The IBM PC game port uses a 15-pin DA-15 D-shell connector that carries signals for two joysticks simultaneously. Joystick A uses the X/Y analogue position inputs on pins 3 and 6, with buttons on pins 2 and 7; Joystick B uses pins 11 and 13 for position and pins 10 and 14 for buttons. This Y-splitter cable routes all fifteen pins from the single game port socket to two separate DA-15 female sockets so that both joysticks can be connected at once. The PC game port interface was defined in the IBM PC Technical Reference (April 1983) and accepts 0–100 kΩ potentiometers per axis, reading position by timing an RC circuit (T = 24.2 µs + 0.011·R µs), with button inputs active-low via 1 kΩ pull-ups to +5 V.
15 PIN D-SUB MALE to the Computer
15 PIN D-SUB FEMALE to the 1st Joystick
15 PIN D-SUB FEMALE to the 2nd Joystick
| PC | Joy 1 | Joy 2 | |
|---|---|---|---|
| +5 VDC | 1 | 1 | - |
| Button 1 | 2 | 2 | |
| Joystick 1 - X | 3 | 3 | |
| Ground | 4 | 4 | 4 |
| Ground | 5 | 5 | 5 |
| Joystick 1 - Y | 6 | 6 | |
| Button 2 | 7 | 7 | |
| +5 VDC | 8 | 8 | |
| +5 VDC | 9 | 9 | 1 |
| Button 4 | 10 | 10 | 2 |
| Joystick 2 - X | 11 | 11 | 3 |
| Ground | 12 | 12 | |
| Joystick 2 - Y | 13 | 13 | 6 |
| Button 3 | 14 | 14 | 7 |
| +5 VDC | 15 | 15 | 8 |
Notes
- The DA-15 game port I/O address range is 200–20F hex; all four one-shot timers are fired simultaneously by a single OUT to address hex 201, and position is read back by an IN from the same address.
- IBM’s Technical Reference labels the button signals Button 4–7 (reflecting data-register bits 4–7); user-facing documentation commonly renumbers them Button 1–4. The physical pin assignments are identical.
- Pin 12 is carried through as a ground in the standard DA-15 game port specification, but is repurposed for MIDI signals on many sound cards equipped with a game port; pins 15 (also +5 V in the IBM spec) is similarly used for MIDI on those cards. When constructing the splitter, use pins 4 and 5 as the reliable ground references rather than pin 12.
- The second joystick socket carries only the Joystick B signals (pins 9–15 of the DA-15); pins corresponding to Joystick A position and button inputs are not connected to that socket.