AVR-Chat

Have you found a solution yet?

The data sheet says that internal osc other than the default requires a startup delay if BOD is not used (page 28).

This problem could be a lessons learned for the rest of us. If someone else notices this they will know what to do.

Brian

--- In AVR-Chat@yahoogroups.com, "Tim Mitchell" <tim@...> wrote:
>
> Hi folks,
> 
> Got a weird problem with a Mega8. It's in a timer device, the customer
> was reporting that the timed periods were half what they should be.
> 
> On testing it, the timed periods were indeed half, unless you reset the
> device using the ISP header, in which case it worked correctly.
> 
> It's running on 8MHz internal oscillator. Timer 0 is set to CK/8 and I
> have put a pin toggle into the Timer 0 overflow interrupt, which should
> give an overflow every 256uS. On power up I get an interrupt every
> 128uS! But if I reset it using the ISP header I get the correct 256uS.
> This suggests that the internal osc is running at 16MHz.
> 
> The fuses are set to shortest startup time 6CK+0ms (but Bod is not
> enabled, which the datasheet says it should be with this setting). If I
> change it to 6CK+64ms then it appears to start up correctly every time.
> 
> I have used Mega8's in loads of designs and I have never come across
> this. Has anyone seen this one before?
> 
> 
> -- 
> Tim Mitchell
>