am79c961a Advanced Micro Devices, am79c961a Datasheet - Page 59

• Manufacturer Part Number: am79c961a
• Description: Pcnet?-isa Ii Jumperless, Full Duplex Single-chip Ethernet Controller For Isa
• Manufacturer: Advanced Micro Devices

The following chart and its bit descriptions show the
internal command registers associated with the Plug
PCnet–ISA II’s Legacy Bit Feature
Description
The current PCnet-ISA II chip is designed such that it
always responds to Plug and Play configuration soft-
ware. There are situations where this response to the
Plug and Play software is undesirable. An example of
this is when a fixed configuration is required, or when
the only possible resource available for the PCnet-ISA
II conflicts with a present but not used resource such as
IRQ, or when the chip is used in a system with a buggy
PnP BIOS.
To function in the situations above, a new feature has
been added to the PCnet-ISA II chip. This new feature
Plug and
Play Register
0x4A
0x4B
0x60
0x61
0x70
0x71
0x74
0x40
0x41
0x42
0x43
0x44
0x48
0x49
0x4c
0xF0
SRAM2
BPAM2
BPSZ2
SRSZ2
IOAM2
Bit 7
0
0
0
0
0
0
1
0
0
1
0
LGCY_EN
SRAM1
BPAM1
SRSZ1
IOAM1
BPSZ1
Bit 6
0
0
0
0
0
0
1
0
0
1
DXCVRP
SRAM0
BPAM0
BPSZ0
SRSZ0
IOAM0
Bit 5
0
0
0
0
0
0
1
0
0
1
Am79C961A
FL_SEL
Bit 4
0
0
0
0
0
0
0
0
1
0
0
0
0
1
0
and Play operation. These registers control the PC-
net-ISA II controller Plug and Play operation.
makes the chip ignore the PnP software’s special initi-
ation key sequence (6A). This will effectively turn the
chip into the “Legacy” mode operation, where it will be
visible in the I/O space, and only special setup pro-
grams will be able to reconfigure it. In case the
EEPROM is missing, empty, or corrupted, the chip will
still recognize AMD’s special initiation key sequence
(6B).
To enable this feature, a one has to be written into the
LGCY_EN bit, which is bit 6 of the Plug and Play regis-
ter 0xF0. A preferred method would be set this bit in
the Vendor Byte (PnP 0xF0) field of the EEPROM
located in word offset 0x1A.
BP_CS
IRQ3
Bit 3
0
0
0
0
1
0
0
1
0
1
0
0
1
0
APROM_EN
DMA2
IRQ2
Bit 2
0
0
0
1
0
0
1
0
1
0
0
1
0
IRQ_LVL
AEN_CS
BP_16B
SRAM4
SR16B
DMA1
IRQ1
Bit 1
1
0
0
0
1
0
0
1
0
IRQ_TYPE
IO_MODE
SRAM3
BPAM3
SRSZ3
IOAM3
BPSZ3
IRQ0
Bit 0
DMA0
0
0
0
0
0
0
0
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