Zitat Zitat von Atmel-doc 2486S–AVR–08/07, Seite 6
AVcc AVcc is the supply voltage pin for the A/D Converter, Port C (3..0), and ADC (7..6). It should be externally connected to Vcc, even if the ADC is not used.
... should be externally connected to Vcc, even if the ADC is not used.

Es ist wie (fast) immer. Im Doc steht (fast) alles, man müsste nur wissen wo.