Path: utzoo!attcan!uunet!husc6!rutgers!gatech!dscatl!galbp!wittsend.LBP.HARRIS.COM!mhw
From: mhw@wittsend.LBP.HARRIS.COM (Michael H. Warfield)
Newsgroups: comp.dcom.modems
Subject: Re: Break definition
Message-ID: <6095@galbp.LBP.HARRIS.COM>
Date: 8 Sep 88 12:59:20 GMT
References: <402@ucrmath.UUCP>
Sender: news@galbp.LBP.HARRIS.COM
Reply-To: mhw@wittsend.UUCP (Michael H. Warfield)
Distribution: na
Organization: Harris/Lanier Network Knitting Circle
Lines: 32

In article <402@ucrmath.UUCP> jantypas@ucrmath.UUCP (John Antypas) writes:
>I purchased a California Communications Corp. 2400 baud internal modem.
>Overall, it works just fine under Unix, but I have yet to be able to
>send a "break tone".  The problem appears to be that CCC didn't know how
>to handle a break.  They claim the modem has a litteral serial port
>on it so there should be no problems but...
>
>CCC is willing to correct the problem but they need to know how to handle
>the break.  After all, there is no such thing as a break character.  What
>must they do to send a break and what do they do when a "break" is received?
>How do external modems do this?
>

        A break is sent on an async line by placing the  line  in
the  "low" or "spacing" state (level, tone, what-ever) for two or
more charracter times.  To a receiver this would  be  seen  as  a
charracter  of  all zeros, with a framing error (no stop bit) and
lasting at least 20 bit times (16 data bits  plus  2  start  bits
plus  two  stop  bits total across the 2 charracter times).  Note
that that is AT LEAST.  Some UARTS support long and short  breaks
where  short  breaks  are  of  the same order of magnitude as two
charracter times but a long break may be 1/4  second  or  longer!
The modem per se should have little to do with a break (he simply
holds his transmission to send a  looooonnnnnnngggggg  series  of
zero  bits)  but  the  UART  or SIO has everything to do with it.
Some modems will, however, disconnect and  drop  carrier  in  the
event of a "long break".  Some, but not all.

Michael H. Warfield  (The Mad Wizard)	| gatech.edu!galbp!wittsend!mhw
  (404)  270-2170 / 270-2098		| mhw@wittsend.LBP.HARRIS.COM
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