pc87591l National Semiconductor Corporation, pc87591l Datasheet - Page 81

• Manufacturer Part Number: pc87591l
• Description: Lpc Mobile Embedded Controllers
• Manufacturer: National Semiconductor Corporation

Revision 1.07
4.0 Embedded Controller Modules
I/O Expansion Read/Write Bus Cycle
These cycles are always preceded by a T
I/O Expansion Example
Figure 25 shows an example of how two ports can be implemented off-chip, using I/O expansion. This example implements
two 8-bit ports by connecting the SELIO, RD and WR0 pins to the latch/buffer controls.
4.1.9
The BIU provides the following support for development systems.
Bus Status Signals
The Bus Status BST0-2 signals indicate whether a transaction on the core bus was issued; they also indicate the transaction
type; see Table 41 on page 273.
Development Support
1. This routing is for late write. If early write, SELIO is routed
Bus State
to CP and WR0 to CE. All other routing is unchanged.
Figure 25. Example of an Implementation of Two Ports Using I/O Expansion
CLK
A0-19
SELIO
D0-15
RD
WR0-1
BST0-2
Figure 24. I/O Expansion Bus Cycles (EWR bit in BCFG Register = 1)
PC87591x
T
Idle
SELIO
D0-7
WR0
RD
idle
1
T1
1
clock cycle (see Figure 24). The I/O zone is not burstable.
Read
(Continued)
T2
In
81
T
8
Idle
74x541
CE
CP
D
OE1
OE2
74x377
T1
Buffer
8-Bit
8-Bit
Latch
Write
T2
Out
8
8
T3
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