AM79C971VCW Advanced Micro Devices, AM79C971VCW Datasheet - Page 176

• Manufacturer Part Number: AM79C971VCW
• Description: PCnet-FAST Single-Chip Full-Duplex 10/100 Mbps Ethernet Controller for PCI Local Bus
• Manufacturer: Advanced Micro Devices

13-4
3-0
BCR30: Expansion Bus Data Port Register
Bit
31-16 RES
15-0
176
RES
EPADDRU
EBDATA
Name
cess to EBDATA (BCR30). When
EBADDRL reaches FFFFh and
LAAINC is set to 1, the Expansion
Port Lower Address (EPADDRL)
will roll over to 0000h. When the
LAAINC bit is set to 0, the Expan-
sion Port Lower Address will not
be affected in any way after an
access to EBDATA (BCR30) and
must be programmed.
Reserved locations. Written as
zeros and read as undefined.
Expansion Port Address Upper.
This upper portion of the Expan-
sion Bus address is used to pro-
vide addresses for Flash/EPROM
port accesses.
Reserved locations. Written as
zeros and read as undefined.
Expansion Bus Data Port. EBDA-
TA is the data port for operations
on the Expansion Port accesses
involving SRAM and Flash ac-
cesses. The type of access is set
by the FLASH bit (BCR 29, bit
15). When the FLASH bit is set to
1, the Expansion Bus access will
follow the Flash access timing.
When the FLASH bit is set to 0,
the Expansion Bus access will
follow the SRAM access timing.
Read accessible always; write
accessible only when the STOP
bit is set. LAINC is 0 after
H_RESET and is unaffected by
S_RESET or the STOP bit.
Read accessible always; write
accessible only when the STOP
bit is set or when SRAM SIZE
(BCR25, bits 7-0) is 0. EPADD-
RU is undefined after H_RESET
and is unaffected by S_RESET or
the STOP bit.
Note: It is important to set the
FLASH bit and load Expansion
Port Address EPADDR (BCR28,
BCR29) with the required ad-
dress before attempting read or
write to the Expansion Bus data
Description
P R E L I M I N A R Y
Am79C971
BCR31: Software Timer Register
Bit
31-16 RES
15-0
STVAL
Name
port. The Flash and SRAM ac-
cesses use different address
phases. Incorrect configuration
will result in a possible corruption
of data.
Flash read cycles are performed
when BCR30 is read and the
FLASH bit (BCR29, bit 15) is set
to 1. Upon completion of the read
cycle, the 8-bit result for Flash ac-
cess is stored in EBDATA[7:0],
EBDATA[15:8]
Flash write cycles are performed
when BCR30 is written and the
FLASH bit (BCR29, bit 15) is set
to 1. EBDATA[7:0] only is valid
for write cycles.
SRAM read cycles are performed
when BCR30 is read and the
FLASH bit (BCR29, bit 15) is set
to 0. Upon completion of the read
cycle, the 16-bit result for SRAM
access is stored in EBDATA.
Write cycles to the SRAM are in-
voked when BCR30 is written
and the FLASH bit (BCR29, bit
15) is set to 0. Byte writes to the
SRAM must use a read-modify-
write scheme since the word is al-
ways valid for SRAM write or
read accesses.
Read and write accessible only
when the STOP is set or when
SRAM SIZE (BCR25, bits 7-0) is
0. EBDATA is undefined after
H_RESET, and is unaffected by
S_RESET and the STOP bit.
Reserved locations. Written as
zeros and read as undefined.
Software Timer Value. STVAL
controls the maximum time for
the Software Timer to count be-
fore
(CSR7, bit 11) interrupt. The Soft-
ware Timer is a free-running timer
that is started upon the first write
to STVAL. After the first write, the
Software Timer will continually
count and set the STINT interrupt
at the STVAL period.
Description
generating
is
the
undefined.
STINT