33.4.3 Accumulate Mode
In Accumulate mode (MD
            = 
    ‘b001), after
            every conversion, the ADC result is added to the ADACC
            register. The ADACC register is right-shifted by the value of the CRS bits. This right-shifted value is copied into the ADFLTR
            register. The Formatting mode does not affect the right-justification of the ADACC or
            ADFLTR values. Upon each sample, ADCNT is incremented, counting the number of samples
            accumulated. After each sample and accumulation, the ADFLTR value has a threshold
            comparison performed on it (see the Threshold
                Comparison section) and the ADTIF interrupt may
            trigger.