In telecommunications, RS-232 is a standard for serial binary data interconnection between a DTE (Data terminal equipment) and a DCE (Data communication equipment). It is commonly used in computer serial ports. A similar ITU-T standard is V.24. RS is an abbreviation for "Recommended Standard".
Scope of the standard
The Electronic Industries Alliance (EIA) standard RS-232-C as of 1969 defines:
• Electrical signal characteristics such as voltage levels, signaling rate, timing and slew-rate of signals, voltage withstand level, short-circuit behavior, maximum stray capacitance and cable length
• Interface mechanical characteristics, pluggable connectors and pin identification
• Functions of each circuit in the interface connector
• Standard subsets of interface circuits for selected telecom applications
The standard does not define such elements as character encoding (for example, ASCII, Baudot or EBCDIC), or the framing of characters in the data stream (bits per character, start/stop bits, parity). The standard does not define bit rates for transmission, although the standard says it is intended for bit rates less than 20,000 bits per second. Many modern devices can exceed this speed (38,400 and 57,600 bit/s being common, and 115,200 and 230,400 bit/s making occasional appearances) while still using RS-232 compatible signal levels.
Limitations of the standard
Because the application of RS-232 has extended far beyond the original purpose of interconnecting a terminal with a modem, successor standards have been developed to address the limitations. Issues with the RS-232 standard include:
• The large voltage swings and requirement for positive and negative supplies increases power consumption of the interface and complicates power supply design. The voltage swing requirement also limits the upper speed of a compatible interface.
• Single-ended signalling referred to a common signal ground limit the noise immunity and transmission distance.
• Multi-drop (meaning a connection between more than two devices) operation of an RS-232 compatible interface is not defined; while multi-drop "work-arounds" have been devised, they have limitations in speed and compatibility.
• Asymmetrical definitions of the two ends of the link make the assignment of the role of a newly developed device problematical; the designer must decide on either a DTE-like or DCE-like interface and which connector pin assignments to use.
• The handshaking and control lines of the interface are intended for the setup and takedown of a dial-up communication circuit; in particular, the use of handshake lines for flow control is not reliably implemented in many devices.