9 PIN D-SUB MALE at the computer
9 PIN D-SUB FEMALE at the joystick cable
The TI-99/4A home computer (Texas Instruments, 1981) exposes a proprietary 9-pin D-SUB MALE joystick port on the console, accepting a mating 9-pin D-SUB FEMALE connector on the joystick cable. Two joysticks share the single physical port: the console selects joystick 1 by asserting pin 7 and joystick 2 by asserting pin 2, using a 74LS156 decoder driven by the column selector. Direction and fire switches connect to the same five lines used by the keyboard row scan, and are read through the TMS9901 Programmable Systems Interface via the CRU (Communications Register Unit) bus; the interface is active-low and electrically incompatible with standard Atari-style joysticks without adaptation. The authoritative specification is Texas Instruments document 1049717-2, published 1983.
| Pin | Dir | Name |
|---|---|---|
| 1 | - | N.C. |
| 2 | OUT | Test joystick 2 |
| 3 | IN | UP |
| 4 | IN | Fire button pressed |
| 5 | IN | Left |
| 6 | - | N.C. |
| 7 | OUT | Test joystick |
| 8 | IN | Down |
| 9 | IN | Right |
Notes
- Direction is Computer relative Device.
- The console connector is 9-pin D-SUB MALE; the joystick cable terminates in a 9-pin D-SUB FEMALE.
- Two joysticks share the single physical port. Pin 7 (OUT) selects joystick 1; pin 2 (OUT) selects joystick 2 via a 74LS156 decoder. Only one joystick is scanned at a time.
- All switch inputs are active-low: a pressed switch pulls the line to −5 V; the released (open) state reads as logic 1 through the TMS9901 CRU interface.
- The joystick direction and fire lines share the five keyboard row lines of the internal scan matrix, so joystick scanning and keyboard scanning use the same CRU read mechanism.
- This interface is electrically incompatible with standard Atari-style (DB-9) joysticks; the voltage levels and selection logic differ.
- The TI-99/4 (1979) predecessor used a different, incompatible joystick connector; the 9-pin D-SUB standard described here applies to the TI-99/4A (1981) and later.
Signals
- N.C. — not connected; pins 1 and 6 carry no signal
- Test joystick 2 — output from console; asserted to select joystick 2 for scanning
- Test joystick — output from console; asserted to select joystick 1 for scanning
- UP — input; active-low signal indicating the up direction switch is pressed
- Down — input; active-low signal indicating the down direction switch is pressed
- Left — input; active-low signal indicating the left direction switch is pressed
- Right — input; active-low signal indicating the right direction switch is pressed
- Fire button pressed — input; active-low signal indicating the fire button is pressed