11.8.6 PPG period min/max limitation
When ATPHR/ATPLR is increasing, if ATPHR/ATPLR value and ATPMAXHR/ATPMAXLR matches,
ATP_MAX (max period matching flag) set to '1'. When ATPHR/ATPLR is decreasing, if ATPHR/ATPLR
value and ATPMINHR/ATPMINLR matches, ATP_MIN (min matching flag) set to '1'.
ATP_MAX and ATP_MIN is assigned to interrupt vector 4 and 5. In the auto period mode, the PPG
period is not greater than the max value, not less than the min value. But when writing to the
PPGPH/PPGPL, even if PPGPH/PPGPL is outside the range of the min and max value,
PPGPH/PPGPL is loaded to the ATPHR/ATPLR, and ATP_MAX or ATP_MIN set to '1'. ATP_MAX and
ATP_MIN is cleared by hardware before interrupt service routine is served or by writing '0'. When
ATP_MAX or ATP_MIN occur, PPG current period is maintained to the next cycle.