GRBL has far too much to handle to worry about the user's intentions regarding HOLD/RESUME/ABORT. That's why it's OK for GRBL to have 3 pins dedicated to interrupting (or resuming) processing. This ...
Grbl is a no-compromise, high performance, low cost alternative to parallel-port-based motion control for CNC milling. This version of Grbl runs on an Arduino with a 328p processor (Uno, Duemilanove, ...