Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!crdgw1!sagittarius!dixon
From: dixon@sagittarius.crd.ge.com (walt dixon)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Generate a BREAK on COMn: ?
Keywords: MSDOS COM1 COM2 BREAK RS-232
Message-ID: <6110@crdgw1.crd.ge.com>
Date: 16 Mar 90 09:57:38 GMT
References: <1990Mar10.014345.5932@wolves.uucp>
Sender: news@crdgw1.crd.ge.com
Reply-To: dixon@sagittarius.crd.ge.com (walt dixon)
Organization: General Electric Corp. R&D, Schenectady, NY
Lines: 22

Typically one has to ask the uart to send a break.  As you pointed out in
your original posting the break is special because the line is held in
the space(?) state (I'm not really into communications) for an extended
period of time (greater than a character time at low speed).  The uart
uses the start/stop bits to frame the character.  Generally it's fairly
easy to get the break generated,  although one usually must do his own
timing.  One trick that might work (depending on how fussy the device
on the other end is) is to drop the transmit baud rate to the slowest
possible speed and send an ascii \000 with no parity.  I know that
this trick has been used on systems that cannot send breaks for one
reason or another.

If you want some code which sends a break on an 8250 type uart, send
me email.  Its really trivial.


Walt Dixon		{arpa:		dixon@crd.ge.com	}
			{us mail:	ge-crd			}
			{		po box 8		}
			{		schenectady, ny 12301	}
			{phone:		518-387-5798		}
Walt Dixon dixon@crd.ge.com