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13.10) What is Omnimon?

--This section was written by Scott Charles, mailto:scharles@blast.net

Omnimon is a add in board for the Atari 400/800 series of computers and
a replacement OS chip for the xl/xe series of computers. The original Omnimon
board fit onto the OS board in the 800 series and had a switch attached to
it to disable the board. The 400 series required you to bend the circuit
board into a right angle for it to fit inside the 400's case. (It was
designed to do this.). The Xl/Xe version replaces the OS Rom chip inside
the computer with one that contains the Omnimon code, and a revised OS to
make the XL more compatible (no translator disks needed).

Omnimon itself is a machine language monitor residing from $C000-$CFFF, with
a few variations. It was designed in 1981 by David C. Young (who also wrote
Cartcopy, a copier for the right slot of the 800) of CDY Consulting in Texas.
The first software revision of Omnimon had a few basic commands and was only
4K long, only for the 400/800. The second revision required the addition of
a bank select switch, and was 8K long. Since it was addressed by the 400/800
as 4K, when you needed to use the code in the other bank, all the text on the
screen flips upside down, you flip the switch and hit any key. The Xl and Xe
versions of Omnimon do their bank selecting through the normal XL port for
this function, so it is seamless.

So what can you use Omnimon for? Its main claim to fame is its ability to
interupt any running program by pressing and holding the SELECT-OPTION-RESET
keys. Depending on the sequence you press determines what kind of warm boot
the Atari does. SELECT+RESET does NO warm boot, preserving the stack and flag
values of the 6502. OPTION+RESET allows a warm boot (as if you had just
pressed RESET) and interupts the vector at $C (initialation vector).

I think you can see where we are going with this - Omnimon was developed as
a machine language developer's tool, much in the same way that the Happy
modification was developed for legitimate backups. I.E. far more people use
both products for software piracy. If you have an Omnimon! in your machine
and you try to boot up an Electronic Arts program, for example, you will get
a message that says "REMOVE ROM AT $C000", and the program hangs. (Hence,the
need for the disable switch on the 400/800 version. There is no way to
disable the xl/xe version, just switch it to an alternative OS.) The 400/800
version, since the disable switch just deselects the mapping of Omnimon to
$c000 area, can be switched on and off at will.

I myself did not know what Omnimon was used for until I was using a sector
editor on a program called Pharaoh's Pyramid, from Master Control Software.
On it is a sector that reads, "REMOVE OMNIMON YOU DIRTY PIRATE". This got me
to thinking, what does that mean? After about 5 months of playing around
with the Omnimon board, I figured out how to use it to pirate software.
In fact, it can be used to make most boot disks into binary files, and remove
copy protection from countless more.

At the risk of sounding melodramatic, I can safely say that Omnimon hastened
the demise of the Atari 8 bit computer by 2-3 years, because of its power.