13.2.6 Bit Positions

The ADC also allows you control where the significant digits are located. Bit ADLAR (bit 5 of ADMUX) selects whether zeros are inserted to the most significant bits, or the least significant bits.

If ADLAR is 0, then the most significant bits are zeros, whereas bit 0 to bit 9 are the results. If ADLAR is 1, then the least significant bits are zeros, whereas bit 6 to bit 15 are the significant bits.