AVR-Chat

> ----- 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
>

Double check that ALL your grounds and power pins on the AVR are connected. 
This sounds like a floating ground pin that drives the I/O structures of the 
AVR.

Missing one connection can cause this problem as well as "data dependant" 
and "chip dependant" operation.  Adding "resistance" to the load improves 
the weak DC ground path through ESD structures that can make the problem 
heal itself.

Larrie.