RS232
RS232 is a serial interface standard defined in 1960 by the USA Electronics Industry Alliance (EIA) with Recommended Standard 232.
An RS-232 serial port was once a standard in many types of computers for connection to modems, printers and other devices. Today’s computers have replaced the RS-232 serial port with the USB serial port.
The RS232 standard specifies a maximum voltage of plus or minus 25V. Normal voltages for signals are +3 to +15 or -15v to -3v.
As such, connecting RS232 equipment, to equipment not designed for the possible plus and minus 25v swings of this interface, can result in permanent damage.
An advantage of the RS-232 standard over other serial interfaces is a cable length of up to 15m, due to the lower serial speeds, and the higher voltages used on the RS232 cables.