Hi,
There is no problem to keep MII pin connected (customer can set MII related pin with another function or keep the default setting at Pin Control Register n (PORTx_PCRn) register [MUX] bits).
The RMII operates at 50 MHz and requires synchronization between the PHY and the ENET RMII interface clock input(EXTAL).
Wish it helps.
Have a great day,
Ma Hui
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