Hi, I've just replaced the SRAM IC in a Pokemon Blue cartridge with a Ramtron FM18W08 FRAM IC, after seeing a few posts around the internet mentioning that it seems to work ok. However, I've found a minor issue with it. Saving works fine, however the sprites during the intro, in battle, and the pokemon on the title screen are missing. Having looked into the mod further, it seems that FRAM only allows the address line to be changed on a /CE falling edge, whereas SRAM allows address line changes as long as /CE is pulled low. Is it feasible that this difference would cause the issue mentioned above? And if so, is it possible to add extra circuitry to mimic the original behaviour?
The address should be valid at the falling edge of /CE, but depending on the MBC speed it could perhaps violate the latch's setup time. That said, I don't understand why it'd only affect the intro. You could try putting a small capacitor in parallel to /CE to add some delay. Maybe 100 pF. Also recheck your address lines, I'm guessing one is open.
Thanks for your reply. I have checked all of the address lines for continuity, and they all seem good. Pin 1 connects to the MBC, the rest to the ROM. I'll give the cap idea a go and see what happens. Just to clarify, it doesn't only affect the intro, it also affects pokemon battle sprites (though move animations are fine) and the pokemon on the title screen.
If you do a quick Google, you'll find that there are glitchy-sprite issues with this mod on some versions of the cartridge. Something called the "MBC". There are different versions of it, and the mod will work properly with some and not others.
I know there can be issues with the mod, just wondering if anyone had any ideas how to solve them. An idea I had earlier was to keep the SRAM in place, lift the pins used to hold the save, and wire these up to the FRAM. Does this sound feasible?
I have the corrupted sprites issue on my Pokemon Red with the FRAM mod also. I have triple checked my work and still, the sprites are messed up. I did the same to Pokemon Yellow and it works flawlessly with correct sprites.
FRAM is non-volatile, so it does not require a save battery. It isn't really needed given that batteries last 10+ years (the battery in mine was still good). I've found an nvSRAM IC (Cypress STK15C88-NF25I) that I'm going to try in place of the FRAM, hopefully this will work ok. I also found a cheaper FRAM IC (Fujitsu MB85R256FPF-G-BNDE1) that I'll also try, its a 3.3v part but I have read people have had success with a 5v Ramtron part by lifting VCC. Something else I've found (possibly related to my idea of using both the SRAM and FRAM) is a link on devrs.com entitled SRAM Fix with the description "This is a very easy SRAM fix involving a new FRAM replacement and 2 wires. This gets rid of the batteries and memory loss." Unfortunately the link is dead, if anyone knows more about this I would be interested to hear about it.
