Path: utzoo!attcan!uunet!cs.utexas.edu!rutgers!texbell!letni!doug
From: doug@letni.UUCP (Doug Davis)
Newsgroups: comp.dcom.modems
Subject: Re: break condition, framing errors
Message-ID: <6395@letni.UUCP>
Date: 22 Nov 89 04:56:20 GMT
References: <5464@yarra.oz.au>
Reply-To: doug@letni.LawNet.Com (Doug Davis)
Organization: Logic Process  Dallas, Texas.
Lines: 47

In article <5464@yarra.oz.au> chris@yarra.oz.au (Chris Jankowski) writes:
>Can somebody explain what is break condition and where is it
>defined ie. in what standard?
Uh, well, like, perhaps the RS232-C standard?? 

>Just to start things off I will give you my intuitive understanding:
I don't mean to pick nits, but you don't understand.. ;-)

>When you press BREAK key on your terminal a voltage on one of the
>RS232C control lines is dropped (which line (?) and for how long (?)).
Welllllll,, the transmit data line goes to a space condition. Zero volts
for 23-27ms.  Normally the transmit data line is at -12VDC in relationship
to ground on pin 1 (frame ground) or 7 (signal ground) depending
on the device.

>A modem if present should detect this condition and pass it to
>the remote modem (by stopping to issue carrier (?) for how long (?)).
Uh, assuming the modem is set up properly it should send spaces for the
amount of time the TD line is at zero.  Otherwise
some modems go into command mode.  Others just freak out and die.

>The remote modem then should pass this condition by dropping
>voltage on one of its RS232C lines - again which (?) and for how long(?).
Again this has to be set up to do this. some modems will eat incoming long
spaces.. (which is what that is called) others will disconnect and some, again,
will freak out die. 

>This in turn may trigger some action in the receiving computer.
This also assumes that the receiveing computer can detect such a condition.
mostly they interpret the existance of a long space to be a frame error,
(the absence of stop bits) and the software in the computer has to deal with
that it's own.


>This however contradicts what my termio(7-att) manual page says:
>....the break condition (a character framing error with data all zeros)...
Your att manual is correct.  A space is a zero, and 23-27ms of them will
almost always be a frame error at any baud rate.


>What is character framing error then?
THe absents of one or more stop bits in a string of spaces..

__
Doug Davis/1030 Pleasant Valley Lane/Arlington/Texas/76015/817-467-3740
{texsun, motown!sys1, uiucuxc!sys1 lawnet, attctc, texbell} letni!doug
    "Act first, solve problem, appologize for the mess later."