AVR-Chat

Not uncommon with AVR's in my experience.  I have yet to get a board 
designed that didn't have problems with resets on an AVR or MEGAAVR 
part.  I've found that if I run the part at its maximum rated frequency, 
I get flaky boards, if I derate by 20% or so then the board gets more 
reliable, and if I derate by 50% the clock speed everything works fine. 
  This seems to indicate that I've got noise on the clock lines - but 
after my first experience with these things I've started designing with 
guard rings on my oscillator circuits, whole plane grounds, bypass caps 
up the nose, low pass filters on my VDD and everything else I've found 
in app notes on the Atmel site, still I can get flaky boards.  I never 
have these problems with PICs <did I say that?>.

I love these chips, they have speed, capability and low cost.  But oh 
the problems with Atmel availability and quirkyness.

IMO, YMMV,
DLC

Timothy D. Lenz wrote:
> Sounds like a flaky batch of chips.
> ----- Original Message ----- 
> From: "kernels_nz" <hein@mediflex.co.nz>
> To: <AVR-Chat@yahoogroups.com>
> Sent: Monday, April 03, 2006 9:37 PM
> Subject: [AVR-Chat] Re: Connecting AVRs directly to inputs of 74HC and LS
> logic chips.
> 
> 
> 
>>hi Jim,
>>
>>Yeah, ive almost given up, sounds a bit like a beginner mistake, but
>>ive been working with AVRs on at least a weekly basis for about 4
>>years now, so it's nothing new. The DDR was set such that the 4 pins
>>connecting to the inputs of the logic chip (74ls138 and 74hc138) were 1's.
>>
>>Ill have a proper proper read through the code again tonite.
>>
>>I didnt have the problem during development, had the pcb made, now
>>it's got the problem on about half the Mega chips I use, if I pull the
>>chip out, and plug an older chip with  the same code in, the problem
>>dissapears.
>>
>>I actually thought it was a problem with the Mega the first time I saw
>>the problem occur, desoldered it and crunched it, before finding one a
>>few boards later doing the same thing.
>>
>>Is definately something in the Megas, just thought it would be worth
>>mentioning to the guys in here in case someone else sees weird things
>>start happening.
>>
>>THANKS for all the suggestions guys !
>>
>>Cheers
>>Hein B
>>
>>--- In AVR-Chat@yahoogroups.com, "James Hatley" <james.hatley@...> wrote:
>>
>>>Hello Hein,
>>>
>>>Yes, sorry... we drifted away from your problem but it was an
>>
>>interesting
>>
>>>discussion between Jose and I.
>>>
>>>Delighted that you were able to find and fix the problem but it is
>>>mysterious just why. I drive 74HC chips in several production
>>
>>environments
>>
>>>without problem using AVR processors, ATmega32 and ATmega644 on one
>>
>>such and
>>
>>>ATmega2560 the other.
>>>
>>>Maybe someone will enlighten us on just how this happens as it seems
>>
>>odd to
>>
>>>me that a just a high value resistance pull down would be required.
>>
>>Wonder
>>
>>>if others have had this problem?
>>>
>>>Jim
>>>
>>>
>>>----- Original Message ----- 
>>>From: "kernels_nz" <hein@...>
>>>To: <AVR-Chat@yahoogroups.com>
>>>Sent: Monday, April 03, 2006 1:41 PM
>>>Subject: [AVR-Chat] Re: Connecting AVRs directly to inputs of 74HC
>>
>>and LS
>>
>>>logic chips.
>>>
>>>
>>>Hmmhm, discussion seems to have strayed a bit, but just in case
>>>anyone ever runs across the same problem:
>>>
>>>* I definately had the pins on the AVRs configured as outputs.
>>>
>>>* The same fault occured with both 74HC and 74LS chips, but only on
>>>   my newer batches of Mega16s and Tiny26s.
>>>
>>>* In both cases, the problem was cured by fitting external 100k
>>>  pulldown resistors. NO CODE CHANGES.
>>>
>>>* I know it sounds like I had the pins configured as inputs and using
>>>  the internal pullup to pull it high, but thats just not the case.
>>>
>>>Cheers
>>>Hein B
>>>
>>><<<< snip >>>>
>>>
>>
>>
>>
>>
>>
>>
>>Yahoo! Groups Links
>>
>>
>>
>>
>>
>>
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-- 
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Dennis Clark          TTT Enterprises
www.techtoystoday.com
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