SFC cartridge development

The 8255 cannot fetch code and the ROM is ON the cartridge bus just like any game. The cart should start up like any game (indicated by the need for the CIC)

It would make the most sense for it to be a SNES-PC interface, but all that is certain is that it's a cart with 3x8bit I/O ports routed to an IDC connector...

 

a) the 8255 is a Peripherial. It doesnt make anything without a CPU controlling it. Noone said it would ever need to fetch code, i was referring to the SNES CPU fetching code thru the 8255 from the EPROM.

b) You can't be sure until you dont know the full pinout of the connector, right? I already asked Thibaut about posting a picture of the rear (front?) of the cartridge. Lets see what pops out!

 

a) The SNES cannot fetch code through the 8255, the 8255 needs a few operations before a I/O transaction takes place of course, the SNES cannot do this. The EPROM and the 8255 are both on the cartridge bus of course!

The SNES can both read the ROM and the 8255 (thanks to the 74138.) It knows how to access the ROM, it does NOT know how to access the 8255, that's what the ROM is for.

b) I am fully sure because that's the only connection that makes sense!

 

Wait, i fear i wasn't clear, let me rewrite it :

a) the 8255 is a Peripherial. It doesnt make anything without a CPU controlling it (through the dedicated registers). Noone said it would ever need to fetch code, i was referring to the SNES CPU fetching code thru the (registers that pilot the) 8255 from the EPROM (through the data bus).


Hope its clear this time

 

When you say "code" that means CPU INSTRUCTIONS, the SNES doesn't read instructions through the 8255, only data.

Yes, the SNES executes instructions off the ROM which instruct the SNES to R/W the 8255 at ports partially decoded to $XX:XXXX.

 

d'oh!

yes now i see what you mean.. :lol:
Thanks!

 

Happy to see that my cartridge is interesting you !

 

Sorry about the delay in getting the pictures up. Here ya go:

http://johan.playoldgames.net/images/demo-16/

Lousy camera, but you get the idea.

 

Thanks man, pretty cool hardware.

 

the other side :



nothing special

 

From those two pictures it appears possible to fully understand the cart, I don't have the time to try tracing the tracks though.

 

If anyone is interesting, I can sell it.