> > So you're basically saying that my frequency is set automatically to
> > 50Hz as long as my timer values add up to 20,000, and alternating
> > the timer values adjusts my PWM without touching the frequency

If you do need to adjust frequency, another option is to use ExternalRC,
with a pot as part of the R. Not as repeatable as a crystal (certainly
tunable to a degree with a 10-turn pot) but infinitely variable. Execution
will obviously be sluggish at very slow speeds (and current consumption
doesn't keep going down either). ExtClk could also be used with a
variable input

Just for reference (probably applies to most PICs)

http://home.clear.net.nz/pages/joecolquitt/16f84a_rc.gif

       22p     47p     100p    220p   470p

2k2   5.84M   3.74M   2.04M   1.10M   548k
3k3   5.32M   3.41M   1.77M    960k   480k
4k7   4.40M   2.62M   1.34M    759k   376k
10k   2.44M   1.49M    704k    396k   192k
22k   1.17M    724k    344k    192k    92k
39k    676k    416k    196k    112k    52k
100k   276k    172k     80k     44k    20k
220k   124k     77k     35k     20k   8.8k
470k    60k     37k     17k    9.6k   4.4k
1M      28k     18k      8k    4.4k     2k
1M5     18k     11k      5k    2.8k   1.3k
2M2     12k    7.6k      3k    1.88k  0.9k

> There are a few things to watch for when you update the timer values
> (to minimize jitter), but I think it's better to look for that when you
have
> this working :)

Helpful Hints

http://www.piclist.com/techref/microchip/timer.htm

Philip, have a look around the rest of PIClist. Routines and methods
there that will help you

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