Dennis Crawley wrote :

> Is it normal that the capture module varies ~1 unit the
> capture of an stable sqare signal in all the range of
> frecuencies?
> 4000Hz 250 and  251
> 2000Hz 500 and  501
> 800Hz 1250 and 1251
> What this capture means?
> There is something wrong in my interrupt routine?

Dont have to be. And there isn't realy something called
"stable" here, there will always be a slight variation, even if
it's "small"). Now if your capture is on "the edge", it will
sometimes fall in one side, sometimes on the other, just
as a tossed coin.

By adjusting the freq of the square signal a little, it might be
possible to get a stable reading, then adjust a little more, and
it will begin to jitter around the next "edge".

> > Since I don't have a stable wave generator to test it, I've
> > done a simple ON-OFF 50% duty oscillator with a 16F873.
> > Using Andy Warren loop generator (625 Inst-cy) achieves
> > full precision in MPLAB simulator, so I use some crystals
> > to change the frequency and I've obtained these captures:

- By using a pencil and paper (like MPSIM does) you can always
  get "full" precision.

- Using real hardware you can never get "full" precision.

- A crystal is not "stable". It has always a jitter.

Jan-Erik.

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu