AVR-Chat

----- Original Message ----- 
From: "Tim Mitchell" <tim@sabretechnology.co.uk>
To: <AVR-Chat@yahoogroups.com>
Sent: Tuesday, October 17, 2006 9:22 AM
Subject: [AVR-Chat] Mega162 crystal osc problem / CKOPT bit


> I'm having an oscillator problem with a Mega162 device ... Dunno if
> anyone has seen it before and might have some advice.
> 
> I've got 4 identical units with Mega162, 16MHz xtal with 15pf
> capacitors. One of them will not start up on power up (no oscillator)
> but the others are fine. If I reprogram the chip in the non-working one,
> it then works fine for the rest of the day, power on and off as much as
> you like, but the next morning when I come in, it does not work again.
> 
> Now I've had this situation before with some units using the Mega8, and
> it turned out to be because I had not set the CKOPT fuse bit on the
> Mega8. This changes the mode of the oscillator to give larger
> oscillations. With CKOPT unprogrammed, they mostly worked but the odd
> one failed to start on first power up as described above. With CKOPT
> programmed everything was fine.
> 
> Unfortunately the Mega162 does not seem to have a CKOPT bit - any ideas
> what I can do to the oscillator circuit to make it work reliably?

I'd try using changing the crystal and the capacitors.

Leon