5.4 Port 3
Port 3 is an 8-bit input/output port that also provides the external data bus. The function of port 3
depends on the MCU mode as indicated in table 5-8.
Table 5-8. Functions of Port 3
Mode 1
Mode 2
Mode 3
Data bus
Data bus
Input/output port
Pins of port 3 can drive a single TTL load and a 90pF capacitive load when they are used as output
pins. They can also drive a Darlington pair. When they are used as input pins, they have program-
mable MOS transistor pull-ups.
Table 5-9 details the port 3 registers.
Table 5-9. Port 3 Registers
Name
Abbreviation
Read/Write
Initial value
Address
Port 3 data direction register
P3DDR
W
H'00
H'FFB4
Port 3 data register
P3DR
R/W
H'00
H'FFB6
Port 3 input pull-up control
P3PCR
R/W
H'00
H'FFAE
register
Port 3 Data Direction Register (P3DDR)—H'FFB4
P3DDR is an 8-bit register that selects the direction of each pin in port 3. A pin functions as an
output pin if the corresponding bit in P3DDR is set to “1,” and as an input pin if the bit is cleared to
“0.”
Bit
7
6
5
4
3
2
1
0
P3
7
DDR P3
6
DDR P3
5
DDR P3
4
DDR P3
3
DDR P3
2
DDR P3
1
DDR P3
0
DDR
Initial value
0
0
0
0
0
0
0
0
Read/Write
W
W
W
W
W
W
W
W
84
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