How do games address save files when loading a game save?

[Pupil]

I have an issue which is vexed me for some time. Files written at certain adresses or large files cannot be read from either system memory or cartridge memory. If i copy the file once or twice on the cartridge so that it is allocated at another address I can then read the file that was once unreadable. At first I thought the SRAM was the issue so I replaced it with an FRAM mod. The behaviour is the same though and it was only after I bought a cartridge memory card that I realized that the same thing was happening on both.

It seems that an address line somewhere is having an issue but I don't really know where to focus my attention on. I figure I'd see if anyone knows how these save files are addressed when loading files in-game. Is there a specific IC that's responsible for relaying data from either memory option to the game?

Thanks

 

[hitomi2500]

Cartridge is on A-Bus interface, while backup is on C-Bus (or CPU-Bus as the block diagram implies). The A-bus is accesed thru SCU and C-bus, but the C-bus is accesed directly, without any SCU usage. So the SCU is probably not the culprit.

One probability of what happens is that someone on C-bus incorrectly decodes the address and clashes with both backup ram and external backup, but not clashing with anything else. Not very probable, but not impossible.

The easiest way to debug this is to try poking backup memory in hex viewer (there is one in PS Kai) and check if writes and reads into backup range are successful or not. Same goes for external backup. Once you'll know the exact "broken" ranges, it will be easier to deduce what's wrong.