Atmel Evaluation Kit AT91SAM9X35-EK AT91SAM9X35-EK Data Sheet

787

SAM9X35 [DATASHEET]

11055E–ATARM–10-Mar-2014

The USART features an IrDA mode supplying half-duplex point-to-point wireless communication. It embeds the
modulator and demodulator which allows a glueless connection to the infrared transceivers, as shown in 

The modulator and demodulator are compliant with the IrDA specification version 1.1 and support data transfer speeds
ranging from 2.4 Kb/s to 115.2 Kb/s.

The USART IrDA mode is enabled by setting the USART_MODE field in the Mode Register (US_MR) to the value 0x8.
The IrDA Filter Register (US_IF) allows configuring the demodulator filter. The USART transmitter and receiver operate
in a normal asynchronous mode and all parameters are accessible. Note that the modulator and the demodulator are
activated.

The receiver and the transmitter must be enabled or disabled according to the direction of the transmission to be
managed.

To receive IrDA signals, the following needs to be done:



Disable TX and Enable RX



Configure the TXD pin as PIO and set it as an output to 0 (to avoid LED emission). Disable the internal pull-up 
(better for power consumption).



Receive data

For baud rates up to and including 115.2 Kbits/sec, the RZI modulation scheme is used. “0” is represented by a light
pulse of 3/16th of a bit time. Some examples of signal pulse duration are shown in 

.

 shows an example of character transmission.

IrDA 

Transceivers

RXD

RX

TXD

TX

USART

Demodulator

Modulator

Receiver

Transmitter

2.4 Kb/s 

78.13 µs  

9.6 Kb/s 

19.53 µs  

19.2 Kb/s 

9.77 µs 

38.4 Kb/s 

4.88 µs

57.6 Kb/s 

3.26 µs

115.2 Kb/s 

1.63 µs