AM79C970 datasheet(20/168 Pages) AMD

20 / 168 page

P R E L I M I N A R Y

AMD

1-887

Am79C970

BASIC FUNCTIONS

System Bus Interface Function

The PCnet-PCI controller is designed to operate as a

Bus Master during normal operations. Some slave I/O

accesses to the PCnet-PCI controller are required in

normal operations as well. Initialization of the PCnet-

PCI controller is achieved through a combination of PCI

Configuration Space accesses, Bus Slave accesses,

Bus Master accesses and an optional read of a serial

EEPROM that is performed by the PCnet-PCI control-

ler. The EEPROM read operation is performed through

the Microwire interface. The ISO 8802-3 (IEEE/ANSI

802.3) Ethernet Address may reside within the serial

EEPROM. Some PCnet-PCI controller configuration

registers may also be programmed by the EEPROM

read operation.

The APROM, on-chip board-configuration registers,

and the Ethernet controller registers occupy 32-bytes of

I/O space which can be located on a wide variety of

starting addresses by modifying the Base Address Reg-

ister in the PCI Configuration Space.

Software Interface

The software interface to the PCnet-PCI controller is di-

vided into three parts. One part is the PCI configuration

registers. They are used to identify the PCnet-PCI con-

troller, and are also used to setup the configuration of

the device. The setup information includes the I/O base

address and the routing of the PCnet-PCI controller in-

terrupt

channel.

This

allows

for

jumperless

implementation.

The second portion of the software interface is the direct

access to the I/O resources of the PCnet-PCI controller.

The PCnet-PCI controller occupies 32-bytes of I/O

space that must begin on a 32-byte block boundary. The

I/O base address can be changed to any 32-bit quantity

that begins on a 32-bit block boundary by modifying the

Base Address Register in the PCI Configuration Space.

The 32-byte I/O space is used by the software to pro-

gram the PCnet-PCI controller operating mode, to en-

able and disable various features, to monitor operating

status and to request particular functions to be executed

by the PCnet-PCI controller.

The third portion of the software interface is the descrip-

tor and buffer areas that are shared between the soft-

ware and the PCnet-PCI controller during normal

network operations. The descriptor area boundaries are

set by the software and do not change during normal

network operations. There is one descriptor area for re-

ceive activity and there is a separate area for transmit

activity. The descriptor space contains relocatable

pointers to the network packet data and it is used to

transfer packet status from the PCnet-PCI controller to

the software. The buffer areas are locations that hold

packet data for transmission or that accept packet data

that has been received.

Network Interfaces

The PCnet-PCI controller can be connected to an 802.3

network via one of two network interfaces. The Attach-

ment Unit Interface (AUI) provides an ISO 8802-3

(IEEE/ANSI 802.3) compliant differential interface to a

remote

MAU

on-board

transceiver.

The

10BASE-T interface provides a twisted-pair Ethernet

port. While in auto-selection mode, the interface in use

is determined by an auto-sensing mechanism which

checks the link status on the 10BASE-T port. If there is

no active link status, then the device assumes an AUI

connection.

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