The IrDA SIR physical layer specifies use of a Return to Zero, Inverted (RZI) modulationscheme that represents logic 0 as an infrared light pulse (see Figure 340).The SIR Transmit encoder modulates the Non Return to Zero (NRZ) transmit bit streamoutput from USART. The output pulse stream is transmitted to an external output driver andinfrared LED. USART supports only bit rates up to 115.2 Kbps for the SIR ENDEC. Innormal mode the transmitted pulse width is specified as 3/16 of a bit period.The SIR receive decoder demodulates the return-to-zero bit stream from the infrareddetector and outputs the received NRZ serial bit stream to the USART. The decoder input isnormally high (marking state) in the Idle state. The transmit encoder output has the oppositepolarity to the decoder input. A start bit is detected when the decoder input is low.• IrDA is a half duplex communication protocol. If the Transmitter is busy (when theUSART is sending data to the IrDA encoder), any data on the IrDA receive line isignored by the IrDA decoder and if the Receiver is busy (when the USART is receivingdecoded data from the IrDA decoder), data on the TX from the USART to IrDA is notencoded. while receiving data, transmission should be avoided as the data to betransmitted could be corrupted.• A 0 is transmitted as a high pulse and a 1 is transmitted as a 0. The width of the pulseis specified as 3/16th of the selected bit period in normal mode (see Figure 341).• The SIR decoder converts the IrDA compliant receive signal into a bit stream forUSART.• The SIR receive logic interprets a high state as a logic one and low pulses as logiczeros.• The transmit encoder output has the opposite polarity to the decoder input. The SIRoutput is in low state when Idle.• The IrDA specification requires the acceptance of pulses greater than 1.41 μs. Theacceptable pulse width is programmable. Glitch detection logic on the receiver endfilters out pulses of width less than 2 PSC periods (PSC is the prescaler valueprogrammed in the USART_GTPR). Pulses of width less than 1 PSC period are alwaysrejected, but those of width greater than one and less than two periods may beaccepted or rejected, those greater than 2 periods will be accepted as a pulse. TheIrDA encoder/decoder doesn’t work when PSC=0.• The receiver can communicate with a low-power transmitter.• In IrDA mode, the STOP bits in the USART_CR2 register must be configured to “1 stopbit”.
The IrDA SIR physical layer specifies use of a Return to Zero, Inverted (RZI) modulationscheme that represents logic 0 as an infrared light pulse (see Figure 340).The SIR Transmit encoder modulates the Non Return to Zero (NRZ) transmit bit streamoutput from USART. The output pulse stream is transmitted to an external output driver andinfrared LED. USART supports only bit rates up to 115.2 Kbps for the SIR ENDEC. Innormal mode the transmitted pulse width is specified as 3/16 of a bit period.The SIR receive decoder demodulates the return-to-zero bit stream from the infrareddetector and outputs the received NRZ serial bit stream to the USART. The decoder input isnormally high (marking state) in the Idle state. The transmit encoder output has the oppositepolarity to the decoder input. A start bit is detected when the decoder input is low.• IrDA is a half duplex communication protocol. If the Transmitter is busy (when theUSART is sending data to the IrDA encoder), any data on the IrDA receive line isignored by the IrDA decoder and if the Receiver is busy (when the USART is receivingdecoded data from the IrDA decoder), data on the TX from the USART to IrDA is notencoded. while receiving data, transmission should be avoided as the data to betransmitted could be corrupted.• A 0 is transmitted as a high pulse and a 1 is transmitted as a 0. The width of the pulseis specified as 3/16th of the selected bit period in normal mode (see Figure 341).• The SIR decoder converts the IrDA compliant receive signal into a bit stream forUSART.• The SIR receive logic interprets a high state as a logic one and low pulses as logiczeros.• The transmit encoder output has the opposite polarity to the decoder input. The SIRoutput is in low state when Idle.• The IrDA specification requires the acceptance of pulses greater than 1.41 μs. Theacceptable pulse width is programmable. Glitch detection logic on the receiver endfilters out pulses of width less than 2 PSC periods (PSC is the prescaler valueprogrammed in the USART_GTPR). Pulses of width less than 1 PSC period are alwaysrejected, but those of width greater than one and less than two periods may beaccepted or rejected, those greater than 2 periods will be accepted as a pulse. TheIrDA encoder/decoder doesn’t work when PSC=0.• The receiver can communicate with a low-power transmitter.• In IrDA mode, the STOP bits in the USART_CR2 register must be configured to “1 stopbit”.<br>
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