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Re: [avr-chat] AVCC / JTAG oddity


From: Russell Shaw
Subject: Re: [avr-chat] AVCC / JTAG oddity
Date: Sat, 25 Mar 2006 10:58:11 +1100
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20060205 Debian/1.7.12-1.1

Gary Douglas wrote:
Hi all,

Just got a new board in, and it's behaving strangely.
It's and ATMEGA64 design, but is not usign the A to D.

I've connected AVCC to +5 observing all of the regular precautions (bypass cap...).

When AVCC is connected The unit cannot be programmed via JTAG (JTAGICE MKII) , and connecting to the unit is spotty. I can read fuses and stuff, but writing doesn't work.

When I cut the track connecting AVCC to +5, the unit works perfectly.

This is contrary to all of the docs, and is quite puzzling.

I have other designs where AVCC is connected to +5 and has NO problems.

The supply looks clean and solid.

Thoughts?

Maybe there's a short between the AVCC pcb track and one of the JTAG tracks.
Solder blobs under an IC?




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