几种流行的串行通信协议(国外英文资料).doc

几种流行的串行通信协议(国外英文资料) Employ incapable men instead of able men, mediocre people are in power. Meet at once, no paper pen, with your message, peace. Love Mo Most people are familiar with the standard serial communication technology is EIA232, EIA-422 and EIA485, which is previously known RS-232, RS-422 and RS-485. Since the proposed standards of EIA are prefixed with RS, they are still used to prefix RS in the field of industrial communication. EIA232, EIA-422 and EIA485 are serial data interface standard, initially by the Electronic Industries Association (EIA) developed and released the EIA-232, released in 1962, later there are many improved version, which is the most commonly used version of EIA-232-C. At present, EIA-232 is one of the most widely used serial interfaces in PC and communication industry. EIA-232 is defined as a single ended standard for increasing communication distance in low rate serial communication. EIA-232 uses unbalanced transmission, known as single ended communications. The standard, EIA232 transmission distance up to 50 feet (about 15 meters), the highest rate of 20kbps. Because EIA-232 existed, the transmission distance was limited, and so on, EIA-422 was born. EIA-422 full name is the electrical characteristics of balanced voltage digital interface circuits, which defines a balanced communication interface, the transmission rate is increased to 10Mbps, the transmission range is extended to 4000 feet (about 1219 meters), and allows a balance on the bus up to 10 receivers. Of course, there are EIA422 defects: because of its equilibrium length and twisted pair transmission rate is inversely proportional to the rate of less than 100kbps, and so on, transmission distance can reach the maximum value, that is to say, only in a very short distance to obtain the highest transmission rate. Generally, the maximum transmission rate of the twisted pair of 100 meter long twisted pair is only 1Mbps. Another point must be pointed out that in EIA-422 com