The RS-232 is a standard developed by the Electronic Industries
Association (EIA) and other interested parties, specifying the serial
interface between Data Terminal Equipment (DTE) and Data
Communications Equipment (DCE). The RS-232 standard includes
electrical signal characteristics (voltage levels), interface mechanical
characteristics (connectors), functional description of interchange circuits
(the function of each electrical signal), and some recipes for common
kinds of terminal-to-modem connections. The most frequently
encountered revision of this standard is called RS-232C. Parts of this
standard have been adopted (with various degrees of fidelity) for use in
serial communications between computers and printers, modems, and
Serial communication uses a transmitter to send data, one bit at a
time,over a single communication line to a receiver.
You can use this method when data transfer rates are low or you must
transfer data over long distances.