Need advice buying a NES-101 and a flash cart

Discuss hardware-related topics, such as development cartridges, CopyNES, PowerPak, EPROMs, or whatever.

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calima
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Re: Need advice buying a NES-101 and a flash cart

Post by calima »

Folks, stop telling the can't-solder-person how to manually build a cart the hard way :lol:

With products like I linked before, you put it in the programmer and press a button on your computer. For discrete carts like NROM there are no downsides, no different behavior.
WedNESday
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Re: Need advice buying a NES-101 and a flash cart

Post by WedNESday »

calima wrote: Fri Jan 07, 2022 2:38 amFolks, stop telling the can't-solder-person how to manually build a cart the hard way :lol:
This made me lol. I actually really grateful for the advice even if I've never done it before. I'll do whatever it takes to get what I need, so maybe I'll buy myself a little soldering kit. ;)

Edit: Now I understand what you mean. But would the retrostage programmer be able to flash a Famicom cartridge? I don't see an adapter for it on their web site which I managed to get working using Google's cache. But one question still lingers, can I flash an original NES cart or would I have to remove at least the PRG chip and replace it with one that can be flashed?

Edit 2: Actually, it wouldn't be possible... right? After all ROM stands for 'read only memory'. But the ROM chip must have been 'writeable' at least once in its life otherwise it wouldn't exist.
lidnariq
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Re: Need advice buying a NES-101 and a flash cart

Post by lidnariq »

You're right: a "Mask" ROM was "programmed" when it was made. You'd need something made to be re-programmable, whether it's flash, EEPROM, or just battery-backed RAM.
WedNESday
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Re: Need advice buying a NES-101 and a flash cart

Post by WedNESday »

Ok, so I'm gonna need to replace the PRG chip on the cart with something that can be written to.

Which leads to my next question. Which do you recommend, EEPROM or flash?
calima
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Re: Need advice buying a NES-101 and a flash cart

Post by calima »

Retrostage's programmer only flashes the carts he sells. If there's no famicom discrete cart for sale, it's easy enough to get a famicom-nes adapter. Using an adapter with a NROM game doesn't matter.
lidnariq
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Re: Need advice buying a NES-101 and a flash cart

Post by lidnariq »

There's no all-new parallel EEPROMs made anymore. Your only choice is old parts or flash.
WedNESday
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Re: Need advice buying a NES-101 and a flash cart

Post by WedNESday »

Brainwave: I buy Zelda 1 for the Famicom. At one point in the game, the PC jumps into the cart's RAM area (6000 - 7FFF). These programmers you can buy allow you to flash the RAM on any cart. The plan is, I have my code waiting there to intercept the PC when it arrives and start doing what I want to do. Granted, it won't give me the ability to get my hands on any start up values but at least I can program the console without the need for a flash cart or installing my own flash chip.

What do you guys think? :)

Edit: Ok, so Zelda 1 sells for like $500 on ebay. Some other game then. Does anyone else know of a game that does just that?

Edit: Come to think of it, are there any games for the NES that allow you to run arbitrary code? Pokemon Red for the Game Boy certainly allows you to with enough manipulation of the game itself. There is also a video on YouTube of somebody finishing Zelda 1 in 3 minutes doing just that.
Fiskbit
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Re: Need advice buying a NES-101 and a flash cart

Post by Fiskbit »

Zelda copies code to RAM at startup, overwriting whatever you put there. You've gotten a perfectly good suggestion about buying a flashable cartridge and an adapter; is that not workable for some reason?
WedNESday
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Re: Need advice buying a NES-101 and a flash cart

Post by WedNESday »

Hmm, that was actually one of my concerns I didn't voice earlier. It's a shame because it takes you virtually the whole way there. I was excited about it because if it did actually work I could avoid having to go through all the trouble of flashing.

In fact, I wonder if it is still possible. For instance, this video highlights a way of running some arbitrary code in NES RAM. I believe that with the 19 bytes of space the glitch gives you (24 from 3 names 8 bytes long - ZELDA), you could get the PC to jump to cart RAM. If Zelda 1 overwrites every single byte of cart RAM when powered up then it wouldn't be possible. But does it?

I know that the method provided to me would be exactly what I needed but all of this research I'm doing into getting an existing cartridge to run my code is just so much fun.
lidnariq
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Re: Need advice buying a NES-101 and a flash cart

Post by lidnariq »

You're basically looking for a corrupted save game that can cause arbitrary code execution. This has been done before on these ancient systems - e.g. on Super Mario World. Time to look for a disassembly?
Fiskbit
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Re: Need advice buying a NES-101 and a flash cart

Post by Fiskbit »

The Zelda ACE only applies to the FDS version. The game doesn't overwrite save files (if the checksums match) or the last page of SRAM.

Loading code in this way does give you access to real mappers, but doesn't give you access to power-on timings and state.
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Ben Boldt
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Re: Need advice buying a NES-101 and a flash cart

Post by Ben Boldt »

You may be able to use a Game Genie to prevent initializing the SRAM.
Fiskbit
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Re: Need advice buying a NES-101 and a flash cart

Post by Fiskbit »

With a Game Genie, you should be able to just override the reset vector.
WedNESday
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Re: Need advice buying a NES-101 and a flash cart

Post by WedNESday »

Fiskbit wrote: Mon Jan 10, 2022 1:55 pmWith a Game Genie, you should be able to just override the reset vector.
Correct. The reset vector could simply be changed to anything within the $6000 - $7FFF area to start running my code within 7 CPU cycles of the console being reset.

Only one problem... the NES I got from ebay is a top loader which doesn't work with Game Genie. :(

Also, isn't there a chance that the Game Genie might do something to influence open bus behaviour like the EverDrive does?

Edit: Grammar.
Fiskbit
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Re: Need advice buying a NES-101 and a flash cart

Post by Fiskbit »

The one major Game Genie limitation is that on carts that map below $8000, you'll get bus conflicts between cart addresses that match in the low 15 bits. You'll want to put your reset vector at $7FFA-7FFB, as well, so they don't conflict.
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