How to put a 20 Mbit splited ROM in respective EPROMs?

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How to put a 20 Mbit splited ROM in respective EPROMs?
by on (#28179)
Hello. :P


I bought a Final Fantasy 5 original Super Famicom cart, and I will try to put a translated version on Eproms by removing the original Mask ROMs.

I learned that I need to split the ROMs and put each part on an EPROM, ok, it's easy for while. Beacuse there's no 20 Mbit eprom's out there (?).

The process to solder, rewire, etc, it's easy.

But the question is: the game ROM is 20 Mbit. If I use 8Mbits EPROMs, I'll need 2 of 8 Mbit and 1 of 4 Mbit. I'm not sure if it will works (sorry, I'm very newbie). I can't even split them in this format (8 + 8 + 4).

So, I was thinking the right way is to use 5 eproms of 4 Mbit (5 * 4 = 20).

What's the best way to do this?
What is the right EPROM to use in this project?


Would like to thanks in advance. :)

by on (#28181)
What size ROMs are already in the cartridge? Or is it a 16 Mbit PRG that was expanded to 20 Mbit during the translation process?

by on (#28183)
It was expanded for the translation.

It would be smartest to use two 8M and a 4M, but you'll need to make a ROM decoder. Since FFV is mode 21 ("HiROM"), address lines A15+ are shifted left one bit and A15 is ignored. To get this game working, you'll need to decode A22 and A21 (physically A21 and A20 of the ROM) to select the first 8M ROM on Y0, the second 8M ROM on Y1 and the 4M ROM on Y2.

by on (#28191)
Oops. :oops:


Both of you are right!

The original FFV Rom is 16 Mbit, it was really expanded when translated.

However, I think this method to decoder is so much tricky to me. But, if I split the ROM in 5 parts of 4 Mbit, it will work even with this "hacked 20 Mbit" version? Running on real hardware, there are any chances to get bugs or the game just doesn't work?

I know that ROM runs in every SNES emulators (probably some are more accurated than others). But on a real console, theoretically will run?

Thanks!

by on (#28216)
I guess FF5 uses the old SHVC-1B3M board (I have Secret of Mana (J) which also uses this borard, whent the newer Secret of Mana (E) uses SHVC-1J3M).
The main difference is that a 74-139 decoder is used instead of a MAD-1. Because half of the 139 is already used to decode SRAM, maye the other half can be used to decode ROMs ??

EDIT : Yes, I can confirm half of the 74LS139 is unused on the SHVC-1B3M-01 board. I guess you'd have to disconnect the unused inputs for either GND or VCC where they're tied tough.

by on (#28336)
Yeah, but I still think I'll can't to do this in that way. :lol:
Probably to use five 4Mbit eproms will be much easier (though can be more expensive).

Anyway, I think I'll try another cart for while, one that I can use only 1 eprom, like Final Fantasy 4 (J). Even though I guess I'll need to buy a loose one on eBay.


By the way, today I found in my bedroom a pirate copy of Dragon Ball Z - Super Saiya Densetsu (J) (RPG in japanese...). I opened the cartridge and have noticed there's real chips on the board. Immediately I figured out that this game could be useful (once the game itself is pretty bad). The board doesn't have the batteries to save progress, however there's a place to put it.

The game is 8 Mbit size, can I put another game on this board without so many "adaptations"? What game can be put there? Is better to throw it over the window? :lol:

I've scanned the board to clear up the things:

Image

A bigger picture can be found HERE.


Thanks! :)

by on (#28355)
Well, your cart seems to have one ROM, one SRAM, one '139 dual-adress decoder and a chip that should serve as a lockout chip with no stuff written on it. I guess it wouldn't be hard to add a battery and a couple of resistors/diodes/capacities (there is slot for them on the bottom right of the board) for battery backup, and change the ROM to another one. You won't be able to go over 8MB because that's the largest size of EPROM available as far I know. I bet this is a Lo-ROM board, because I think Hi-ROM is useless below 16MB of ROM. You will be able to play FF4 with this, but not FF5 I guess.