Re: [stella] 7800 DevCart (Was: Where can I find something like a cuttle cart)

Subject: Re: [stella] 7800 DevCart (Was: Where can I find something like a cuttle cart)
From: "Eckhard Stolberg" <Eckhard_Stolberg@xxxxxx>
Date: Fri, 13 Dec 2002 23:07:21 +0100
> > Will this cartridge play 2600 titles as well in a 7800? or is it limited
> to
> > 7800 titles only?
> That's what I'd like to know.  In theory it should be simple as 7800 only
> checks a certain portion of memory for checksum.  If it's valid, the
> locks in 7800 mode.  Otherwise it goes to 2600 mode.  I'm not sure if it
> be done with the 7800 dev cart without any modification.

The NTSC 7800 BIOS only locks the 2600 modus. A valid 7800
cartridge can chose the mode itself and lock it if nessessary.
Therefore our cartridge will have a possibility to play 2600
games. We haven't yet decided, if it will be possible to add
2600 bankswitching modes, but at this point in time it seems
very unlikely that it will.

The cartridge will be able to map in RAM linearily at
$3000-$FFFF, of which you will be able to use the 4K
blocks at $3xxx, $5xxx, ..., $Fxxx in 2600 mode. That
way you can create 4K games on it and even simulate
some of simpler bankswitching modes with it, if you
adjust the code for accessing the hotspots and the
SARA RAM a bit. Atari's 7800 development cart worked
similarily, and most of the later F8 and F6 games were
written on it.

Come to think of it, this might be the reason for the stange
bankswitching code in RIOT RAM that Manuel mentioned a couple
of days ago. This code would work in a linear address space
too, where one bank was placed at $F000 and the other one
at $B000.

Ciao, Eckhard Stolberg

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