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IrDA interface for an embedded systems

2017-12-22 23:04  
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IrDA is a transmission standard commonly used in computer and peripherals like mobile phones. The basic purpose of IrDA is to provide device-to-device communication over short distances. IrDA solves the problem of usage cables, that may differ from machine to machine. With IrDA no cables are required so this is easy to connect same device to multiple device types like your mobile phone to laptops, other mobile phones or PDA’s. Full IrDA description can be found at http://www.irda.com.

IrDa standard require close communication of devices. This is low power transmission. It is important because there are regulations guarding the maximum level of IR radiation that can be emitted. Also, it is reasonable to assume that the two devices that are to communicate will be physically pointed toward each other prior to use. And only two devices can communicate at the same time. So IrDA doesn’t have to deal with collisions. And the main thing that IrDa is simple, cheap and require low cost parts.

Tha IrDA standard specification states that supported data rates can be between 2400bps and 115.2kbps over 1 meter distances. Later standard has expanded to support 1.152 and 4 mbps. Transmitter beam angle is from 15 to 30 degrees and receiver has

viewing angle of 15 degrees. So devices doesn’t have to be aimed directly to each other:

IrDA_beam

 

IrDA standard is specified by a number of protocols. The IrPHY (IR Physical layer) is a hardware layer, which includes the requirements for modulation. HDLC is a High-level Data Link Control protocol is used used to control access to connection medium.

One IrLAP exists per device. An IrLAP connection is essentially a master-slave configuration, or, as they are known in IrDA parlance, primary and secondary devices. The primary device starts communication, sends commands, and handles data-flow control (handshaking). It is rare for a primary device to be anything other than a computer. Secondaries (such as printers) simply respond to requests from primaries. Two primary devices can communicate by one primary assuming the role of a secondary device. Typically, the device that initiates the transfer remains the primary, while the other device becomes a secondary for the duration of the transaction.

IrLMP (Infrared Link Management Protocol) provides the device’s software with a means of sharing the single IrLAP between multiple tasks that wish to communicate using IrDA. IrLMP also provides a query protocol by which one device may interrogate another to determine what services are available on the remote system. This query protocol is known as LM-IAS, or Link Management Information Access Service. These are the basic IrDA protocols that all devices must support. Beyond these, IrDA also provides a number of optional services. IrCOMM provides emulation of standard serial-port and parallel-port devices. For application software, the IR port can then be used as if it were just another serial or parallel port. Using IrCOMM, a laptop or PDA can communicate with an IR-enabled printer just as though that printer were physically plugged into the mobile computer. IrLAN allows access to local area networks via the IR interface. IrOBEX provides a mechanism for object exchange between devices, in software that supports object-oriented programming.

IRDA_protocol

IrDa is using light to send data, so there is some agreement to distinguish logic 0 and logic 1 during transmission. IrDA uses Return-to-Zero (RZ) bit encoding. Logic zero is represented as pulse interval and 1 is an absence of pulse.

Return-to-Zero

At data rates of 4 Mbps, PPM, or Pulse Position Modulation, is used to distinguish different bits. With PPM, the position of the pulse is varied. Its location within the subinterval determines the transmitted bit pattern. The PPM used in IrDA is known as 4PPM and uses one of four positions to provide the transmission of two data bits

IrDA_packet

For Infrared transmitting there are IRDA transceivers used. They incorporate IR LED and IR photodiode. There are many manufacturers pf IRDA modules like Agilent.

IrDA_transceiver.jpg

IR light is invisible for naked eye, but if you point digital camera to remote control, you will se what light is generated by remote control IR LED in cameras LCD.

Related

To understand things like IrDA, which is referred to infrared signals in phones and computers, you will need to understand networks through 70-293 exams. 642-642 exams provide you with the basic knowledge for QoS. To become a certified gateway gatekeeper, you will need to pass the 642-453 exams. Courses 2273-75 require you to complete the 70-290 exams. The 70-270 exams are required only by course 2272. You can find study guides to help you through your Citrix presentation server 1Y0-259 exams. The mcsd certification is the top level of certification for advanced developers.


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