AVR-Chat

At 09:31 PM 15/05/2009, you wrote:
>This suggests that the internal osc is running at 16MHz.

You are a MIRACLE worker. :-)

>(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.

So why not used the BOD as the data sheet says you should? Do you 
have a cap on the
reset line?

Most likely the chip and oscillators are wobbly at power up and
the chip is not being initialised correctly seeing the a reset
gets it working correctly after the oscillator has stabilised.


Regards

John Samperi

********************************************************
Ampertronics Pty. Ltd.
11 Brokenwood Place Baulkham Hills, NSW 2153 AUSTRALIA
Tel. (02) 9674-6495       Fax (02) 9674-8745
Website  http://www.ampertronics.com.au
*Electronic Design * Custom Products * Contract Assembly
********************************************************

I think John is correct. Also, the default setting per the datasheets is 1MHz and calibration is set (page 28 of the datasheet). When programed at 8MHz the calibration is not set and requires manual setting and a longer startup time. Page 29 talks about saving the value to eprom to use on startup by software to set the cal. I think by not setting the cal or allowing delayed startup times could cause all kinds of problems.

Brian

--- In AVR-Chat@yahoogroups.com, John Samperi <samperi@...> wrote:

>
> At 09:31 PM 15/05/2009, you wrote:
> >This suggests that the internal osc is running at 16MHz.
> 
> You are a MIRACLE worker. :-)
> 
> >(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.
> 
> So why not used the BOD as the data sheet says you should? Do you 
> have a cap on the
> reset line?
> 
> Most likely the chip and oscillators are wobbly at power up and
> the chip is not being initialised correctly seeing the a reset
> gets it working correctly after the oscillator has stabilised.
> 
> 
> Regards
> 
> John Samperi
> 
> ********************************************************
> Ampertronics Pty. Ltd.
> 11 Brokenwood Place Baulkham Hills, NSW 2153 AUSTRALIA
> Tel. (02) 9674-6495       Fax (02) 9674-8745
> Website  http://www.ampertronics.com.au
> *Electronic Design * Custom Products * Contract Assembly
> ********************************************************
>

At 12:10 PM 16/05/2009, you wrote:
>I think John is correct.

It seems a case of "premature initialization".

The cpu may start and finish before the oscillator has
started to get warmed up......


Regards

John Samperi

********************************************************
Ampertronics Pty. Ltd.
11 Brokenwood Place Baulkham Hills, NSW 2153 AUSTRALIA
Tel. (02) 9674-6495       Fax (02) 9674-8745
Website  http://www.ampertronics.com.au
*Electronic Design * Custom Products * Contract Assembly
********************************************************