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CHAPTER 4 I/O PORTS
4.2.2 Operations of Port 0 Functions
This section describes the operation of port 0.
■ Operation of Port 0
● Operation in output port mode
When "1" is written to a bit of the DDR0 register, the bit corresponding to a pin of port 0, the pin functions
as an output port.
In output port mode, the output transistor operation is enabled and the output latch data is output to the pin.
Once data has been written into the PDR0 register, the written data is held in the output latch and output to
the pin as it is.
The value state of the pin can be read by reading the PDR0 register.
● Operation in input port mode
When "0" is written to a bit of the DDR0 register, the bit corresponding to a pin of port 0, the pin functions
as an input port.
In input port mode, the output transistor is OFF and the pin status is Hi-Z.
Once data has been written into the PDR0 register, the written data is held in the output latch but is not
output to the pin.
The value state of the pin can be read by reading the PDR0 register.
● Operation in external interrupt input mode
Set a bit of the DDR0 register to "0", the bit corresponding to a pin of port 0 that is to serve as an external
interrupt input pin, to set the pin to function as an input port.
The value state of the pin can be read by reading the PDR0 register regardless of whether external interrupt
inputs or interrupt request outputs are enabled or disabled.
● Operation in analog input mode
To use a pin of port 0 as analog input and to inhibit output transistor operation, set the bit corresponding to
the analog input pin to "0" on the DDR0 register. The value state of the pin can be read by reading the
PDR0 register.
Set the bit of the ADEN register of the A/D converter to "1", the bit corresponding to the analog input pin
in use.
● Operation when a reset is performed
When the CPU is reset, the bits of the DDR0 register are initialized to "0". Thus, all output transistors
become OFF and the pins become Hi-Z.
However, CPU resets do not initialize the PDR0 register. If a pin is used as an output port after the reset,
reinitialize the PDR0 register to contain new output data in the bit position corresponding to the pin and
then set the corresponding bit of the DDR0 register so that the pin will function as an output port.