[stella] Misc 7800

Subject: [stella] Misc 7800
From: Keith Gerdes <kwg@xxxxxxxxxxxx>
Date: Wed, 19 Jan 2000 10:55:23 -0600
> That's fairly recent.
> How did Harry encrypt the monitor cart?

His was the last to be encrypted by Atari.

Here's the "Acknowledgments":
Special thanks to Juli Wade at Atari Corp for her help.
She assisted with getting the encryption code for both
versions of the 7800 Monitor and sorting thru the legal
issues of including Space War, Combat, and Slot Racers
on my cartridge.

Juli was a developer rep for games & computers.

He sent the binary to Atari, and they sent back the key.
The second time around I assume he got smart and figured
this would be the last so he made it flexible enough where
he didn't need it encrypted again.
 e.g. upper 4K only, jump to vectors outside the 4K, etc
This left the "backdoor" (as I called it) open.

> Is the encryption software really lost?
> It's really silly how these things get lost and that
> there are no backups anywhere.

At General Computer Corp, supposedly.  Someone used to
work with/for GCC from the list.

Atari/Hasbro still has it somewhere, but it's in limbo
just like the Jag's.


> And why would these have back doors if they're Atari games?

For various reasons....  :-)

The main one being that the 2 main vectors (reset & NMI) jump
to code outside the keyed area (intentionally or unintentionally,
they didn't care).  As mentioned, various games do this.  Harry's
Monitor cart does this too.

Maybe a programmer got tired of waiting on the key process,
so they froze the keyed area.  Of course this probably wasn't
the case since the devkit didn't require a keyed cart.


> Why not just replace the rom with a non-domestic chip?

That was the original proposal but it requires -opening-
the 7800 and -replacing- the boot ROM (which may not be
-socketed-).  And replacing the ROM with an EPROM requires
an -extra- TTL chip.

> other than acquiring a European chip?

That too.  Who knows how much it -costs- now.


> And yet it doesn't seem to affect anything when you do
> bus conflict with the wrong 'fix-up' value in the ROM
> on a homemade cart (dunno about the Atari, but on the NES,
> it doesn't do any form of damage that I know of).

There isn't a bus conflict on a 7800 in that situation.
It just runs the cart in 2600 mode.

During the key check, the boot ROM flips between itself
and the game ROM.  You cannot enable both at the same time.

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