NI RS-232C Standard Conformance
My serial device states that it requires an RS-232C Standard protocol. Do the National Instruments serial products conform to this protocol? What is the difference between RS-232 and RS-232C?
The RS-232 Standard has gone through several revisions over the years. In the original RS-232, the signal would flip between positive and negative 25 volts.
Since that point there have been three revisions, RS-232A, RS-232B, and RS-232C; these revisions lowered the acceptable voltage from 25 to 12 to 5 volts respectively. In 1969, the Electronic Industries Association Standards Committee adopted RS-232C as a standard for computer manufacturers.
Because this adoption date was so long ago, most manufacturers, including National Instruments, have dropped the "C" from the name and simply refer to the protocol as RS-232. In common, modern usage, there is no difference between RS-232 and RS-232C, protocol.
White Paper: Serial Communication Overview
Report Date: 02/18/2005
Last Updated: 06/12/2017
Document ID: 3IHB97HS