4.7.2 Reference Clock (REFCLKIN)

The REFCLKIN pin is used to connect an external 50.0 MHz reference clock source for RMII operation. The input reference clock must be between 1.8-3.3V amplitude. The clock source must become stable after the assertion of reset and remain stable to begin proper operation. In addition, the LAN8670 XTO pin should be left floating.

For reference clock requirements refer to the section RMII Clock Source - 50 MHz Oscillator.