In FIFO (First In First Out) type, the conversion data is always written in memory after the latest data, and is always read out the oldest data from memory.
If the conversion data is stored in all of the memory and more conversion data will be stored in the memory, overflow error occurs and the conversion stops.
In FIFO type, data can be read during AD conversion. By reading data regularly so that the memory does not overflow, it is possible to perform sampling for a long time than the memory capacity.