A matter of perspective
Most folks understand NO and NC because it relates to the deenergized contacts in the physical world.
This is how I look at XIC and XIO...
(Using "true" to mean power passes to the next rung function)
From the data table perspective:
XIC: 1 is true; XIO: 0 is true;
It's simple for my little brain.
From the ladder logic perspective:
XIC: energized coil is true;
XIO: denergized coil is true:
This is simple for "real" technicians
From the I/O perspective:
XIC: high for sourcing input = true
(at least for the PLC's I've known)
low for sinking input = true
(or false for negative logic sinking inputs)
XIO: low for sourcing input = true
(there's bound to be an exeption out there)
high for sinking input = true
(or true for negative logic sinking inputs)
This is simple for somebody, I'm sure... just not me.
Bob