9.2.2 Register Descriptions
Table 9-2 summarizes the registers of port 1.
Table 9-2 Port 1 Registers
Initial Value
Address
*
Name
Abbreviation
R/W
Modes 1 to 4
Modes 5 to 7
H'FFC0
Port 1 data direction register
P1DDR
W
H'FF
H'00
H'FFC2
Port 1 data register
P1DR
R/W
H'00
H'00
Note:
*
Lower 16 bits of the address.
Port 1 Data Direction Register (P1DDR): P1DDR is an 8-bit write-only register that can select
input or output for each pin in port 1.
Modes 1 to 4 (Expanded Modes with On-Chip ROM Disabled): P1DDR values are fixed at 1
and cannot be modified. Port 1 functions as an address bus.
Modes 5 and 6 (Expanded Modes with On-Chip ROM Enabled): A pin in port 1 becomes an
address output pin if the corresponding P1DDR bit is set to 1, and a generic input pin if this bit is
cleared to 0.
Mode 7 (Single-Chip Mode): Port 1 functions as an input/output port. A pin in port 1 becomes an
output pin if the corresponding P1DDR bit is set to 1, and an input pin if this bit is cleared to 0.
Bit
Modes
1 to 4
Initial value
Read/Write
Initial value
Read/Write
Modes
5 to 7
7
P1 DDR
1
—
0
W
7
6
P1 DDR
1
—
0
W
6
5
P1 DDR
1
—
0
W
5
4
P1 DDR
1
—
0
W
4
3
P1 DDR
1
—
0
W
3
2
P1 DDR
1
—
0
W
2
1
P1 DDR
1
—
0
W
1
0
P1 DDR
1
—
0
W
0
Port 1 data direction 7 to 0
These bits select input or
output for port 1 pins
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