Double sampling is enabled by setting the ADDSEN
bit. When this bit is set, two conversions are required before the module will calculate
threshold error. Each conversion must still be triggered separately when ADCONT =
0. The first conversion will set the ADMATH bit and update ADACC, but will not calculate ADERR or trigger ADTIF. When the second
conversion completes, the first value is transferred to ADPREV (depending on the setting of
ADPSIS) and the value of the second conversion is placed into ADRES. Only upon the
completion of the second conversion is ADERR calculated and ADTIF triggered (depending on
the value of ADCALC).