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I know about RS-232. Later, I heard about RS-232-C.

  • Are these two standards the same or not?
  • If not, what are the differences?
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  • \$\begingroup\$ Briefly: RS stands for "recommended standard". It was an early draft that became industry de facto standard before formal standardization. The formal standard that later became mainstream was EIA 232 C, where EIA is the standard institute and C is revision. This one is sloppily referred to as RS-232-C, since RS-232 is such a well-known name. But strictly speaking, it is slang and not the correct term to use. \$\endgroup\$ – Lundin Jan 29 at 14:59
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RS232C is just the third version of the EIA's Recommended Standard 232. The current version is revision F. The major difference between the original standard and the C version was that the voltage levels for the signals were reduced from \$\pm\$25V to \$\pm\$5V.

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    \$\begingroup\$ This is too broad for a question here. Get your hands on the standard and look for yourself. \$\endgroup\$ – Elliot Alderson Jun 28 '18 at 13:48
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    \$\begingroup\$ @shafeeq Wikipedia also has some good notes on this as well. \$\endgroup\$ – KingDuken Jun 28 '18 at 14:27
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    \$\begingroup\$ The last rev now supports +/-3V signals \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jun 28 '18 at 14:33
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    \$\begingroup\$ @ElliotAlderson Your advice is not generally practical though in this case might fly as the C version might be in the wild, many standards are not freely available and spending tens or hundreds of dollars to check this progression is likely not warranted. Having a printed copy of the standard from way back when I can also say they are overpriced. \$\endgroup\$ – KalleMP Jun 28 '18 at 18:36
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    \$\begingroup\$ @KalleMP What would you recommend? I certainly can't reproduce the entire revision history, much less the entire (copyrighted) standard, as part of an answer. The OP didn't restrict the range of his question to any specific aspects of the standard. I agree that the standards are overpriced, but if you really need to know then there's not much choice. \$\endgroup\$ – Elliot Alderson Jun 28 '18 at 19:48
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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.

Source (NI RS-232C Standard Conformance)

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  • \$\begingroup\$ Welcome to EE.SE! \$\endgroup\$ – winny Jan 29 at 11:09
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    \$\begingroup\$ Welcome. Please use block-quote if you quote text from other sources. \$\endgroup\$ – Rev1.0 Jan 29 at 11:15

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