I don't have any experience with any of the Xylotex boards, but here's how I would hook it up:
- The Xylotex manual says that there are available pins on the I/O screw terminals. I'll leave it up to you & Mach2 to determine which one to use.
- The picture shows how I would connect it. If your probe is Normally Closed, then you need to set Mach2 to active high (the probe keeps the port shorted to ground until it opens when 'touched' and the 10K resistor pulls up the port to VCC). You could make it active low by switching VCC, but I've always preferred to switch ground and pull-up VCC through a resistor. Slightly safer in some cases.
Does your probe have electrically isolated connections? If not you could have tricky connections to consider.
Any plans to publish or produce your design? Let us know how it turns out!
Hope this helps.