Motorola 6847

The MC6847 is a video display generator (VDG) first introduced by Motorola and used in the TRS-80 Color Computer, Dragon 32/64, Laser 200, TRS-80 MC-10, NEC PC-6000 series, Acorn Atom, Philips VG5000 (used the Thomson EF9345 compatible chip) and the APF Imagination Machine, among others. It is a relatively simple display generator compared to other display chips of the time. It is capable of displaying text and graphics contained within a roughly square display matrix 256 pixels wide by 192 lines high.

Mitsubishi clone M5C6847
Motorola 6847 Pinout[1]

It is capable of displaying nine colors:[2] black, green, yellow, blue, red, buff (almost-but-not-quite white), cyan, magenta, and orange. According to the MC6847 datasheet, the colors are formed by the combination of three signals: Y (6 possible levels), ϕA (3 possible levels) and ϕB (3 possible levels), based on the YUV colorspace.

The low display resolution is a necessity of using television sets as display monitors. Making the display wider risked cutting off characters due to overscan. Compressing more dots into the display window would easily exceed the resolution of the television and be useless.[3][4]

Video modes
Video ModeResolutionColoursBytes
Alphanumeric Internal 32 × 16 2 512
Alphanumeric External 32 × 16 2 512
Semigraphics 4 64 × 32 8 512
Semigraphics 6 64 × 48 4 512
Color Graphics 1 64 × 64 4 1024
Resolution Graphics 1 128 × 64 1 + Black 1024
Color Graphics 2 128 × 64 4 2048
Resolution Graphics 2 128 × 96 1 + Black 1536
Color Graphics 3 128 × 96 4 3072
Resolution Graphics 3 128 × 192 1 + Black 3072
Color Graphics 6 128 × 192 4 6144
Resolution Graphics 6 256 × 192 1 + Black 6144

Y'UV levels

According to the MC6847 datasheet,[5] colors are formed by the combination of three signals: Y luminance, ϕA chroma and ϕB chroma, according to the YUV colorspace. Y may assume one of these voltages: "Black" = 0.72V; "White Low" = 0.65V; "White Medium" = 0.54V; "White High" = 0.42V. ϕA and ϕB may be: "Output Low" = 1.0V; "R" = 1.5V; "Input High" = 2.0V.

ColorYϕAϕB
Green0.541.01.0
Yellow0.421.01.5
Blue0.722.01.5
Red0.721.52.0
Buff0.421.51.5
Cyan0.541.51.5
Magenta0.542.02.0
Orange0.541.02.0
Black0.721.51.5
Dark Green0.721.01.0
Dark Orange0.721.02.0

Hardware Color palette

Colors generated by the hardware,[6] adjusted for maximum brightness.

green yellow blue red buff cyan magenta orange black dark green dark orange

See also

References
  1. "Chip datasheet in PDF" (PDF).
  2. "Motorola VDG Colours".
  3. Benchoff, Brian (29 January 2016). "VGA In Memoriam". Hackaday.
  4. Posey, Bruce Charles (1982). Graphics Using the Motorola 6847 Integrated Circuit. W.S.U. Printing Service.
  5. "MC6847* datasheet & applicatoin notes - Datasheet Archive". www.datasheetarchive.com.
  6. "floooh/chips". GitHub.
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