Timer ticks occurring much more faster

Hi All ,

I am implementing RTC code on an AVR Atmega2560  I have a 32Khz clock
crystal to TSOSC1 which is used by timer2 in async mode. I have
configured the clock divide to 8 so the clock to the timer is 32768/8
= 4096. It is a 8bit so a interrupt should be generated every 16hz
(4096/256).

So on 16 ticks make one second. If I add up second to make 5 minutes
and light an LED on this event , it is happening within 2minutes. Why
is this. I have checked the crystal is oscillation at 32Khz.

Has any on encountered this?


BR
Rate

ratemonotonic escribi�:
> Hi All ,
> 
> I am implementing RTC code on an AVR Atmega2560  I have a 32Khz clock
> crystal to TSOSC1 which is used by timer2 in async mode. I have
> configured the clock divide to 8 so the clock to the timer is 32768/8
> = 4096. It is a 8bit so a interrupt should be generated every 16hz
> (4096/256).
> 
> So on 16 ticks make one second. If I add up second to make 5 minutes
> and light an LED on this event , it is happening within 2minutes. Why
> is this. I have checked the crystal is oscillation at 32Khz.

�Exactly 2 minutes, or perhaps 1 minute and 40 seconds?

On Jul 10, 1:43 pm, "Ignacio G.T." <igtorque.rem...@evomer.yahoo.es>
wrote:
> ratemonotonic escribi=F3:
>
> > Hi All ,
>
> > I am implementing RTC code on an AVR Atmega2560  I have a 32Khz clock
> > crystal to TSOSC1 which is used by timer2 in async mode. I have
> > configured the clock divide to 8 so the clock to the timer is 32768/8
> > =3D 4096. It is a 8bit so a interrupt should be generated every 16hz
> > (4096/256).
>
> > So on 16 ticks make one second. If I add up second to make 5 minutes
> > and light an LED on this event , it is happening within 2minutes. Why
> > is this. I have checked the crystal is oscillation at 32Khz.
>
> =BFExactly 2 minutes, or perhaps 1 minute and 40 seconds?

Investigating further I have varified the it is seeing a clock of
exactly 200Khz. Just as an experiment I freeze sprayed the chip and it
stopped seeing the 200khz clock.
It looks like it is some kind of switching noise it was picking up.