              register value after initialization: PTP_CLKSRC = 0x8028

We expect that the PTP logic uses the external clock with this setup, but it doesn't work. What are we doing wrong ? 

Thanks for your help!
Reto