Use frames to group a single measurement result together.
In most, but not all, modes the ES51919 reports two separate
analog values for each measurement sample. These values are
mapped to two separate channels and sent in two separate
packets.
A client program needs a way to determine which results are
parts of the same measurement and also know when a complete
measurement is received so it can process the sample. Use
the frame begin and end packets to separate groups that each
represent a single complete measurement.