I don't know if this is a known bug, but if you leave $4016 set to 1, it's supposed to consistently return the status of the A button. I tested it out in Mesen and puNES and they work as expected, but FCEUX keeps flipping between 40/41 regardless of button presses
I was trying to get just the A button press using this technique but if it doesn't work on a common emulator then it's not that useful I suppose
FCEUX doesn't handle leaving $4016 high correctly
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