9 PIN D-SUB MALE at the computer
9 PIN D-SUB FEMALE at the joystick cable
The MSX joystick port is a 9-pin AMP-compatible DE-9 connector defined in the MSX Technical Data Book (1984, ASCII Corporation/Sony Corporation) as part of the MSX hardware standard. Each MSX computer provides two such ports, carrying TTL-level active-low digital inputs for four directions and two trigger buttons, together with +5 V DC power and a dedicated output line for device-side hardware control. The interface is broadly pin-compatible with the de-facto Atari joystick standard for direction and primary trigger, but differs from Atari and Commodore implementations in placing +5 V on pin 5 rather than an analogue POT line, and GND on pin 9 rather than an analogue return.
| Pin | Name | Dir | Description |
|---|---|---|---|
| 1 | /FORWARD | IN | Forward |
| 2 | /BACK | IN | Backward |
| 3 | /LEFT | IN | Left |
| 4 | /RIGHT | IN | Right |
| 5 | +5V | OUT | +5 VDC (50mA max) |
| 6 | /TRG1 | IN/OUT | Trigger A / Output 1 |
| 7 | /TRG2 | IN/OUT | Trigger B / Output 2 |
| 8 | OUTPUT | OUT | Output 3 |
| 9 | GND | —— | Signal Ground |
Notes
- Direction is computer relative to joystick.
- All direction and trigger inputs are active-low TTL: the pin reads logic 1 (high) when inactive and logic 0 (low) when the switch is closed to GND.
- Pin 5 carries +5 V at up to 50 mA per port. This differs from Atari and Commodore DE-9 joystick ports, where pin 5 is an analogue paddle (POT) line. Connecting an Atari paddle controller to an MSX port will place +5 V on the paddle circuitry.
- Warning: Pin 5 is +5V on MSX and Mouse Button 2 on Amiga. Since Amiga mousebutton is active low, connecting an Amiga mouse to a MSX and pressing mousebutton 2 will shortcut the supply voltage.
- The MSX standard defines two joystick types: Type A has one trigger button (TRG1 only); Type B has two independent trigger buttons (TRG1 and TRG2). Manufacturers are required to label the type on the joystick.
- Pin 8 (OUTPUT) is a host-driven output that can control device-side hardware, such as a select line for multiplexed inputs.
- Signals are routed via the PSG (AY-3-8912 or equivalent) I/O port; port 1 uses TRGA1/TRGB1 and port 2 uses TRGA2/TRGB2.
Signals
- /FORWARD — Active-low input; direction switch closed to GND for forward/up movement.
- /BACK — Active-low input; direction switch closed to GND for backward/down movement.
- /LEFT — Active-low input; direction switch closed to GND for left movement.
- /RIGHT — Active-low input; direction switch closed to GND for right movement.
- +5V — +5 V DC supply from the host computer; maximum 50 mA per port.
- /TRG1 (TRGA) — Bidirectional (IN/OUT); primary trigger input (active-low) or output signal depending on device type. Used as the sole trigger on Type A joysticks.
- /TRG2 (TRGB) — Output; secondary trigger signal used on Type B joysticks for a second independent fire button.
- OUTPUT — Host-driven output line; used to control device-side hardware or act as a multiplexer select.
- GND — Signal ground reference for all digital logic on the port.
References
- MSX Technical Data Book — ASCII Corporation / Sony Corporation, 1984