Nick,

 If the prescaler is not assigned to TMR0, then TMR0 will be at 1:1.
 If it is assigned to the WD timer, but the WD timer is not used,
 then there are no consequences.

                                             Regards,

                                               Jim



On Fri, 27 April 2001, Nick Veys wrote:

>
> Ok, so I have the clock coming in @ 4MHz, effectively 1MHz to the processor.
> If I set the prescalar to 1 and assign it to the WDT I'll get a 1:1
> prescalar and an interrupt every ~244us.  Now I know that I can add to that
> value to speed it up so that's good, but my one problem with this is, I
> don't want to use the Watchdog timer... If I have it disabled but still
> assign the prescalar to the watchdog, will it be disabled?  The /only/
> interrupt I want is the tmr0 one.
>
> > >Just double checking this.  At 4MHz, the timer will interrupt every:
> > >256((2^(prescaler+1)/(2^22)) seconds.  So with a 0 prescalar you'll be
> > >getting an interrupt every: 256(2/(2^22)) seconds (122us)?  This
> > appears to
> > >be the smallest obtainable period with this clock speed.  If anyone can
> > >confirm this, it'd be much appreciated!!
> >
> > No, actually at 4MHz, TMR0 will interrupt every 256us with a 1:1
> > prescaler.
> >
> > >sheet, I'd appreciate that too.  The datasheet merely says 1:2 .. 1:256
> > >prescalars are available and I only assume that means
> > clock/2^(prescale+1).
> >
> > The datasheet says that the minimum prescale value for TMR0 is 1:2 when
> > assigned to TMR0.  To achieve a 1:1 scale for TMR0, assign the
> > prescaler to
> > the WDT instead of TMR0.
> >
> > --Andrew
>
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jim@jpes.com

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