AM79C971VCW Advanced Micro Devices, AM79C971VCW Datasheet - Page 33
AM79C971VCW
Manufacturer Part Number
AM79C971VCW
Description
PCnet-FAST Single-Chip Full-Duplex 10/100 Mbps Ethernet Controller for PCI Local Bus
Manufacturer
Advanced Micro Devices
Datasheet
1.AM79C971VCW.pdf
(265 pages)
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Expansion ROM Transfers
The host must initialize the Expansion ROM Base Ad-
dress register at offset 30H in the PCI configuration
space with a valid address before enabling the access
to the device. The Am79C971 controller will not react to
any access to the Expansion ROM until both MEMEN
(PCI Command register, bit 1) and ROMEN (PCI Ex-
pansion ROM Base Address register, bit 0) are set to 1.
After the Expansion ROM is enabled, the Am79C971
controller will assert DEVSEL on all memory read ac-
cesses with an address between ROMBASE and
ROMBASE + 1M - 4. The Am79C971 controller aliases
all accesses to the Expansion ROM of the command
types Memory Read Multiple and Memory Read Line to
the basic Memory Read command. Eight-bit, 16-bit,
and 32-bit read transfers are supported.
Since setting MEMEN also enables memory mapped
access to the I/O resources, attention must be given
the PCI Memory Mapped I/O Base Address register
before enabling access to the Expansion ROM. The
host must set the PCI Memory Mapped I/O Base Ad-
dress register to a value that prevents the Am79C971
controller from claiming any memory cycles not in-
tended for it.
The Am79C971 controller will always read four bytes
for every host Expansion ROM read access. TRDY will
DEVSEL
FRAME
TRDY
STOP
IRDY
C/BE
CLK
PAR
AD
1
DEVSEL is sampled
ADDR
CMD
2
PAR
Figure 5. Expansion ROM Read
3
BE
4
Am79C971
5
not be asserted until all four bytes are loaded into an in-
ternal scratch register. The cycle TRDY is asserted de-
pends on the programming of the Expansion ROM
interface timing. The following figure (Figure 5) as-
sumes that ROMTMG (BCR18, bits 15-12) is at its de-
fault value.
Note: The Expansion ROM should be read only during
PCI configuration time for the PCI system.
When the host tries to write to the Expansion ROM, the
Am79C971 controller will claim the cycle by asserting
DEVSEL. TRDY will be asserted one clock cycle later.
The write operation will have no effect. Writes to the Ex-
pansion ROM are done through the BCR30 Expansion
Bus Data Port. See the section on the Expansion Bus
Interface for more details.
The Am79C971 controller supports fast back-to-back
transactions to different targets. This is indicated by the
Fast Back-To-Back Capable bit (PCI Status register, bit
7), which is hardwired to 1. The Am79C971 controller
is capable of detecting a memory cycle even when its
address phase immediately follows the data phase of a
transaction to a different target without any idle state in-
between. There will be no contention on the DEVSEL,
TRDY, and STOP signals, since the Am79C971 con-
troller asserts DEVSEL on the second clock after
FRAME is asserted (medium timing). See Figure 5.
42
43
DATA
44
PAR
45
20550D-8
33
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