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Re: [avr-gcc-list] supply pins on atmega32

From: Erik Christiansen
Subject: Re: [avr-gcc-list] supply pins on atmega32
Date: Wed, 15 Sep 2004 15:23:41 +1000
User-agent: Mutt/1.5.6+20040722i

On Tue, Sep 14, 2004 at 07:07:13PM -0700, Reza Naima wrote:
> First off, the atmega32 has 3 VCC pins, and 4 GND pins.  Do 
> they all have to be supplied for the circuit to work, or can I get by 
> with just one?  

The data sheet refers to just one VCC in the pin description, so I'd bet
they're common. A continuity check, with no other pins connected, and
using less than 600 mV, should resolve any doubts, though. I'd still
connect and bypass each, especially if you're running at high speed.

Quadrupling ground impedance, by connecting only one ground pin is
probably asking for trouble. At 16 MHz, the flanks of output signals are
likely to generate internal ground bounce, especially on capactive loads.

At least the 32 doesn't seem to have the external bus. I've seen VCC
spiking to +7V, when driving a few inches of bus at 16 MHz, without
adequate bypassing (on all VCC pins) or series bus termination. (On the

> I was also wondering, should the AREF and AVCC be attached to
> something? 

My recollection is that AVCC needs to be within 300 mV of VCC, so I'd
play safe. The data sheet insists that AREF not be connected when the
internal reference is used (IIRC), so there's no worry there.

Good luck!


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