The Sega Master System (1985/1986) and Mega Drive/Genesis (1988/1989) both use a DE-9 female socket — a D-Sub 9-pin connector that Sega’s own parts lists call “D-SUB CONNECTOR 9P” (part number 209-5017-01) — on the console, with a DE-9 male plug on the controller cable. The pinout derives from the Atari 2600 joystick standard for pins 1–4 and GND, extended by Sega with +5 V on pin 5, a second button on pin 9, and a TH line on pin 7 used for peripheral detection and Light Phaser synchronisation. All signal lines are TTL-compatible and active-low: a pressed button or asserted direction connects its pin to ground, whilst unpressed lines are pulled high internally. On the Mega Drive/Genesis, the same DE-9 shell serves three identical I/O ports (CTRL1, CTRL2, EXP), and pin 7 (TH/Sel) is driven by the console to multiplex the button states reported by 3-button and 6-button controllers.
9 pin D-SUB female connector
9 pin D-SUB male connector
| Pin | Signal | Description |
|---|---|---|
| 1 | Up | |
| 2 | Down | |
| 3 | Left | |
| 4 | Right | |
| 5 | Power | |
| 6 | Button 1 | |
| 7 | N/C | |
| 8 | GND | |
| 9 | Button 2 |
Signals
- Up — directional input, active-low; logic 0 when up is pressed.
- Down — directional input, active-low; logic 0 when down is pressed.
- Left — directional input, active-low; logic 0 when left is pressed.
- Right — directional input, active-low; logic 0 when right is pressed.
- Power — +5 V supply (Vcc) from the console to the controller; confirmed by the SMS service manual test step “Is Vcc 5V power present?”.
- Button 1 — designated TL (Trigger Left) in Sega hardware documentation; active-low button input, also serves as the Light Phaser photodiode input line on that accessory.
- N/C — designated TH in Sega hardware documentation; on the standard SMS control pad this line carries no active button signal, but the console drives it as an output for Light Phaser synchronisation. On the Mega Drive/Genesis this pin becomes the Sel (select) line, toggled by the console to multiplex 3-button and 6-button controller states.
- GND — signal and power ground reference.
- Button 2 — designated TR (Trigger Right) in Sega hardware documentation; active-low button input.
Notes
- The connector shell is a DE-9 (D-Sub 9-pin), often incorrectly referred to as DB-9. The console carries the female socket; the controller plug is male.
- On the Sega Master System, controller signals pass through a dedicated gate array IC (315-5216 in SMS1; UPD65005C-114 in SMS II) between the DE-9 ports and the Z80 CPU. Series 330-ohm resistors (R114–R117) on each signal line provide EMI protection.
- On the Mega Drive/Genesis, the 3-button controller uses a 74HC157 quad 2:1 multiplexer. With TH (Sel) low, pins 1–2 report Up/Down and pins 6/9 report A/Start; with TH high, pins 1–4 report Up/Down/Left/Right and pins 6/9 report B/C.
- The 6-button Mega Drive controller requires TH to be toggled at least twice within 1.1 ms; reliable data is available for 1.6 ms after the first rising edge, with a 1.8 ms lockout before the sequence can restart.
- The Mega Drive I/O port also supports RS-232C serial communication at 300, 1200, 2400, or 4800 bps through the same DE-9 pins, selectable via the S-CTRL register.
- The controller cable is a 9-conductor assembly; Sega part number 600-5306 (“Assy Cable 9P L=2m 3020”) for the SMS control pad confirms all nine pins are wired.
- Regional hardware variants (PAL, NTSC, RGB) all use the same D-SUB 9P connector family (Sega part 209-5017-01).