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RS232C Standard

Hardware: Serial

Problem:
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?

Solution:
The RS-232 Standard has gone through several revisions through the years. In the original RS-232, the signal would flip between positive and negative 25 volts. There were then three revisions, RS-232A, RS-232B, and RS-232C, which lowered the acceptable voltage from 25 to 12 to 5 volts. 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.

Related Links:
Serial Communication Overview

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Report Date: 02/18/2005
Last Updated: 08/24/2007
Document ID: 3IHB97HS

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