AM79C970 datasheet(109/168 Pages) AMD

109 / 168 page

AMD

P R E L I M I N A R Y

1-976

Am79C970

Bus Configuration Registers

The Bus Configuration Registers (BCR) are used to pro-

gram the configuration of the bus interface and other

special features of the PCnet-PCI controller that are not

related to the IEEE 8802-3 MAC functions. The BCRs

are accessed by first setting the appropriate RAP value,

and then by performing a slave access to the BDP.

All BCR registers are 16 bits in width in WIO mode and

32 bits in width in DWIO mode. The upper 16 bits of all

BCR registers is undefined when in DWIO mode. These

bits should be written as ZEROs and should be treated

as undefined when read. The Default value given for any

BCR is the value in the register after H_RESET, and is

hexadecimal unless otherwise stated. BCR register val-

ues are unaffected by S_RESET and are unaffected by

the assertion of the STOP bit.

Note that several registers have no default value. BCR3

and BCR8-15 are reserved and have undefined values.

BCR2, BCR16, BCR17 and BCR21 are not observable

without first being programmed through the EEPROM

read operation or a user register write operation. There-

fore the only observable values for these registers are

those that have been programmed and a default value is

not applicable.

BCR0, BCR1, BCR6, BCR16, BCR17, and BCR21 are

reserved in the PCnet-PCI controller. These registers

are used by other devices in the PCnet family. Writing to

these registers have no effect on the operation of the

PCnet-PCI controller.

Writes to those registers marked as “Reserved” will

have no effect. Reads from these locations will produce

undefined values.

BCR

MNEMONIC

Default

Description

User

EEPROM

MSRDA

0005h

Reserved

MSWRA

0005h

Reserved

N/A*

Miscellaneous Configuration

Yes

Reserved

N/A

Reserved

LNKST

00C0h

Link Status Status (Default)

Yes

LED1

0084h

Receive Status (Default)

Yes

LED2

0088h

Reserved

Yes

LED3

0090h

Transmit Status (Default)

Yes

8–15

Reserved

N/A

Reserved

IOBASEL

N/A*

Reserved

Yes

IOBASEU

N/A*

Reserved

Yes

BSBC

2101h

Burst Size and Bus Control

Yes

EECAS

0002h

EEPROM Control and Status

Yes

SWS

0000h

Software Style

Yes

INTCON

N/A*

Reserved

Yes

* Registers marked with an “*” have no default value, since they are not observable without first being programmed through the

EEPROM read operation or a user register write operation. Therefore, the only observable values for these registers are those

that have been programmed and a default value is not applicable.

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