Ok,i will look into timer2.Thank you.

On Thu, Mar 5, 2009 at 12:45 PM, Olin Lathrop <olin_piclist@embedinc.com>wrote:

> kilgarenone wrote:
> > I want to produce a frequency(I use PWM) for a certain period of
> > time(timer0),then interrupt-on-overflow to stop the frequency for
> > another period of time.So i should have tones play at certain
> > interval.
>
> Using the PWM hardware to generate the frequency makes sense, but using
> timer 0 to stop a tone seems awkward.  Is this tone for humans to hear?  If
> so, you don't need much accuracy on starting and stopping it.  You could
> use
> timer 2 to set up a periodic interrupt and have it count to stop the tone.
> You will probably find other uses for a master clock tick.
>
> A interrupt every 1mS takes only a tiny fraction of average CPU cycles, and
> is much more resolution than you need to start and stop a tone for humans
> to
> hear.  Even 50mS is probably fine for that.
>
>
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