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CHAPTER 4 I/O PORT
4.3.2
Operation of the Port 1
This section describes the operations of port 1.
I
Operation of Port 1
H
Operation as an output port
If "1" is set to the corresponding DDR1 register bit, the port becomes an output port.
The operation of the output transistor is allowed when port 1 operates as an output port and
data of the output latch is output to the pins.
If data is written into the PDR1 register, the data is retained on the output latch and then
output directly to the pins.
Pin values can be read by reading the PDR1 register.
H
Operation as an input port
If "0" is set to the corresponding DDR1 register bit, the port becomes an input port.
The output transistor is "OFF" and the pins are in high impedance when port 1 operates as
an input port.
If data is written into the PDR1 register, the data is retained on the output latch but is not
output to the pins.
Pin values can be read by reading the PDR1 register.
H
Operation for analog input
To use port 1 for analog input, write "0" into the bit of the DDR1 register corresponding to the
analog input pin or "1" into the corresponding bit of the ADEN2 register.
H
Operation during a reset
If CPU is reset, the value of the DDR1 register is initialized to "0". Thus, the output transistor
is turned "OFF" (input port) and the pins are put into high impedance.
The PDR1 register is not initialized by a reset. Thus, if port 1 is used as an output port, it is
necessary to set output data to the PDR1 register and then set output to the corresponding
DDR1 register.
The ADEN2 register is initialized "1" by a reset. Thus, if port 1 is used for port input, "0" must
be set to the corresponding bit of the ADEN2 register.
H
Operation in stop mode and watch mode
If the pin state designate bit (STBC: SPL) of the standby control register is set to "1" when a
transition to the stop mode or watch mode occurs, prohibition of the port input is effected
regardless of the value of the DDR1 register and the pins are put into high impedance. The
input is fixed to prevent leakage due to input opening.