AVR-Chat

Yup, been there, seen that, was chastised by the group for it.  I was 
very relieved to have that pointed out, I missed it totally in the spec 
sheets.

DLC

Larry Barello wrote:
> I recently fought with some AVR CPU malfunction and it had NOTHING to do
> with power supply noise.  The target system was a mega128 with a 16 mhz
> resonator.   The symptoms?  Oh, the stack pointer would randomly be off by
> one.  Or it would just start executing code at random locations, most often
> off in empty flash which would just NOP (0xFFFF) until the PC wrapped and
> the code restarted (I knew this was the case since there was *no* reset
> source at the start of my code - it never reset).
> 
> The problem, it turned out after much investigation, was having the CKOPT
> fuse cleared.  That puts the crystal driver into a very low power mode and,
> apparently, noise in the system (the biggest problem was a brushed DC motor
> controller) was causing extra clock cycles which were way too fast for the
> CPU to keep up with.
> 
> Anyway, checking the CKOPT fuse and reprogramming the chip solved the
> problem.  The signal at the resonator was ~4v pp vs 200mv and the code is
> rock solid.
> 
> 
> -----------
> Larry Barello
> www.barello.net
> 
> 
> | -----Original Message-----
> | From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
> | Of Zack Widup
> | Sent: Monday, July 10, 2006 9:30 AM
> | To: AVR-Chat@yahoogroups.com
> | Subject: Re: [AVR-Chat] AVR Power Supply Noise
> | 
> | On Mon, 10 Jul 2006, behrooz_hariri wrote:
> | 
> | > I connected a car battery (12v) to LM7805 to fully minimize power
> | > supply noise. But still get errors in executing codes.
> | > I read a film capacitor 0.1uF is necessary after regulator. I used
> | > electrolyte one 0.15uF.  Does it make difference?
> | >
> | 
> | Electrolytics aren't the best things for bypassing RF.  Since a value of
> | 0.1 uF or so is meant to keep RF out of the chip's power leads, you might
> | do better with a different kind of capacitor.
> | 
> | Make sure you put it as close as you can get to the supply and
> | ground pins on the AVR chip.
> | 
> | > I use a breadboard with some wire rather twisted and 10cm long. Is
> | > this a reason for MCU malfunction?
> | >
> | 
> | Possibly. Breadboards are notorious for coupling between
> | wires/connections.
> | 
> | There are quite a few development boards out there that are made to get
> | around this problem.
> | 
> | Zack
> | 
> 
> 
> 
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 

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Dennis Clark    TTT Enterprises
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