AM79C976 Advanced Micro Devices, AM79C976 Datasheet - Page 197

• Manufacturer Part Number: AM79C976
• Description: PCnet-PRO 10/100 Mbps PCI Ethernet Controller
• Manufacturer: Advanced Micro Devices

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.
8/01/00
10-15
RAP
16
17
18
19
20
21
22
23
24
0
1
2
3
4
5
6
7
8
9
MSRDA
MSWRA
MC
Reserved
LED0
LED1
LED2
LED3
Reserved
FDC
Reserved
IOBASEL
IOBASEU
BSBC
EECAS
SWS
Reserved
PCILAT
PCISID
PCISVID
Mnemonic
Default
00C0h
0005h
0005h
0000h
0094h
1080h
0081h
0004h
0000h
1818h
9000h
0000h
0000h
0000h
N/A
N/A
N/A
N/A
N/A
N/A
P R E L I M I N A R Y
Table 89.
Reserved
Reserved
Miscellaneous Configuration
Reserved
LED0 Status
LED1 Status
LED2 Status
LED3 Status
Reserved
Full-Duplex Control
Reserved
Reserved
Reserved
Burst and Bus Control
EEPROM Control and Status
Software Style
Reserved
PCI Latency
PCI Subsystem ID
PCI Subsystem Vendor ID
Am79C976
BCR Registers
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.
Name
User
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
No
No
No
No
No
Programmability
EEPROM
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
No
No
No
No
No
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