Known AX5904/AX5202 Issues?

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

Moderator: Moderators

Post Reply
User avatar
poorstudenthobbyist
Posts: 147
Joined: Fri Jun 24, 2016 4:20 pm

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?
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.

You can also follow me on Twitter for infrequent updates and bad jokes!

lidnariq
Posts: 9881
Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

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.

User avatar
poorstudenthobbyist
Posts: 147
Joined: Fri Jun 24, 2016 4:20 pm

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)
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.

You can also follow me on Twitter for infrequent updates and bad jokes!

lidnariq
Posts: 9881
Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

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
Posts: 1246
Joined: Tue Oct 06, 2015 10:16 am

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.

Post Reply