I'm using 20F tower model and tired of battery runouts. I did FRAM mod for Sega Saturn, Turbo DUO and NEOGEO CD before so I wondered if I can do same thing for it. Tried to find SRAM on the mainboard of 20F, and I found 2 SRAMs.
(https://i.imgur.com/k729By3.jpeg)
First one is 'MB81C78A-45' and it located on backside of the mainboard.
https://datasheet.octopart.com/MB81C78A-45P-SK-Fujitsu-datasheet-182339813.pdf
(https://i.imgur.com/oyYaXzz.jpeg)
Second one is 'MB8464A-15L' and it located on frontside of the mainboard.
https://www.alldatasheet.com/datasheet-pdf/view/1438743/FUJITSU/MB8464A.html
I compared the pin map with my FM1808, and found something:
* Those two SRAMs have CS1(pin 20), CS2(pin 26)
* FM1808 have only CE(pin 20). pin 26 is A13.
ChatGPT said to me that's a kind of 'Chip Select Structure', but I don't have any idea about it.
I just tried to replace all SRAMs with my FM1808. It seems working good at the beginning - My setting data was alive even after reconnect power code. But the data disappeared after test of several times, so I found it's not stable.
Is there any hero who have good idea or any thoughts about this?
Don't trust chatGPT for answers, it's not a smart machine. It just repeats words in the order it found them - sometimes - and you don't know if its source was correct or not.
According to the PDFs you linked (thanks for that!) The two CS lines, if I'm reading this right, allow one to make the chip sit in standby, awake but not active, or awake and active.
If your new chip only has one CS line, you might check the old chip circuit and see if both CS lines are actually being used. Perhaps one of them is permanently tied H or L, in which case you can basically ignore it for the new chip installation.
Don't trust NFG either, he is guessing.