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ISD91200 Series Technical Reference Manual
Release Date: Sep 16, 2019
- 291 -
Revision 2.4
5.13.4 IrDA Mode
The UART supports IrDA SIR (Serial Infrared) Transmit Encoder and Receive Decoder. IrDA mode is
selected by setting the UART_FUNCSEL.IRDAENbit.
When in IrDA mode, the UART_BAUD.BAUDM1 register must be zero and baud rate is given by:
Baud Rate = UART_CLK / (16 * BRD), where BRD is Baud Rate Divider in the UART_BAUD.BRD
register.
UART
TX
RX
IrDA
SIR
IR_SOUT
IR_SIN
SOUT
SIN
IR
Transceiver
Emit Infrared ray
Detect Infrared ray
IRCR
BAUD
IrDA_EN
TX_SELECT
INV_TX
INV_RX
TX pin
RX pin
Figure 5-74 IrDA Block Diagram
5.13.4.1
IrDA SIR Transmit Encoder
The IrDA SIR Transmit Encoder modulates Non-Return-to Zero (NRZ) transmission bit stream from
UART serial output. The IrDA SIR physical layer specifies use of Return-to-Zero, Inverted (RZI)
modulation scheme which represents logic 0 as an infrared light pulse. The modulated output pulse
stream is transmitted to an external output driver and infrared LED (Light Emitting Diode).In normal
mode, the transmitted pulse width is specified as 3/16the period of the baud rate.
5.13.4.2
IrDA SIR Receive Decoder
The IrDA SIR Receive Decoder demodulates the return-to-zero bit stream from the input detector and
outputs the NRZ serial bit stream to the UART received data input. The IR_SIN decoder input is
normally high in the idle state. Because of this, UART_IRDA.RXINV should be set 1 by default). A start
bit is detected when the IR_SIN decoder input is LOW.
5.13.4.3
IrDA SIR Operation
The IrDA SIR Encoder/decoder provides functionality which converts between UART data stream and
half duplex serial SIR interface. Below figure shows the IrDA encoder/decoder waveform: