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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
P3 /D
P3 /D
P3 /D
P3 /D
P3 /D
P3 /D
P3 /D
P3 /D
0
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
P3 (input/output)
P3 (input/output)
P3 (input/output)
P3 (input/output)
P3 (input/output)
P3 (input/output)
P3 (input/output)
P3 (input/output)
7
6
5
4
3
2
1
0
D (input/output)
D (input/output)
D (input/output)
D (input/output)
D (input/output)
D (input/output)
D (input/output)
D (input/output)
7
6
5
4
3
2
1
0
Port 3 pins
Mode 7
Modes 1, 3, 5, and 6
Figure 7-9 Port 3 Pin Configuration
7.4.2 Register Descriptions
Table 7-5 summarizes the registers of port 3.
Table 7-5 Port 3 Registers
Address
*
Name
Abbreviation
R/W
Initial Value
H'FFC4
Port 3 data direction register
P3DDR
W
H'00
H'FFC6
Port 3 data register
P3DR
R/W
H'00
Note:
*
Lower 16 bits of the address.