2.3 Single-Ended and Differential Modes
In Single-Ended mode, the ADC reads the voltage of a single selectable input source, while in Differential mode, the ADC reads the voltage difference between two input sources.
The Differential mode is configured by writing ‘1’ to the
            DIFF bit as shown below.
/* Differential Mode Configuration */ ADC0.COMMAND |= ADC_DIFF_bm;
The Single-Ended mode is configured by writing ‘0’ to DIFF
            bit as shown below.
/* Single-Ended Mode Configuration */ ADC0.COMMAND &= ~ADC_DIFF_bm;
