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Path: utzoo!linus!vaxine!wjh12!genrad!decvax!harpo!ihnp4!zehntel!hplabs!hao!hull
From: hull@hao.UUCP (Howard Hull)
Newsgroups: net.unix
Subject: Re: transmitting BREAK
Message-ID: <914@hao.UUCP>
Date: Tue, 10-Apr-84 15:34:49 EST
Article-I.D.: hao.914
Posted: Tue Apr 10 15:34:49 1984
Date-Received: Thu, 12-Apr-84 01:30:10 EST
References: <16800@sri-arpa.UUCP> <3864@genrad.UUCP> <941@inuxc.UUCP>, <323@oliveb.UUCP>
Organization: High Altitude Obs./NCAR, Boulder CO
Lines: 22

I take exception with respect to Rob Warnock's (!fortune!rpw3) statement:
     Sorry, Mcferrin, Nelson is right.

     While it is true that a <NUL> is all zeroes and a <DEL> is all ones,
>>>>>the idle state of RS-232 data lines is MARK == ONE == +Volts.  A start
>>>>>bit is a SPACE == ZERO == -Volts, and stop bits are ones.  Therefore,
     if you want a big wide BREAK == "long space" == "long zeroes", better
     send a slow <NUL>.
doesn't seem to ring true for the RS232 coming out of pin 2 of my terminal.
An oscilloscope shows the idle state at -12 volts (MARKING) is the level for
logical ONE ; the +12 volt state (SPACING) is for logical ZERO.  The additional
information can be added to Jerry Aguirre's contribution (thanks for accurate
graphics, Jerry):

-12V ------        ......................................------//--        MK
           | start .                                    . stop     | next
 0V   idle | bit   .   your character  with parity      . bit      | start
       1   |  0    .                                    .  1       | bit
+12V        -------......................................           -----  SP

So you can either be positively logical, or stand on your head when you look
at your oscilloscope.				Howard Hull	!hao!hull