>I have an application where I want to PWM a FET to drive a gauge. Is there
any
>rule for the frequency PWM should be applied. I don't want to dedicate my
>16F84 to a PWM task. Can I run at i.e. 50HZ and complete other tasks in
>between, kind of like a R/C servo? I suppose it really depends on the
>characteristics of the driven device, but I am looking for some general
rules.


A car gauge?  They are pretty slow. I'd say experiment, take it down till
the needle wiggles, then use
twice that.   You can probably use a single timer int to do both sides,
(different length) and that would
give you most of the bandwidth back.