On a standalone AVR processor, does it matter about AVCC and AGND?

Projects General Guidance
1

I'm working out a circuit using an AVR processor and some interfacing. I don't need the ADC features at all.
The breadboards I have made so far have left AVCC and AGND open circuit, and seem to work find. Some
circuits I have seen have the pins connected and some have not.
The duemilanove schematic shows the pins as connected.
Does that matter? Should they be connected to VCC and GND for better performance?

(using Atmega328PU processor)

Edit: I've found it in the datsheet now.
"AVCC is the supply voltage pin for the A/D Converter, PC3:0, and ADC7:6. It should be externally
connected to VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC
through a low-pass filter. Note that PC6..4 use digital supply voltage, VCC."

And the datasheet just calls AGND just GND which give a good clue about what I should do.

2

If you dont connect the AVcc pins then you wont have some internal parts of the Atmega powered and also part of portC wont work, and all the GND's must be connected, so yes you should connect all power and ground pins if you want your micro-controller to behave as expected.

3

AVCC is the supply voltage pin for the A/D Converter, PC3:0, and ADC7:6. It should be externally connected to VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC through a low-pass filter............You get the choice of filtering because AVCC and AGND connected externally........
if it was internal, you couldnt do it.