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5.2 Port 1
Port 1 is an 8-bit input/output port that also provides the low bits of the address bus. The function
of port 1 depends on the MCU mode as indicated in table 5-2.
Table 5-2. Functions of Port 1
Mode 1
Address bus (Low)
(A
to A
)
7
0
Note: * Depending on the bit settings in the data direction register: 0—input pin; 1—address pin
Pins of port 1 can drive a single TTL load and a 90pF capacitive load when they are used as output
pins. They can also drive light-emitting diodes and a Darlington pair. When they are used as input
pins, they have programmable MOS transistor pull-ups.
Table 5-3 details the port 1 registers.
Table 5-3. Port 1 Registers
Name
Port 1 data direction register P1DDR
Port 1 data register
Port 1 input pull-up control
register
Port 1 Data Direction Register (P1DDR)—H'FFB0
Bit
7
P1
DDR P1
7
Mode 1
Initial value
1
Read/Write
—
Modes 2 and 3
Initial value
0
Read/Write
W
Mode 2
Input port or
Address bus (Low)
(A
to A
)*
7
0
Abbreviation Read/Write Initial value
W
P1DR
R/W
P1PCR
R/W
6
5
DDR P1
DDR P1
6
5
4
1
1
—
—
—
0
0
W
W
W
77
Mode 3
Input/output port
H'FF (mode 1)
H'00 (modes 2 and 3)
H'00
H'00
4
3
2
DDR P1
DDR P1
DDR P1
3
2
1
1
1
—
—
0
0
0
W
W
Address
H'FFB0
H'FFB2
H'FFAC
1
0
DDR P1
DDR
1
0
1
1
—
—
0
0
W
W
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