Campbell designs breakout board

I have a Campbell designs Mach2 breakout board that I am in the
process of wiring.

My question is if anyone knows what an acceptable voltage level on the
signal termial for the Home/Limit switches are? There is a 12v supply
there to power proximity sensors ect... I think there is optical
isolation between that input and the parallel port, so I'm not sure if
that terminal can take a 12v input or if it needs a 5v input.

Any help would be great.
Ryan