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| Acmlm's Board - I3 Archive - ROM Hacking - 74LS139 vs MAD-1.... encoded? |
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Beauford Octorok                   Since: 08-02-06 From: Arizona... yeah. Last post: 6276 days Last view: 6275 days |
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| I'm trying to put together an SNES cart with the J2e retranslation of FF4 on it... and I have failed three consecutive times. The game is LoRom, and I'm trying to stick it in a compatible cartridge (NBA Live 95, the old warhorse)--the thing is, NBA Live uses a MAD-1 to address the rom and sram, whereas FF4j uses a 74LS139.
Same rom pinout, same SRAM size, everything except that chip. So my question is, is the rom image of a given game coded specifically for the type of chip it uses? I'm not much of a rom-hacker, so I haven't been able to find out myself. Hopefully, somebody in this forum knows. I have successfully made cartridges of other games, including another hack (Zelda Parallel Worlds), so failing 3 times on this game is a good indication to me that something is not right. |
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Cellar Dweller + Red Koopa   Since: 11-18-05 From: Arkansas Last post: 6284 days Last view: 6275 days |
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| I took a quick look at the pinouts for the MAD-1 and 74LS139. It looks like they work very differently. Therefore, I'd not expect FF4 to work on a MAD-1 cart.
You will need to get a hold of a 74LS139 cart or rewire a cart to use a 74LS139. For that, you will need a schematic of a FF4 cart and quite a bit of work. Just swapping the chips will not work. If you try that, you might even let the magic smoke out. |
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BMF54123  Since: 11-18-05 From: MOOGLES Last post: 6275 days Last view: 6275 days |
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| I do believe a game's ROM/SRAM addressing greatly depends on the type of chip it uses. MAD-1 sounds a lot more custom (and likely different) than a stock 74LS139.
[edit] *BMF the Snowman smashes Cellar Dweller with a giant sledgehammer (edited by BMF the Snowman on 01-20-07 04:47 AM) |
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magno Goomba Since: 01-04-06 From: Spain Last post: 6284 days Last view: 6276 days |
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| Differences between both chips are about how many chips they can address; it is said that MAD-1 can address two code ROMs and a SRAM (although it can only a code ROM, of course) whereas LS only can address a ROM and a SRAM.
I will look for the doc where it talks about all these, which I was actually reading yesterday.... |
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Beauford Octorok Since: 08-02-06 From: Arizona... yeah. Last post: 6276 days Last view: 6275 days |
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| I've found a few docs myself, and I think my question is answered (also through experience):
The rom image of a particular game is not hard-coded to deal with a particular address chip; any rom will work in any kind of cartridge, as long as (obviously) the rom and the cart are both hirom/lorom, have matching sram size, etc. Apparently I had just been too careless in handling the pcbs of all those failed FF4 attempts, since I made one last week and it finally worked. Even though (according to a list of serial numbers I found) the original FF4j cart used a 72LS139 and my cart is mad1. I had thought that maybe the method of addressing data (as it relates to the chips in question) was somehow intrisically accounted for in the game's code. It seems like it isn't, which is nice. Thanks for the info; it got me started. |
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MathOnNapkins  1100  In SPC700 HELL Since: 11-18-05 Last post: 6275 days Last view: 6275 days |
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| I've never messed around with stuff like this (due to ignorance mostly), but I looked up the specs on these a bit and it one of them said it was capable of addressing more than one chip. Does this mean that they are capable of a "bank switch" of some sort? Or does that mean that it supports multiple maskroms which are treated as one ROM. I'm just curious b/c it would be interesting if you could find some ways to get around that 64 megabit limitation on game size. Just to say you can do it and all. I know the SA-1 has bankswitching, but I'm not sure if it is bank switching as I understand it, (i.e. like with NES games where you swap in different rom data by using the mappers) | |||
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Beauford Octorok Since: 08-02-06 From: Arizona... yeah. Last post: 6276 days Last view: 6275 days |
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| I'm not positive about this (haven't tested it in any way), but my gut tells me that there isn't bankswitching going on in the way you described. Using a 74LS139 "externally" (i.e. one that isn't already soldered into the pcb) to connect up to 4 proms to a single mask rom slot does treat everything as one rom, and the mad1 is used normally.
However, I really don't know what goes on in the mad1 when it's connected to 2 mask roms by itself. I thought it just has an address decoder mode that works like the 74LS139 to treat both as one rom, but that could be bullshit. And anyway, wouldn't it have been cheaper to not have to develop something like the SA-1 for larger games if the mad1 has bankswitching capabilities in the first place? I will freely admit that I don't fully understand how this stuff works; I have availed myself of the work of others (like Kogami and Rylefury at fudjiland.com, and the guys at Romlab) to gain a basic knowledge of how it's connected, but that's about it. |
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HyperHacker Star Mario Finally being paid to code in VB! If only I still enjoyed that. <_< Wii #7182 6487 4198 1828 Since: 11-18-05 From: Canada, w00t! My computer's specs, if anyone gives a damn. STOP TRUNCATING THIS >8^( Last post: 6276 days Last view: 6276 days |
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| The SA-1 is an entire coprocessor. I'm not sure what MAD-1 is, but I doubt it could do what SA-1 was used for. |
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