Feedback from Driver, how does Mach3 know where it is?

[Darc]

Howdy peeps, just enquiring as to how Mach3 comunicates withe a servo driver to know it's position?
From the driver I have inputs of STEP, DIR & ENABLE and an output of RUN.
Currently when the drive trips the DRO keeps counting and the program keeps operating.
I'm guessing I need to set the output of RUN as an input on the computer, I'm just not sure how I tell Mach3 to halt the program when it stops recieving a signal from the RUN terminal.

[ger21]

Mach3 can't keep track of where your servos are. It just tells them where to go.

It is poosible to write a macro that will read encoder signals and compare them to the commanded position. There is a commercial add-on product that does this at www.rogersmachine.net

[ViperTX]

Well with the hobby type drivers you have an "open loop" system, it's never truly a "closed loop" system.....the system that ger21 references...alerts you when a discrepancy occurs and expects you to correct it........a "closed loop" system would be auto-correcting without manual intervention.

[Darc]

Thanks guys, I didn't realise that it is technically an open loop system, now I can understand why you don't need feedback from the encoder to the pc.