The RS-232C interface is still most commonly used interface although it was designed in 1962 as RS-232 interface
(RS – Recommended Standard). This interface was slightly modified in 1969 and is known as RS-232C. The RS-232C is USA standard and also is described in international standards (as V24 and V28) (Axelson 1999). 

     Because it has been designed a long time ago its performance is rather poor – speed of transmission not faster than 20 kbps (bps – bits per second), connection not longer than 15 m, poor immunity to interferences. But it is still in use because it is traditional equipment of computers – as so-called COM serial port. Moreover, its relatively poor performances are sufficient in many applications. In comparison with the GPIB parallel interface it is useful that the connection cable is simpler and it is not necessary to install special card and drivers to the computer.




Figure 6.21. Connection of two data terminals using RS-232C interface