RS-232 - Scope of The Standard

Scope of The Standard

The Electronic Industries Association (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, and maximum load capacitance.
• 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 the character encoding or the framing of characters, or error detection protocols. The standard does not define bit rates for transmission, except that it says it is intended for bit rates lower than 20,000 bits per second. Many modern devices support speeds of 115,200 bit/s and above. RS-232 makes no provision for power to peripheral devices.

Details of character format and transmission bit rate are controlled by the serial port hardware, often a single integrated circuit called a UART that converts data from parallel to asynchronous start-stop serial form. Details of voltage levels, slew rate, and short-circuit behavior are typically controlled by a line driver that converts from the UART's logic levels to RS-232 compatible signal levels, and a receiver that converts from RS-232 compatible signal levels to the UART's logic levels.