AVR-Chat

On Fri, 30 Nov 2007 18:25:13 -0500
 "Jim Wagner" <jim_d_wagner@applelinks.net> wrote:
> On Fri, 30 Nov 2007 22:42:04 -0000
>  "Rick" <bit.tricks@gmail.com> wrote:
> > --- In AVR-Chat@yahoogroups.com, "Philippe Habib"
> > <phabib@...> wrote:
> > >
> > > Thanks for the reply.  I looked through the data
> sheet
> > for guidance
> > about
> > > the various counters but I wasn't able to figure out
> > what I need.  Maybe
> > > someone here can help.
> > > 
> > > I am using an ATMega 128 clocked at 16 mhz.  What I'm
> > trying to get is a
> > > 10khz PWM from timer 1 and a 2 khz pwm from timer2.
>  I
> > am using the
> > Bascom
> > > BASIC.
> > > 
> > > I expect that what I need to do is to use these like
> I
> > use timer0 to
> > set up
> > > my 10ms timer tick. For that, I set the prescale to
> > 1024 and by
> > reloading
> > > the timer to 99 each time my timer ISR executes, I
> get
> > a 10ms tick.
> > > 
> > > Since this is a PWM and I don't have an ISR, I'm
> > looking for the way
> > to set
> > > that reload value one time when I configure the PWM.
> >  That's what
> > I've been
> > > unable to find.
> > > 
> > > I have experimented with trying to set various timer
> > related things but
> > > haven't gotten it to work.
> > > 
> > > Here are my declarations:
> > > 
> > > Config Timer0 = Timer , Prescale = 1024
> > > Config Timer1 = Pwm , Pwm = 10 , Compare A Pwm =
> Clear
> > Up , Prescale = 1
> > > Config Timer2 = Pwm , Pwm = On , Compare Pwm = Clear
> Up
> > , Prescale = 8
> > > 
> > > 
> > > I'd appreciate any help from someone who knows the
> > answer on this one.
> > > 
> > > Thanks.
> > > 
> > 
> > Philippe:
> > 
> I think there is more than a little confusion here.
> 
> When you say "PWM", are you talking abou a PWM signal
> that
> is generted by internal hardware? Or, are you talking
> about
> a software PWM.
> 
> This quesion arises because you say that you are using
> the
> timer to generate "10ms tics" and you also talk abou a
> 10KHz PWM.
> 
> Normally, the PWM frequency is the repetition frequency
> of
> the entire PWM waveform. Otherwise, one would talk about
> "PWM clock". Yet, I think of "ticks" as the clock applied
> as the input of a PWM. So, if the PWM is generating
> "ticks", I would think of those as clocks to a software
> PWM. 
> 
> Further, a 10MHz clock and 1024 prescale will give that
> counter a clock of 9.765... KHz. There is no way that you
> could get a 10KHz PWM out of that setup.
> 
> Thus, we need to make sure what it is that you are
> talking
> about.
> 
> Jim Wagner
> Oregon Research Electronics
> Tangent, OR, USA

Ooops,. clock is 16MHz. So 1024 prescale gives 15.625KHz
clock ticks for that counter. Still, no way you can get a
10KHz PWM from that.

Jim
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