Limit Switch
When a limit switch is triggered, what state does GRBL/chilipeppr go into? Where is the e-stop switch generally connected to?
The controller limit pins state depends on your actual configuration. Active High in conjunction with NC switches is better for noise avoidance.
Emergency Stop goes to A0 pin on ArduinoUno. I think there is no pin dedicated to E-STOP on the TinyG, I wired it to Reset button.