user276: I'm designing a circuit that will use a 2.5v reference for the AREF. Should AVCC be powered from 5V or 2.5V?

user2881: 
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.

So it should be connected to 5V.

276: <p>I'm designing a circuit that will use a 2.5v reference for the AREF. Should AVCC be powered from 5V or 2.5V?</p>
 2881: <blockquote>
  <p>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.</p>
</blockquote>

<p>So it should be connected to 5V.</p>
