Dragon 32

Pubblicato: giugno 24, 2011 in Tandy
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From Wikipedia, the free encyclopedia

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

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 contemporary 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 would synthesise 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.[1]

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

Technical notes

Hardware and peripherals

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

It was possible to increase the speed of the computer by using POKE 65495,0 which accelerates the ROM-resident BASIC interpreter, but temporarily disables correct functioning of the cassette/printer ports. Manufacturing variances means that not all Dragons are able to function at this higher speed, and use of this POKE can cause some units to crash or run highly unstable, though with no permanent damage. POKE 65494,0 returns the speed to normal. POKE 65497,0 pushes the speed yet higher but the display is lost until a slower speed is restored.

The Dragon also used the SN74LS783/MC6883 Synchronous Address Multiplexer (SAM) and the MC6847 Video Display Generator (VDG). I/O was provided by two MC6821 Peripheral Interface Adapters (PIAs). Many Dragon 32s were upgraded by their owners to 64 KB of memory. A few were further expanded to 128 KB, 256 KB, or 512 KB, with home-built memory controllers/memory management units (MMUs).

A broad range of peripherals exist for the Dragon 32/64, and on top of this there are add-ons such as the Dragon’s Claw which give the Dragons access to the BBC Micro’s large range of accessories (a particularly important factor in the UK home market). Although neither machine has 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 allows hobbyists to attach a diverse range of equipment.

An unusual feature was a monitor port for connection of a computer monitor, as an alternative to the TV output. This was rarely used due to the cost of dedicated monitors at that time. The port is actually a Composite Video port and can be used to connect the Dragon 32 to most modern TVs to deliver a much better picture.

The Dragon uses analogue joysticks, unlike most systems of the time which used less versatile but cheaper digital systems. Other uses for the joystick ports include light pens.

Tony Clarke and Richard Wadman laid out the specifications for the Dragon.[2]

The units had a robust motherboard in a spacious case, reminiscent of the BBC Micro, and so were more tolerant of home-modification than some of their contemporaries, which often had their components crammed into the smallest possible space.

Video Modes

The Dragon’s main display mode is ‘black on green’ text (actually the black was a deeper, muddier green). The only graphics possible in this mode are quarter-tile block based. It also has a selection of five high resolution modes, named PMODEs 0-4, which alternate monochrome and four-colour in successively higher resolutions, culminating in the black and white 256×192 PMODE 4. Each mode has two possible colour palettes. Unfortunately, these are rather garish and cause the system to fare poorly in visual comparisons with other home computers of the time. It is also impossible to use standard printing commands to print text on the graphical modes, causing software development difficulties.

Full colour scanline based 64×192 “semi-graphics” modes are also possible, though their imbalanced resolution and programming difficulty (they are not accessible via BASIC) meant they were not often utilised.

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 principal 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.

System software

The Dragon comes with a Microsoft BASIC interpreter in 16 KB of ROM. The BASIC appears to be identical to Tandy Color Computer’s Extended Basic.[2]

Unlike a modern PC with the operating system on disk, a Dragon starts instantly when powered up. Some software providers also produced compilers for BASIC, and other languages, to produce binary (or “machine”) code which would run many times faster and make better use of the small system RAM. Towards the end of its life, Dragon Data produced an assembler/disassembler/editor suite called Dream.

In addition to the DragonDOS disk operating system, the Dragon 32/64 is 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 are able to run OS-9 Level 2.

Differences from the CoCo

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

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

It was possible to permanently convert a CoCo 1/2 into a Dragon. The process required swapping the original CoCo ROM with and rewiring the keyboard cable.[3]

The Dragon has 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.

Dragon 32 vs. Dragon 64

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

A minor difference between the two Dragon models is the outer case colour; the Dragon 32 is beige and the 64 is light grey. Besides the colour and the Dragon 64’s serial port (and the model name stickers, of course), the two machines look exactly the same. The Dragon 32 is upgradable to Dragon 64.

 

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