AVR-Chat

Hi Dave,
 
>That would be bad. There's nothing to balance in this case, you're just 
>using the xtal sections as amplifiers. 
 
I disagree, depending on the internal design of the oscillator not using a
capacitor could cause it to stop oscillate (I have tried it without just now
and it works but I would still recommend it)
 
>>On the MASTER a 1Mohm between XTAL1/2 and a series resistor from XTAL2 to
crystal of a hundred ohms is a good idea.


>Why?


The 1Mohm parallel resistor gives a nicer oscillation (check your scope) and
the 100R resistor reduces harmonics.
 
If you have a spectrum analyzer available try first without the 1Mohm then
try adding it would maybe see that this also reduces harmonics from the
crystal a little but the 100R resistor does the job much better. I got this
information attending an EMC coarse because one of our PCB's failed to
comply with EMC standards adding the 1M and 100R resistor did the job.
 
Best regards
Lasse M.
 
 
 




 
  _____  

From: Dave VanHorn [mailto:dvanhorn@dvanhorn.org] 
Sent: 4. januar 2005 15:21
To: AVR-Chat@yahoogroups.com; AVR-Chat@yahoogroups.com
Subject: RE: [AVR-Chat] multiprocessing with AVR (2)
 
At 08:46 AM 1/4/2005, Lasse Madsen wrote:

>While we are at it (EMI) one should probertly also connect a 10nF 
>capacitor to the last unused XTAL2 output to balance the pierce.

That would be bad. There's nothing to balance in this case, you're just 
using the xtal sections as amplifiers.  I would fuse the slaves for 
external osc though, it will take less power. (not sure if the output 
remains active then though. I've never tried that config)


>On the MASTER a 1Mohm between XTAL1/2 and a series resistor from XTAL2 to 
>crystal of a hundred ohms is a good idea.

Why?

>take output from XTAL2 pin directly through a second resistor (100R) to 
>the XTAL1 pin of a slave.
>

This part I agree with, you'll find that your trace impedance is roughly 
100 ohms-ish.



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