The 10 Mbps or 100 Mbps core provides an MII interface. This is typically used to connect the MAC to an external PHY device. The MII defined in IEEE Std 802.3-2008 clause 22, is a parallel interface that connects a 10 Mbps and/or 100 Mbps capable MAC to the physical sublayers.
The voltage standard used depends on the type of I/O used: HR I/O supports MII at 3.3 V or lower and HP I/O only supports 1.8 V or lower. Therefore, an external voltage converter is required to interoperate with any multi-standard PHY.