Path: utzoo!utgpu!jarvis.csri.toronto.edu!torsqnt!lethe!tvcent!andrew
From: andrew@tvcent.uucp (Andrew Cowie)
Newsgroups: comp.binaries.ibm.pc.d
Subject: Re: Warm-boot program
Summary: Use debug to create BOOT.COM
Message-ID: <1990Jan4.124333.25943@tvcent.uucp>
Date: 4 Jan 90 12:43:33 GMT
References: <5894@uhccux.uhcc.hawaii.edu>
Reply-To: andrew@tvcent.UUCP (Andrew Cowie)
Organization: TVC Enterprises
Lines: 44


What you need is to use the same interrupt that is generated when you
type Ctrl-Alt-DEL. This interrupt is interrupt 19 hex, 25 in decimal.
This can be generated with the assembly command INT 19.

A small file can be made by using DEBUG. (comes with DOS) A full
assembler could be used, but is unnecessary.

The following is a short transcript of a session with DEBUG. Note that case
is not significant. I have shown all text entered by the user as lower case.
My comments will appear on the right side of the screen. XXXX represents some
segment number. This is chosen by debug.



C> debug
-                                         The DEBUG prompt.
-a 0100                                   Assemble code, offset 0100.
XXXX:0100  int 19
XXXX:0102
-u 0100 0100                              Display the code at offset 0100.
XXXX:0100 CD19       INT    19            CD19 is the actual machine code.
-r bx
BX YYYY                                   (current value of the BX register)
: 0000                                    Set BX to 0000
-r cx
CX YYYY                                   (current value of the CX register)
: 0002                                    Set CX to 0002
-n boot.com
-w
WRITING 0002 BYTES
-q                                        Quit.

C> boot                                   Hey Presto! It works!



The idea is to create one two byte machine code instruction, CD19, and write it
to disk with the name BOOT.COM This works on my machine. I hope it works on
yours.

--
Andrew F. Cowie at TVC Enterprises, Toronto, Canada.
uunet!mnetor!lethe!tvcent!andrew  andrew@tvcent.uucp