43.6.2.2 Operation
A trigger event initiates the start of the ADC sampling of the selected analog input. After the expiration of the SAMC sample time the conversion sequence is automatically initiated by the hardware assuming CTRLB.SWCNVEN = 0. For maximum efficiency, in the case of SCAN mode, at the conclusion of sampling for the current active analog input and while the conversion cycle is in progress, the analog channel input multiplexer will switch to the next analog input in the users scan sequence in preparation to initiate the next channel sampling sequence immediately once the previous channel conversion is complete. In SCAN mode, sample/conversion progression is always lower to higher numbered channels as selected by the user in the CHNCFG2n.CSSx registers for the respective ADCn module.