For development purposes, you can construct a "+2" adapter from two 25-pin male d-sub connectors. One connector attaches to the parallel port, while the other accepts the two 9-pin female joystick plugs. Simply build the "number 3" joystick connector into the leftmost 9 pins, and the "number 4" connector into the rightmost 9 pins. The pin-outs for this setup are in the "Non-Production +2 Interface" chart below. Parallel function Parallel port JOY3 JOY4 Joystick function (25 pin male) (9pm) (9pm) --------------------------------------------------------------------- Data bit 0 2 1 JOY3 UP Data bit 1 3 2 JOY3 DOWN Data bit 2 4 3 JOY3 LEFT Data bit 3 5 4 JOY3 RIGHT Data bit 4 6 9 JOY4 UP Data bit 5 7 10 JOY4 DOWN Data bit 6 8 11 JOY4 LEFT Data bit 7 9 12 JOY4 RIGHT Busy 11 22 JOY4 FIRE Select (Online) 13 14 JOY3 FIRE ground 18 24 JOY4 GROUND ground 19 16 JOY3 GROUND The Non-Productive "+2" Interface This arrangement is attractive to developers primarily because it has few parts and it's easy to construct. It is appropriate only for developer use and testing. Do not consider it for any sort of user distribution, because the connectors for certain brands of joysticks are too big to fit side by side into a 25-pin connector. Users will become quite irate upon finding that they can't use their "wiz-stik 5000" with their 4 player game adapter. With this in mind, adapters intended for use by end users should be built into some sort of casework. The box should include two suitably spaced joystick connectors, and a cable that allows the user to easily attach the adapter to the parallel port. Be sure that the cable is long enough to allow users to place the adapter where they can get to it easily. Alternatively, the device could simply be a pair of long cables in a "Y" shape, with a parallel connector at the base of the "Y", and joystick connector on the other ends. Such an adapter would probably be the cheapest way to go. Developers must caution end users to turn their computer's power off before plugging in a "+2" adapter. This will prevent users from accidentally destroying the 8520 chips which control the parallel port. To further prevent 8520 damage, developers should choose 25-pin connectors without a metal case or shield. While plugging the device in, it's rather easy to accidentally brush (and short) the metal shields of certain connectors against the pins of the parallel port. No matter what the decision regarding implementation, remember that game players can be quite rough. All cables should be suitably long, and all connectors should utilize a proper strain relief system.
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