Changing output format Step/Dir to Integer value

Hi everyone, as this is my first post, i'll introduce myself briefly.

My name is Aleix, i'm from Barcelona and an estrange thought came to my mind recently... Is it possible to modify the output format of an axis in LinuxCNC through a mathematic op before the signal is forwarded to the parallell port?

let's say (without knowing the real deal) that just before the signal exits my computer i've got this:

A commanded move of 100mm in X axis.

I know that:

100 pulses = 1mm
Step output == active HIGH (pin 2)
Dir output == active HIGH (for cw rotation) (pin3)

so, theoretically 10.000 pulses would boost out my PP through pin2 while pin3 outputs 1 (+5v).

Right before this, is it possible to do something like this:

1.- initialise a counter variable, this will track all the steps.) -> counter = 0
2.- if we advance 1mm (100pulses) Clockwise (Dir pin == HIGH) , then counter adds 100 -> counter = 100
3.- if we back 0,5mm (50pulses) CCW (DIR pin == LOW) , then counter subtracts 50 -> counter = 50

That's the best way to express my doubt, i know it's not really clear but i hope it does the job. Thanks for your time and help!

A friend asked if it was possible to drive an analog servo drive that found "abandoned" on his dad's shop, i've only used Mach3, and at first i said no (i don't think you can "modify" the mach's internal ops) but then i started thinking that maybe this was possible to do on linuxCNC.

Anyway, i thought if the machine can generate that step recount, i can set some sort of spi bus to an external DAC, and then map the signal to a specific step count. I've seen some external motion controllers out there, but i just want to know whether this is possible or not

i'd think by the time you're done , it would be simpler to obtain a mesa 5i25 and 7i77 daughter card , but don't let that put you off , if it's only one servo motor , take a pwm pin and convert that to 10v analog

all depends on what you want to do with it

Andypugh:

Interesting, vref goes from -12 to +12, but yes, i think i can try that way

I do not really need it for anything, just to spend an afternoon playing and learning some linuxCNC
Thanks for the advise, i'll give it a try on summertime, now i feel way more relaxed (mentally speaking)

Cncbasher:

Sure it'd be faster and way more easy, but i just want to have some fun and see if it works or not !