AVR-Chat

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 >>>>
>