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1、外文资料The foundation of Serial Port CommunicationThe string mouth is on the computer one kind of extremely general purpose equipment correspondence agreement (does not want and universal serial bus USB Universal Serial Bus or the USB confusion).The majority computer contains two based on the RS232 str
2、ing mouth. At the same time the string mouth also is the instrument instrumental equipment general correspondence agreement; The very many GPIB compatible equipment also has the RS-232 mouth. At the same time ,strings together the mouth correspondence agreement also to be allowed to use in to gain t
3、he long-distance gathering equipment the data. The string mouth correspondence concept is extremely simple, strings together the mouth (bit) to transmit and the receive byte according tot he position. Although presses the byte (byte) the parallel correspondence is slower than, but the string mouth m
4、ay use a line transmission data simultaneously to use another line to receive the data. It is very simple and can realize the remote communication. When for instance IEEE488 defines the parallel general condition, stipulated the equipment line always often does not have to surpass 20meters, and will
5、 fully lengths between two equipment do not have to surpass 2 meters; But says regarding the string mouth, the length may amount to 1,200 meters.The typical place, strings together the mouth to use in the ASCII code character transmission. The correspondence uses 3 lines to complete:(1) the groundin
6、g, (2) transmits, (3) receives. Because the string mouth correspondence is asynchronous, the port can transmit the data while on-line to receive the data in another on-line. Other lines use in to shake hand, but is not must. The string mouth corresponds the most important parameter is the baud rate,
7、 the data position, stops the position and the parity check. Carries on the general porter regarding two, these parameters must match:A, baud rate: This is a weight correspondence speed parameter. It expresses each second transmission bit integer. For example 300 bauds expressed each second transmit
8、s 300 bit. When we mentioned when clock cycle, we are refer to the baud rate for example if the agreement needs 4,800 bauds rate, then the clock is 4800Hz. This meant the string mouth correspondence in the data line sampling rate is 4800Hz.The usual telephone line baud rate is 14,400, 28,800 and 36,
9、600. The baud rate may be bigger than these values by far, but the baud rate and the distance have the inverse ratio. The high baud often uses in correspondence between the very near instrument which lays a side, the typical example is the GPIB equipment correspondence.B, data position: This is weig
10、hs in the correspondence the actual data position parameter. When the computer transmits a information packet ,the actual data cannot be 8, the standard value is 5, 7 and 8. How establishes is decided the information which wants to transmit to you. For instance, the standard ASCII code is 0 127 (7).
11、 The expansion ASCII code is 0 255 (8). If data use simple text (standard ASCII code), then each data packet uses 7 figures according to. Each package refers to a byte, including starts/to stop the position, the data position and the parity check position. Because the actual data position is decided
12、 by the correspondence agreement selection, the terminology the package points to any correspondence the situation.C, stops the position: Uses in to express individually wraps last. The typical value is 1, 1.5 and 2. Because the data is in the transmission line fixed time, and each equipment has its
13、 own clock, very possibly between two equipment appeared small not synchronization in the correspondence. Therefore stops the position not merely expresses the transmission conclusion, and provides the computer to adjust clock synchronization the opportunity. Is suitable to stops the position the fi
14、gure many, the different clock synchronization tolerance regulation goes past in a big way, but at the same time the data output rate is also slower.D, parity check position: One kind simple examines the wrong way in the string mouth correspondence. Some four kinds examine the wrong way: The partner
15、, is wonderful, Gao Hedi. Certainly has not verified the position also is may. Regarding the partner and the wonderful verification situation, strings together the mouth to be able to establish the verification position (behind data position), guarantees the transmission with a value the data to hav
16、e the partner or the wonderful logical top digit. For example, if the data is 011, then regarding the partner verification, the verification position is 0,the guarantee logic high figure is even number. If is the wonderful verification, verification position , like this some 3logical top digit. The top digit and the low position untrue inspection data, simply sets at the position logic to be high or the logical low verification. Like this enables the receiving apparatus to
