152
Am79C965A
Bus Configuration Registers
The Bus Configuration Registers (BCR) are used to
program 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
observable without first being programmed, either
through the EEPROM read operation or through the
Software Relocatable Mode. Therefore, the only
observable values for these registers are those that
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
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 values for these registers are those that have been programmed and a default value is not
applicable.
BCR0: Master Mode Read Active
Bit
Name
Description
31-16 RES
Reserved locations. Written as
zeros and read as undefined.
15-0
MSRDA
Reserved
H_RESET, the value in this register
will be 0005. The settings of this
register will have no effect on any
PCnet-32 controller function.
locations.
After
Writes to this register have no effect
on the operation of the PCnet-32
controller and will not alter the value
that is read.
BCR1: Master Mode Write Active
Bit
Name
Description
31-16 RES
Reserved locations. Written as
zeros and read as undefined.
RAP
Addr.
Mnemonic
Default
(Hex)
Name
Programmability
User
EEPROM
SRM
1
MSWRA
0005
Master Mode Write Active
No
No
No
2
MC
N/A*
Miscellaneous Configuration
Yes
Yes
Yes
3
Reserved
N/A
No
No
No
4
LNKST
00C0
Link Status (Default)
Yes
No
No
5
LED1
0084
Receive (Default)
Yes
No
No
6
LED2
0088
Receive Polarity (Default)
Yes
No
No
7
LED3
0090
Transmit (Default)
Yes
No
No
8
–
15
Reserved
N/A
No
No
No
16
IOBASEL
N/A*
I/O Base Address Lower
Yes
Yes
Yes
17
IOBASEU
N/A*
I/O Base Address Upper
Yes
Yes
Yes
18
BSBC
2101
Burst Size and Bus Control
Yes
Yes
No
19
EECAS
0002
EEPROM Control and Status
Yes
No
No
20
SWSTYLE
0000
Software Style
Yes
No
No
21
INTCON
N/A*
Interrupt Control
Yes
Yes
Yes