In some electrical industry, we can relate to RS-232C protocol. Then gradually expand as the network's use of all walks of life will be applied to different places. So now RS-232C protocol to accommodate a number of network applications.
 RS-232-C

 The full name of RS-232C protocol is EIA-RS-232C protocol, which EIA (Electronic Industry Association) on behalf of American Electronics Industry Association, RS (recommeded standard) on behalf of recommendation, is the identification number 232, C on behalf of the latest in a modified RS232 (1969 ), before that, there RS232B? RS232A?? It provides cable and mechanical? electrical characteristics? signal functions and transfer process?

 There are common physical standard RS-232-C? RS-422-A? RS-423A? RS-485? here only RS-232-C (referred to as 232, RS232)? For instance, in IBM PC machine on COM1? COM2 interface is RS-232C Interface?

 1. Electrical Characteristics

 EIA-RS-232C protocol on the electrical characteristics? logic levels and features are made ​​of various provisions of the signal line?

 On the TxD and RxD: Logic 1 (MARK) =- 3V ~-15V

 Logic 0 (SPACE) = 3 ~ 15V

 In the RTS? CTS? DSR? DTR and DCD control line such as:

 Signal is active (ON, ON state, positive voltage) = 3V ~ 15V

 Signal is invalid (disconnected, OFF state, a negative voltage) =- 3V ~-15V

 Foregoing illustrates RS-323C standard definition of the logic level?

 The data (message code):

 Logic "1 "(mass number) level lower than-3V, logic "0 " (A space) level Informing 3V; for the control signal; connected to the state (ON) is a valid signal level higher than 3V , off state (OFF) signal is invalid level that is lower than-3V, that is, when the transmission is greater than the absolute level of 3V, the circuit can effectively check out, ranging from -3 ~ 3V voltage between the non-Significance of less than-15V or higher than the voltage 15V that meaningless, so the actual work, should ensure that levels in the ± (3 ~ 15) V between