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 >bankswitching? 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: http://www.geocities.com/siliconvalley/9461/ -- Archives available at http://www.biglist.com/lists/stella/archives/ E-mail UNSUBSCRIBE in the body to stella-request@xxxxxxxxxxx to be removed.