[avr-chat] Re: weak crystal driving mode

[Clemens Koller]

David VanHorn wrote:
> > > Check your CKOPT fuse. You should not run with that fuse in the
> > > default state without a lot of research as to wether your crystal will
> > > work on that drive.
> > As I said, I verified that it works reliable, so I can recommend
> > using that feature _if_done_right_ to save power, since the
> > internal oscillator isn't really precise, even if calibrated
> > (and it still depends on temperature).
>
> Yeah, that's what we thought too. Unfortunately, with standard
> crystals, it's a major disaster.

Yes, you might fail with the cheap HC49 standard stuff.

> IF you have a crystal designed for working in this mode, then it
> works. No argument there.
> Atmel USA was not able to refer me to any part number that they
> thought would work, and were unable to tell me how to qualify a
> crystal for that mode.

Yes, because then they would have been responsible for that...

> In fact, they asked me to point them to anything that I found on those lines.

That's poor. IMO it's not really magic. You can even simulate
the oscillator and checkout driving powers with swings to several 100mVs.

I've chosen a typical low "drive level", low voltage AT-cut crystal
(i.e. 25uWatts typ.) in fundamental mode. But no, I cannot
recommend any crystal for use in the low-drive mode. :-P

Unfortuntely only available in german, but still very good:
"Das Quarzkochbuch"
http://www.qsl.net/dk1ag/buch.html

Regards,

Clemens Koller
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