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Pin Functions in Single-Chip Mode: In the single-chip mode (mode 7), each of the port 3 pins
can be designated as an input pin or an output pin, as indicated in figure 9-7, by setting the
corresponding bit in P3DDR to "1" for output or clearing it to "0" for input.
9.5 Port 4
9.5.1 Overview
Port 4 is an 8-bit input/output port with the pin configuration shown in figure 9-8. In the
expanded modes it provides the low bits (A
operates as a general-purpose input/output port.
Outputs from port 4 can drive one TTL load and a 90pF capacitive load. They can also drive a
Darlington transistor pair or LED (with 8mA current sink).
Port
4
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Port
3
Figure 9-7 Port 3 Pin Functions in Single-Chip Mode
Pin
Expanded Modes
P4
/ A
A
(output)
7
7
7
P4
/ A
A
(output)
6
6
6
P4
/ A
A
(output)
5
5
5
P4
/ A
A
(output)
4
4
4
P4
/ A
A
(output)
3
3
3
P4
/ A
A
(output)
2
2
2
P4
/ A
A
(output)
1
1
1
P4
/ A
A
(output)
0
0
0
Figure 9-8 Pin Functions of Port 4
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
– A
) of the address bus. In the single-chip mode it
7
0
Single-Chip Mode
P4
P4
P4
P4
P4
P4
P4
P4
154
(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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