When either Input or Output [Type] is set to
"Word", Special I/O cannot be selected in CH1 to CH4. When setting
Special I/O, set all [Type] to "Bit".
Be careful when changing [Type] while I/O is
already allocated. I/O mapping may be canceled, or errors may occur
when saving or transferring.
31.5.3.3 Cautions When
Changing Types