Max cartridge capacity

[kamaleon70]

Hi everyone, I know that the Vic 20 game cartridges were limited to 16k. I am curious… do you know the reason? Why not using the entire memory available like the memory expander cartridges do? Thanks.

[beamrider]

I didn't realise they were limited to 16K?

Can't you put ROM in blocks 1&2?

[kamaleon70]

I may be wrong. But all the cartridges I saw were in block at $a000 (for auto start) and or $2000 or $6000 but not both. I believe the cartridges were 8k or 16k max.

[brain]

$$$ is the most likely reason. In the era, 8kB was expensive, 16kB was hard to justify due to expense (otherwise, KERNAL and BASIC would have been loaded onto a single 23128). I suspect, knowing that, Michael and company stipulated games under development by internal and/or external resources needs to be 16kB max as a boundary.

As well, if you wanted to test your game/util, you only had the 16kB RAM expander to work with.

Jim

[kamaleon70]

So, in theory, it is possible to create a cartridge for a game using all the 35Kbytes... Thanks for the clarification.

[brain]

Indeed, you could go all the way to 37kB if you put RAM in the IO regions (3 1kB blocks [RAM1,2,3] + 4 8kB blocks [BLK1,2,3,5] + 2 IO 1kB blocks [IO2/3]

And, if you use a bank switcher, like UltiMem, you can use as much RAM as you want (or can afford)

Jim

[beamrider]

I can't imagine a 32K ROM cartridge would be that useful. Most games require workspace RAM of some kind, so perhaps 24K of ROM + 8K of RAM would be the sweet spot.

[Mike]

I can't imagine a 32K ROM cartridge would be that useful.

Well, Cheese & Onion is 32K ROM, so there ...

[Rich]

So could we get Elite on a cartridge as this would be very nice..... box art and a nice white case mmmmmmm..

[AndyH]

So could we get Elite on a cartridge as this would be very nice..... box art and a nice white case mmmmmmm..

That would be dangerous. The Vic would never see the READY prompt ever again if someone did that!

[Mike]

A dedicated ROM image for Ultimem should do the job for ELITE. Any takers?

Other than that, and quoting Aleksi from a reply posting in the ELITE thread, in the Games section:

I don't think there's a big enough standard cartridge format, any non-standard banking would be out of question. Also, there's self-modifying code and small workspaces in middle of the code blocks, so it's not feasible to turn it into a ROM image just like that.

It should be possible to put it on PenUltimate carts later, as they have some kind of internal file loader that can load any files from cartridge memory to anywhere in RAM and then run it. (I don't know exactly how that works, and whether the preloaded package of software on the cart can be updated as a firmware update.)

[kamaleon70]

Yes in case of a lot of self-modifying code, cartridge is not the way to go...
Do you know if there is a ram expander project that, just for fun, I can try to modify, replacing some ram with eprom? Maybe to have 32K of rom and using also the additional 3K available still as ram...

[kamaleon70]

Probably this one could be a good starting point to test... https://www.pcbway.com/project/sharepro ... 375ab.html

[mythic66]

aeb wrote:
I don't think there's a big enough standard cartridge format, any non-standard banking would be out of question. Also, there's self-modifying code and small workspaces in middle of the code blocks, so it's not feasible to turn it into a ROM image just like that.

A cartridge with a FRAM would works as it will retain the data and it make it possible to the self-modifying code
do to it's job as the chip act as a SRAM.

[kamaleon70]

I am not sure in this case about the use of FRAM. It can be written and retains the changes, but depending on how the self-modified code is used, it is possible that at the next start of the game the code is not in the "initial state" as it is supposed to be and the game could have problems. In fact, in the case of Elite, the game is always loaded, at the initial start, to RAM from the same non modified source (the floppy - that in this case acts like a "ROM").