Re: [stella] Larger games... brainstorming

Subject: Re: [stella] Larger games... brainstorming
From: Nick S Bensema <nickb@xxxxxxxxxxxx>
Date: Sat, 12 Apr 1997 13:33:41 -0700 (MST)
>As we know, the 6507 address space between 297h (T1024T) and 1000h is
>unused on the 2600.  The cartridge address space is supposed to be 4k, but
>all 13 address lines do connect to the cart slot, so the entire 8k could be
>addressed on the cart.
>Suppose one used a 2764 8K EPROM, with the chip enable tied to a logical OR
>of A11 and A12 (and inverted if necessary - I think it would be), and the
>EPROM's 13 address lines simply connected to the cart slot's 13 address
>lines.  Would this allow access to ROM data between addresses 0800h and
>0FFFh, reclaming 2k of address space and allowing 6k carts with no

I'm sure if it were possible, someone would have tried it by now.

[possible complication snipped]
>Even in this case, it might be feasible to map a 4k RAM chip on the cart
>between $000 and $FFF (chip enable A12), and only use addresses $30 - $3F,
>$70 - $7F, $130 - $13F, etc.  Stella shouldn't respond to those addresses,
>so no conflicts would happen.  This would provide an extra 512 bytes of
>RAM, or 256 bytes if separate read-write addresses must be used like on
>Superchip and other programs with cart-based RAM.  One definite advantage
>of this is it can be done to an existing board, recycled with a new
>EPROM... it doesn't affect the function of the EPROM, and it involves
>adding nothing but the RAM chip (no bankswitching hardware.)

That area would probably be better used for ROM.  There is, however,
the possibility that even that won't work if all 000-FFF locations are
mapped to collision registers and console RAM anyway.

>Even if I'm completely wrong about all of this, is there any way to reclaim
>any of the lower 4k address space and direct it into the cart slot?

I'm no hardware expert, but here's what I'd do just to check:

Write a Supercharger program that checks to see if collisions, RAM,
and TIA writes take place past T1024T.

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