The first question is, why build something that already exists? I mean, if you want to build a Famicom copier which will have support for all mappers that exist, I understand, but if you want to build a SNES back up unit? I mean, the SWCDX2 does the job for 99.9% of all games, there are like 20 games that aren't playable on the SWCDX2, why not concentrate on making those work, instead of trying to make your own...
To make everything simple, just answer me this in your own words:
"Why do you want to build your own SNES back up unit?"
A simple question with a hopefully simple answer.
mikael