INTRODUCTION
Data communication now become important when the rapid transfer of data becomes both necessary and feasible. Thus data communications emerged as a natural result of line development of sophisticated computer system. In data communication. It is necessary to transmit pulse, which are the output of some data source, from one point to other. Quit often this data must go back of the system existing in the world’s data transmission system are further developed and expended data transmission must after take place over the analog system, since these have been designed mainly for the speech transmission they are not particularly suitable for transmission of data. According steps must be taken the compensate for the inadequate of telecommunication network to ensure that data are sent in the form which is acceptable to the networks. This section will introduce those requirement of data transmission and put forward the method by which they are met. The work of telemetry may be considered as falling into this category of data communication.
Interfacing diagnostics and monitoring equipment with computers plays a vital role when huge amounts of measurement data must be processed. One of the mostly widely spread interface is RS-232 (serial-port). However this interface has some limitations, like for example: the distance between terminals is limited to approximately 10m, it has high sensitivity to electromagnetic noise, etc.