Re: [avr-chat] avrdude-ATMega32 fuse bits issues

[Brian Dean]

On Wed, Dec 21, 2005 at 09:58:34AM -0500, Graham Davies wrote:

> In a post on November 12, I described an experiment in which an
> ATmega16-16PC ran with a 15.36 MHz crystal with a wide variety of
> fuse setting, including CKOPT not programmed.  The experiment
> included long traces and lots of stray capacitance at the crystal
> pins and I later extended it to include a large imbalance in the
> load capacitors.  It always worked.  So, it seems to me that the
> crystal circuit is not really so sensitive.  I withhold an opinion
> about those plug-in breadboards, though.  I would not use one
> myself.

No offense, but your experiment is just one data point.  Contrary to
your experiment, I've had problems with the oscillator starting when
CKOPT is unprogrammed using a 16 MHz crystal.  Simply program CKOPT
and it works fine, so I guess my experience contradicts yours - I used
an ATmega128, perhaps it is more sensitive to this than the ATmega16,
maybe it was just that particular batch of chips, I don't know.
Anyway, the datasheet also says CKOPT should be programmed for these
higher speed settings.  So when people have trouble with the
oscillator when using a 16 MHz crystal or resonator, and they are not
following the recommendations of the datasheet, the first thing they
should do is get in-line with the datasheet recommendations and verify
that CKOPT is programmed.  This is just standard checklist stuff when
troubleshooting.

-Brian
-- 
Brian Dean
ATmega128 based MAVRIC controllers
http://www.bdmicro.com/