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 (A7 – A0) of the address bus. In the single-chip mode it
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).
P37 (input/output)
P3
6 (input/output)
P3
5 (input/output)
Port P3
4 (input/output)
3P3
3 (input/output)
P3
2 (input/output)
P3
1 (input/output)
P3
0 (input/output)
Pin Expanded Modes Single-Chip Mode
P4
7 / A7 A7 (output) P47 (input/output)
P4
6 / A6 A6 (output) P46 (input/output)
P4
5 / A5 A5 (output) P45 (input/output)
Port P4
4 / A4 A4 (output) P44 (input/output)
4P4
3 / A3 A3 (output) P43 (input/output)
P4
2 / A2 A2 (output) P42 (input/output)
P4
1 / A1 A1 (output) P41 (input/output)
P4
0 / A0 A0 (output) P40 (input/output)
Figure 9-7 Port 3 Pin Functions in Single-Chip Mode
Figure 9-8 Pin Functions of Port 4
154
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