Using Atari 7800 gamepads on C64?

[Raticon]

I have recently bought a gamepad for the 7800 with the intent of using it on my 2600 and other old DB9-plug systems.

I want to try it on my C64, but i know from experience that plugging in certain controllers can damage the C64 by zapping chips inside it. I had half the keyboard on my C64 die on me after i plugged in a Sega Mega Drive controller. Managed to easily fix it though and i'm very wary of plugging in anything except a normal Atari joystick and a Competition Pro.

The C64 has no problems with the standard 2600 joystick, and i use that all the time on it, but will it take the 7800 gamepad without zapping the chips?

Consulting this list i can not see any major differences in wiring between the 7800 and C64 except pin 5 being Button right / Button 3, pin 6 being Button common / Button 1 and pin 9 being Button left / Button 2, respectively, with the Mega Drive/Genesis wiring being very different, hence the zap.

Can any of you tech gurus tell me if plugging the 7800 gamepad into the C64 will make it ride the lightning or work normally like the standard Atari Joystick?

[carlsson]

VCC and GND at the right locations, that is a good start. However it seems the buttons connect to the POT X and POT Y which are analog pins used for paddles so even if it wouldn't break anything, I doubt it would work very well? Isn't Button Common a kind of GND too or the combined signal of both buttons, so it would read as fire anyhow?

[Raticon]

Yes. My little knowledge tells me that VCC differences from pin 5, 7and 9 is what kills the CIA or whichever it was, with signals going directly into the chip from one pin or the other. I might be wrong though, i usually am.

With VCC and GND being in the same places and nothing else of major concern i would at least assume it wont kill the C64 to try. Worst case svenario is that the D-pad will work but no buttons.

The new Competition Pro i got has that little switch that lets you switch between having all 4 buttons act as the same button (should be common, no?), or switch over to "activate" pin 9 and button 2/POT X on the upper 2 buttons i believe. I always only let it sit in 1-button mode though.

Edited: Pin 9 instead of 5 for POT X

Edited November 18, 2017 by Raticon

[White Flame]

The standard C64 joysticks ground the digital lines when active, and leaves them floating (the C64 has +5V pullup resistors internally) when non-active. The paddle lines are driven via +5V -> resistance -> POTX/Y, and are handled separately by the SID chip.

 

As far as I understand it, the Genesis controller will ground digital lines when active, but also actively connects to +5V when non-active instead of being left floating. That 5V assertion is the problem, because the CIA can ground those lines when driving the keyboard scan, which forms a short-circuit.

 

So even if the pinout is exactly the same, you need to ensure that its behavior toggles the pins between disconnected & ground, and not between 5V and ground.

Edited November 20, 2017 by White Flame

[Gohmca]

I was just wondering if I could use the seagul 78 adaptor from Atariage on my Commodore 64 with a 3button Sega genesis controller without damaging the c64 because sense that adaptor essentially rewires the Sega genesis controller to act just like a two button Atari 7800 gamepad/joystick. Just wondering 

 

thanks:)