AVR-Chat

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
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