AVR-Chat

From: AVR-Chat@yahoogroups.com
[mailto:AVR-Chat@yahoogroups.com] On Behalf Of
art3@granzeier.com Sent: 06 October 2009 21:02 To:
AVR-Chat@yahoogroups.com Subject: [AVR-Chat] ISP Port
Restictions 
> My questions are these:
> 
> 1)  Are there any restrictions on use of the ISP pins for
> other than 
> during programming?  In other words, what other things
> may/will cause the 
> programmer to not find the AVR chip?
> 
> 2) Also, is this related specifically to the Sample
> Electronics 
> programmer, or will I find the same limitations with one
> of the buffered 
> ISP cables (6- or 10-pin)?
> 


Yes, if you put too much loading on the ISP pins, the programmer will
not work. This applies to all programmers.
In my experience the max loading is about 150 ohms down to ground when
using the Atmel AVRISP.

Obviously you also need to make sure your external circuit is not
driving any of the ISP pins (eg output of an opamp or something like
that).

-- 
Tim Mitchell