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Article #16293Re: RS 232 & RS-422 voltage specs wanted
From: Henry Spencer
Date: Tue, 05 Jan 1993 22:31
Date: Tue, 05 Jan 1993 22:31
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In article <1ic8hnINNn10@uwm.edu> albrecht@csd4.csd.uwm.edu (Chad Edward Albrecht) writes:
>Standard RS-232 uses +/- 5VDC
Sigh. WRONG. Or at least, not very right.
Standard RS232 transmitters must produce something between +5 and +15
and something between -5 and -15. Note that that is +5.000 and -5.000,
so you can't do it with +/-5V supplies (although some sleazy people
try anyway). Most RS232 nowadays is done with either +/-12V or +/-9V,
the former popular with people who already have +/-12V supplies and
the latter popular with chips that generate their own supplies (because
+5, doubled, less a diode drop or two, either straight or inverted,
comes out at about +/-9).
RS232 receivers must accept anything between +3 and +25, and anything
between -3 and -25, with the threshold slightly positive so that
0 looks negative.
RS423 uses +/-5. It is roughly RS232 compatible and can run faster.
RS422 (real RS422, not the differential RS423 that Macs use) uses
+5 and 0. It is not RS232 compatible.
--
"God willing... we shall return." | Henry Spencer @ U of Toronto Zoology
-Gene Cernan, the Moon, Dec 1972 | henry@zoo.toronto.edu utzoo!henry
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Newsgroups: sci.electronics Path: arc1-ca.pugleaf.net!sparky!uunet!zaphod.mps.ohio-state.edu!swrinde!cs.utexas.edu!torn!utzoo!henry From: henry@zoo.toronto.edu (Henry Spencer) Subject: Re: RS 232 & RS-422 voltage specs wanted Message-ID: <C0EJx6.FBo@zoo.toronto.edu> Date: Tue, 5 Jan 1993 22:31:52 GMT References: <1993Jan5.022447.20082@uts.uni-c.dk> <1ic8hnINNn10@uwm.edu> Organization: U of Toronto Zoology Lines: 25