
SECTION 3
PCI 9080
FUNCTIONAL DESCRIPTION
PLX Technology, Inc., 1997
Page 17
Version 1.02
3.4.1 PCI Bus Access to Internal Registers
PCI 9080 “PCI configuration registers” can be accessed
from the PCI bus with a configuration Type 0 cycle.
PCI 9080 internal registers can be accessed by a
memory cycle, with the PCI bus address that matches
the base address specified in the PCI Base Address 0
for Memory Mapped Configuration Register of PCI 9080.
They can also be accessed by an I/O cycle, with the PCI
bus address matching the base address specified in the
PCI Base Address 1 for I/O Mapped Configuration
Register of the PCI 9080.
All PCI read or write accesses to the PCI 9080 registers
can be byte, word, or Lword accesses. All PCI memory
accesses to the PCI 9080 registers can be burst or non-
burst. PCI 9080 responds with a PCI Disconnect for all
burst I/O accesses to PCI 9080 registers.
3.4.2 Local Bus Access to Internal
Registers
The local processor can access all the internal registers
of the PCI 9080 through either internal or external
address decode logic. PCI 9080 provides an Address
Decode Mode Pin (ADMODE) that selects whether the
internal address decode logic is used or whether the
designer will supply an external chip select from an
external address decoder. Figure 3-3 illustrates how the
dual address decode logic works.
If the Address Decode Mode pin is set to 1, internal PCI
9080 address decode logic is enabled. In this mode, PCI
9080 internal registers are selected when local address
bits LA[31:29] match input address select pins S[2:0]. If
the Address Decode Mode pin is set to 0, PCI 9080
responds to local bus access when S0 is asserted low
through external chip select logic.
Notes:
S0 must be decoded while ADS# is low.
If ADMODE is 1 LA[31:29], specify 512 MB of
local memory space allocated for accessing internal
registers.
All local read or write accesses to the PCI 9080 registers
can be byte, word, or Lword accesses. All local
accesses to the PCI 9080 registers can be burst or non-
burst.
For C and J modes, accesses must be for a 32 bit
nonpipelined bus. PCI 9080 READYo# indicates a data
transfer is complete.
For S mode, accesses must be for a 16 bit nonpipelined
bus. PCI 9080 READYo# indicates a data transfer is
complete.
0
Figure 3-3. Dual Address Decode Mode