R

-- DISCONTINUED PRODUCT --

Chapter 8: Configuration and Status

Read Transaction

Figure 8-7shows a Read transaction; this is defined by OP=”10”. The addressed MMD (PHYAD) device returns the 16-bit word from the register at REGAD.

STA drives MDIO

 

MMD drives MDIO

mdc

mdio

Z Z

1 1 1

0 1

1 0 P4 P3 P2 P1 P0 R4 R3 R2 R1 R0 Z 0 D15 D13 D11 D9

D7

D5

D3

D1

Z Z

 

 

 

 

 

 

D14

D12

D10

D8

D6

D4

D2

D0

IDLE

32 bits

ST

OP

PRTAD

REGAD

TA

 

16-bit READ DATA

 

 

IDLE

 

PRE

 

 

 

 

 

 

 

 

 

 

 

 

Figure 8-7:MDIO Read Transaction

For details of the register map of MMD (PHY layer devices) and a detailed description of the operation of the MDIO Interface itself, see IEEE 802.3-2005.

Accessing MDIO With GEMAC

More information about MDIO with GEMAC can be found in the following sections of this guide:

For the GEMAC port definition of the MDIO, see “MDIO Interface” in Chapter 2

“Connecting the MDIO to an Internally Integrated PHY,” on page 76

“Connecting the MDIO to an External PHY,” on page 76

The management interface is also used to access the MDIO interface of the GEMAC core. The MDIO interface supplies a clock to the connected PHY, mdc. This clock is derived from the host_clk signal using the value in the Clock Divide[4:0] configuration register. The frequency of mdc is given by the following equation:

fMDC

=

fHOST_CLK

(-------------------------------------------------------------------1+ Clock Divide[4:0]) ⋅ 2

 

 

The frequency of mdc given by this equation should not exceed 2.5 MHz to comply with the IEEE 802.3-2005specification for this interface. To prevent mdc from being out of specification, the Clock Divide[4:0] value powers up at 00000. While this value is in the register, it is impossible to enable the MDIO interface.

For details of the register map of PHY layer devices and a detailed description of the operation of the MDIO interface itself, see IEEE 802.3-2005.

88

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1-Gigabit Ethernet MAC v8.5 User Guide

 

 

UG144 April 24, 2009

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Xilinx UG144 manual Read Transaction, Accessing Mdio With Gemac

UG144 specifications

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