The CM-8/CoCo RGB connector is a proprietary 10-pin single-inline header (berg-style) located on the underside of the Tandy Color Computer 3 (CoCo 3), introduced in 1986. It carries analogue RGB video, separate horizontal and vertical sync (TTL positive), and an audio signal to the Tandy CM-8 Analog Monitor (catalogue number 26-3215). No industry standard governs the connector; Tandy defined the pinout independently for exclusive use with the CM-8, whose cable is permanently attached to the monitor. Pin 6 is physically absent as a keying feature to ensure correct orientation.
| Pin | Name | Description |
|---|---|---|
| 1 | GND | Ground |
| 2 | GND | Ground |
| 3 | R | Red |
| 4 | G | Green |
| 5 | B | Blue |
| 6 | KEY | No Pin |
| 7 | AUDIO | Audio |
| 8 | HSYNC | Horizontal Sync |
| 9 | VSYNC | Vertical Sync |
| 10 | n/c | No Connection |
Signals
- GND — two ground return pins (pins 1 and 2) for signal reference.
- R, G, B — analogue RGB video signals; levels 0.8 (+0.1) to 2.0 (+0.2) Vdc into a 75-ohm load (NTSC). A PAL variant operates at 0.6–1.8 Vdc.
- KEY — pin 6 is physically absent (no pin) to key the connector and prevent reverse insertion.
- AUDIO — mono audio output; less than 1.0 V peak-to-peak into a 600-ohm load.
- HSYNC — TTL-positive horizontal sync; nominal frequency 15.701 kHz ±500 Hz.
- VSYNC — TTL-positive vertical sync; nominal frequency 59.7 Hz ±1.0 Hz.
- n/c — pin 10 carries no signal and is present only for mechanical symmetry.
Notes
The connector is a 10-pin single-inline (SIP/berg) header, not a DIN or D-sub. Pin 6 is omitted as a mechanical key. The CM-8 monitor cable is permanently wired into the back of the monitor and plugs directly into the RGB OUT header on the CoCo 3; the cable is not field-detachable at the monitor end. RGB signals are analogue; sync signals are TTL positive logic. The CM-8 is designed exclusively for the Color Computer 3 RGB interface and is not compatible with other computers without an adapter.