Re: [avr-chat] ATmega32 @ 16MHz : fuse bits ??

[David Kelly]

On Nov 10, 2005, at 11:38 PM, Vincent Trouilliez wrote:

> I set my function generator to 1MHz to be safe. My
> generator is a bit old and at that frequency the square wave looks  
> more
> like a sine, but somehow the AVR is happy with it... who said digital
> circuits were picky...

The crystal oscillator circuit is analog. The delta voltage the  
crystal swings is pretty low. Way out of normal TTL or CMOS switching  
ranges. You observed about 2 volts on the pins. If the crystal was  
running it might have been only 50 mV AC on that 2V DC bias.

There is some magic to making crystals oscillate. Not all crystals  
are alike. Motorola/Freescale is very good about spec'ing crystals,  
Atmel is sloppy. Wrote to Atmel once asking and was told the page  
number to consult in the manual for setting oscillator fuses. Wrong  
answer. I wanted to know, "Series, parallel, A/T cut, drive level,  
capacitance, etc?"

--
David Kelly N4HHE, address@hidden
========================================================================
Whom computers would destroy, they must first drive mad.