Start-up Sequencing - 16.2 English

IEEE 802.3-2008 clause 22.2.4.1.6 states that by default, a PHY should power up in an isolate state (electrically isolated from the GMII).

• If you are using the core with the optional management interface, it is necessary to write to the PCS Configuration Register 0 to take the core out of the isolate state.
• If using the core without the optional management interface, it is the responsibility of the client to ensure that the isolate input signal in the configuration_vector is asserted at power-on.