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7.2
Port 4
7.2.1
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 7.1. The pin functions differ depending on the operating mode.
In the H8/3008, 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.
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
142
Port 4 pins
P4 /D
7
7
P4 /D
6
6
P4 /D
5
5
P4 /D
4
4
P4 /D
3
3
P4 /D
2
2
P4 /D
1
1
P4 /D
0
0
Figure 7.1 Port 4 Pin Configuration
Modes 1 to 4
P4 (input/output)/D
7
P4 (input/output)/D
6
P4 (input/output)/D
5
P4 (input/output)/D
4
P4 (input/output)/D
3
P4 (input/output)/D
2
P4 (input/output)/D
1
P4 (input/output)/D
0
(input/output)
7
(input/output)
6
(input/output)
5
(input/output)
4
(input/output)
3
(input/output)
2
(input/output)
1
(input/output)
0
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