AVR-Chat

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 >>>>
> >
>
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