The Ethernet standard specifies two interfaces for access to the registers that contain the PHY s management information. Clause 22 contains the specification of the MII (also see the section Operation of MAC and MII in Chapter 2), including an optional serial interface for station management (STA). Clause 45 specifies a management data input/output (MDIO), also optional, which is an extension to the MII management interface, originally intended for transceivers operating at 10 Gbps or above. It provides access to more registers while retaining logical compatibility with the original MII management interface.

EFM Copper provides complete access to all features of the PHYs by means of the Clause 45 MDIO. A large set of dedicated registers was added for this purpose to Clause 45. These registers correspond to or are derived from state machine variables and signals in the various parts of the PHY. The management entity that presents these registers to the MDIO has pervasive access to this information (i.e., there are no interfaces defined between the management entity and the sublayers within the PHY).

For the benefit of implementers who do not wish to include full Clause 45 management, the EFM Copper specifications also contain a number of profiles; these are typical settings that should cover most real-life deployment and usage scenarios. If a simpler management interface than the one specified in Clause 45 is present in an EFM Copper implementation, it should allow users or operators to select a mode of operation from these...