Hello folks, I'm trying to backward engineer a DC servo drive pinout. The drive has a db9 connector, thus nine pins. The drive apparently uses 0 or 5 volts to determine what state it's in. Btw, the drive runs under Mach3, using the manufacturer's proprietary BoB.

I have already figured out most of the pins, such as forward /reverse, start-stop, fault, etc. The one pin is kinda of a mystery. It's the spindle speed. I know that the speed is controlled with a pwm signal. Using a RMS DMM when the spindle is off, I get a 5 volt DC reading. As the speed is increased, the voltage goes down proportantly. For instance, at half speed I get approx. 2.5 volts DC...at full speed I read 0 volts. I was under the assumption that the reading would go up as the speed was increased.

I removed the drive from the mill and I plan on using a spare breakout board to run it on the bench. I'm wondering if it's how Mach3 is set up under ports and pins.

Any thoughts before I experiment

thanks
pete