RS-232 (Recommended Standard 232) is a standard that describes a serial interface between a data terminal equipment (DTE) and a data communication equipment (DCE). This is also referred to as point-to-point connections.

The standard was defined in the early 1960s by the American standardization body Electronic Industries Association (EIA). The standard specifies the time and electrical transmission characteristics of the interface. The minimum configuration of an RS-232 interface requires a transmit line, a receive line, and another line as a reference potential. Data bits are signaled by voltage values, where a logic zero is represented by a signal level between +3V and 15V, and a logic 1 is represented by a signal level between -3V and -15V.

Due to the relatively large signal levels, the transmission is relatively insensitive to interference signals. Serial transmission is asynchronous, which means that there is no common synchronous clock signal between the transmitter and receiver. Therefore, the transmitter and receiver must be configured in advance for the same transmission speed so that the receiver can scan the line at the correct speed. Normally, the interface is only used with low transmission speeds of a few kBit/s to approx. 115200 bit/s. Thus, even with simple cables, line lengths of up to 30 m are possible without any problems.

Typical connector formats are D-Sub 9 and D-Sub 25.

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