Default value of PPGO is high, it is toggled when duty matching and period matching (duty matching:
reset, period matching: set). To export the pulse output as PPG port, set the PPG_PE bit in the PPGCR1
register.
When PPGH/PPGL are read, PPGL should be read first. Because when PPGL is read, PPGH is
captured to buffer, and when PPGH is read, the captured value of PPGH is read.
NOTE: The duty value should not set the same to the period value.