Re: [stella] Larger games... brainstorming

Subject: Re: [stella] Larger games... brainstorming
From: danboris@xxxxxxxxxxxxxxxx (Dan Boris)
Date: Tue, 15 Apr 1997 08:07:45 -0400
>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

Unfortunetly this will not work. The 2600 hardware does not completely decode addresses so that any access from $00 - $FFF will enable either the TIA or the RIOT. Normally we only use the $00-$FF and $280-$297 to access these chips, but the do appear repeated all through this address space. If you were to hook up a EPROM in the above fashion you would end up having the EPROM and either the TIA or RIOT enabled at the same time and this would mess things up.

I do not think there is anyway to access more the 4K in a cart without bankswitching and without modifying the 2600.

							Dan B.

PS: For any electronic oriented people you can look at the 2600 schematics on my page:

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