AM79C976 datasheet(197/309 Pages) AMD

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Am79C976

197

P R E L I M INARY

Bus Configuration Registers

The Bus Configuration Registers (BCRs) are included

for compatibility with older PCnet Family software All

BCR functions can be accessed more efficiently

through the memory-mapped registers.

BCRs are used to program the configuration of the bus

interface and other special features of the Am79C976

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. See Table 89.

All BCR registers are 16 bits in width in Word I/O mode

(DWIO = 0, BCR18, bit 7) and 32 bits in width in DWord

I/O mode (DWIO = 1). The upper 16 bits of all BCR reg-

isters is undefined when in DWord I/O 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.

Some of these values may be changed shortly after

H_RESET when the contents of the external EEPROM

is automatically read in. None of the BCR register val-

ues are affected by the assertion of the STOP bit or

S_RESET.

Note that several registers have no default value.

BCR0, BCR1, BCR3, BCR8, BCR10-17, and BCR21

are reserved and have undefined values. BCR2 and

BCR34 are not observable without first being pro-

grammed through the EEPROM read operation or a

user register write operation.

BCR0, BCR1, BCR16, BCR17, and BCR21 are regis-

ters that are used by other devices in the PCnet family.

Writing to these registers have no effect on the opera-

tion of the Am79C976 controller.

Writes to those registers marked as “Reserved” will

have no effect. Reads from these locations will produce

undefined values.

Table 89.

BCR Registers

RAP

Mnemonic

Default

Name

Programmability

User

EEPROM

MSRDA

0005h

Reserved

MSWRA

0005h

Reserved

0000h

Miscellaneous Configuration

Yes

Reserved

N/A

Reserved

LED0

00C0h

LED0 Status

Yes

LED1

0094h

LED1 Status

Yes

LED2

1080h

LED2 Status

Yes

LED3

0081h

LED3 Status

Yes

Reserved

N/A

Reserved

FDC

0004h

Full-Duplex Control

Yes

10-15

Reserved

N/A

Reserved

IOBASEL

N/A

Reserved

IOBASEU

N/A

Reserved

BSBC

9000h

Burst and Bus Control

Yes

EECAS

0000h

EEPROM Control and Status

Yes

SWS

0000h

Software Style

Yes

Reserved

N/A

Reserved

PCILAT

1818h

PCI Latency

Yes

PCISID

0000h

PCI Subsystem ID

Yes

PCISVID

0000h

PCI Subsystem Vendor ID

Yes

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