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From: SHOSTAK%SRI-CSL@sri-unix.UUCP
Newsgroups: net.micro.pc
Subject: Re: Control-Break
Message-ID: <4341@sri-arpa.UUCP>
Date: Thu, 18-Aug-83 13:17:00 EDT
Article-I.D.: sri-arpa.4341
Posted: Thu Aug 18 13:17:00 1983
Date-Received: Sun, 21-Aug-83 06:16:42 EDT
Lines: 14

When a control-break is entered, the keyboard interrupt handler in the
bios clears the keyboard queue, then enters scan code 0 and character
code 0 into the queue; if the keyboard input bios call to inquire as
to whether the queue is empty is then called, it will report that the
queue is nonempty.  Moreover, if the call that does keyboard input is
issued, it will return 0 in both halves of the AX.  Control-break may
thus be viewed as extended code 0.  All of this is quite independent
of DOS, and occurs whether or not DOS notices the control-break.

If it is desired to detect control-break through the DOS interrupt
rather than by checking the keyboard queue, you can indeed place the
address of your interrupt service routine into location 1b.  Be
careful, however, to save all the registers in your routine and to end
it with an IRET rather than an ordinary return.