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PostPosted: Wed Mar 23, 2005 1:00 pm 
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Joined: Wed Mar 23, 2005 12:55 pm
Posts: 2
I have for a long time thought about the possibility of playing the VS-version
of Duckhunt on a NES using a Zapper! Why, you ask?

Because the VS-version had a third gaming-mode, where the dog chased the ducks
out of the bushes. But the real cool thing was that the annoying dog is shootable
too, and it is coming out with bandages and stuff if it is. =)

As I just bought a famicom disc system(which will soon arrive), and have read
Brad Taylors excellent instructions on the possibility to transfer discgames
directly to the memoryadapter(or the disc drive to rewrite games), maybe my
little dream is possible too?

In the early days in japan, I believe lots of cart-based games was converted
to disc system by pirates, so I don't believe it should be that hard.

Concerning that the arcade version requires the coin to be inserted, I read in
another thread that the famicom player2-mic uses the same adress as the coinslot,
so I believe that shouldn't be a problem (or maybe it is possible to hack the
game to freeplay, somehow). The VS-games usually had different palettes,
often just totally switched around, as noticed when playing the converted
arcade-VS-roms in NES emulators. But in this game, that isn't the case, luckily =).

I haven't missed a tool somewhere, that converts early mapper-less
games to famicom disc format, have I?

Anyway, as the problem is that I don't possess any lowlevel hacking-knowledge
myself, and as there is quite a few people here that have knowledge in NEShardware
and such, maybe someone can help me out a tad in the constructing of a working disc-image.

I have currently asked my little more lowlevel-knowledge brother to hack this
up as a birthdaypresent for me, as soon as I can provide all info I can get,
but I won't count on it, as he doesn't really have any NES-programming-experience.

Anyway, I'm very happy and grateful for ANY help and expertise I can get in this
little project of mine.

Thanks! =]
/Rickard


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PostPosted: Wed Mar 23, 2005 7:13 pm 
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Location: Indianapolis
Neat idea. Have you checked the ROMs to make sure they add up to 32kB PRG + 8kB CHR? I've never played VS Duckhunt, but I wouldn't be too surprised if it did some bankswitching.

I don't have an FDS or any dev experience with it, so I can't help you much. But I can tell you that FDS has a different memory map (because the BIOS), so you'll probably need to disassemble and reassemble the game's code to make it start at $6000 instead of $8000. That could be tricky. It's not easy to get a re-compilable dissassembly, but some dissassemblers by Hyde and Snowbrow manage to do it (with a little user intervention, I think).

Once it runs, you might need to modify the palette. That's real easy, I could help with that if/when you get to that point.

I think it would probably be easier though to put it on a cart instead of disk. If it doesn't bankswitch, it wouldn't even need any code modifications (except palette).

VS System also has some dip switches, I don't know what the game will do if they're not present. Probably nothing bad.


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PostPosted: Wed Mar 23, 2005 7:43 pm 
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Joined: Sun Nov 14, 2004 11:24 am
Posts: 330
So, you want to modify the VS rom to run on a normal NES?
I think the VS mapper is 99, and I'm not familiar with it, or what is the closest mapper.

I'm not sure how different a VS zapper is from a regular one.


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PostPosted: Thu Mar 24, 2005 9:49 am 
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Joined: Sun Sep 19, 2004 11:12 pm
Posts: 19104
Location: NE Indiana, USA (NTSC)
Memblers wrote:
Have you checked the ROMs to make sure they add up to 32kB PRG + 8kB CHR? I've never played VS Duckhunt, but I wouldn't be too surprised if it did some bankswitching.

VS Unisystem versions of Famicom/NES NROM games typically use what has been called Mapper 99, a bankswitch system very similar to CNROM. If that document is correct, then hacking a Mapper 99 game to use CNROM instead is straightforward: just run it in a debugger and watch for $4016 writes.


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PostPosted: Mon Mar 28, 2005 10:45 am 
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Joined: Wed Mar 23, 2005 12:55 pm
Posts: 2
First of all, thanks for all the replies!

>It's not easy to get a re-compilable dissassembly, but some
>dissassemblers by Hyde and Snowbrow manage to do it (with a little
>user intervention, I think).

Where can I find these?
I checked the main parodius nesdev site, but these couldn't be found.
Anyway, as it looks like now, my workplan is like this:

1. Make the game work in cart mode using a nes-emulator, running using mapper 0. Make sure the zapper works correctly (if it isn't), and somehow set to freeplay, fixing the coin somehow. Maybe the coin insert can be mapped to a button, like select, as I don't think that button is needed in this version.

2. Somehow put it on a famicom disc, fix the adresses for that and so on.

So well, can anyone point me to a recommended dissassembler for this?

Thanks!
/Rickard


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