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AM79C971

PCnet™-FAST Single-Chip Full-Duplex 10/100 Mbps Ethernet Controller for PCI Local Bus

Advanced Micro Devices 

PIN DESCRIPTIONS

PCI Interface

AD[31:0]

Address and Data

Input/Output

Address and data are multiplexed on the same bus in-

terface pins. During the first clock of a transaction,

AD[31:0] contain a physical address (32 bits). During

the subsequent clocks, AD[31:0] contain data. Byte or-

dering is little endian by default. AD[07:0] are defined

as the least significant byte (LSB) and AD[31:24] are

defined as the most significant byte (MSB). For FIFO

data transfers, the Am79C971 controller can be pro-

grammed for big endian byte ordering. See CSR3, bit 2

(BSWP) for more details.

During the address phase of the transaction, when the

Am79C971 controller is a bus master, AD[31:2] will ad-

dress the active Double Word (DWord). The

Am79C971 controller always drives AD[1:0] to ’00’ dur-

ing the address phase indicating linear burst order.

When the Am79C971 controller is not a bus master, the

AD[31:0] lines are continuously monitored to determine

if an address match exists for slave transfers.

During the data phase of the transaction, AD[31:0] are

driven by the Am79C971 controller when performing

bus master write and slave read operations. Data on

AD[31:0] is latched by the Am79C971 controller when

performing bus master read and slave write operations.

When RST is active, AD[31:0] are inputs for NAND tree

testing.

C/BE[3:0]

Bus Command and Byte Enables Input/Output

Bus command and byte enables are multiplexed on the

same bus interface pins. During the address phase of

the transaction, C/BE[3:0] define the bus command.

During the data phase, C/BE[3:0] are used as byte en-

ables. The byte enables define which physical byte

lanes carry meaningful data. C/BE0 applies to byte 0

(AD[07:0]) and C/BE3 applies to byte 3 (AD[31:24]).

The function of the byte enables is independent of the

byte ordering mode (BSWP, CSR3, bit 2).

When RST is active, C/BE[3:0] are inputs for NAND

tree testing.

CLK

Clock

Input

This clock is used to drive the system bus interface and

the internal buffer management unit. All bus signals are

sampled on the rising edge of CLK and all parameters

are defined with respect to this edge. The Am79C971

controller normally operates over a frequency range of

10 to 33 MHz on the PCI bus due to networking de-

mands. See the Frequency Demands for Network Op-

eration section for details. The Am79C971 controller

will support a clock frequency of 0 MHz after certain

precautions are taken to ensure data integrity. This

clock or a derivation is not used to drive any network

functions.

When RST is active, CLK is an input for NAND tree

testing.

DEVSEL

Device Select

Input/Output

The Am79C971 controller drives DEVSEL when it de-

tects a transaction that selects the device as a target.

The device samples DEVSEL to detect if a target

claims a transaction that the Am79C971 controller has

initiated.

When RST is active, DEVSEL is an input for NAND tree

testing.

FRAME

Cycle Frame

Input/Output

FRAME is driven by the Am79C971 controller when it

is the bus master to indicate the beginning and duration

of a transaction. FRAME is asserted to indicate a bus

transaction is beginning. FRAME is asserted while

data transfers continue. FRAME is deasserted before

the final data phase of a transaction. When the

Am79C971 controller is in slave mode, it samples

FRAME to determine the address phase of a transac-

tion.

When RST is active, FRAME is an input for NAND tree

testing.

GNT

Bus Grant

Input

This signal indicates that the access to the bus has

been granted to the Am79C971 controller.

The Am79C971 controller supports bus parking. When

the PCI bus is idle and the system arbiter asserts GNT

without an active REQ from the Am79C971 controller,

the device will drive the AD[31:0], C/BE[3:0] and PAR

lines.

When RST is active, GNT is an input for NAND tree

testing.

IDSEL

Initialization Device Select

Input

This signal is used as a chip select for the Am79C971

controller during configuration read and write transac-

tions.

When RST is active, IDSEL is an input for NAND tree

testing.

1. Not including test features.

18

Am79C971

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