The Dragon 32 is 30
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Feature The Dragon 32, arguably the best-known and most-successful of the UK's early 1980s home computer also-rans, was introduced 30 years ago this month.
The micro's story goes back more than a year before its launch. Tony Clarke, a senior manager at Swansea-based toy company Mettoy - best known for its Corgi die-cast metal car brand - had witnessed the arrival of the Acorn Atom, the Sinclair ZX81 and the Commodore Vic-20, and noticed kids' growing interest in the new technology. He sensed a fresh opportunity for Mettoy, a firm founded back in the 1930s.
Would-be saviour of the UK toy industry
Source: Wikimedia
Children were soon going to be turning to computers for play, Clarke reasoned, and that would move them away from more traditional toys, Mettoy's mainstay. Mettoy had, then, to move with the times and break into the home computer business.
To that end, Clarke initiated 'Project Sam' in the Autumn of 1981. He approached the PA Technology (PAT) of Cambridge - part of PA Consulting - to design a new microcomputer. Appreciating the fast-moving nature of the computer business, Clarke gave the PAT team, headed by Ian Thompson-Bell, a tight deadline. That, Thompson-Bell would admit the following year, forced the team to select an off-the-shelf Basic interpreter; there wasn't time to write one of their own.
The obvious choice back then for a buy-in Basic was Microsoft, and that selection immediately limited the range of possible processors the new micro could use. Thompson-Bell and his team selected the Motorola 6809, unquestionably a better processor than the 6502 and Z80A, but, more importantly, one readily available with a set of Motorola support chips: the 6883 Synchronous Address Multiplexer (SAM) memory controller, and the 6847 video controller.
The reference design? Tandy's TRS-80 CoCo
Source: Wikimedia
With those products, said Thompson-Bell at the time, "you have virtually a home computer in three chips". PAT also fitted two of Motorola's 6821 Peripheral Interface Adaptor (PIA) chips to handle the machine's I/O.
It helped that Tandy had paved the way. The US manufacturer launched the 6809-based TRS-80 Color Computer in 1980. The 'CoCo', as it was affectionately named, was certainly available in the UK at the time the Dragon was being developed, but wasn't well known by Britain's new generation of young computer enthusiasts, not least because of it was only available in Tandy shops and cost a whopping £499.
Tandy had created the CoCo as a games-centric home machine to compete with Commodore's Vic-20. Tandy, as Dragon would later, chose Microsoft Basic and turned to Motorola - then keen to break into the booming US home computer market - to provide the machine's off-the-shelf, ready-to-use components and reference designs.
Family friendly: Dragon 32 promo pic, later used for box art
It has been claimed that PAT simply aped the CoCo, but that seems unlikely. A more plausible scenario is that reliance on the silicon and reference designs eagerly provided by Motorola ensured that the Dragon and the CoCo were always going to be effectively the same machine, cosmetic and minor specification differences aside. Machine code programs were interchangeable, for example.
Next page: The Motorola factor
COMMENTS
Re: You've made a happy woman feel very old
'The Girl With The Dragon Thirty-Two', eh?
You've made a happy woman feel very old
This machine is where it started for me. If it hadn't been the Dragon then it would have been something else, but this was the first machine on which I cut any code of any sort, for which reason I feel very kindly inclined to it.
Memories of the Project Leader
I was the project leader for the Dragon 32 at PAT, or Patcentre as is was then known. I thought you might like to know what I remember of that time.
I remember spending a lot of time talking to a really helpful Motorola chip salesman called Robin Saxby. Yes, the same guy who later ran ARM and is now Sir Robin.
We certianly did not copy the CoCo. It was not really available in the UK because it had an NTSC video system which would not work on UK TVs in those days. The Motorola application for the SAM chip (synchronous address multiplxer) showed a complete home computer to which the CoCo was identical. We made numerous improvements to this app note. We included a real A/D and D/A convertors for generating the FSK signals used to store programs on tape. We added a parallel printer port and used the same chip to scan the keyboard. We had a separate power supply PCB which also contained the TV modulator. It was a single sided PCB so it saved cost but also allowed variants to different TV standards to be made cost effectively. We made a SECAM variant for France and also an RGB and US version.
I do not rmemeber Motorola suppying a BIOS. Microsoft wrote the Basic interpreter, which was essentially the same as the one they licensed to Tandy but with a few add-ons, but you were expected to create all your own peripheral drivers - a situation unchanged to this day. It was these drivers that Duncan (Smeed) wrote. I do not remeber the keyboard speed up being his alone. The nromal way to scan a key board is to activate a row and read the columns to see if a key has been pressed and repeat that for each row. Of course, most of the time there was no key pressed and this routine just wasted a lot of time getting a no key preessed result. We realised that becuase we had used the same chip to scan the keyboard as drive the parallel printer port, we could do one thing the CoCo could not, and that was activate all the rows at once. If you do this and then look at the columns, in one go you get to know if there are no keys pressed, the most common situation, and you can exit straight away. If you find a key has been pressed you scan as usual to find which one. This is what saved the time.
The PAL output had nothing to do with the CoCo. PAL was essntial for it to work on UK TVs. Few if any had SCART sockets so you had to create genuine PAL. Persuading a chip designed to make 525 line 60Hz NTSC to make 625 line 50Hz PAL instead is a non trivial exercise and needed a lot of descrete logic - ASICs were in their infancy then.
Two weeks before the official launch, the Spectrun 16K came out. The piggy back RAM PCB was designed, tested and ramped up for production in that two weeks. Later we used a bunch of Siemens 32K RAM chips that consisted of two 16K RAM chips literally piggy backed on eachother and later still upgraded the main PCB to 32K then 64K.
We then worked on the disk drive unit which was abandoned when Tony Clarke left and all development work went in house. What is probably not well known is that at the same time we were working on the successor to the Dragon, code named Draconis. This used a Motorola 68K processor and a very powerful graphics chip from NEC. Along with OS/9 as a true real time executive, this would have beaten the PC hands down as a business machine. But for the vagaries of the home computer market, we might all be using Dragons today.
Cheers
Ian Thompson-Bell
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