The MDIO can connect to more than one device. If an internal PHY is present (such as the Ethernet 1G/2.5G BASE-X PCS/PMA or SGMII cores ), performing as SGMII, and you want to connect the MDIO to an external PHY device, then an arbitration circuit is required. An example circuit is shown in the following figure. Both PHY devices must be assigned a unique none zero physical address (PHYAD). This description is included for reference, and is not expected to be common.
The SGMII specification contains a method of transferring PHY configuration information across the SGMII link. Therefore, all relevant PHY information can be obtained directly from the internal SGMII core.
