DB25 Pin 15 of the G540 is connected to pin 15 of the parallel port.
In Mach3 config>port and Pins> Inputs scroll down to ESTOP. There should be Green check mark on Enable then port 1 and pin 15 with a red X mark on low active.
When I was in business I have built hundreds of those G540's They are great Much better than the chinese stuff. On my systems that I use to build I added a wire from terminal 10(Disable/Estop) to a SPST switch the other side of the switch is then tied to Ground. With that switch you can manually repositio
n your motors. In the connected side of the switch the motor are engergize
d and if you have a fault or you fip the switch off you will be the estop and your motors and mach3 will stop.
I recently replaced a Chinese control box to a Gecko 540 control for my CNC router. I shielded all control wires and the spindle wire in the process because I'm fighting a noise issue. My motion control issues have been rectified but I occasiona lly get a fault on the Gecko that does not trigger the E-stop switch so Mach3 continues on it's merry way even though the machine is not moving. This creates a major problem because it's hard to recover when the machine and DRO's don't match. The Gecko 540 manual says pin #15 is used for FAULT (Input to PC). Does anyone know how to use this signal to stop Mach3 at the point of the fault?