Fujitsu F2MC-16LX Hardware Manual page 202

CHAPTER 8 I/O PORT
❍ Handling of ports 76 and 77
These ports have no DDR. Since they always function as ports in which data is to be effective,
specify the value of PDR to "1" when using P76 and P77 as pins for I
using them as P76 and P77, stop I
Furthermore, these ports are open-drain output ports, so to turn off the transistor when they are
used as input ports, specify the output data register to have a value of "1" and attach a pull-up
resistor to the external pin.
Note:
If this register is accessed with a command of the read-modify-write type (such as the bit-set
command), the contents of the output registers corresponding to the other bits specified for
input are replaced with the input value of the pin at the time of access even if the bit
specified by the command is set to the required value. Therefore, when a pin for input is
switched to a pin for output, be sure to define DDR after writing the desired value to PDR,
and then switch it to a pin for input.
186
2
C.)
2
C. (Incidentally, when