AMD
P R E L I M I N A R Y
150
Am79C965
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-32 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
values 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-BCR15 are reserved and have undefined
values. BCR2, BCR16, BCR17 and BCR21 are not ob-
servable without first being programmed, either through
the EEPROM read operation or through the Software
Relocatable Mode. Therefore, the only observable val-
ues for these registers are those that have been pro-
grammed and a default value is not applicable. See
Table 46.
Writes to those registers marked as “Reserved” will
have no effect. Reads from these locations will produce
undefined values.
Table 46. Bus Configuration Registers
RAP
Default
Addr.
Mnemonic
(Hex)
Name
User
EEPROM
SRM
0
MSRDA
0005
Master Mode Read Active
No
1
MSWRA
0005
Master Mode Write Active
No
2
MC
N/A*
Miscellaneous Configuration
Yes
3
Reserved
N/A
No
4
LNKST
00C0
Link Status (Default)
Yes
No
5
LED1
0084
Receive (Default)
Yes
No
6
LED2
0088
Receive Polarity (Default)
Yes
No
7
LED3
0090
Transmit (Default)
Yes
No
8–15
Reserved
N/A
No
16
IOBASEL
N/A*
I/O Base Address Lower
Yes
17
IOBASEU
N/A*
I/O Base Address Upper
Yes
18
BSBC
2101
Burst Size and Bus Control
Yes
No
19
EECAS
0002
EEPROM Control and Status
Yes
No
20
SWSTYLE
0000
Software Style
Yes
No
21
INTCON
N/A*
Interrupt Control
Yes
Key: SRM = Software Relocatable Mode
* Registers marked with an asterisk (*) have no default value, since they are not observable without first being programmed,
either through the EEPROM read operation or through the Software Relocatable Mode. Therefore, the only observable val-
ues for these registers are those that have been programmed and a default value is not applicable.
Programmability
BCR0: Master Mode Read Active
Bit
Name
Description
31-16
RES
Reserved locations. Written as
zeros and read as undefined.
15-0
MSRDA
Reserved
locations.
After
H_RESET, the value in this
register will be 0005. The set-
tings of this register will have no
effect on any PCnet-32 controller
function.
Writes to this register have no ef-
fect on the operation of the
PCnet-32 controller and will not
alter the value that is read.