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Path: utzoo!linus!decvax!mcnc!ecsvax!hes
From: hes@ecsvax.UUCP (Henry Schaffer)
Newsgroups: net.micro
Subject: Re: RS232 Voltages
Message-ID: <1720@ecsvax.UUCP>
Date: Sun, 21-Jul-85 20:27:33 EDT
Article-I.D.: ecsvax.1720
Posted: Sun Jul 21 20:27:33 1985
Date-Received: Tue, 23-Jul-85 05:33:12 EDT
References: <55@ssc-vax.UUCP>
Organization: NC State Univ.
Lines: 14

As I remember it, the official voltages (i.e. according to 
the RS-232C standard) are something like -3 to -12 for one
state and 3 to 12 for the other for RECEIVE.  For TRANSMIT
they change the 3's to 5's.  Therefore if you transmit
according to the standard there is alot of leeway in
receiving - and alot of hacks will receive reliably, although
with some (often negligeable) degradation - particularly just
slicing at or near the TTL 1.4V.  However, if you take shortcuts
in transmitting, (which would work with a receiver which works
according to the standard) and then you meet a receiver which
also takes shortcuts -- you can end up with something between
high error rates, intermittent operation, and complete lack of
info exchange.  (I have the standard at my office - so if you
really want to know, ask me for details.)  --henry schaffer