[xg15]

This is really cool!

One thing I'm wondering is how the SNES implemented its Multitap support[1] with such a simple "wire protocol". Could it be that the two missing wires and/or 4 unused slots in the polling cycle are used for some kind of adressing scheme when a multitap is plugged in?

https://nintendo.fandom.com/wiki/Super_Multitap

[ooterness]

RGMX has a video series on a lot of the low-level SNES functions. If you've ever wanted to know how Mode-7 works, it's great.

The video below goes over the controllers, Super Scope, mouse, etc. A brief discussion of the multi-tap starts around 16:00. You are correct that it leverages the spare pins.

https://www.youtube.com/watch?v=2Dw7NFm1ZfY

[dougg3]

The schematics for the multitap are out there in the SNES developer manual [1]. I actually made one on a breadboard for fun [2] and eventually turned it into a PCB. It's a pretty simple circuit with an analog mux and some tri-state buffers.

[1] https://archive.org/details/SNESDevManual/book2/page/n385/mo...

[2] https://www.downtowndougbrown.com/2013/04/homebrew-snes-4-pl...

[wharvle]

The NES also had “multitaps”. One model was wired (the “Four Score”), the other was wireless (battery powered; the “Satellite”) with an IR receiver unit that plugged into both controller ports.

The IR wireless one was, in my experience (it was the only one I had) far less janky and failure-prone than one might suppose. Actually worked quite well.