Connecting a DB9 multisystem controller.

[spruce_m00se]

https://github.com/retropie/retropie-setup/wiki/GPIO-Modules

I am looking into (once I can sort using multiple joypads without them conflicting) adding some db9 multi system controllers directly to the Pi3.
I would like to be able to use a Competition pro joystick or two for old emulation, and some old master system and megadrive pads, I may consider converting some old nes and snes to db9 later.

I have found the link at the start of the post. but the problem is that it looks like the post suggests that each controller only uses one "data" pin along with power and ground. However all of these old joypads have common grounds and then one pin per button, so I dont understand what this tutorial is on about and I cant find anything else on the topic.

Does anyone have any pointers?
The other option is to buy a lot of china snes ripoff controllers and transplant the guts, but id rather not have to massacre all of my old controllers as I want to use them on original hardware also without having to invest in a whole new set of original controllers.

thanks in advance

[edmaul69]

@spruce_m00se for using tons of db9 controllers i recommend either a vision-daptor or ultimate pc interface (upci is 2player version. Has some other controllers the vision-adapter doesnt have. Both made by the same person.) The master system also has the two extra pins as functiong buttons. They match the same button numbers as start and mode button on the genesis mode. He added these so i could use my db9 modified nes and turbografx/pc engine controllers. He makes some other controller adapters too. His adapters truly are the best i have ever used.