AVR-Chat

Thanks to everyone for all the Timer/Counter information and tips.

Jeff

--- In AVR-Chat@yahoogroups.com, "arhodes19044" <spamiam@c...> wrote:
> I do not think it is necessary to interrupt early, then dawdle for a 
> few cycles, then execute the interrupt code.  In the simpler  
> method, there is a slight "phase delay" of the interrupt code 
> execution, but since it executes everytime with the same delay, then 
> the next time it executes will be (for instance) exactly one 
> millisecond after the last time.  So, there might be a slight delay 
> compared to world time, but I doubt most people (and even most 
> software) would ever notice this discrepancy.  It is more important 
> that the interval between executions is the exact same.
> 
> -Tony
> 
> --- In AVR-Chat@yahoogroups.com, "Roy E. Burrage" <RBurrage@b...> 
> wrote:
> > You can also set up the prescaler and count registers for 
> something 
> > slightly less than what you require, then waste a few cycles in 
> the ISR 
> > to get your required time.
> > 
> >     System clock = 1 MHz
> > 
> > Using a prescaler value of 32 and a count register value of 31 
> would 
> > give 992 timer overflows per second, or 1 overflow every 992 
> uSec.  Then 
> > if you either waste or do something else for 7 cycles you'll have 
> 999.
> > 
> > Application note AVR130 explains this pretty well.
> > 
> > 
> > REB
> > 
> > 
> > arhodes19044 wrote:
> > 
> > >I agree that it is a major pain in the neck having powers of 2 as 
> > >the prescaler, but NOT powers of 2 as the usual crystal freq.
> > >
> > >In my case I needed a 1 millisecond clock.  So, I used a 16 bit 
> > >clock for my 16MHz crystal.  (8 bits would not do).
> > >
> > >I uses CTC mode with a prescaler of zero, and triggered the 
> > >interrupt after 16,000 clock cycles.  (16e6/16e3 = 1e3).  This 
> > >worked out fine.  
> > >
> > >  
> > >