AM79C961AVIW AMD (ADVANCED MICRO DEVICES), AM79C961AVIW Datasheet - Page 51

• Manufacturer Part Number: AM79C961AVIW
• Manufacturer: AMD (ADVANCED MICRO DEVICES)

Specifications of AM79C961AVIW

• Operating Supply Voltage (typ): 5V
• Operating Supply Voltage (min): 4.75V
• Operating Supply Voltage (max): 5.25V
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 144
• Lead Free Status / Rohs Status: Not Compliant

If a card was driving the bus or if the card was in high
impedance and did not sense another card driving the
bus, then it should prepare for the next pair of I/O
reads. The card shifts the serial identifier by one bit and
uses the shifted bit to decide its response. The above
sequence is repeated for the entire 72-bit serial
identifier.
At the end of this process, one card remains. This card
is assigned a handle referred to as the Card Select
Number (CSN) that will be used later to select the card.
Cards which have been assigned a CSN will not partic-
ipate in subsequent iterations of the isolation protocol.
Cards must be assigned a CSN before they will
respond to the other commands defined in the
specification.
It should be noted that the protocol permits the 8-bit
checksum to be stored in non-volatile memory on the
card or generated by the on-card logic in real-time. The
same LFSR algorithm described in the initiation key
section of the Plug and Play specification is used in the
checksum generation.
Software Protocol
The Plug and Play software sends the initiation key to
all Plug and Play cards to place them into configuration
mode. The software is then ready to perform the isola-
tion protocol.
The Plug and Play software generates 72 pairs of l/O
read cycles from the READ_DATA port. The software
checks the data returned from each pair of I/O reads for
the 0x55 and 0xAA driven by the hardware. If both 0x55
and 0xAA are read back, then the software assumes
that the hardware had a “1" bit in that position. All other
results are assumed to be a “0.”
Am79C961A
During the first 64 bits, software generates a checksum
using the received data. The checksum is compared
with the checksum read back in the last 8 bits of the
sequence.
There are two other special considerations for the soft-
ware protocol. During an iteration, it is possible that the
0x55 and 0xAA combination is never detected. It is also
possible that the checksum does not match If either of
these cases occur on the first iteration, it must be
assumed that the READ_DATA port is in conflict. If a
conflict is detected, then the READ_DATA port is
relocated. The above process is repeated until a non-
conflicting location for the READ_DATA port is found.
The entire range between 0x203 and 0x3FF is avail-
able, however in practice it is expected that only a few
locations will be tried before software determines that
no Plug and Play cards are present.
During subsequent iterations, the occurrence of either
of these two special cases should be interpreted as the
absence of any further Plug and Play cards (i.e. the last
card was found in the previous iteration). This
terminates the isolation protocol.
Note:
the first pair of isolation reads, and must wait 250 sec
between each subsequent pair of isolation reads. This
delay gives the ISA card time to access information
from possibly very slow storage devices.
Plug and Play Card Control Registers
The state transitions and card control commands for
the PCnet-ISA II controller are shown in the following
figure.
The software must delay 1 ms prior to starting
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