RS-232
In telecommunications, RS-232 (Recommen-
ded Standard 232) is a standard for serial
binary data signals connecting between a
DTE (Data Terminal Equipment) and a DCE
(Data Circuit-terminating Equipment). It is
commonly used in computer serial ports. A
similar ITU-T standard is V.24.
Scope of the standard
The Electronics Industries Association (EIA)
standard RS-232-C[1] 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
• character encoding (for example, ASCII,
Baudot code or EBCDIC)
• the framing of characters in the data
stream (bits per character, start/stop bits,
parity)
• protocols for error detection or algorithms
for data compression
• bit rates for transmission, although the
standard 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
• power supply to external devices.
Details of character format and transmission
bit rate are controlled by the serial port hard-
ware, 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 compat-
ible signal levels to the UART’s logic levels.
History
The original DTEs were electromechanical
teletypewriters and the original DCEs were
(usually) modems. When electronic terminals
(smart and dumb) began to be used, they
were often designed to be interchangeable
with teletypes, and so supported