Hardware manual

Rev. 3.0, 09/98, page 92 of 361
6.4 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 6.8.
Table 6.8 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
programmable MOS transistor pull-ups.
Table 6.9 details the port 3 registers.
Table 6.9 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 register P3PCR R/W H'00 H'FFAE
Port 3 Data Direction Register (P3DDR)H'FFB4
Bit:76543210
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:00000000
Read/Write: W W W W W W W W
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.”
Port 3 Data Register (P3DR)H'FFB6
Bit:76543210
P3
7
P3
6
P3
5
P3
4
P3
3
P3
2
P3
1
P3
0
Initial value:00000000
Read/Write: R/W R/W R/W R/W R/W R/W R/W R/W