- Ensure that the MDIO is driven properly. See MDIO Management Interface for detailed information about performing MDIO transactions.
- Check that the
mdc
clock is running and that the frequency is 2.5 MHz or less. - Read from a configuration register that does not have all 0s as a default. If all 0s are read back, the read was unsuccessful. Check that the PHYAD field placed into the MDIO frame matches the value placed on the phyad[4:0] of the core.