Thanks to the great documentation about the SNES all over the internet, it wasn't that hard to find out everything necessary from pin-outs, address and data lines, RAM organisation etc.

Basically, there are 2 address busses (24-bit and 8-bit) and an 8-bit data bus, whereof until now only the 24-bit address bus and the 8-bit data bus is of interest. Unfortunately, the 24-bit adress bus is not accessible from the expansion port, but both busses are accessible through the cartridge pins.