NXP Semiconductors K22F series, Reference Manual, Page: 1332 / 1407

48.3.3.4 Infrared decoder
The infrared decoder converts the received character from the IrDA format to the NRZ
format used by the receiver. It also has a OSR oversampling baud rate clock counter that
filters noise and indicates when a 1 is received.
48.3.3.4.1 Start bit detection
When STAT[RXINV] is cleared, the first falling edge of the received character
corresponds to the start bit. The infrared decoder resets its counter. At this time, the
receiver also begins its start bit detection process. After the start bit is detected, the
receiver synchronizes its bit times to this start bit time. For the rest of the character
reception, the infrared decoder's counter and the receiver's bit time counter count
independently from each other.
48.3.3.4.2 Noise filtering
Any further rising edges detected during the first half of the infrared decoder counter are
ignored by the decoder. Any pulses less than one oversampling baud clock can be
undetected by it regardless of whether it is seen in the first or second half of the count.
48.3.3.4.3 Low-bit detection
During the second half of the decoder count, a rising edge is decoded as a 0, which is sent
to the receiver. The decoder counter is also reset.
48.3.3.4.4 High-bit detection
At OSR oversampling baud rate clocks after the previous rising edge, if a rising edge is
not seen, then the decoder sends a 1 to the receiver.
If the next bit is a 0, which arrives late, then a low-bit is detected according to Low-bit
detection . The value sent to the receiver is changed from 1 to a 0. Then, if a noise pulse
occurs outside the receiver's bit time sampling period, then the delay of a 0 is not
recorded as noise.
48.3.4 Additional LPUART functions
The following sections describe additional LPUART functions.
Functional description
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
1332 NXP Semiconductors