Interactive Connector Diagram
Click or tap any pin in the diagram below to inspect its signal assignment, electrical specification, and wire colour standard.
Click any pin to view its signal assignment, electrical spec, and wire colour.
Used in Retro Machine Hubs
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Connector Specifications
Side Joystick Port
9-Pin D-Sub Male (DE-9M) — Multiplexed Joy 1 (Pin 2 Strobe) & Joy 2 (Pin 7 Strobe)
Blocking Diodes
Five 1N4148 / 1N914 diodes per joystick (cathodes toward Pin 2 or Pin 7) prevent ALPHA LOCK ghosting!
Rear Cassette Port
9-Pin D-Sub Female (DE-9F) — Supports Cassette 1 (CS1) and Cassette 2 (CS2)
Full Pin Assignment & Wiring Reference
| Pin | Signal Name | Direction | Electrical Spec / Role | Wire Colour / SCART / Adapter Target |
|---|---|---|---|---|
| Joy Pin 2 | /SELECT JOYSTICK 1 | Out | Active-Low Strobe for Joystick 1 (connects via diode cathodes to Joy 1 DB9 Pin 8) | Joy 1 DB9 Pin 8 (Common) |
| Joy Pin 3 | UP (Shared) | In | Shared UP input to TMS9901 (connects to Joy 1 & Joy 2 DB9 Pin 1 via diodes) | Joy 1 & 2 DB9 Pin 1 (Up) |
| Joy Pin 4 | FIRE (Shared) | In | Shared FIRE input to TMS9901 (connects to Joy 1 & Joy 2 DB9 Pin 6 via diodes) | Joy 1 & 2 DB9 Pin 6 (Fire) |
| Joy Pin 5 | LEFT (Shared) | In | Shared LEFT input to TMS9901 (connects to Joy 1 & Joy 2 DB9 Pin 3 via diodes) | Joy 1 & 2 DB9 Pin 3 (Left) |
| Joy Pin 7 | /SELECT JOYSTICK 2 | Out | Active-Low Strobe for Joystick 2 (connects via diode cathodes to Joy 2 DB9 Pin 8) | Joy 2 DB9 Pin 8 (Common) |
| Joy Pin 8 | DOWN (Shared) | In | Shared DOWN input to TMS9901 (connects to Joy 1 & Joy 2 DB9 Pin 2 via diodes) | Joy 1 & 2 DB9 Pin 2 (Down) |
| Joy Pin 9 | RIGHT (Shared) | In | Shared RIGHT input to TMS9901 (connects to Joy 1 & Joy 2 DB9 Pin 4 via diodes) | Joy 1 & 2 DB9 Pin 4 (Right) |
| Tape 1–9 | REAR CASSETTE DE-9 | I/O | Pins 1&2=Motor 1, Pin 3=Audio Out (Red), Pin 5=Shield, Pins 6&7=Motor 2, Pin 8=Audio In (White), Pin 9=Return (Black) | Red=MIC, White=EAR, Black=GND |
Why the 1N4148 Diodes Stop the TI-99/4A <ALPHA LOCK> Bug
On the left side of the TI-99/4A console sits a single 9-pin D-Sub male port that handles TWO joysticks simultaneously by pulsing Pin 2 low to read Joystick 1 and pulsing Pin 7 low to read Joystick 2 across five shared direction/fire lines (Pins 3, 4, 5, 8, 9). On the rear sits a 9-pin D-Sub female port for connecting one or two cassette recorders.
- Because the TI-99/4A shares the five joystick return lines (Pins 3, 4, 5, 8, 9) with the keyboard matrix — and specifically with the latching <ALPHA LOCK> key — pressing UP on an Atari joystick while <ALPHA LOCK> is pressed down will back-feed the keyboard scan unless blocking diodes (1N4148, cathode banded end pointing toward TI Pin 2 / Pin 7) are installed!