Modify genesis controllers for dumb operation (JAMMA)

In trying to build a small portable Jamma test rig around a little CRT the subject of controls came up.  The obvious answer to me was the genesis controller as it contains the joystick (d-pad) three buttons and start, which is the primary Jamma standard per player.  The 6 button controller could allow for the extended Jamma button set but for now I just needed to get Tetris going.

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The genesis controllers have 8 buttons, which would allow for a simple pinout of 8 buttons and a ground, but they didn’t do that.  They seemed to adopt the standard that was the pinout for the Atari2600.  The problem with that as a standard meant one pin was for 5v because the spinners were really potentiometers and they used all three pins of the pot instead of just having a variable resistance between two pins (I don’t blame them, I would have done the same).  The 5v line meant that in order for these controllers to not cause the 2600 problems when inserted that they couldn’t have a button there (pressing it would connect 5v to ground and you would have a bad day).  That leaves one too few lines for the classic genesis controller.

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The solution was to put a logic chip in the controller to multiplex the buttons.  That meant using the existing 5v line to power the chip, but also using another line to take in the select signal for the multiplexer.  This means that the genesis controller presents the states of Up, Down, Left, Right, B, and C or Up, Down, A, and Start.  Don’t ask me why it doesn’t always show left and right, or why A isn’t in the default layout (I just don’t know, ok?).  The 6 button controller is even more complex having Z, Y, and X replace Up, Down, and Left every third cycle.  Truthfully you can do a sort of detection using left and right to determine which cycle you are on but it’s hacky and doesn’t always work.

I decided to dumb down these controllers, breaking compatibility with the genesis, but making them good general purpose controllers for future projects.  That involved re-wiring the DE-9 ports to get rid of the crappy molded connectors and wiring around the multiplexer chips to make them 8 buttons and a common ground.  I ended up having two different style controller PCBs so I had to do the reverse engineering twice.  In the end I also had to do a lot of cleaning to the carbon pads and the PCB where they make contact but now the controllers seem to work well. All the pictures are located here.

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One Response to “Modify genesis controllers for dumb operation (JAMMA)”

  1. Portable arcade test rig | Evan's Techie-Blog Says:

    […] dumb genesis controllers can be seen in their first […]

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