Programable SNES cart - How do I make one
- Thread starter Fabrizo
- Start date
I'm mostly familiar with the principles involved, but couldn't give you step-by-step instructions because I've not done it myself. In terms of connecting an SRAM or Flash memory to SNES, it's not too complex. The SNES CPU also has the notable advantage of being 8-bit, which lowers the hardware and interconnect requirements a bit. The only really significant problems with it I can think of are:
1) You need to do something about the lockout chip. You could take one from a crappy game, put a pass-through slot in the cart, use one of the better import adapters (i.e. one with a CIC pass-through slot, popular in PAL countries since they need this kind to play US/Japanese games), or disable the chip in the SNES (which supposedly will break SA-1 games, though you could wire a switch to avoid that).
2) There are two different mapping schemes for SNES games: LoROM and HiROM. HiROM uses the full address bus, while LoROM ignores A15. If you don't mind cutting the capacity in half for LoROM, I think it would work to tie A15 low or high to enable LoROM mapping. Otherwise, you need to shift the address bus somehow. However, this isn't likely to matter anyway unless your cart is bigger than 16Mb to begin with, since pretty much all < 16Mb games use LoROM (it's more convenient from a programming standpoint).
Then there's the issue of writing to the memory. For a simple integrated parallel port interface, you could probably get away with using just an 8255 as long as you limit the cart to one memory chip. That would be a bit slow to write, but it should work and only requires one chip for the interface...
1) You need to do something about the lockout chip. You could take one from a crappy game, put a pass-through slot in the cart, use one of the better import adapters (i.e. one with a CIC pass-through slot, popular in PAL countries since they need this kind to play US/Japanese games), or disable the chip in the SNES (which supposedly will break SA-1 games, though you could wire a switch to avoid that).
2) There are two different mapping schemes for SNES games: LoROM and HiROM. HiROM uses the full address bus, while LoROM ignores A15. If you don't mind cutting the capacity in half for LoROM, I think it would work to tie A15 low or high to enable LoROM mapping. Otherwise, you need to shift the address bus somehow. However, this isn't likely to matter anyway unless your cart is bigger than 16Mb to begin with, since pretty much all < 16Mb games use LoROM (it's more convenient from a programming standpoint).
Then there's the issue of writing to the memory. For a simple integrated parallel port interface, you could probably get away with using just an 8255 as long as you limit the cart to one memory chip. That would be a bit slow to write, but it should work and only requires one chip for the interface...
Actuallly, there is a doc out there on building writable SNES and Genesis carts, but I forgot about it because I didn't like the design 
. I can't actually provide you with the file or a direct link on account of my ISP's current crappiness, but try going to http://www.programmersheaven.com and doing a search for GAMEMEDC.ZIP
. I can't actually provide you with the file or a direct link on account of my ISP's current crappiness, but try going to http://www.programmersheaven.com and doing a search for GAMEMEDC.ZIPSimilar threads
