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PostPosted: Mon May 16, 2005 10:02 pm 
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I've been attempting to make a custom game and run it on my NES. I started with a Gyromite cart, removed the PRG and CHR PROMs, added bridges in their place, and popped in my own burned PRG and CHR EPROMs. All I get, however, is a solid grey screen (no blinking).

My NES absoloutely works, and I tested this board specifically before I modded it and it played fine. The board was not damaged at all during the removal of the original PROMs.

My code runs fine in FCEU. I tried splitting it into CHR and PRG manually and with a utility, and they produced the same result.

I then tried burning Gyromite back on to my EPROMs, and again, I was greeted with the same solid grey screen.

Any ideas what might be going on?


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PostPosted: Tue May 17, 2005 12:45 am 
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Are the original maskroms still in a condition where they can be used on it? The pinout should be the same as EPROMs, as I suppose you know.

I'm not sure what's wrong, with NROM there's not much that can mess up. Seems like it would have to be a ROM splitting or electrical issue (open or short on a pin?), sounds like you've ruled out the ROM split already though.


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PostPosted: Tue May 17, 2005 8:56 am 
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All the pins of the bridges should be connected back to the original spots where the CHR and PRG EPROMs were, right? I noted that one some tutorials using boards with mappers that they left some pins unconnected..

EDIT: Here's the code for the PRG and CHR.


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PostPosted: Tue May 17, 2005 5:12 pm 
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Hm. I see it's a 16kB PRG and the code is at $80xx. That's shouldn't be a problem though, since the NES should mirror a 16kB rom $8000 and $C000.

If you have a 32kB EPROM, perhaps you could try copying your PRG into it twice and burning that. I remember there's a couple different NROM board types though, NROM-128 and NROM-256, I can't recall what the differences were exactly (maybe search the forum if you want to).


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PostPosted: Tue May 17, 2005 5:46 pm 
Just double it up with no buffer between them? Or are there specific locations on the EPROM it should go in?

Should I double the CHR and PRG both, or just the PRG?


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PostPosted: Tue May 17, 2005 5:50 pm 
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^^^ That post was mine, I forgot to log in.
You mentioned that $80xx might be a bad location?
But would the 32k EPROM explain why Gyromite wouldn't run again on it's own board?


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PostPosted: Tue May 17, 2005 6:12 pm 
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Yeah, just doubling up the PRG is what I meant.

Starting at $8xxx is generally fine for 16kB games, I've seen some games (I think Lunar Pool was one) that do exactly that.

So yeah, I'm a bit mystified about why your cart isn't working. Doubling up the PRG really shouldn't fix Gyromite, it should work already like you suspected.

If you're new to soldering stuff, make sure the rom socket is joined to the board properly (using a multimeter or just up-close visual inspection).


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PostPosted: Tue May 17, 2005 9:23 pm 
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Yeah, the board looks clean, just from a visual inspection. Taking out the original PROMs was pretty involved, and I ruined a bunch of boards before finally getting this one right, which made it twice as frustrating when this board turned out not to work, either. Unfortunately I don't have a multimeter to test with.

One other thing, as I trying to get the cart into the correct vertical position, I noticed a few stray tiles appeared on the screen for a moment, but I couldn't get them back. I could have been random, but I doubt it..

Can you provide me with any more info about "doubleing up"? An example, maybe?


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PostPosted: Tue May 17, 2005 10:48 pm 
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At the command prompt (or batch file, or anything) you can type "copy /b file1.prg+file1.prg file2.prg"


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PostPosted: Wed May 18, 2005 4:15 pm 
Ah ha! It did work!
There's still an inssue, though, in that it will display the a weird glitched out version of what I should see (it's a single screen), and only when I press reset, but at least this rules out the board not working!

Thanks so much!
If you have any further suggestions, I'd love to hear them :)


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PostPosted: Wed May 18, 2005 4:50 pm 
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I can almost get it to display properly if I don't seat the CHR EPROM all the way. Are there pins that should be bridged or not inserted?


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PostPosted: Thu May 19, 2005 11:44 am 
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Just a stab in the dark here, but did you check that the pinouts of your EEPROMS match the ROM pinouts? When you say you "bridged" the chips, I'm assuming you connected pin 1 to pin 1, pin 2 to pin 2 etc. There are a couple of pins that don't match on most EEPROMS, so you have to re-route a bit. What is the part number of the EEPROMS you have?


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PostPosted: Thu May 19, 2005 12:37 pm 
They're M27C256B
I was looking through the "Cart Types" doc, and I couldn't find anything that matched the Gyromite board (it's listed at the bottom, though).


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PostPosted: Thu May 19, 2005 2:39 pm 
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It's cool then, it's the 28xxx series ones that are EEPROMs. Gyromite board is probably NROM-128, you should be able to see it printed in gold on the board.

However, CHR uses 8kB ROM (which would be a 27C64 EPROM, but it's possibly not worth getting those because they're older/rarer). So I think I realize the CHR problem now, maybe you burned CHR into the lower 8kB then the NES is probably displaying the upper 8kB. So try duplicating the CHR.

Like "copy /b file.chr+file.chr+file.chr+file.chr file2.chr"


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PostPosted: Thu May 19, 2005 3:13 pm 
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I'm going to give that a go in a few minutes (it's finals week, and I've got a huge stack of Art History flashcards in front of me :( ). I really want to thank all you guys for helping me out. I can say without a doubt that I wouldn't have gotten as far as I have in this project without the input from this board. I really, really appreciate it :)


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