29.3.2.4.1 ADC Input Channels
When changing channel selection, the user must observe the following guidelines to ensure that the correct channel is selected:
In Single Conversion mode: The channel should be selected before starting the
         conversion. The channel selection may be changed one ADC clock cycle after writing
            ‘1’ to the STCONV bit.
In Free-Running mode: The channel should
         be selected before starting the first conversion. The channel selection may be changed one
         ADC clock cycle after writing ‘1’ to the STCONV bit. Since the next
         conversion has already started automatically, the next result will reflect the previous
         channel selection. The subsequent conversions will reflect the new channel selection.
The ADC requires a settling time after switching the input channel - refer to the Electrical Characteristics section for details.
