In all the searching I've done against the G540 and wiring it to a VFD, it seems that the majority of the problems are with people getting voltage out.
My problem seems to be the opposite... I can't get the G540 to stop outputting voltage when I tell Mach3 to turn the spindle off.
I'm using the G540 in conjunction with a Minarik MM23001C drive which is powering a treadmill motor. According to the spec sheet, the analog input voltage range for the drive (using the 90VDC armature setting) is 0 - 1.4VDC. I'm supplying that voltage to the G540 directly from the drive itself. S1 (-) is wired to pin 7, S2 (signal) is wired to pin 8, and S3 (+) is wired to pin 9. Spindle control is enabled in Mach3, PWM enabled, and once everything is plugged in and turned on, pin 8 is outputting about 0.3VDC when the spindle is turned OFF in Mach3. When I turn the spindle ON in Mach, the motor spins up to full speed and works fine. I have the pulley setup to go from 1 to 5000rpm, and I can control the motor speed from within Mach3 without a problem, other than it won't completely turn off.
Has anyone seen this before? Is there a bit of wiring I overlooked or missed? Why is the G540 outputting voltage over pin 8 when it shouldn't be?