Re: Homebrew STG card - 8254

["bfp" <bfp-at-earthlink.net>]

----- Original Message -----
From: "Jon Elson" <jmelson-at-artsci.wustl.edu>
To: "Multiple recipients of list" <emc-at-nist.gov>
Sent: Wednesday, March 01, 2000 12:48 PM
Subject: Re: Homebrew STG card - 8254


>
> No, it is TOTALLY INSANE!  (Sorry to be rude.)

No problem

> I was not in favor of other stepper to servo conversions, but, now
> that EMC is actually emulating a servo drive in software, and then
> using that modeled behavior to generate step pulses, converting that
> information to servo is really going off the deep end.

I didnt mean to convert  step pulses back to servo but instead to generate
a PWM signal directly,sort of a poor-man's DAC.just change the software
driver'A'  puts out a square wave for a stepper board
driver'B' generates PWM for servo amps

>If you want
> servos, you should either just pay the price for the servo-to-go
> card, or roll a substitute either from scratch, or by combining a
> commercial D/A card with an encoder counter card, and throwing
> together a driver for it.  Either way, having the computer directly
> communicating with the servo amp and encoders sounds like a
> much better idea.

I agree, the 8254 idea was more of a quick&dirty hack I thought up
while looking at options for my own homebrew design,the resolution
would have been down around 8 bits even with a 10mhz clock input
(10mhz/256 = ~39khz PWM using only LSB of counter)
and it would have required some extra work in the software initialization
so I decided to use a real DAC instead

> Stringing so may conversions together is bound to lead to
> undesirable behavior.
>
> Jon

true ,but the 8254 would just be emulating a DAC chip,it wouldn't
be a stepper to servo translator but more of a dirt cheap,low
resolution,"both-ways" card.
for some applications the flexibility could come in handy and it might ease
the transition
to servos for some people
I never intended it to be a direct replacement for a real servo control card

Brian