MDIO Transactions - 9.0 English

Tri-Mode Ethernet MAC LogiCORE IP Product Guide (PG051)

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9.0 English

All transactions, read or write, are initiated by the MDIO master. All MDIO slave devices must respond when addressed. MDIO transactions take the form of an MDIO frame, containing fields for the transaction type, address and data. This MDIO frame is transferred across the MDIO wire synchronously to MDC. The abbreviations used in this section are explained in the following table.

Table 1. Abbreviations and Terms
Abbreviation Term
PRE Preamble
ST Start of frame
OP Operation code
PHYAD Physical address
REGAD Register address
TA Turnaround

Write Transaction

Figure 1. MDIO Write Transaction

The previous figure shows a Write transaction across the MDIO which is defined by OP = 01. The addressed PHY (PHYAD) device takes the 16-bit word in the data field and writes it to the register at REGAD.

Read Transaction

Figure 2. MDIO Read Transaction

The previous figure shows a Read transaction, defined by OP = 10. The addressed PHY (PHYAD) device returns the 16-bit word from the register at REGAD. For details of the register map of PHY layer devices and a fuller description of the operation of the MDIO interface itself, see IEEE 802.3-2008 specification.