Functional Description
The PHY address is 5 bits allowing 32 unique values. The first bit transmitted is the MSB of the PHY
address.
Register Address
The Register address is 5 bits allowing 32 registers to be addressed within each PHY. Refer to the 10/100
PHY address map for addresses of individual registers.
Turnaround
An idle bit time during which no device actively drives the MDIO signal shall be inserted between the
register address field and the data field of a read frame in order to avoid contention. During a read frame,
the PHY shall drive a zero bit onto MDIO for the first bit time following the idle bit and preceding the Data
field. During a write frame, this field shall consist of a one bit followed by a zero bit.
Data
The Data field is 16 bits. The first bit transmitted and received is the MSB of the data word.
14.3.8.2 Functional Description
The MII Management I/F will remain idle until enabled by setting the enable bit in the MDIOControl
register. The MII Management I/F will then continuously poll the link status from within the Generic Status
Register of all possible 32 PHY addresses in turn recording the results in the MDIOLink register.
The linksel bit in the MDIOUserPhySel register determines the status input that is used. A change in the
link status of the two PHYs being monitored will set the appropriate bit in the MDIOLinkIntRaw register
and the MDIOLinkIntMasked register, if enabled by the linkint_enable bit in the MDIOUserPhySel register.
The MDIOAlive register is updated by the MII Management I/F module if the PHY acknowledged the read
of the generic status register. In addition, any PHY register read transactions initiated by the host also
cause the MDIOAlive register to be updated.
At any time, the host can define a transaction for the MII Management interface module to undertake
using the data, phyadr, regadr, and write fields in a MDIOUserAccess register. When the host sets the go
bit in this register, the MII Management interface module will begin the transaction without any further
intervention from the host. Upon completion, the MII Management interface will clear the go bit and set the
userintraw bit in the MDIOUserIntRaw register corresponding to the MDIOUserAccess register being used.
The corresponding bit in the MDIOUserIntMasked register may also be set depending on the mask setting
in the MDIOUserIntMaskSet and MDIOUserIntMaskClr registers. A round-robin arbitration scheme is used
to schedule transactions which may queued by the host in different MDIOUserAccess registers. The host
should check the status of the go bit in the MDIOUserAccess register before initiating a new transaction to
ensure that the previous transaction has completed. The host can use the ack bit in the MDIOUserAccess
register to determine the status of a read transaction.
It is necessary for software to use the MII Management interface module to setup the auto-negotiation
parameters of each PHY attached to a MAC port, retrieve the negotiation results, and setup the
MACControl register in the corresponding MAC.
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Ethernet Subsystem
SPRUH73H – October 2011 – Revised April 2013
Copyright © 2011–2013, Texas Instruments Incorporated