AM79C972BVCW datasheet(26/130 Pages) AMD

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Am79C972

BASIC FUNCTIONS

System Bus Interface

The Am79C972 controller is designed to operate as a

bus master during normal operations. Some slave I/O

accesses to the Am79C972 controller are required in

nor mal operations as well. Initialization of the

Am79C972 controller is achieved through a combina-

tion of PCI Configuration Space accesses, bus slave

accesses, bus master accesses, and an optional read

of a ser ial EEPROM that is pe rfor med by the

Am79C972 controller. The EEPROM read operation is

performed through the 93C46 EEPROM interface. The

ISO 8802-3 (IEEE/ANSI 802.3) Ethernet Address may

reside within the serial EEPROM. Some Am79C972

controller configuration registers may also be pro-

grammed by the EEPROM read operation.

The Address PROM, on-chip board-configuration reg-

isters, and the Ethernet controller registers occupy 32

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

accesses 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 Am79C972 controller sup-

ports a ROM or Flash-based (both referred to as the

Expansion ROM throughout this specification) boot de-

vice of up to 1 Mbyte in size. The host can map the boot

device to any memory address that aligns to a 1-Mbyte

boundary by modifying the Expansion ROM Base Ad-

dress register in the PCI configuration space.

Software Interface

The software interface to the Am79C972 controller is

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

tion registers used to identify the Am79C972 controller

and to setup the configuration 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 Am79C972 controller interrupt chan-

nel. This allows for a jumperless implementation.

The second portion of the software interface is the di-

rect access to the I/O resources of the Am79C972 con-

troller. The Am79C972 controller occupies 32 bytes of

address space that must begin on a 32-byte block

boundary. The address space can be mapped into I/O

or memory space (memory mapped I/O). The I/O Base

Address Register in the PCI Configuration Space con-

trols the start address of the address space if it is

mapped to I/O space. The Memory Mapped I/O Base

Address Register controls the start address of the ad-

dress space if it is mapped to memory space. The 32-

byte address space is used by the software to program

the Am79C972 controller operating mode, to enable

and disable various features, to monitor operating sta-

tus, and to request particular functions to be executed

by the Am79C972 controller.

The third portion of the software interface is the de-

scriptor and buffer areas that are shared between the

software and the Am79C972 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 Am79C972 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 Am79C972 controller can be connected to an

IEEE 802.3 or proprietary network via one of two net-

work interfaces. The Media Independent Interface (MII)

provides an IEEE 802.3-compliant nibble-wide inter-

face to an external 100- and/or 10-Mbps transceiver

device. The General Purpose Serial Interface (GPSI) is

functionally equivalent to the GPSI found on the

LANCE.

While in auto-selection mode, the interface in use is de-

termined by the Network Port Manager. If the quiescent

state of the MII MDIO pin is HIGH, the MII is activated.

The GPSI port can only be enabled by disabling the

auto-selection and manually selecting the GPSI as the

network port.

The Am79C972 controller supports both half-duplex

and full-duplex operation on network interfaces (i.e.,

GPSI and MII).

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