33.2.3 ADC Operation During Sleep
The ADC module can operate during Sleep. This
            requires the ADC clock source to be set to the ADCRC option. When the ADCRC oscillator
            source is selected, the ADC waits one additional instruction before starting the
            conversion. This allows the SLEEP instruction to be executed, which can
            reduce system noise during the conversion. If the ADC interrupt is enabled, the device
            will wake up from Sleep when the conversion completes. If the ADC interrupt is disabled,
            the device remains in Sleep and the ADC module is turned off after the conversion
            completes, although the ON bit remains set.
