Colibri IMX6ULL: Second Ethernet PHY Clock


We have a custom board using the Colibri iMX6ULL module. We wanted to have another ethernet port. So we used the external RMII interface to add an additional PHY (KSZ8873RLL - it is a 3-port switch).
At the moment, the problem is that I don’t get any response from the new PHY. I think I may have a clock problem.

Our board connects the ENET1_TXCLK (ENET_REF_CLK1) of the Colibri module with the clock inputs of the new PHY (oscillator input and reference clock input on the PHY). The idea was that the Colibri module supplies the clock to the PHY.

But what I have read so far is that the ENET1_TXCLK need an external clock signal. Is this true? I’m able to activate the 50MHz reference clock output (ENET_REF_CLK1). But the signal seems to be an sine wave signal with 50MHz frequency. I suppose that the ENET1_TXCLK isn’t using it internally, right?

So, do I need an external e.g. 50MHz clock signal on the ENET1_TXCLK pin?


Hi Andreas

Could you please check this topic here:

It’s the same external switch with the same PHY address.

Best regards Andrija