Known AX5904/AX5202 Issues?

Discuss technical or other issues relating to programming the Nintendo Entertainment System, Famicom, or compatible systems.

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poorstudenthobbyist
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Known AX5904/AX5202 Issues?

Post by poorstudenthobbyist » Sat Nov 21, 2020 7:46 pm

I'm starting to make my own MMC1 and MMC3 boards, and want to know if there are any known issues (outside of the ones on the wiki) that I should look out for going forward.

Where do these clone chips even come out of? Are they still being manufactured new, or is it like the old EPROMs and they're old stock that are refurbished for sale?
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lidnariq
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Re: Known AX5904/AX5202 Issues?

Post by lidnariq » Sat Nov 21, 2020 7:57 pm

I think they're all New Old Stock, and not part pulls, although I don't really have any evidence for this.

The SMD132/SMD133 mega-MMC3s appear to actually be all new, however.

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poorstudenthobbyist
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Re: Known AX5904/AX5202 Issues?

Post by poorstudenthobbyist » Sat Nov 21, 2020 8:05 pm

These things are such an enigma to me. It's like, they come from a mysterious unknown manufacturer, and they're (presumably) only used by a very niche group of people for a very niche purpose, especially in 2020.

I'm wondering because I had set up an SNROM board, but missed the pull-down resistor on CPU A14 (pin 21). I had thought it might have been my clone MMC1 at first. (Of course, first to blame the hardware instead of the design)

By the way, what's up with the pull-down on CPU A14 for SNROM games? The game doesn't save properly if I don't have it in there, but I don't know why I need it. (I'm looking more now and it seems any MMC1 game that saves requires that resistor)
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lidnariq
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Re: Known AX5904/AX5202 Issues?

Post by lidnariq » Sat Nov 21, 2020 8:14 pm

Looks like it's present on all the battery-using MMC1 games, if you check SAROM, SKROM, SUROM pictures too.

My guess is that pulling A14 down causes the MMC1 to de-select PRG RAM, since that requires A13 and A14 both high.

calima
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Re: Known AX5904/AX5202 Issues?

Post by calima » Sun Nov 22, 2020 2:33 am

If there's a market, some enterprising Chinese person will provide.

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poorstudenthobbyist
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Re: Known AX5904/AX5202 Issues?

Post by poorstudenthobbyist » Fri Feb 26, 2021 8:47 pm

Just to let y'all know, during my testing with Holy Mapperel on my SxROM boards, I encountered a problem - the "detailed test" result was coming back as 0x1000, which corresponds to an issue with enabling/disabling the PRG RAM. As it turns out, the AX5904 is based on MMC1A, which has PRG RAM always enabled. I tested an MMC1A and MMC1B2 in my board just to make sure it wasn't something I did, and the result came back the same for A, and all 0's for the B2.

tepples has already updated the wiki to reflect this (thanks for the help!)
Check out my website for NES, SNES, and Genesis tutorials here. And visit my store for some custom tools and boards for making games here.

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