GX1 Datasheet, PDF (34/247 Pages) National Semiconductor (TI) – Processor Series Low Power Integrated x86 Solution

Signal Definitions (Continued)
2.2.2 PCI Interface Signals (Continued)
Signal Name
BGA SPGA
Pin No. Pin No
Type
AD[31:0]
Refer
Refer
I/O
to
to
Table 2-3 Table 2-5
C/BE[3:0]#
D5,
B6,
I/O
B8,
B12,
C13, B18, E21
A15
PAR
B12
C17
I/O
Description
Multiplexed Address and Data
Addresses and data are multiplexed together on the same pins. A
bus transaction consists of an address phase in the cycle in which
FRAME# is asserted followed by one or more data phases. Dur-
ing the address phase, AD[31:0] contain a physical 32-bit
address. During data phases, AD[7:0] contain the least significant
byte (LSB) and AD[31:24] contain the most significant byte (MSB).
Write data is stable and valid when IRDY# is asserted and read
data is stable and valid when TRDY# is asserted. Data is trans-
ferred during the SYSCLK when both IRDY# and TRDY# are
asserted.
Multiplexed Command and Byte Enables
C/BE# are the bus commands and byte enables. They are multi-
plexed together on the same PCI pins. During the address phase
of a transaction when FRAME# is active, C/BE[3:0]# define the
bus command. During the data phase C/BE[3:0]# are used as
byte enables. The byte enables are valid for the entire data phase
and determine which byte lanes carry meaningful data. C/BE0#
applies to byte 0 (LSB) and C/BE3# applies to byte 3 (MSB).
The command encoding and types are listed below.
0000 = Interrupt Acknowledge
0001 = Special Cycle
0010 = I/O Read
0011 = I/O Write
0100 = Reserved
0101 = Reserved
0110 = Memory Read
0111 = Memory Write
1000 = Reserved
1001 = Reserved
1010 = Configuration Read
1011 = Configuration Write
1100 = Memory Read Multiple
1101 = Dual Address Cycle (Reserved)
1110 = Memory Read Line
1111 = Memory Write and Invalidate
Parity
PAR is used with AD[31:0] and C/BE[3:0]# to generate even par-
ity. Parity generation is required by all PCI agents: the master
drives PAR for address and write-data phases, the target drives
PAR for read-data phases.
For address phases, PAR is stable and valid one SYSCLK after
the address phase.
For data phases, PAR is stable and valid one SYSCLK after either
IRDY# is asserted on a write transaction or after TRDY# is
asserted on a read transaction. Once PAR is valid, it remains valid
until one SYSCLK after the completion of the data phase. (Also
see PERR# description on Page 35.)
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