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Port 3 Data Direction Register (P3DDR): P3DDR is an 8-bit write-only register that can select
input or output for each pin in port 3.
Bit
P3 DDR
7
Initial value
Read/Write
W
• Modes 1 to 5 (Expanded Modes)
Port 3 functions as a data bus, regardless of the P3DDR settings.
• Modes 6 and 7 (Single-Chip Mode)
Port 3 functions as an input/output port. A pin in port 3 becomes an output port if the
corresponding P3DDR bit is set to 1, and an input port if this bit is cleared to 0.
P3DDR is a write-only register. Its value cannot be read. All bits return 1 when read.
P3DDR is initialized to H'00 by a reset and in hardware standby mode. In software standby mode
it retains its previous setting. Therefore, if a transition is made to software standby mode while
port 3 is functioning as an input/output port and a P3DDR bit is set to 1, the corresponding pin
maintains its output state.
Port 3 Data Register (P3DR): P3DR is an 8-bit readable/writable register that stores output data
for port 3. When port 3 functions as an output port, the value of this register is output. When a bit
in P3DDR is set to 1, if port 3 is read the value of the corresponding P3DR bit is returned. When a
bit in P3DDR is cleared to 0, if port 3 is read the corresponding pin logic level is read.
Bit
P3
Initial value
Read/Write
R/W
P3DR is initialized to H'00 by a reset and in hardware standby mode. In software standby mode it
retains its previous setting.
7
6
5
P3 DDR
P3 DDR
6
5
0
0
0
W
W
7
6
5
P3
P3
7
6
0
0
0
R/W
R/W
4
3
P3 DDR
P3 DDR
4
3
0
0
W
W
Port 3 data direction 7 to 0
These bits select input or output for port 3 pins
4
3
P3
P3
5
4
3
0
0
R/W
R/W
Port 3 data 7 to 0
These bits store data for port 3 pins
2
1
P3 DDR
P3 DDR
P3 DDR
2
1
0
0
W
W
2
1
P3
P3
2
1
0
0
R/W
R/W
0
0
0
W
0
P3
0
0
R/W
177
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