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9.4 Port 3
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9.4.1 Overview
Port 3 is an 8-bit input/output port with the pin configuration shown in figure 9-3. Port 3 is a data
bus in modes 1 to 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
9.4.2 Register Descriptions
Table 9-5 summarizes the registers of port 3.
Table 9-5 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 to 6
P3 /D
D
(input/output)
7
15
15
P3 /D
D
(input/output)
6
14
14
P3 /D
D
(input/output)
5
13
13
P3 /D
D
(input/output)
4
12
12
P3 /D
D
(input/output)
3
11
11
P3 /D
D
(input/output)
2
10
10
P3 /D
D
(input/output)
1
9
9
P3 /D
D
(input/output)
0
8
8
Figure 9-3 Port 3 Pin Configuration
Abbreviation
P3DDR
P3DR
253
Mode 7
P3 (input/output)
7
P3 (input/output)
6
P3 (input/output)
5
P3 (input/output)
4
P3 (input/output)
3
P3 (input/output)
2
P3 (input/output)
1
P3 (input/output)
0
R/W
Initial Value
W
H'00
R/W
H'00
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