Hi Josh,
You can put the counterupdates in the interrupt routine if u want
to control the PWM freq. independently from your mainloop.

First of all I'd like to present a way to think about how it works:
Think of it as 2 cam-wheels (like in a washing machine)
One wheel sets the PWM output to 0 once each turn.
The other one sets the PWM output to 1 once each turn.

Now if these two wheels were on the same axle, and u start
turning the axle around... the axle rpm decides the PWM-freq.
And the phase-difference between the wheels decides the
pulsefactor 0-100%. So it is perfectly okay that the counters
roll over, they are supposed to !

You do not need to reload the counters unless u want to change
the pulsefactor. And then all you do is add say 1 to the PWM-
counter and the phase will shift slightly.

Above method is dead simple and works like a charm, the routine
below is more complicated and doesnt offer anything extra (i think)
*ducks*

I prolly could dig up some code I wrote using above techinqe
for a recent project if ure interested... for the 877 tho.
I figured id put it on piclist.com but no time to mess w that now :-)



----- Original Message -----
From: "Josh Koffman"
> I am looking to use the code at
> http://www.dattalo.com/technical/software/pic/pwm8.asm
> to do multiple PWMs on one chip. My basic question is...where and when
> do I update the PWM counters? I plan on putting the timer checking and
> updating in an ISR, and triggering it with a TMR0 interrupt. This will
> work on the first iteration, but once a counter has hit zero, doesn't it
> just start again at 255? Therefore, I would need to reload the value I
> want in the counter so that it will start to count down again. What if
> after:
>          DECFSZ  pwm0,F          ;If the first counter has not reached 0
>          IORLW  00000001b       ;then we don't want to turn it off.
> I add something to the effect of:
>         check pwm0 for zero
>         if zero, reload pwm0 with proper value

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