MC6847 VDG
Motorola video chip
The Motorola Video Display Generator used in the Dragon and TRS-80 Color Computer, offering text and graphics modes but limited colour flexibility compared to custom chips.
Overview
The MC6847 (Video Display Generator) was Motorola’s video chip used in the Dragon 32/64 and TRS-80 Color Computer. While capable of respectable resolutions, its fixed colour sets and limited flexibility made it less competitive against custom chips like the VIC-II.
Fast Facts
- Manufacturer: Motorola
- Used in: Dragon, CoCo, others
- Text: 32×16 characters
- Graphics: Up to 256×192
- Colours: 8 from fixed sets
Display Modes
| Mode | Resolution | Colours |
|---|---|---|
| Text | 32×16 | 2 (green/orange) |
| Semigraphics 4 | 64×32 | 8 |
| Semigraphics 6 | 64×48 | 8 |
| Graphics | 128×192 | 4 |
| Graphics | 256×192 | 2 |
Colour Limitations
| Issue | Impact |
|---|---|
| Fixed sets | Can’t choose arbitrary colours |
| Green/orange text | Distinctive but limiting |
| Two-colour hi-res | Four-colour required lower resolution |
vs Contemporary Chips
| Aspect | MC6847 | VIC-II | ULA |
|---|---|---|---|
| Sprites | None | 8 | None |
| Colours | 8 fixed | 16 | 15 |
| Flexibility | Low | High | Medium |
Legacy
The MC6847’s limitations constrained Dragon and CoCo games compared to C64 and Spectrum. However, skilled programmers achieved impressive results within its constraints, and its simplicity made it accessible for learning graphics programming.