Dragon Computers  Dragon 64
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The Dragon 32 + 32 = 64

The Dragon 64 is very similar to the Dragon 32 with 32K of extra memory and a new RS232C Serial port. Also the Dragon 63 had the OS9 operating system. The case color of the 64 is light grey, while that of the 32 was beige. All of the Dragon computers are very similar to the TRS-80 Color Computer (the CoCo 1). The similarities with the TRS-80 Color Computer were small enough that a significant amount of software written for the CoCo could run on both. BASIC tokens are different, but if a program was re-tokenized, the software would typically run without too many changes. In fact the Dragon BASIC version is almost identical to Tandy's Color Computer Extended Basic. There are only a few tweaks in order to access certain Dragon features.

It is even possible to permanently convert a Color Computer into a Dragon by swapping the Orinal Color Computer ROM and rewiring the keyboard cable. The dragon also has a centronics parallel printer port, that was not present on the TRS-80 Color Computer.

The Dragon's main display mode is a black on green quarter-tile block mode. There are also five high-resolution modes, named PMODE 0 to 4. The highest resolution possible is 256x192 in monochrome. The lower resolutions allow for more color.

Motorola MC6847 Video Display Generator

The MC6847 is a video display generator (VDG) first introduced by Motorola and used in the following machines (this is not a full list):

  • TRS-80 Color Computer
  • Dragon 32/64
  • Laser 200
  • TRS-80 MC-10/Matra Alice
  • NEC PC-6000 series
  • Acorn Atom
  • APF Imagination Machine

The VDG is a relatively simple display generator compared to other display chips of the time. It is capable of displaying alphanumeric text, semigraphics and raster graphics contained within a roughly square display matrix 256 pixels wide by 192 lines high.

The ROM includes a 5 x 7 pixel font, compatible with 6-bit ASCII. Effects such as inverse video or colored text (green on dark green; orange on dark orange) are possible.

The MC6847 is capable of displaying nine colors:

  • black
  • green
  • yellow
  • blue
  • red
  • buff (almost-but-not-quite white)
  • cyan
  • magenta
  • and orange
Two extra colors, dark green and dark orange, are only possible as backgrounds for alphanumeric text modes.

Motorola 6809 CPU

The Motorola 6809 is an 8-bit microprocessor with some 16-bit features. It was designed by Motorola's Terry Ritter and Joel Boney and introduced in 1978. Although source compatible with the earlier Motorola 6800, the 6809 offered significant improvements over it and 8-bit contemporaries like the MOS Technology 6502, including a hardware multiplication instruction, 16-bit arithmetic, system and user stack registers allowing re-entrant code, improved interrupts, position-independent code and an orthogonal instruction set architecture with a comprehensive set of addressing modes.

Technical Details
Released 1983 Brand Dragon Data Type Dragon Computers Name Dragon 64 Clone Of Color Computer 1 CPU Class 6800 CPU Motorola 6809E@0.89MHz Memory RAM: 64kB
ROM: 16kB
Sound Chip none Sound 1-bit sound Display Chip MC6847 Video Display Generator Display 64x192 semi-graphics 4 color
256x192 Mono graphics
Best Text 32x22 Best Color 8 colors Best Graphics 256x192 in 2 colors Sprites none System OS Microsoft Extended BASIC
Related Systems
Dragon Computers
Dragon  64 (1983)
Related Media
Books for the TRS80 and CoCo Computers
TRS80 Portable
Books on the TRS-80 Portable computers
Dragon User
Dragon User Magazine
The 6502/6809 Journal
Rainbow Magazine
Monthly magazine by the Tandy Corporation
World Wide Web Links

WikiPedia: Motorola MC6847 Display Chip

The MC6847 is a Video Display Generator (VDG) first introduced by Motorola in 1978

Wikipedia: Motorola 6809 CPU
Wikipage about the Motorola 6809 CPU and compatibles