Path: utzoo!attcan!uunet!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!emory!mephisto!ncar!ico!ism780c!randvax!ucla-an!stb!mep
From: mep@stb.uucp (Marty)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Generate a BREAK on COMn: ?
Keywords: MSDOS COM1 COM2 BREAK RS-232
Message-ID: <1990Mar18.201049.2670@stb.uucp>
Date: 18 Mar 90 20:10:49 GMT
References: <1990Mar10.014345.5932@wolves.uucp>
Reply-To: mep@stb.uucp (Marty)
Organization: The Serial Tree BBS, +1 213 397 3137
Lines: 26

In article <1990Mar10.014345.5932@wolves.uucp> ggw@wolves.UUCP (Gregory G. Woodbury) writes:
>
>	I find myself in a situation where I have to write a quick and dirty
>program to generate a break on a DOS COMn: port.  The break (in this case)
>is that peculiar state of the RS-232 line that hold the transmit signal in
>mark state for a particular length of time.
>	I am dealing with a rather vanilla multi-port COM card and a modern
>(Phoenix or AMI) BIOS.  Is there a bios function to do this?  The machines are
>ISA bus '286 and '386 machines running DOS 3.3.
>	Any particulars or hints appreciated.
>
>-- 
>Gregory G. Woodbury
>Sysop/owner Wolves Den UNIX BBS, Durham NC
>UUCP: ...dukcds!wolves!ggw   ...dukeac!wolves!ggw           [use the maps!]
>Domain: ggw@cds.duke.edu  ggw@ac.duke.edu  ggw%wolves@ac.duke.edu
>Phone: +1 919 493 1998 (Home)  +1 919 684 6126 (Work)
>[The line eater is a boojum snark! ]           <standard disclaimers apply>


There is no bay to generate a BREAK using either DOS or the BIOS.
You have to do it yourself. Assert the BREAK signal and time it out
for however long you desire... I believe it should be about 2
character times, if I recall correctly.

marty