Special care should be taken when changing differential channels. Once a differential channel
has been selected, the gain stage may take as much as 125 μs to stabilize to the new value.
Thus conversions should not be started within the first 125 μs after selecting a new differential
channel. Alternatively, conversion results obtained within this period should be discarded.
The same settling time should be observed for th
e first differential conversion after changing
ADC reference (by changing the REFS1:0 bits in ADMUX).