The DP83867 SMI function supports read or write access to the extended register set using registers REGCR (0x000Dh) and ADDAR (0x000Eh) and the MDIO Manageable Device (MMD) indirect method defined in IEEE 802.3ah Draft for clause 22 for accessing the clause 45 extended register set.

The standard register set, MDIO registers 0 to 31, is accessed using the normal direct-MDIO access or the indirect method, except for register REGCR (0x000Dh) and ADDAR (0x000Eh) which is accessed only using the normal MDIO transaction. The SMI function ignores indirect accesses to these registers.

REGCR (0x000Dh) is the MDIO Manageable MMD access control. In general, register REGCR(4:0) is the device address DEVAD that directs any accesses of ADDAR (0x000Eh) register to the appropriate MMD.

The DP83867 supports one MMD device address. The vendor-specific device address DEVAD[4:0] = 11111 is used for general MMD register accesses.

All accesses through registers REGCR and ADDAR must use the correct DEVAD. Transactions with other DEVAD are ignored. REGCR[15:14] holds the access function: address (00), data with no post increment (01), data with post increment on read and writes (10) and data with post increment on writes only (11).

• ADDAR is the address and data MMD register. ADDAR is used in conjunction with REGCR to provide the access to the extended register set. If register REGCR[15:1] is 00, then ADDAR holds the address of the extended address space register. Otherwise, ADDAR holds the data as indicated by the contents of its address register. When REGCR[15:14] is set to 00, accesses to register ADDAR modify the extended register set address register. This address register must always be initialized to access any of the registers within the extended register set.
• When REGCR[15:14] is set to 01, accesses to register ADDAR access the register within the extended register set selected by the value in the address register.
• When REGCR[15:14] is set to 10, access to register ADDAR access the register within the extended register set selected by the value in the address register. After that access is complete, for both reads and writes, the value in the address register is incremented.
• When REGCR[15:14] is set to 11, access to register ADDAR access the register within the extended register set selected by the value in the address register. After that access is complete, for write accesses only, the value in the address register is incremented. For read accesses, the value of the address register remains unchanged.

The following sections describe how to perform operations on the extended register set using register REGCR and ADDAR. The descriptions use the device address for general MMD register accesses (DEVAD[4:0] = 11111).