AVR-Chat

At 10:10 AM 4/28/2004 -0600, Craig Limber wrote:


>Hi there;
>
>I am looking for a little advice on debugging my latest AVR project.  I
>have an ATmega32 (40 pin DIP, high voltage version) on a custom
>single-sided printed circuit board.  I bought a 16 meg/20pf load
>crystal (CTS Frequency Controls model ats16a) and wired in 18pf caps
>(didn't have 20 but I figured stray capacitance should get me close
>enough).  The crystal and caps are mounted as close as I could on the
>board.  

AARRGGHH..  While 18pF will likely run, you're closer to needing 35.
http://www.dvanhorn.org/Micros/All/Crystals.php
Sorry, it's a pet peeve.

>My processor won't start.  I adjusted the fuses for the high frequency
>range and programmed the CKOPT fuse.

CKOPT is not something you want to mess with.
High speed crystal, and CKOPT not checked (1, not programmed)


>A frequency counter on either XTAL pins shows 15.9989xx MHz and a scope
>on either pin shows either a nice sinewave (rail to rail which tells me
>that CKOPT is programmed as I expected) on one and a slightly deformed
>sine wave on the other (but still regular and rail to rail).  

Normal. 

>If I put an 8 meg crystal in it works perfectly using the exact same
>settings and load caps.  A scope on the XTAL pins shows almost
>identical waveforms at 8 meg as 16 meg but at half the frequency, of
>course.

Ok, are you getting near rail-to-rail amplitude?
If it's low (1-2Vpp) then change CKOPT and watch it start running, and then never mess with that fuse again. 

CKOPT selects a very low power "Vittoz" oscillator, that is VERY touchy.