AMD
P R E L I M I N A R Y
30
Am79C970A
DETAILED FUNCTIONS
Slave Bus Interface Unit
The slave bus interface unit (BIU) controls all accesses
to the PCI configuration space, the Control and Status
Registers (CSR), the Bus Configuration Registers
(BCR), the Address PROM (APROM) locations and the
Expansion ROM. The table below shows the response
of the PCnet-PCI II controller to each of the PCI com-
mands in slave mode.
Table 2. Slave Commands
C[3:0]
Command
Use
0000
Interrupt Acknowledge
Not Used
0001
Special Cycle
Not Used
0010
I/O Read
Read of CSR, BCR and APROM
0011
I/O Write
Write to CSR, BCR and APROM
0100
Reserved
0101
Reserved
0110
Memory Read
Memory Mapped I/O Read of CSR, BCR and APROM
Read of the Expansion ROM
0111
Memory Write
Memory Mapped I/O Write of CSR, BCR and APROM
Dummy Write to the Expansion ROM
1000
Reserved
1001
Reserved
1010
Configuration Read
Read of the Configuration Space
1011
Configuration Write
Write to the Configuration Space
1100
Memory Read Multiple
Aliased to Memory Read
1101
Dual Address Cycle
Not Used
1110
Memory Read Line
Aliased to Memory Read
1111
Memory Write Invalidate
Aliased to Memory Write
Slave Configuration Transfers
The host can access the PCnet-PCI II controller PCI
configuration space with a configuration read or write
command. The PCnet-PCI II controller will assert
DEVSEL
during the address phase when IDSEL is as-
serted, AD[1:0] are both ZERO, and the access is a con-
figuration cycle. AD[7:2] select the DWord location in the
configuration space. The PCnet-PCI II controller ig-
nores AD[10:8], because it is a single function device.
AD[31:11] are don’t care.
The active bytes within a DWord are determined by the
byte enable signals. 8-bit, 16-bit and 32-bit transfers are
supported.
DEVSEL
is asserted two clock cycles after
the host has asserted
FRAME
. All configuration cycles
are of fixed length. The PCnet-PCI II controller will as-
sert
TRDY
on the 4th clock of the data phase.
The PCnet-PCI II controller does not support burst
transfers for access to configuration space. When the
host keeps
FRAME
asserted for a second data phase,
the PCnet-PCI II controller will disconnect the transfer.
When the host tries to access the PCI configuration
space while the automatic read of the EEPROM after
H_RESET is on-going, the PCnet-PCI II controller will
terminate the access on the PCI bus with a disconnect/
retry response.
The PCnet-PCI II 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 ONE. The PCnet-PCI II con-
troller is capable of detecting a configuration 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
PCnet-PCI II controller asserts
DEVSEL
on the second
clock after
FRAME
is asserted (medium timing).
AD31
—
AD11
AD10
—
AD8
AD7
—
AD2
AD1
AD0
Don’t care
Don’t care
DWord index
0
0