Bigger ram cart

[chriswhit]

I have a 7800 dev system and a home built 48KB RAM Cart. My question is can a bigger ram cart be built? If so is there any info on this floating around? Thanks

[jaybird3rd]

Good question. Anything larger than 48K would have to be bankswitched, and I don't think building a bankswitched RAM cartridge is as simple as replacing the ROM with an SRAM chip. As I recall, 7800 bankswitching is controlled by writing the bank number into the ROM space, but this would change the contents if that space was writable (as it would be with a RAM chip in it). In addition to that, I doubt DevOS is currently set up to write to such a cartridge, since none currently exist.

 

I'd love to see more support for the XBoard, which adds 128K of RAM to the system in addition to a POKEY chip. That would be ideal for game development/testing, since it would eliminate the need to have RAM/POKEY on the cartridge. Granted, you'd have to modify the game for a standard cartridge when it's finished, but that wouldn't be too difficult.

[chriswhit]

Good question. Anything larger than 48K would have to be bankswitched, and I don't think building a bankswitched RAM cartridge is as simple as replacing the ROM with an SRAM chip. As I recall, 7800 bankswitching is controlled by writing the bank number into the ROM space, but this would change the contents if that space was writable (as it would be with a RAM chip in it). In addition to that, I doubt DevOS is currently set up to write to such a cartridge, since none currently exist.

 

I'd love to see more support for the XBoard, which adds 128K of RAM to the system in addition to a POKEY chip. That would be ideal for game development/testing, since it would eliminate the need to have RAM/POKEY on the cartridge. Granted, you'd have to modify the game for a standard cartridge when it's finished, but that wouldn't be too difficult.

 

I'm ordering an Xboard. Will I have to take it out to run games with a pokey?

[+Mitch]

Graham Percy designed a larger RAM cart for the DevOS system. Unfortunately, his website is no longer up. I think this is the last version of the instructions. You also need to email Eckhard for the updated software to go with it.

 

Mitch

devcarts4.pdf

[chriswhit]

Graham Percy designed a larger RAM cart for the DevOS system. Unfortunately, his website is no longer up. I think this is the last version of the instructions. You also need to email Eckhard for the updated software to go with it.

 

Mitch

 

That is an awesome post the info is far better than what I hoped for. Thank you

[jaybird3rd]

Graham Percy designed a larger RAM cart for the DevOS system. Unfortunately, his website is no longer up. I think this is the last version of the instructions. You also need to email Eckhard for the updated software to go with it.

Wow, thanks for posting this! I hadn't heard of these designs before, but it looks like he successfully implemented bankswitched RAM. I've got some seven-hundred C300565 boards at my disposal, so I'm going to try building some of those cartridges. Thanks again!