Re: [avr-chat] Error in Timing.

[Royce Pereira]

Hi,
On Wed, 01 Mar 2006 10:02:08 +0530, Erik Christiansen <address@hidden> wrote:

> On Sun, Feb 26, 2006 at 05:55:06PM +0530, Royce Pereira wrote:
> > However, the Crystal oscillator also gives an error of about 5 seconds in
> > 300 seconds. I tried using different capacitor values at the crystals pins,
> > but this made no difference.
>
> One way to check is to select the internal 1 MHz rate, confirm that
> rate, then select external crystal, and confirm 4 MHz. Then we can be
> more certain that RC 4 MHz is not still selected. Do you have a crystal
> that is not 1/2/4/8 MHz, to absolutely confirm clock source selection?

I believe it is selecting the 4 MHz crystal, as I used the 1MHz internal RC osc. 
earlier, & then had to change all my dividing counter values for 4MHz, to get 
the same timings.
> If the crystal were in control, the oscillator should be within 100 ppm
> (or even 50), not 16,700 ppm off. Are you using something vaguely like
> 12 to 22 pf capacitors?

I used 2 33pf caps in series at each pin to GND. This gives 16pF each.
I set the low fuse bits to 0xFF, ckopt=1 (unprogrammed). This means external 
xtal, 3-8 MHz, xtal osc-slowest rise time (right?).

Thanks,
--Royce.

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