12.2.4.4.1 RZI to NRZ Demodulation
The RZI to NRZ demodulator looks for High to Low transitions on the input, marking each one as an RZI pulse for applications such as IrDA. As High to Low transitions are detected, it is important to have any noise suppressed before entering the demodulator. The input filter block (see 12.2.4.2 Input Filters) of the MMUART is used to suppress noise.
However, true IrDA compliant optical transceivers must perform noise suppression and supply the MMUART with noise free digital signals as per the IrDA specification.
After input filtering, the demodulator waits for a positive edge and sets a down counter based on the internal 16 samples per bit time baud rate clock. The output NRZ signal is set Low until the counter reaches 0, then automatically it goes High.
When back-to-back pulses occur, the incoming pulse may not be aligned with the internal baud count enable and as such may generate a 1/16 NRZ 1 level. This 1/16th pulse is a do not care situation because the sampling occurs in the middle of the Tbit time (bit time).
The input to the demodulator can be an inverted version of the following figure using the EIRX configuration bit in the multi-mode control register 1 (Table 12-23). Also, the EIRD bit in Table 12-23 has to be set to 1.
