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From: dwa@sdcc12.UUCP (Don Anderson)
Newsgroups: net.micro.pc
Subject: Sending control-Z to a device driver
Message-ID: <223@sdcc12.UUCP>
Date: Wed, 27-Mar-85 10:20:31 EST
Article-I.D.: sdcc12.223
Posted: Wed Mar 27 10:20:31 1985
Date-Received: Sat, 30-Mar-85 00:40:36 EST
Organization: U.C. San Diego, Academic Computer Center
Lines: 29

I am running MS-DOS 2.11 on an AT&T 6300. I have a modified COM driver
which I am using to drive async port #2 (ASYNC from Mike Higgins) to
which I have the source assembly code, so I can tell what it does. In
trying to use this driver to send data out to various devices, I
discovered that control-Z's weren't making it if I used the write
function for a text file from Turbo Pascal. To eliminate the
possiblility that it was Turbo that was intercepting the character, I
switched over to MS-DOS systems calls - specifically, I opened the file
with a call 03DH and wrote to it with a call 040H. Everything goes
through just fine except when I try to write a control-Z to the device.
I get back a result of 0 characters written and nothing goes out the
port. Insofar as I can tell, MS-DOS is intercepting this character,
presumably because it considers it to be an end of file character. When
one is driving a graphics printer, this is excessively "user-friendly".
I can kludge my way around this by creating a special variant call
indicating the intention to send a control-Z, through DOS call 044H 
(IOCTL) if I modify the device driver. Otherwise, I could bypass DOS 
entirely, but I hate to do that. The AT&T provided COM2: driver and the
IOCTL service provided through MODE seem not to work at all, producing
write fault errors on everything sent to COM2:, though GW BASIC
can use this port if one opens a file to it using the "ds" option to do
some undocumented thing to the dsr line. I have not checked whether or
not GW can send a control-Z to COM2: successfully, as it is against my
principles to use BASIC.

Has anyone else had this problem? Is this a feature of MS-DOS? Is there
any "standard" way to get around it? 

-don anderson