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7.4 Port 3
7.4.1 Overview
Port 3 is an 8-bit input/output port with the pin configuration shown in figure 7-9. Port 3 is a data
bus in modes 1, 3, 5, and 6 (expanded modes) and a generic input/output port in mode 7 (single-
chip mode).
Pins in port 3 can drive one TTL load and a 90-pF capacitive load. They can also drive a
Darlington transistor pair.
Port 3
7.4.2 Register Descriptions
Table 7-5 summarizes the registers of port 3.
Table 7-5 Port 3 Registers
Address*
Name
H'FFC4
Port 3 data direction register
H'FFC6
Port 3 data register
Note: * Lower 16 bits of the address.
Port 3 pins
Modes 1, 3, 5, and 6
P3 /D
D
7
7
7
P3 /D
D
6
6
6
P3 /D
D
5
5
5
P3 /D
D
4
4
4
P3 /D
D
3
3
3
P3 /D
D
2
2
2
P3 /D
D
1
1
1
P3 /D
D
0
0
0
Figure 7-9 Port 3 Pin Configuration
Abbreviation
P3DDR
P3DR
Mode 7
(input/output)
P3 (input/output)
(input/output)
P3 (input/output)
(input/output)
P3 (input/output)
(input/output)
P3 (input/output)
(input/output)
P3 (input/output)
(input/output)
P3 (input/output)
(input/output)
P3 (input/output)
(input/output)
P3 (input/output)
R/W
W
R/W
7
6
5
4
3
2
1
0
Initial Value
H'00
H'00
141
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