Dragon 32/64

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This article is about the Dragon home computers. For other uses, see Dragon (disambiguation).
A Dragon 32 home computer.
Dragon 32/64
Type Home computer
Released August, 1982
Discontinued 1984
Processor Motorola 6809E @ 0.89 MHz
Memory 32KB/64KB
OS Microsoft Extended BASIC

The Dragon 32 and Dragon 64 were home computers built in the 1980s. The Dragons were very similar to the TRS-80 Color Computer (CoCo), and were produced for the European market by Dragon Data, Ltd., in Port Talbot, Wales. The model numbers reflect the primary difference between the two machines, which had 32 and 64 kilobytes of RAM, respectively.

Contents

[edit] Product history

In the early 1980s, the British home computer market was booming. New machines were released almost monthly. In August 1982, Dragon Data joined the fray with the Dragon 32; the Dragon 64 followed a year later. The computers sold quite well initially and attracted the interest of several independent software developers, most notably Microdeal. A magazine, Dragon User also began publication shortly after the machine's launch.

In the private home computer market, where games were a significant driver, the Dragon suffered due to its graphical capabilities, which were inferior to other machines such as the Sinclair ZX Spectrum and Commodore 64.

The Dragon was also unable to display lower-case letters easily. Some more sophisticated applications synthesised them using high-resolution graphics modes (in the same way that user-defined characters would be designed for purely graphical applications such as games). Simpler programs just managed without lower case. This effectively locked it out of the then-blooming educational market, which came to be dominated by the Acorn-built BBC Micro.

As a result of these limitations, the Dragon was not a commercial success, and Dragon Data collapsed in June 1984.

Despite the demise of the parent company, Dragons still proved quite popular. They had a robust motherboard in a spacious case, and were much more tolerant of home-modification than many of their contemporaries, which often had their components crammed into the smallest possible space.

[edit] Technical notes

[edit] Hardware and peripherals

The Dragon was built around the Motorola MC6809E processor running at 0.89 MHz. This was the most advanced 8-bit CPU design of the time, having, among other things limited 16-bit capabilities. In terms of raw computational power, the Dragon beat most of its contemporary rivals (which were based on the older MOS Technology 6502 or Zilog Z80), but this made little difference in a market where graphical capabilities and software library were much more important to consumers.

Many Dragon 32s were upgraded by their owners to 64K. A few were further expanded to 128K, 256K, or 512K, with home-built memory controllers/memory management units (MMUs).

A broad range of peripherals existed for the Dragon 32/64, and on top of this there were add-ons such as the Dragon's Claw which gave the Dragons access to the BBC Micro's large range of accessories (a particularly important factor in the UK home market). Although neither machine had a built-in disk operating system (cassette tapes being the default data-storage mechanism in the home computer market at the time), DragonDOS was supplied as part of the disk controller interface from Dragon Data Ltd. The numerous external ports (by the standards of the time), including the standard RS-232 on the 64, also allowed hobbyists to attach a diverse range of equipment.

[edit] Video Modes

The Dragon's main display mode was 'black on green' text (in actual fact the black was a deeper and muddy green). The only graphics possible in this mode were block based. It also had a selection of five high resolution modes, named PMODEs 0-4, which alternated monochrome and four-colour in successively higher resolutions, culminating in the black and white 256x192 PMODE 4. Each mode had two possible colour palettes. Unfortunately, these were rather garish and caused the system to fare poorly in visual comparisons with other home computers at the time. It was also impossible to use standard printing commands to print text on the graphical modes, causing software development difficulties.

Full colour scanline based 64x192 'semi-graphics' modes were also possible, though their imbalanced resolution and programming difficulty (they were not accessible via BASIC) meant they were not often utilised.

[edit] Disk Systems

A complete Disk Operating System was produced for the Dragon by a third party supplier, Premier Microsystems located near Croydon, South London. The system was sold as the 'Delta' disk operating system. Although Premier offered the Delta system to be marketed by Dragon themselves, Dragon were not happy that a third party were hijacking the standards for their computer, and produced their own rival DragonDOS system making it clear that the third party Delta was not compatible with the 'standard' Dragon Disk system.

Inevitably, with Delta's head start, software was marketed in either system (but rarely both). The result was the inevitable confusion with customers upset that a particular piece of software was not available for the Disk system that they had. Although this was far from the principle driver for the Dragon's demise, it was nevertheless a factor and had Dragon adopted the established Delta system, the machine may well have had a greater following and a longer life.

[edit] System software

In addition to the DragonDOS disk operating system the Dragon 32/64 were capable of running several others, including FLEX, and even OS-9 which brought UNIX-like multitasking to the platform. Memory-expanded and MMU-equipped Dragons were able to run OS-9 Level 2.

[edit] Differences from the CoCo

Both the Dragon and the TRS-80 Color Computer (CoCo) were based on a Motorola data sheet design for the MC6883 SAM chip for memory management and peripheral control.

The systems were sufficiently similar that a significant fraction of the compiled software produced for one machine would happily run on the other. Software running via the built-in Basic interpreters also had a high level of compatibility, but only after they were re-tokenized (which could be achieved fairly easily by transferring via cassette tape with appropriate options).

The Dragon had additional circuitry to make the MC6847 VDG compatible with european 625-line television standards, rather than the US 525-line NTSC standard, and a Centronics parallel printer port not present on the CoCo. Some models were manufactured with NTSC video for the US market.

[edit] Dragon 32 vs. Dragon 64

Aside from the amount of RAM, the 64 also had an RS-232 serial port which was not included on the 32.

A minor difference between the two Dragon models was the outer case colour; the Dragon 32 was beige and the 64 was light grey. Besides the colour and the Dragon 64's serial port (and the model name stickers, of course), the two machines looked exactly the same.

[edit] Special features trivia

Like with most other home computers, accessing and/or modifying the value of various operating system structures or memory mapped control registers would invoke more or less useful features of the OS or hardware. The Dragon's "secret incantations" included the following:

  • POKE 65495,0 let the processor double its ROM access speed. This accelerated the ROM-resident BASIC interpreter, but temporarily disabled correct functioning of the cassette/printer ports. Manufacturing variances meant that not all Dragons were able to function at this higher speed, and use of this POKE could cause some units to crash or run highly unstable, though with no permanent damage. POKE 65494,0 returned the speed to normal.
  • POKE 113,18 would cause the computer to perform a warm start.
  • Amount of available RAM was 24.2880859K

[edit] References

  • Vander Reyden, John (1983). Dragon 32 programmer's reference guide. Beam Software/Melbourne House. ISBN 0-86161-134-9.
  • Smeed, D.; Sommerville, I. (1983). Inside the Dragon. Addison-Wesley. ISBN 0-201-14523-5

[edit] External links

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