RS-232-C interface is a serial interface of synchronous and asynchronous data transmission defined by the EIA RS-232-C standard and V.24 CCITT recommendations, this interface was initially created to connect the computer with a terminal.

Today it is widely used for various purposes.

The purpose of creating the RS-232-C interface was to maintain connection between Data Terminal Equipment (DTE) and Data Communications Equipment (DCE) using consistent binary data communication. Usually DTE is a terminal or a computer, and DCE - a modem or any other communications device.

The transmitting line of the first device connects with the receiving line of the second device and vice versa (by this organizing full duplex). To control the connected devices the programme approval is used (that is introducing control characters into the transmitted data flow). It is possible to organize hardware approval by providing additional RS-232-C lines to maintain status defining and control functions.