GX1 Datasheet, PDF (174/247 Pages) National Semiconductor (TI) – Processor Series Low Power Integrated x86 Solution

Integrated Functions (Continued)
4.7.8 PCI Cycles
The following sections and diagrams provide the functional
relationships for PCI cycles.
4.7.8.1 PCI Read Transaction
A PCI read transaction consists of an address phase and
one or more data phases. Data phases may consist of wait
cycles and a data transfer. Figure 4-18 illustrates a PCI
read transaction. In this example, there are three data
phases.
The address phase begins on clock 2 when FRAME# is
asserted. During the address phase, AD[31:0] contains a
valid address and C/BE[3:0]# contains a valid bus com-
mand. The first data phase begins on clock 3. During the
data phase, AD[31:0] contains data and C/BE[3:0]# indi-
cate which byte lanes of AD[31:0] carry valid data. The first
data phase completes with zero delay cycles. However, the
second phase is delayed one cycle because the target was
not ready so it deasserted TRDY# on clock 5. The last data
phase is delayed one cycle because the master deas-
serted IRDY# on clock 7.
For additional information refer to Chapter 3.3.1, Read
Transaction, of the PCI Local Bus Specification, Revision
2.1.
CLK
FRAME#
AD
C/BE#
IRDY#
TRDY#
DEVSEL#
ADDR
BUS CMD
DATA-1
BE#s
DATA-2
DATA-3
ADDR
PHASE
DATA
PHASE
DATA
PHASE
BUS TRANSACTION
Figure 4-18. Basic Read Operation
DATA
PHASE
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