am79c974 Advanced Micro Devices, am79c974 Datasheet - Page 27

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

DETAILED FUNCTIONS
Bus Interface Unit (BIU)
The bus interface unit is built of several state machines
that run synchronously to CLK. One bus interface unit
state machine handles accesses where the Am79C974
controller is the bus slave, and another handles ac-
cesses where the Am79C974 controller is the bus mas-
ter. All inputs are synchronously sampled. All outputs
are synchronously generated on the rising edge of CLK.
In the descriptions that follow, GNT, REQ, INT, and
IDSEL are used to refer to the set of GNTA, REQA,
INTA, and IDSELA for the SCSI controller and to the set
of GNTB, REQB, INTB, and IDSELB for the Ethernet
Controller, respectively.
Slave Configuration Transfers
The host can access the Am79C974 PCI configuration
DEVSEL
FRAME
IDSEL
TRDY
STOP
IRDY
C/BE
PAR
CLK
AD
Figure 1. Slave Configuration Read
1
ADDR
1010
P R E L I M I N A R Y
2
Am79C974
PAR
3
BE's
space with a configuration read or write command. The
Am79C974 controller will assert DEVSEL if the IDSEL
input is asserted during the address phase and if the ac-
cess is a configuration cycle. DEVSEL is asserted two
clock cycles after the host has asserted FRAME. All
configuration cycles are of fixed length. The Am79C974
controller will assert TRDY on the 3rd clock of the
data phase.
Slave Configuration Read
The Slave Configuration Read command is used by the
host CPU to read the configuration space in the
Am79C974 controller. This provides the host CPU with
information concerning the device and its capabilities.
This is a single cycle, non-burst 8-bit, 16-bit, or 32-bit
transfer.
4
DATA
5
PAR
6
18681A-5
AMD
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