Greg,
Thanks for clarifying some of this for me - I think I'm close. I have a pin assigned to "Probe", and I can see it toggle an LED state in the Diagnostics screen when I ground the touch pad. However, its state (i.e., grounded or not) doesn't affect the running of the macro, which runs to the limit of it's travel, retracts, and displays the "z axis now zeroed" message.
I guess I don't understand what in the macro tells it which pin is hooked up to the probe...
Again, my thanks for the help.
SF