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AM79C970A

PCnet™-PCI II Single-Chip Full-Duplex Ethernet Controller for PCI Local Bus Product

Advanced Micro Devices 

BASIC FUNCTIONS

System Bus Interface Function

The PCnet-PCI II controller is designed to operate as a

bus master during normal operations. Some slave I/O

accesses to the PCnet-PCI II controller are required in

normal operations as well. Initialization of the PC-

net-PCI II controller is achieved through a combination

of PCI Configuration Space accesses, bus slave ac-

cesses, bus master accesses and an optional read of a

serial EEPROM that is performed by the PCnet-PCI II

controller. 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 II controller con-

figuration registers may also be programmed by the

EEPROM read operation.

The Address PROM, on-chip bus-configuration regis-

ters, and the Ethernet controller registers occupy 32

bytes of address space. Both, I/O and memory mapped

I/O access are supported. Base Address registers in

the PCI configuration space allow locating the address

space on a wide variety of starting addresses.

For diskless stations, the PCnet-PCI II controller sup-

ports an Expansion ROM of up to 64 Kbytes in size.

The host can map the Expansion ROM to any memory

address that aligns to a 64K boundary by modifying the

Expansion ROM Base Address register in the PCI con-

figuration space.

Software Interface

The software interface to the PCnet-PCI II controller is

divided into three parts. One part is the PCI configura-

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

II controller, and are also used to setup the configura-

tion of the device. The setup information includes the

I/O or memory mapped I/O base address, mapping of

the Expansion ROM and the routing of the PCnet-PCI

II controller interrupt channel. This allows for a jumper-

less implementation.

The second portion of the software interface is the di-

rect access to the I/O resources of the PCnet-PCI II

controller. The PCnet-PCI II controller occupies 32

bytes of address space that must begin on a 32-byte

block boundary. The address space can be mapped

into both I/O or memory space (memory mapped I/O).

The I/O Base Address Register in the PCI Configura-

tion Space defines the start address of the address

space if it is mapped to I/O space. The Memory

Mapped I/O Base Address Register defines the start

address of the address space if it is mapped to memory

space. The 32-byte address space is used by the soft-

ware to program the PCnet-PCI II controller operating

mode, enable and disable various features, monitor op-

erating status, and request particular functions to be

executed by the PCnet-PCI II controller.

The third portion of the software interface is the de-

scriptor and buffer areas that are shared between the

software and the PCnet-PCI II controller during normal

network operations. The descriptor area boundaries

are set by the software and do not change during nor-

mal network operations. There is one descriptor area

for receive activity and there is a separate area for

transmit activity. The descriptor space contains relocat-

able pointers to the network frame data and it is used

to transfer frame status from the PCnet-PCI II controller

to the software. The buffer areas are locations that hold

frame data for transmission or that accept frame data

that has been received.

Network Interfaces

The PCnet-PCI II controller can be connected to an

802.3 network via one of three network interfaces. The

Attachment Unit Interface (AUI) provides an ISO

8802-3 (IEEE/ANSI 802.3) compliant differential inter-

face to a remote MAU or an 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.

The PCnet-PCI II controller implements half or full-du-

plex Ethernet over all three network interfaces.

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Am79C970A

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