4-player adapter progress

The past few weeks have been a fun balance between working on my NES game (still slogging through getting my scrolling engine right!) and the Atari 4-player adapter.

I'm too tired tonight to go into too much detail, but the adapter is moving along great!  The way it works is this:

• The Atari allows setting 4 of each joystick port's pins to either input or output mode. Normally you want them on input mode, because they are the pins that read the 4 directions of the joystick. But they planned well for future-proofing the console, and set it up so that you can control them as outputs as well.
• So to allow 4 controllers, I use a really simple multiplexing scheme -- the first joystick port is used in normal input mode for reading all 4 controllers, and the second joystick port is used in output mode to select which controller to read at any given time.

So with just a few multiplexer ICs and some pull-up resistors, we have a working adapter!

Well, mostly-working. So far, the left, right, and up directions work. I still need to finish wiring up the down and fire buttons!

Right now my desk is just a giant mess of wires waiting to be soldered.

I was a bit nervous at first that the Atari wouldn't let me write to the output pins fast enough to switch to each joystick during a frame, or that the input might be latched once in a frame and not updated as I switched it.  But neither of those were the case, and so far, it seems to be working perfectly!

Next step: finish wiring the last pins, and put this thing into some sort of sturdy box. Then hopefully get it all cleaned up to possibly show off at PRGE!