SFG-Cartridge slot adapter
  It's really very simple, but a wrong connection WILL blow the module (don't say I didn't warn you)!
When you look at the cartridge connector pinout from a normal MSX you'll see that they're completely identical exept for the first 10 pins. All you have to do is skip these and have your adapter. You can expand any MSX/2/2+/Turbo R with the SFG-0x and use all your favourite tools with it. (A lot better than the original CX5M without a disc-drive etc.)
  You can't really call it a circuit but ok. The picture below shows the basic layout of the adapter: