Sega Genesis controlers use the same pinout as Atari joysticks (they were sued for this as Atari had a patent on the layout). The B, C, and start buttons are just attached to unused pins. If you use any of the Atari joystick - pc gameport plans, it will get the d-pad and A button working. Then you should be able to attach the other pins to get the rest of the buttons working.