16 MB Multi cart: Is a 16 MB game possible?

[RetroCircuits]

Here is a multi cart that is new to the scene.....

[DEATH]

​First of all it is wrong to say "the jaguar has a maximum 6MB of ROM size" or something like that.
The right term is "The Jaguar has 6MB of cartridge adress space". This mean you have 6MB (6 mega bytes, or 48Mb, mega bit) of direct adress space (without trick like bankswitching) for whatever you want, ROM, RAM, device, etc. for the cartridge you plug into the Jaguar.
Also, all the processor and coprossesor can access this adress space (68000, Riscs, OBJ, Blitter). OBJ coproc can handle graphics data directly from this adress space if you want. Yeah ok, it's not recommended because of bandwidth of the cartridge bus, but...

[+CyranoJ]

Enjoy not being able to save between games with that cart....

 

[edit]

 

Oops, thought that was the shitty dial cart.

[neo_rg]

What is your price point for a board with no eproms on if I was interested.

[VladR]

​First of all it is wrong to say "the jaguar has a maximum 6MB of ROM size" or something like that.

The right term is "The Jaguar has 6MB of cartridge adress space". This mean you have 6MB (6 mega bytes, or 48Mb, mega bit) of direct adress space (without trick like bankswitching) for whatever you want, ROM, RAM, device, etc. for the cartridge you plug into the Jaguar.

Also, all the processor and coprossesor can access this adress space (68000, Riscs, OBJ, Blitter). OBJ coproc can handle graphics data directly from this adress space if you want. Yeah ok, it's not recommended because of bandwidth of the cartridge bus, but...

For great majority of 2D games, the bandwidth hit shouldn't be a big deal (unless you're hitting the per-scanline limit of OP objects). For example, if you have a 768x240x16 bit background bitmap, that's 360 KB out of 2,048 that you just freed for other stuff. So, pretty big deal, honestly.

Same goes for 2D animation frames. You can just keep all frames in ROM and have more frames available, than if you tried to cram it all to RAM.

 

But, this is all academical, if real-world benchmark would prove a huge hit to OP.

 

 

 

Looking at the jag_v8.pdf, page 9, Memory Map, ROMHI = 1, it makes you wonder if it'd be easy to upgrade jaguar's RAM from 2 MB to 8 MB, as that's the address space that is directly available by memory controller (DRAM0: $000000-$400000, DRAM1: $400000-$800000).

8 (RAM) + 6 (ROM) = 14 MB, almost like on Falcon. Hmmmm, nice....

[DEATH]

unfortunately it is not so "easy" to upgrade internal RAM to 8MB. In all cases it will take lots of unsoldering/soldering.
First, you have to find the right memory chips. For the "easyest way" you must find, at least, 8*1MB fast page mode DRAM. 512Kb*16 with double WE signals witch is very uncommon... Actually, i think this memory chips probably never existed, even with more capacity. I've already looked for it a long time ago. You can find the right ones, but only with double CAS, not double WE.
Then you have to desolder the 4 memory chips inside the Jaguar, solder the new ones (4), find a way to solder the other 4 (2nd bank), on top of the first ones for exemple, and of course, you have to wire the missing RAS1/CAS1 signals for 2nd bank.
Quite difficult....
Another "easy way" is to upgrade to 4MB instead. You have to find the same DRAM chips than the Jaguar (not so easy, or in a broken Jaguar), solder them on the top, and of course, you have to wire the missing RAS1/CAS1 signals for 2nd bank. (I think this is the way used by SPCD or zerosquare).

You probably need to add some deccupling capacitors.

OR... you can use whatever DRAM you want/found but you have to add the logic to decode missings/needed signals (double WE > double CAS, etc.)

Not so easy.
But fun to see.