I just did a little write up on adding an inexpensive pendant to Mach3.
It is not very configurable, but I found a way to change the buttons.
See my write-up here:
https://www.kronosrobotics.com/inexpensive-cnc-pendant
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Author of: The CNC Construction Set Books, the KRMx01, KRMx02, KRmc01, and KRmf70 CNC Books, the HANS Electric gear clock book. All available at www.kronosrobotics.com.