ADMUX = _BV(REFS1) | _BV(MUX1) | _BV(MUX0);
// 1.1V reference, PB3 pin, single-ended
DIDR0 |= _BV(ADC3D); // PB3 pin as analog input
ADMUX = _BV(REFS1) | _BV(MUX1) | _BV(MUX0);
// 1.1V reference, PB3 pin, single-ended
DIDR0 |= _BV(ADC3D); // PB3 pin as analog input