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7.5
Port 4
7.5.1
Overview
Port 4 is an 8-bit input/output port which also functions as a data bus. It's pin configuration is
shown in figure 7.4. The pin functions differ depending on the operating mode.
In modes 1 to 5 (expanded modes), when the bus width control register (ABWCR) designates
areas 0 to 7 all as 8-bit-access areas, the chip operates in 8-bit bus mode and port 4 is a generic
input/output port. When at least one of areas 0 to 7 is designated as a 16-bit-access area, the chip
operates in 16-bit bus mode and port 4 becomes part of the data bus. In modes 6 and 7 (single-chip
mode), port 4 is a generic input/output port.
Port 4 has software-programmable built-in pull-up transistors.
Pins in port 4 can drive one TTL load and a 90-pF capacitive load. They can also drive a
darlington transistor pair.
Port 4
178
Port 4 pins
Modes 1 to 5
P4 /D
P4 (input/output)/D
7
7
7
P4 /D
P4 (input/output)/D
6
6
6
P4 /D
P4 (input/output)/D
5
5
5
P4 /D
P4 (input/output)/D
4
4
4
P4 /D
P4 (input/output)/D
3
3
3
P4 /D
P4 (input/output)/D
2
2
2
P4 /D
P4 (input/output)/D
1
1
1
P4 /D
P4 (input/output)/D
0
0
0
Figure 7.4 Port 4 Pin Configuration
Modes 6 and 7
(input/output)
P4 (input/output)
7
(input/output)
P4 (input/output)
6
(input/output)
P4 (input/output)
5
(input/output)
P4 (input/output)
4
(input/output)
P4 (input/output)
3
(input/output)
P4 (input/output)
2
(input/output)
P4 (input/output)
1
(input/output)
P4 (input/output)
0
7
6
5
4
3
2
1
0
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