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CHAPTER 9 I/O PORT
Table 9.3-3 lists the functions of the port 0 registers.
Table 9.3-3 Port 0 Register Functions
Register
Data During reading
0
Port 0 data
register (PDR0)
1
Port 0 data
0
direction register
(DDR0)
1
0
Port 0 pull-up
resistor setting
register (RDR0)
1
R/W: Read/write enabled
X
: Undefined
170
The output latch is loaded with 0. When
The pin is at the
the pin functions as an output port, the
low level.
pin is set to the low level.
The output latch is loaded with 1. When
The pin is at the
the pin functions as an output port, the
high level.
pin is set to the high level.
The direction
The output buffer is turned off to place
latch is "0".
the port in input mode.
The direction
The output buffer is turned on to place
latch is "1".
the port in output mode.
The setting
The pull-up resistor is cut and the port is
latch is "0".
placed in the Hi-Z state in input mode.
The pull-up resistor is selected and the
The setting
port is held at the high level in input
latch is "1".
mode.
During writing
Read/
Address
Initial value
Write
000000
XXXXXXXX
R/W
H
000010
00000000
R/W
H
00001C
00000000
R/W
H
B
B
B
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