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PostPosted: Wed Sep 30, 2015 2:44 pm 
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Hello everyone!
It was my intention to replace SRAM with an equivalent FRAM.
Is it possbile?

I saw different ram (SRAM) in the cartridges

Hyundai GM76C256CLLFW70
Sanyo LC35256DM-70W
Sanyo LC35256FM-70U
Inbond W24258S-70LE
BSI BS62LV256SC-70

FRAM FM18W08 / FM1808B / FM1808 might be a good candidate.

Searching on the web some users say it works perfectly on MBC5 cartridges but on MBC3 there are graphical glitches.
Is possible to fix this problem with the addiction of diode, capacitor or resistance?
Or is possible to replace SRAM with NVRAM or EEPROM (I think no for the lower read/write speed)

I'd like to understand the differences in the operation of F/Sram but I'm pretty ignorant.
I just know that both models work at 5V and they have the same pinout.

Thanks to all those who will answer


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PostPosted: Wed Sep 30, 2015 8:50 pm 
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I haven't looked at the FM1808 specifically, but back when the Ramtron FRAMs were new, I got some samples and used them on an NES cartridge and they worked fine there. The interface is 100% identical to SRAM, it's designed to be a drop-in replacement.

I don't know why, but from what I recall it seems that the 5V ones have limited read/write endurance, while the 3.3V ones didn't. I'm not sure if that applies to all manufacturers, but the FM1808 datasheet does mention the limited endurance. I never used them other than experimentally, since they cost like 10x as much as a normal SRAM. Seems like it's only any use if you absolutely can't fit a battery + NV controller on your board.

Quote:
Or is possible to replace SRAM with NVRAM or EEPROM (I think no for the lower read/write speed)

Even without an SRAM, you could use FlashROM in place of the ROM, and save data to that. The program would have to specifically support this. EEPROM can't replace SRAM. NVSRAM could, but it's just an SRAM with an NV controller and battery built-in, these tend to be pretty huge and certainly won't fit in a Gameboy cart case.


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PostPosted: Wed Sep 30, 2015 10:10 pm 
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Doesn't FRAM have a limited number of *reads*? If you took an existing game boy game, it wouldn't necessarily use the cartridge RAM for only saving games. For example, Super Mario Land 2 puts the stack there. For games that just use it as save space, I bet it would be fine, but for games that copy code there and execute it, maybe not so much.

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PostPosted: Wed Sep 30, 2015 11:47 pm 
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Yeah, I know at least the 5V ones I'd looked at get worn out by reads as well as writes. Funny story, when I was testing the FRAM out on Squeedo (would have been in 2005) I accidentally left the NES on (top-loader doesn't have an LED) for maybe 30+ hours with my code running a small loop inside the FRAM (waiting for IRQ). I don't know how many cycles that put on it, but it was still running when I came back to it, and didn't seem to ruin the chip or anything.


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PostPosted: Fri Oct 02, 2015 4:57 am 
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Thanks for the answers
I do the replacement and will keep you updated!


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