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MII / RMII: Interface between MAC and PHY
The MAC communicates with the PHY via the Media Independent Interface (MII) or the Reduced Media Independent Interface (RMII). The MII is defined in IEEE 802.3u. The RMII is a subset of the MII and is defined in the RMI specification. The MII/RMII interfaces can handle control over the PHY which makes it possible to configure select transmission criteria as line speed, duplex mode, etc.
In theory, up to 32 PHYs can be connected to a single MAC. In praxis, this is never done; only one PHY is connected.
To allow multiple PHYs to be connected to a single MAC, individual 5-bit addresses have been be assigned to the different PHYs. If only one PHY is connected, the IAR PowerPac TCP/IP driver automatically finds the address of it.
The standard defines 32 16-bit PHY registers. The first 6 are defined by the standard.
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