MegaDrive pads can work with their 6+select+mode buttons all supported. This has been discussed on many other threads but to sum it up what is needed is:
- Use an adapter to swap pin 7 and 5, this allows the Amiga +5V (pin 7) to reach the controller (pin 5) and the Amiga third button line (pin 5) to reach the controller select line (pin 7).
- Modify the Amiga joystick code to program button 3 as an output (the Amiga DB9 ports are very flexible).
- Follow the standard MegaDrive controller protocol, driving its select line up and down as required and read the corresponding outputs on the regular directions+buttons-1-2 lines.
The protocols to follow for the 6 buttons pad is an extension of the 3 buttons protocol, just adding more steps to detect the controller type as well as fetching the extra buttons but it follows he same principle (cf
http://www.db-elec.com/home/technica...mepad-protocol).
Unless all the above is done only two buttons will be accessible because the Amiga +5V line will go to the select input of the controller forcing it to output only directions + 2 buttons.