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Digital Apple IIe Joystick

Great Hierophant

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Most games that are "Apple IIe aware" use the cursor keys for movement. Interestingly, the Apple IIe has a numeric keypad connector which provides the X/Y output/input lines for a keypad. This allows you to use any passive keyboard matrix as a keypad if you connect the pins properly.

The numeric keypad connector does not bring out all X and Y lines, it brings out X4-X7 and Y0-Y5. What any combination of X and Y are is defined by the keyboard decoder ROM, a simple 2KiB chip with EPROM compatible pinouts. The AY-3600 Keyboard Decoder reads this ROM to determine which ASCII to send when a key is pressed.

Fortunately, with Keyboard ROM 341-0123-C or D, the cursor keys are mapped to the matrix that the numeric keypad uses. Y1 + X4 is down, Y1 + X5 is Up, Y1 + X6 is Left and Y1 + X7 is Right. Map those appropriately to a digital joystick (Y1 is the common) and there you have a digital joystick. However, the numeric keypads for the IIe had keys for Esc and Space, not Up and Down, and the Keyboard ROMs 341-0123-A and 341-0123-B would give keyboard inputs corresponding to those keys. 

But what about buttons? Well, PB0 and PB1 are typically used as buttons and connections for those are available on the Game I/O connector. They are also assigned to Open Apple and Closed Apple on the IIe keyboard.  One thing to be aware of is that the button inputs connect to +5v, not ground, but they do not need pulldown resistors as in an Apple II or II+.

So it is quite possible to make an Apple IIe Joystick that has digital inputs. Of course as contemplated this is the only Apple II system in which this idea will work.

I have attached a file showing what modifications would need to be made to something common like an NES gamepad which would be needed to get a gamepad working. The PCB must be stripped of its chip and any passives without destroying the holes in the process. I would suggest using a DE-9 cable and soldering the wires on one end to the PCB as shown. The cable can plug into a mated DE-9 connector mounted on the IIe's rear and from there the other ends would connect to their appropriate pins.


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I wonder if you could make a board that plugs into the keyboard encoder socket (assuming it's socketed; I don't remember) and then the original keyboard encoder plugs into that, but the board also breaks out the parts of the matrix needed to get at the arrow keys and whatever else, which you could then route to some variety of DB connector in the back.


Even if it's not socketed, maybe you could use those grabber clips like are used on oscilloscope leads to hook into the matrix without needing to desolder anything.


I mean, for boxen that don't have the right keyboard encoder IC.

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