am79c974 Advanced Micro Devices, am79c974 Datasheet - Page 131

• Manufacturer Part Number: am79c974
• Description: Pcnettm-scsi Combination Ethernet And Scsi Controller For Pci Systems
• Manufacturer: Advanced Micro Devices

Designing a Single Motherboard for AMD
PCI Family
Three devices in the AMD PCI family, the Am53C974,
the Am79C970, and the Am79C794, were designed
with very similar pin assignments so that a single mothe-
rboard design could be used for three different prod-
ucts: one with a built-in SCSI controller, one with a
built-in Ethernet controller, and one with both a SCSI
controller and an Ethernet controller. This discussion
describes some implementation details.
Pin Out Differences
The table below shows the pins that are not the same on
the three devices. All pins that are shown as NC are not
INTx (Pins 117 and 118)
The Am79C970 and Am53C974 devices have only one
interrupt output, which is connected to pin 117. The
Am79C974, on the other hand, has two interrupt out-
puts:
101, 102, 104, 105, 106, 107
89, 90, 92, 93, 94, 95
110, 111, 112, 114
68, 69, 70, 71, 73,
64, 65, 66, 80, 81,
INTA, which is used for SCSI interrupts, is
Pin Numbers
74, 75, 77, 78
83, 85, 86, 87
APPENDIX F
115
116
117
118
126
127
123
124
10
58
60
97
99
9
Am79C970 (Ethernet)
EEPROM interface &
RESERVED_DNC
10Base-T lines
RESERVED
RESERVED
RESERVED
Function
LED pins
AUI lines
SLEEP
XTAL1
XTAL2
IDSEL
INTA
REQ
GNT
NC
NC
NC
NC
NC
Am79C974
bonded to the die inside the device package. These pins
can be driven by any signal without affecting the opera-
tion of the device. Those pins that are shown in the PCI
family data sheets as RESERVED are connected to test
logic on the die. These pins are active only during stand-
alone chip testing, and therefore they may also be con-
nected to signals on the board without affecting the
operation of the device. On the other hand, pin 116
which is shown as RESERVED-DNC (for Do Not Con-
nect) must not be connected to anything on the board.
connected to pin 117; while INTB, which is used for
Ethernet interrupts, is connected to pin 118. The
motherboard can connect these pins directly to dedi-
cated inputs to its interrupt controller, or it can connect
SCSI data & parity bus
Am53C974 (SCSI)
RESERVED_DNC
SCSI control lines
SCSICLK1
SCSICLK2
Function
PWDN
IDSEL
INTA
REQ
GNT
NC
NC
NC
NC
NC
NC
NC
NC
NC
Am79C974 (Combination)
SCSI data & parity bus
EEPROM interface &
RESERVED_DNC
SCSI control lines
10Base-T lines
Function
SCSICLK
SCSICLK
LED pins
AUI lines
IDSELA
IDSELB
SLEEP
PWDN
XTAL2
REQB
REQA
GNTB
GNTA
INTA
INTB
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