Legacy serial communication protocol still widely used for AV device control.
Key points:
- 9-pin D-sub connector (DB9) or 3.5mm TRS (on smaller devices)
- Point-to-point only — one controller to one device
- Typical baud rate: 9600 or 115200
- Max reliable distance: ~15m (50ft)
- Used for: display control, projector control, DSP commands
- Being replaced by IP control but still found on most commercial displays
- Always check null modem vs. straight-through wiring requirements