FWIW, my controller has a Matsushita (Panasonic) MN4021B. Who knows what age, but probably contemporary (80s).
That's interesting. The controllers must have gone through several revisions that involved IC supplier changes. Possibly because NEC was expensive and high-quality, so they sacrificed quality for price and went with a cheaper IC.
A bit amusing they didn't even put in a supply bypass capacitor, let alone anything else ESD or EMC related, but the choice of CD4000 (a fairly underpowered family, especially at 5V supply) is pretty deliberate, I would say.
You aren't wrong there. My controller has two unused, naked pads between VCC and GND where an (electrolytic?) capacitor would be placed. I think that they DID add in a capacitor during the first few revisions, but removed it in later revisions to conserve budget. If I added my own capacitor, I wonder if that would make any difference...
EXPERIMENT TIME!![/b]
You certainly wouldn't want to substitute a 74HCxxx, but that wouldn't be pin-compatible anyway (hrm, would it?).
I mean, if I decided for whatever reason to use one of those series chips in my own controller design, I wouldn't mind rerouting a few traces. But I think that for the sake of keeping it original, I'll just go with a similar part with identical pin layout. I tested the controller experimental prototype board I built at school using an OEM IC from one of my working NES controllers, then with the SIL4021BE I had laying around, and it worked exactly the same. (I replaced where the IC would go with an IC socket so I can swap out ICs and test various chips' functionalities, thus why I called it an "experimental" prototype board. I'm using it to find what chips will work in my own controller designs. It's actually a pretty nifty board, I'll send a pic of it when I can if you are interested
).
Also, I just opened up my Genesis controller, it actually uses a 74HC157N. So the irony is incredible here
Though, that is curious... It looks to be a quad 2-input multiplexer. I wonder why they would use a multiplexer in this controller... Unless... They're using it to switch the data between a corresponding wire when a certain button is pressed. Why couldn't they just use transistors or just have done like the Atari and straight up used the buttons to short the voltage to the output?