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PostPosted: Tue Oct 10, 2006 11:47 pm 
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Hello. I want to make my first reproduction NES cartridge. I want to reproduce Zelda Outlands.

I have everything that is required to reproduce the game. However, I am unsure if my EEPROMs will work for the project. They are 28pin 27C512, and were pre-used. I read somewhere that they will be ruined if exposed to static, and I'm pretty sure mine have been. How can I know if they will work?

If you look inside a Zelda cartridge, there are 3 28 pin ROMs. One is marked "PRG" so I know that's the PRG rom. How do I know which other ROM is the CHR one? I only have to remove PRG and CHR correct? I do not have to remove the 3rd one (whatever it may be)?

Thanks for any help. I am hoping somebody can answer my incredibly n00bish questions and guide me through this entire process. Thanks!

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PostPosted: Wed Oct 11, 2006 12:36 am 
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I don't have enough knowledge to completely help you, but I do know the following:

Zelda 1 has CHR-RAM, not CHR-ROM. The two other chips besides PRG-ROM are the CHR-RAM and WRAM. Unless I'm overlooking something, those do not have to be removed (although you might want to temporarily pull the battery to erase any existing save data, since the official game's save data probably isn't fully compatible with the hack).

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PostPosted: Wed Oct 11, 2006 12:45 am 
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First off, that is the wrong size ROM (512kbits = 64kbytes). Zelda is 128kbyte. You'll need a 27C010/27C1001 (or larger) ROM, which are 32-pin.

As for static, probably the only way to know if it's been zapped is if you saw (or felt) the spark yourself, heheh. You could probably only test it by burning a ROM to it and doing a verify with the programmer.

Zelda uses CHR-RAM, so you don't need to remove that (CHR ROMs are marked CHR and game title like you see with the PRG). The 3rd chip is RAM also, backed up by the battery.


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PostPosted: Wed Oct 11, 2006 11:25 am 
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If i need 27C010/27C1001 EEPROMs and they are 32 pins, then how am I supposed to get them into my Zelda donor cartridge, which uses 28 pin ROMs?

So to reproduce Zelda Outlands I only have to remove and replace the PRG ROM chip? Am I understanding this correct?

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Last edited by NMorgan on Wed Oct 11, 2006 11:29 am, edited 1 time in total.

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PostPosted: Wed Oct 11, 2006 11:26 am 
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Use wires?

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PostPosted: Wed Oct 11, 2006 12:42 pm 
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Yes, remove the PRG-ROM chip. Then you'll have to bend up some pins and wire them to the board (as the guide for your board type say here - http://nesdev.com/NES%20EPROM%20Conversions.txt). Nintendo's ROMs have a somewhat different pinout as you can see.

I've never wired a 32-pin chip to the 28-pin board. My old UNROM dev board just used 64kB, then the one I designed just uses standard EPROMs.


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PostPosted: Wed Oct 11, 2006 12:49 pm 
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The pinouts of the chip you are going to put on the board will hardly match the original ROM, so you'd have to rewire anyway.

You have to bend the extra pins up and solder wires to them, and the other end of the wires to wherever they're supposed to go. You'll have to that to any other pin that doesn't have the same function as the original ROM.

Use the document that describes the pinouts of the original Nintendo chips (found on the main NESDEV page), and compare each pin to the ones in your chip (you can find datasheets for any chip quite easily). Whatever is different, needs to be rewired.

I usually have a little trouble when I can't find exact matches for the pins, and some knowledge of electronics (wich I don't have) is needed to decide what can substitute what.


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PostPosted: Thu Oct 12, 2006 1:38 pm 
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Zelda is on a SNROM PCB.
Its PRG is only 28 pins, but there should be 4 extra holes (filled with solder) where a 32 pin PRG would fit.

Just solder suck out the extra 4 holes and you will be putting a 32 pin chip in 32 holes.

Be sure to follow Memblers advice on that page (and use a 128 KB chip like he said. 27C1001 EPROM or 29F1001 Flash.


Warning: In my opinion, the desoldering part is the hardest. If you are new to de-soldering, you should practice on a cart you dont mind destroying first. I'd suggest testing that each pin can move freely, before attempting to extract the chip, otherwise you might tear up the traces.

Al


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PostPosted: Thu Oct 12, 2006 3:58 pm 
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albailey wrote:
I'd suggest testing that each pin can move freely, before attempting to extract the chip, otherwise you might tear up the traces.


Yeah, good point. When you try to move it you normally should hear/feel a slight snap, shouldn't take much force, then the pin will be loose. Make sure it's done for every pin.


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