Information

45.4.3.7 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 16-RT clock counter that filters noise and
indicates when a 1 is received.
45.4.3.7.1 Start bit detection
When S2[RXINV] is cleared, the first rising 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.
45.4.3.7.2 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 RT clocks can be undetected by it
regardless of whether it is seen in the first or second half of the count.
45.4.3.7.3 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.
45.4.3.7.4 High-bit detection
At 16-RT 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.
45.4.3.8 Baud rate tolerance
A transmitting device may be operating at a baud rate below or above the receiver baud
rate. Accumulated bit time misalignment can cause one of the three stop bit data samples
(RT8, RT9, and RT10) to fall outside the actual stop bit. A noise error will occur if the
Functional description
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
1118 Freescale Semiconductor, Inc.