Problem description:
I only read it in my notebook, but I can't understand it! ! !
Ask for an answer! !
Analysis:
Brief introduction of IrDA infrared data communication
Infrared is an electromagnetic wave with a wavelength between 750nm and 1mm, and its frequency is higher than that of microwave and lower than that of visible light, which is invisible to human eyes.
Infrared communication generally uses near infrared in infrared band, and the wavelength is between 0.75um-25um and 25 um. After the establishment of the Infrared Data Association (IRDA), in order to ensure that infrared products from different manufacturers can obtain the best communication effect, the infrared communication protocol limits the wavelength range of light waves used in infrared data communication to 850nm to 900nm.
At present, radio waves and microwaves have been widely used in long-distance wireless communication. However, due to the short infrared wave, the diffraction ability of obstacles is poor, so they are more suitable for short-distance wireless communication occasions and point-to-point linear data transmission.
Infrared communication has the characteristics of low cost, convenient connection, simple use and compact structure, so it has been widely used in small mobile devices. These devices include notebook computers, palmtop computers, set-top boxes, game consoles, mobile phones, calculators, pagers, instruments, MP3 players, digital cameras and printers. Imagine that if there is no infrared communication, there must be a special cable to connect the two devices. How many connections do you need if you want to connect and transmit data at will? With the infrared port, these problems will be solved.
Unified software and hardware specifications are very important to enable various devices to connect freely through infrared ports. However, in the early stage of the development of infrared communication, there is just such a problem that the specifications are not uniform: many companies have their own set of infrared communication standards, and the devices produced by the same company can naturally communicate with each other, but they cannot communicate with the devices with infrared function of other companies. At that time, the popular infrared communication systems were HPSIR of HP, ASKIR of Sharp and MagicBeam of General Magic. Although their communication principles are similar, they cannot perceive each other. The chaotic standards bring great inconvenience to users and give people the illusion that infrared communication is not practical.
In order to establish a unified standard of infrared data communication, more than 20 companies such as Hewlett-Packard, Compaq and Intel initiated the establishment of Infrared Data Association (IRDA) on 1993. 1On June 28th, 1993, 120 representatives from more than 50 enterprises attended the first meeting of the Infrared Data Association and agreed to establish a unified system. One year later, the first IRDA infrared data communication standard was released, namely IRDA 1.0.
IRDA 1.0 is simply referred to as SIR (serial infrared), which is an asynchronous half-duplex infrared communication mode based on HP-SIR. SIR relies on the asynchronous communication transceiver (UART) of the system to realize infrared data transmission through the encoding and decoding process (3/ 16 EnDec) of waveform compression of serial data pulse and waveform expansion of received optical signal electric pulse. Due to the limitation of UART communication rate, the highest communication rate of SIR is only 1 15.2Kbps, which is the highest rate of computer serial port.
1996, IRDA released the standard of IRDA 1. 1, that is, fast infrared, or FIR for short. Compared with SIR, because FIR no longer depends on UART, its highest communication rate has made a qualitative leap, reaching 4Mbps. FIR adopts a brand-new 4PPM modulation, that is, it distinguishes the transmitted data information by analyzing the phase of the pulse, and its communication principle is completely different from that of SIR. However, FIR still uses the encoding and decoding process of SIR at the rate below 1 15.2Kbps, so it can still communicate with low-speed devices that support SIR. Only when communication partners also support FIR can the communication rate be raised to a higher level.
Just like USB and IEEE 1394 technology, the speed of infrared data communication is also increasing. Following FIR, IRDA released VFIR technology with communication rate as high as 16Mbps, and incorporated it into IRDA 1. 1 standard as a supplement. Higher communication speed enables infrared communication to occupy a place in those devices that need to transmit a large amount of data, rather than just replacing connecting wires.
IRDA standard includes three basic specifications and protocols: physical layer link specification, link access protocol (IrLAP) and link management protocol (IrLMP). The physical layer specification specifies the objectives and requirements of infrared communication hardware design. IrLAP and IrLMP are two software layers, which are responsible for setting up, managing and maintaining connections. On the basis of IrLAP and IrLMP, IRDA has successively issued some higher-level infrared protocols for some specific infrared communication applications, such as TinyTP, IrOBEX, IrCOMM, IrLAN, IrTran-P, etc. I won't go into details here.
With the increasing popularity of mobile computing and mobile communication equipment, infrared data communication has entered a golden age of development. Since the establishment of 1993 IRDA, the membership of the infrared data association has grown to more than 150, and almost all the big companies in IT industry and communication industry are among them. This shows that the IRDA standard has been widely recognized and supported by the industry. At present, more than 100 kinds of equipment with infrared communication capability have been developed and produced, and the annual installed capacity of infrared modules has reached one million sets, which is still growing at a high speed of 40% every year. Although there is Bluetooth technology, it is also short-distance wireless communication, but infrared data communication will play an important role in the field of short-distance wireless data communication for a long time to come with the advantages of low cost and wide compatibility of infrared communication technology.