GRBL is software that runs on the Arduino (and a few other platforms) and performs the
CNC controller function starting from G code. It will not function as a plug-in device under
Mach3 or Mach4. It may be possible to code a program running on an Arduino to work
with Mach3 or Mach4, but it would not be GRBL.
I've been running Mach 3 on a older router and would like to use Mach 4 on another CNC router I have that's controlled by a Ardrino Uno loaded with GRBL firmware. Short of ditching the Ardrino and replacing it with a smoothstepper or another USB board of some type, can Mach 4 address the GRBL board?