12.2.4.4 RZI Modulation and Demodulation

The RZI modulation/demodulation blocks are intended to allow for IrDA Serial Infrared (SIR) communications. The SIR specification uses RZI signaling for improving the peak power to average power ratio in low rate wireless applications such as remote controls. The following figure shows the RZI modulation scheme, where a logic 0 is represented as an infrared light pulse. A logic 0 is represented as a 3/16^th high pulse, while no pulse in a given baud rate bit time equates to logic 1. UART 16x over-sampling, start and stops bits are used. Modifications to a standard UART consist of adding an IrDA modulator and demodulator in the TxD and RxD signal paths.

RZI demodulation takes pulses that are 3/16^th of a baud rate clock long and transforms it to the standard non-return to zero (NRZ) UART signal, which is then fed into the main UART Rx blocks. Similarly, RZI modulation takes the outgoing UART NRZ Tx signal and creates 3/16^th pulses out.