116 www.xilinx.com Ethernet 1000BASE-X PCS/PMA or SGMII v9.1
UG155 March 24, 2008
Chapter 9: Configuration and Status
R
.
The MDIO bus system is a standardized interface for accessing the configuration and
status registers of Ethernet PHY devices. In the example illustrated, the Management Host
Bus I/F of the Ethernet MAC is able to access the configuration and status registers of two
PHY devices via the MDIO bus.
MDIO Transactions
All transactions, read or write, are initiated by the MDIO master. All MDIO slave devices,
when addressed, must respond. MDIO transactions take the form of an MDIO frame,
containing fields for transaction type, address and data. This MDIO frame is transferred
across the MDIO wire synchronously to MDC. The abbreviations are used in this section
are explained in Table 9-1.
Figure 9-1: A Typical MDIO-managed System
Configuration
Registers 0 to 31
(REGAD)
MDIO slave
UG194_5_01_011906
PHY1 (MMD)
Physical
Address
(PHYAD)
= 1
Configuration
Registers 0 to 31
(REGAD)
MDIO slave
PHY2 (MMD)
Physical
Address
(PHYAD)
= 2
MDIO
master
MAC (STA)
MDC
MDIO
Host
Bus I/F
Table 9-1: Abbreviations and Terms
Abbreviation Term
PRE Preamble
ST Start of frame
OP Operation code
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