e stop and spindle motor

When I first purchased my router it was set up with Mach 3 and I could independently control the power to the spindle motor with a button on the interface. Since changing over to EMC I am trying to get that button set up for the same type of operation. Right now the only way I can stop or start the spindle is using the external e stop or the switch on the router itself. There must be a pin that will trigger the relay that powers the spindle motor independent of physically pressing the e stop. Just trying to figure that out. Any suggestions?