AM79C975VCW datasheet(245/304 Pages) AMD

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APPENDIX B

Am79C973/Am79C975

245

Serial Management Interface Unit

(Am79C975 only)

APPENDIX B: Serial Management Interface Unit (Am79C975 only)

Related Documents:

n System Management Bus Specification Revision

1.0, February 15, 1995

n Phillips Semiconductors: The I2C-bus and how to

use it (including specifications), April 1995

Overview

The Am79C973 and Am79C975 devices are fully-

integrated 32-bit PCI bus 10/100 Mbps Ethernet con-

trollers with advanced power and network manage-

ment features. With the Serial Management Interface,

the Am79C975 device offers a very powerful system

management feature in addition to the management

features offered with the Am79C973 device.

The Serial Management Interface Unit (SMIU) is based

on the industry standard Inter-IC (I2C) bus and System

Management Bus (SMBus) specifications. It enables a

system to exchange short message with another net-

work station (e.g., management console) for remote

monitoring and alerting of system management param-

eters and events. The SMIU is capable of communicat-

ing within the system and over the network during

normal operation or in low power mode, even if the

Am79C975 controller is not initialized or setup for

transmit or receive operation by a network driver.

One application for the Serial Management Interface is

a system where a dedicated microcontroller monitors

various hardware components (e.g., fan, memory, chip

set) and parameters (e.g., temperature, voltage) in

order to obtain information about the status of the sys-

tem. If there is any problem or issue with the system,

the microcontroller can send a message via the serial

management interface of the Am79C975 Am79C975

controller to another station on the network, for exam-

ple, to alert the system administrator of the trouble

event.

A less robust (but more cost effective) implementation

in a typical PC system simply uses the host processor

to control operation of the I2C/SMBus interfaces of the

PCI chipset (southbridge) and hardware monitoring de-

vice, and the Serial Management Interface of the

Am79C975 controller.

The independent interface allows access to the net-

work even at times when there is no operating system

and network driver running on the system. The inter-

face, however, also allows access to the network in par-

allel to the normal traffic.

The electrical interface of the SMIU is comprised of 3

pins: clock, data, and interrupt. The host can access a

set of registers via the interface to identify the

Am79C975 controller, to obtain information about the

status of the device, to get the network address of the

local node and the management station of the network,

and to control the transmission and reception of man-

agement frames. The Am79C975 controller provides

internal transmit and receive data memories of 128

bytes each to store the management frames. The re-

ceive path includes a pattern match filter to qualify in-

coming frames.

The SMIU is designed such that the amount of software

running on the microcontroller in order to transmit or re-

ceive management frames is minimized. The SMIU

does not use the PCI clock (CLK). It will operate with

CLK stopped or running.

The electrical interface of the SMIU follows the I2C

specification. The signaling and register access proto-

col of the SMIU is a subset of the System Management

Bus (SMBus) protocol.

79C975 PIN DESIGNATIONS

Listed by Pin Number

160-pin PQFP package

176-pin TQFP package

Pin No

Pin Name

Pin No

Pin Name

MIRQ

106

MIRQ

MDATA

108

MDATA

100

MCLOCK

110

MCLOCK

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