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4.2 Port 0
4.2.2
Explanation of Operations of Port 0 Functions
This section describes the operation of port 0.
s Operation of Port 0
r Operation in output port mode
When 1 is written for 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 is.
The value state of the pin can be read by reading the PDR0 register.
r Operation in input port mode
When 0 is written for 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.
r 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.
r 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.
r 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 PDR 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.