gauauu

That's genius. I'll give it a try.

Thanks @Danjovic! I've got a prototype PCB off at the fab that I'm waiting for. The circuit should be fine (I've done another version of the board in the past), but getting the physical dimensions right for a case is the tricky part. I might bug you for advice if I have trouble getting the physical design right.

I did some experiments early on with changing the timing of the switching to see if I could improve things by doing that. I don't remember the exact behavior, but I seem to recall that it didn't entirely fix it, but did help a bit.

Yeah, the famicom 4-player adapter works differently, with a different protocol, than the American NES adapter. Also, I'm not an expert on the NES but I've made a handful of NES games so I might be able to help.

I'm late to the party, but just now saw the mention of me above. I've used dasm for one project (Anguna) and ca65 for another (Robo-Ninja Climb). My suggestion is sticking with dasm if you're really focusing on atari (it's easy, it works well, and the majority of folks here use it so it's easier to get help when you're stuck), but ca65 if you plan to work on other 6502 systems. It's got a higher learning curve for setting up your rom output, but is really nice and configurable once you learn it.

Yes, I'm sorry, I mean the previous iterations. (my point was that I doubt it's related to the TV connector specifically)

I haven't measured the ohms off the connector, but I've tested on a Jr, a Vader, and a 4-switch woody, and get the same issues on each with the 4-player adapter (and with a crystal clear signal without the adapter)

Yeah, that sounds like an easy to way to test if the driven-high is really causing the interference. I'll dig around and see if I can try testing this way.

Thanks all. Yeah, they're more reliable on player 2 than player 1. What y'all are saying makes a lot of sense, and seems to match up with what I'm experiencing. I haven't -- I didn't realize that that existed (I'm a newbie to this sort of thing, thinking this would be a fun project to learn on -- which I'm starting to regret). I'll definitely take a look at that.

Thanks for chiming in. I'll measure it and see when I get a chance.

This is the exact issue I had with most iterations of my design. I tried adding various caps and didn't have any luck.

Yeah, I had used conceptually 2 separate 1-to-2 splitters, but kept a single select line going through a single inverter just to simplify the circuit.

Is there any similar type of thing but for diodes? I tried doing some searching but didn't find anything, but it didn't help that I didn't know what search terms to look for :-)

Another question for you smart people. The last method I tried (switching the grounds and using diodes for isolation) works great for actual Atari joysticks, but during testing, we ran into trouble with Genesis pads. Apparently the internal circuitry in these causes them to actually hold the outputs high when a button isn't pressed, even if the ground pin isn't low. Which means that if you plug in a Genesis pad into one of the two ports, the other controller never registers. So the current design works wonderfully for original sticks, but doesn't let you use Genesis pads at all. The only solutions I can think of for this are: 1. Add a ton of diodes, one for each output pin for each controller, so that each controller can only drive a pin low, but can't hold it high. (This would require adding 20-24 diodes to the design, ugh) 2. Completely redesign the circuit again Before I go down either of those routes, I wondered if any of you might have suggestions of simple solutions that I may have missed? You can see the schematic I was using at https://www.dropbox.com/s/42wj6c96hu93fup/319x2.zip?dl=0

I've never owned one, so unless one suddenly appears for cheap at a garage sale, an intellivision version won't be coming soon. The most likely next port will be original Gameboy or Apple II