(Recommended Standard-232).An Electronics Industries Association standard asynchronous serial line which is used commonly for modem, computer terminals, and serial printers.RS-232 uses a 25-pin or 9-pin connector.The standard designates the purpose for each of the 25 or 9 lines, including lines for sending and receiving data, ground connections, and control lines.However, often not all of the lines are used.Some connections use only three: one for data in each direction, and one for a ground.