The AT&T 53D410 uses a 25-pin D-sub (DB-25) connector for monochrome video output. It appears to be a proprietary AT&T graphics terminal or display interface, with only four signal functions positively identified: vertical sync, horizontal sync, composite video, and ground. No formal ANSI or EIA standard governs this connector’s pin assignments; the majority of pins remain undocumented. The connector carries a single composite monochrome VIDEO signal rather than the RGB analogue signals found on contemporaneous colour workstation interfaces.
25 PIN D-SUB Connector at the computer.
| Pin | Name | Description |
|---|---|---|
| 1 | ? | ? |
| 2 | VSYNC | Vertical Sync |
| 3 | HSYNC | Horizontal Sync |
| 4 | ? | ? |
| 5 | VIDEO | Video |
| 6 | ? | ? |
| 7 | ? | ? |
| 8 | ? | ? |
| 9 | ? | ? |
| 10 | ? | ? |
| 11 | ? | ? |
| 12 | ? | ? |
| 13 | GND | Ground |
| 14 | GND | Ground |
| 15 | GND | Ground |
| 16 | ? | ? |
| 17 | ? | ? |
| 18 | ? | ? |
| 19 | ? | ? |
| 20 | ? | ? |
| 21 | ? | ? |
| 22 | ? | ? |
| 23 | ? | ? |
| 24 | ? | ? |
| 25 | ? | ? |
Signals
- VSYNC — Vertical synchronisation pulse; establishes the frame rate for the attached display.
- HSYNC — Horizontal synchronisation pulse; defines the line scan rate.
- VIDEO — Composite monochrome video signal carrying luminance/picture information.
- GND — Signal ground reference (pins 13, 14, and 15 are all ground returns).
- ? (remaining pins) — Pins 1, 4, 6–12, and 16–25: purpose not publicly documented.
Notes
The DB-25 shell is physically identical to the RS-232 serial connector of the same era, but the pinout is entirely proprietary and unrelated to RS-232. The large number of unassigned pins suggests that power rails, control signals, or additional video channels may be present.
References
- AT&T UNIX PC Reference Manual 1986 (Document 999-300-1891S) — AT&T Information Systems / Bitsavers collection.