AM79C874VC datasheet(28/60 Pages) AMD

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Am79C874

P R E L I M INARY

PHY CONTROL AND MANAGEMENT

BLOCK (PCM BLOCK)

PHY Device

The management interface specified in Clause 22 of

the IEEE 802.3u standard provides for a simple two

wire, serial interface to connect a management entity

and a managed PHY for the purpose of controlling the

PHY and gathering status information. The two lines

are Management Data Input/Output (MDIO), and Man-

agement Data Clock (MDC). A station management

entity which is attached to multiple PHY entities must

have prior knowledge of the appropriate PHY address

for each PHY entity.

Description of the Methodology

The management interface physically transports man-

agement information across the MII. The information is

encapsulated in a frame format as specified in Clause

22 of IEEE 802.3u draft standard and is shown in

Table 6.

Clause 22 Management Frame Format

The PHYAD field, which is five bits wide, allows 32

unique PHY addresses. The managed PHY layer de-

vice that is connected to a station management entity

via the MII interface has to respond to transactions

addressed to the PHY address. A station management

entity attached to multiple PHYs, such as in a managed

802.3 Repeater or Ethernet switch, is required to have

prior knowledge of the appropriate PHY address. See

Table 7 and Figure 7.

Table 7.

PHY Address Setting Frame Structure

Figure 7.

PHY Management Read and Write Operations

PRE

PHYAD

REGADD

DATA

IDLE

READ

1.1

AAAAA

RRRRR

D...........D

WRITE

1.1

AAAAA

RRRRR

D...........D

PRE

PHYAD

REGADD

DATA

IDLE

READ

1.1

00000

RRRRR

XXXXXXXXXPPAAAAA

WRITE

1.1

00000

RRRRR

XXXXXXXXXPPAAAAA

Idle

Start

Opcode

(Read)

PHY Address

16h, Port 2

MII Status, 1h

Idle

MDC

MDIO

(PHY)

MDIO

(STA)

010

Read Operation

Idle

Start

Opcode

(Write)

PHY Address

16h, Port 2

MII Control, 0h

Idle

MDC

MDIO

(STA)

Write Operation

22235I-9

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