SECTION 2
PCI 9080
BUS OPERATION
PLX Technology, Inc., 1997
Page 6
Version 1.02
2. BUS OPERATION
2.1 PCI BUS CYCLES
PCI 9080 is compliant with PCI Specification v2.1. Refer
to the PCI 2.1 spec for any specific features of the PCI
bus.
2.1.1 PCI Target Command Codes
As a target, PCI 9080 allows access to PCI 9080 internal
registers and local bus, using the commands listed in
Table 2-1.
Table 2-1. PCI Target Command Codes
Command Type
Code (C/BE[3:0]#)
I/O Read
0010 (2h)
I/O Write
0011 (3h)
Memory Read
0110 (6h)
Memory Write
0111 (7h)
Memory Read Multiple
1100 (Ch)
Memory Read Line
1110 (Eh)
Memory Write and Invalidate
1111 (Fh)
Configuration Read
1010 (Ah)
Configuration Write
1011 (Bh)
All read or write accesses to PCI 9080 can be byte,
word, or longword (Lword) accesses. All memory
commands are aliased to the basic memory commands.
All I/O accesses to PCI 9080 are decoded to an Lword
boundary. The byte enables are used to determine
which bytes are read or written. An I/O access with
illegal byte enable combinations is terminated with a
Target Abort.
2.1.2 PCI Master Command Codes
PCI 9080 can access the PCI bus to perform DMA
transfers or Direct Master Local to PCI Bus transfers.
During the Direct master or DMA transfer, the command
code assigned to PCI 9080 internal register location
(PCI:6Ch)(LOC:ECh) bits [15:0] is used as the PCI
command code (refer to Table 4-59[15:0]). Table 2-2
through Table 2-5 list the various PCI Master Command
codes.
Note:
command codes when the PCI 9080 is master.
Programmable internal registers determine PCI
Note:
accesses.
DMA cannot perform I/O or configuration
2.1.2.1 DMA Master Command Codes
DMA controllers of PCI 9080 can generate the memory
cycles listed in Table 2-2.
Table 2-2. DMA Master Command Codes
Command Type
Code (C/BE[3:0]#)
Memory Read
0110 (6h)
Memory Write
0111 (7h)
Memory Read Multiple
1100 (Ch)
Memory Read Line
1110 (Eh)
Memory Write and Invalidate
1111 (Fh)
2.1.2.2 Direct Local to PCI Command
Codes
For direct local to PCI bus accesses, PCI 9080
generates the cycles listed in Table 2-3 through
Table 2-5.
Table 2-3. Local to PCI Memory Access
Command Type
Code (C/BE[3:0]#)
Memory Read
0110 (6h)
Memory Write
0111 (7h)
Memory Read Multiple
1100 (Ch)
Memory Read Line
1110 (Eh)
Table 2-4. Local to PCI I/O Access
Command Type
Code (C/BE[3:0]#)
I/O Read
0010 (2h)
I/O Write
0011 (3h)
Table 2-5. Local to PCI Configuration Access
Command Type
Code (C/BE[3:0]#)
Configuration Memory Read
1010 (Ah)
Configuration Memory Write
1011 (Bh)
2.1.3 PCI Arbitration
PCI 9080 asserts output REQ# to request the PCI bus.
PCI 9080 can be programmed using bit 23 of (PCI:08h
or PCI:ACh)(LOC:88h or LOC:12Ch) (refer to Table 4-
35[23]) to de-assert REQ# when it asserts FRAME#
during a bus master cycle, or to keep REQ# asserted for
the entire bus master cycle. PCI 9080 always de-asserts