British designed and built, this 6809-based system could represent the first ‘off-the-peg’ home computer. We venture inside for a close look.
By Henry Budgett
Ove the last 18 months, the computer market has seen a considerable number of microcomputer systems which all seem to offer the same basic specification. In general, these are based around the well-proven Z80 processor and feature the maximum allowance of RAM (64K) together with twin discs, the CP/M Disc Operating System and a variety of software packages and language options.
The main reason for this proliferation has been that it is, in general, cheaper to fully equip a system of this type than to offer memory expansion and hardware add-ons as extras. Memory and disc drive prices have fallen as a result of the increased demand and this can be passed on to the bulk buyers allowing them to build comprehensive systems at the same price as the basic unit would have cost some 12 months ago.
Now, the main reason for the similarity is that there are only a finite number of ways in which you can assemble a certain family of chips: CPU, RAM, I/O and peripheral devices. It took about two years before the manufacturers started to capitalise on this and reduce their design costs significantly. It is therefore, interesting to note that one new manufacturer has followed the example of his predecessors and produced a 6809-based system by following the same route.
A new start
The new computer is called the Dragon 32 and hails from South Wales, courtesy of Dragon Data who are building the system for Mettoy – the well-known toy makers. On the surface it simply appears to be a 6809-based system with colour graphics and 32K of user memory. Added features are the ability to plug in ROM-based cartridges, to attach joysticks and add a limited number of peripherals through the various ports. If, at this point, you are beginning to feel a slight sense of deja vu then take a brief bow. The system is aimed directly at the home market and, on price at least, must be taken as a competitor to the Texas Instruments TI-99/4A, the Atari 400 and the BBC Model A systems.
I mentioned earlier that the system is designed from the standard range of support devices for the 6809 CPU. Well, there are only two other 6809-based systems currently on the market: the Fujitsu triple processor system which can be discounted as it is very much more powerful; and the Tandy Color Computer which we reviewed in April of this year. The similarity between the Tandy and the Dragon 32 is almost uncanny and the reason is not simply because the same chips have been used.
I don’t know how Tandy produced the design for the Color Computer but the Dragon 32 was designed with the aid of the PAT Centre, a high technology design group who have been responsible for such devices as Moore and Wright’s digital micrometer. As far as I can unravel the story, the basic specification was taken to them with the brief to produce a result from off-the-peg components. Time being of the essence, they appear to have opted for the standard chip set approach and then equipped the resulting hardware with the only commercially available 6809-coded version of BASIC, Microsoft Extended Colour BASIC.
The inside story
The Dragon 32 arrives in a single box complete with power supply, TV lead, manual and quick reference chart. (Don’t waste time looking for the cassette lead, it’s an extra!) The first thing that strikes you about the system is that it has a ‘proper’ keyboard although the quality of the particular unit chosen is a little dubious.
The system is enclosed in a cream plastic box which is considerably larger than one might have expected. Quite why they made it this big is beyond me, it could have been at least an inch thinner and nearly the same reduction could have been made in width too. The power supply’s transformer is external and there is adequate ventilation, so overheating is unlikely to be the reason. Still, it’s a nice chunky case and styled so that it looks narrower than it really is because all the sockets are recessed at the side.
Inside the box (no mention, appears in any of the documentation to dissuade you from undoing the screws but I don’t recommend it unless you’re certain of what you’re doing) the layout is almost clinically neat. Excluding the keyboard assembly there are two PCBs, one holding the logic and the other, the regulator circuitry and the modulator. The latter is larger than usually found as it allows the sound channel to be heard through the TV speaker. Connection to the TV is made by a conventional phono to UHF lead which uses considerably better quality cable than most, potentially removing some of the interference caused by stray mains cables and the like. If you don’t fancy suffering the degraded quality pictures from a TV, you can take a monitor feed directly from the RGB drive circuitry. Although no connection details are given in the manual, it would appear to be a straight RGB plus sync output.
The main PCB shows the small number of ICs used. The socket at the right-hand side is the cartridge port.
The main PCB is equipped with all the expected devices and even uses the twin video processing chips found in the Tandy, the SAM and VDG which we covered in detail when we reviewed the Color Computer. The RAM is provided in the form of eight Hitachi 4864 chips and there is a total of 16K of ROM provided by two 2716s. The 6809, the two ROMs and the eight RAMs are all socketed, none of the other devices are. One interesting point is the provision of a number of ‘patches’ on the layout, these are in the vicinity of the RAM chips and it is possible that an alternative memory capacity system could be produced using pin compatible devices. It would, at least in theory, be possible to use the new 64K by 1 RAMs to produce a 64K Dragon but whether this is something planned I cannot say.
Readers who are familiar with the TRS-80 range of systems might be hoping that the format of the text screen found on the Dragon 32 would be an improvement. No such luck, it’s still 16 lines of 32 characters in text mode with no lower case letters, reversed upper case being used instead. Other screen formats include a low resolution plotting capability of 32 by 64 pixels and a high resolution mode of 192 by 256 points. A total of 16 predefined graphics shapes are available, all the variations of a two by two matrix, but these are supplied in eight colour options as some form of compensation. The same eight colours can be defined as background colours for the text screen area, although in text mode only green and black are available as the foreground colour depending on the background selected. The displayed colour picture is of reasonable quality but nothing exceptional. It has been tested on a Philips and an Hitachi portable but the best picture was obtained on my own 22″ Ferguson, the TX chassis series proving itself once again.
Slight to noticeable colour fringing occurs and there is some sound pickup too, but the main objection is that the primary colours are not clean; red, blue and green should be red, blue and green and not ‘off’ shades.
The initial screen display simply announces the machine and its version of BASIC. What it does not tell you is how much memory you have available. Typing PRINT MEM returns a value of around 24K which might seem a little surprising since you just bought a 32K computer! The missing 8K of RAM hasn’t really vanished, it is being used for the system variables and to create the high resolution graphics areas. While this means less space for you to program in, it does mean that when you come to use the high resolution graphics your memory doesn’t shrink dramatically like some other systems we could mention!
Screen editing is through a standard Microsoft line editor system which is initiated by the command EDIT<linenumber>. All the usual commands operate and you either like or hate it depending on what you’re used to. Bulk line deletion and program renumbering are available under BASIC although automatic line numbering is not. The usual trace functions, TRON and TROFF (Walt Disney take note), are included.
For those into data handling the cassette interface can be used for data files through BASIC although the reliability of the system is not particularly good. The interface seems to be slightly level sensitive but my main criticism would have to be the lack of decent messages, single letters displayed on the screen don’t count as messages in my book! The main stumbling point over the cassette interface is the lack of any supplied lead and, as the manual fails to give connection details for the frustrated DIY-er, Fig. 1 should be welcome. There are only two interesting commands on the cassette side: SKIPF which allows you to skip over the named file in order to position the tape for recording or loading files which are not at the beginning; and MOTOR which allows the cassette motor to be controlled by the keyboard and saves having to keep unplugging the remote control lead.
Fig. 1. The connections to the cassette recorder socket for those wishing to make their own leads.
Possibly the only remaining function, other than the graphics which I’ll cover in a moment, is the ability to halt a program at any point during execution by pressing Shift @. Pressing any other key, excluding Break (although this is not made clear in the manual) restarts the program so you can take a break in the middle of that dogfight to answer the phone or perform other necessary functions.
The Microsoft Extended Colour BASIC implemented on the Dragon 32 is as complete an example of microcomputer BASIC for this level of machine as any you’ll find. It supports all the normal BASIC functions, including IF…THEN…ELSE, as well as offering a comprehensive colour graphics command set. Full line drawing with both absolute and relative positioning is available and the single LINE command can be extended to produce rectangles, draw in either foreground or background colour and even fill in a completed box. For filling larger areas of the screen with colour the PAINT command can be used but be warned of leaving holes.
If you’re into things round, then the CIRCLE command will certainly satisfy all your needs. As well as producing simple rings of given colour and radius at any point on the screen, it can be extended to produce ellipses by changing the height/width ratio parameter or arcs rather than complete circles. All these high resolution commands are just the basic set, animation using the multiple pages of graphics memory and shape tables using the ingenious DRAW command can be mastered with a modicum of experiment and practice.
As an added extra dimension to graphics games the BASIC JOYSTK function allows up to two joysticks to be used, complete with ‘fire’ buttons. The values returned by the expression can be related to the x and y positions of either stick and it takes a total of six statements to examine both sticks together with the fire buttons. Now, the BASIC isn’t exactly slow, (Table 1 gives the Benchmark results) but there must be a better way than this to recover the values which then have to be scaled to suit the screen size in current use.
Wherever you find a home computer, which the Dragon 32 unreservedly is, with colour graphics you almost invariably find sound facilities as well. Simple, single tone noises are produced by the SOUND command where two parameters, frequency and duration, are all that is needed to produce the desired effect through the TV speaker. More complex sound sequences are best constructed under the PLAY function. Here, in a manner similar to that used by the Sharp systems, a complete note passage is programmed into a string which is made up of the note name, octave, duration and volume. Pauses and changes in tempo can also be programmed and as the notation used is similar to ‘real’ music, it is remarkably easy to use. My personal favourite in the sound department is AUDIO OFF which disables the audio output completely, but then again…
Ins and outs
The interfacing options of the Dragon 32 appear somewhat limited. The system provides for the basic requirements of a cassette and TV or RGB monitor together with the option joysticks. The only remaining options are the parallel printer port, Centronics compatible and fully supported under BASIC, and the ROM cartridge slot. It is interesting to note that the Tandy Color Computer chose to offer a serial port. A quick count of the available peripheral devices inside the Dragon 32 leads one to wonder just how they managed to create this extra parallel port as there simply aren’t enough bits available. The only possible explanation of this is that the printer shares the same PIA as the joysticks; it uses the port as an output whereas the joysticks use it as an input. All the rest is fairly conventional in terms of operation and design but it should be noted that the internal TIMER function will be upset by the use of the cassette interface as it is interrupt driven and not a hardware device.
The left-hand side sockets include UHF, two joystick ports and a cassette connector plus the
printer port. The black button is the Reset.
The rear panel features the power inlet, power switch and monitor output.
Further expansion does not, at first glance, seem possible until one remembers the ROM pack slot. All the indications are that most of the address, data and control bus lines should be available through here for expansion. Quite whether the range of Program Paks offered by Tandy will operate in this slot is open to question. The indications are that they should but without complete information on the pin connections of the Dragon 32, I’d rather not suggest that you plug one in to try! If the connectors are the same, expansion to include discs and make use of the 6809’s own DOS, FLEX, becomes a strong possibility as many US companies are offering these facilities for the Tandy Color Computer. Tandy themselves offer a range of add-ons but these ignore both FLEX and the S50 bus structure which is so suited to the 6809 CPU.
Currently, the only options available from Dragon Data/Mettoy are the cassette lead, a small choice of ROM packs and a joystick. I’ve played with their version of a Pacman-type game and while the game was OK, the control offered by the joystick left an awful lot to be desired. Whether the design will be improved or not I do not know but a strong suggestion is to find another source if the joystick you’re offered simply flops from side to side like our review sample. For those into building their own joysticks or modifying commercial offerings, the connections shown in Fig. 2 should be of some assistance. You can also use this information to connect other analogue devices to the Dragon 32 such as temperature sensors and the like.
Fig 2. How the joysticks are assembled together with the necessary connection information.
Words of wisdom
Two pieces of documentation accompanied our review machine: a manual and a quick reference guide to the BASIC. The manual is written by Richard Wadman with the assistance of University College, Swansea, and, as manuals go, is not too bad. There are a number of small errors which may well have been cleared up by the time the machine hits the streets in a big way, but the main feeling is one of missing information. There are no details of any of the hardware, interface connections or add-ons. Nor are there any facts about the monitor program and how to get 6809-code into the system. There are brief references to the fact that it can be done, you can certainly save machine code programs on tape, but as to how you create them…
On the whole, it will satisfy the beginner as it is all clearly laid out and important pages have green edges to highlight their contents. The quick reference guide is a welcome addition as it enables those familiar with another version of BASIC to start trying out the extra commands available without having to rummage through acres of text.
One suggestion I will make though is that if you are really interested in pursuing the BASIC on the Dragon 32, you pay a visit to your local Tandy shop. There you can buy for the princely sum of £3.95 an excellent book called Going Ahead With Extended Color BASIC which contains more detail on Microsoft, provides colour pictures of many of the example programs in action and, best of all, a memory map and a list of operating system entry points. Now, as far as I and another colleague can discover, all these entry points work on the Dragon 32 so you can start to try out simple machine code calls to recover data from peripherals such as the joysticks, etc. One other book you might like to cast your eyes over while in the Tandy shop is the Color Computer Technical Reference Manual. Now, I will concede that it is not directly related to your Dragon 32 but it does explain the workings of the SAM and VDG devices and should give an overview at least of the internal operations. Another good reason for buying it is that according to my copy at least, while it costs nearly $15 in the States, it only cost me 99p here!
In the end
Just what has the Dragon 32 got to offer over its rivals? Well, if you were looking for a home computer to play games with and maybe try a little programming on, it does have the advantage of a reasonable amount of RAM and an almost decent keyboard. The BASIC is powerful enough for domestic use but if you really want a programming tool then BBC BASIC still stands out ahead, although the Model A offers less memory at the price. As an alternative to the Tandy Color Computer it wins on price alone although it certainly doesn’t look as nice.
As for its other rivals, the Atari and Texas systems, the choice of ready-to-run games and add-ons possibly tends to weigh against the Dragon 32. Another possible source of concern is that Mettoy have never been in the computer market before whereas both the others have a long pedigree but, in reality, there is little that can go wrong in a system like this that cannot be simply and easily fixed.
All these systems are readily available in the High Street, at least the Dragon 32 should be by now, and as is so often the case, it must come down to personal choice. There is certainly nothing wrong with the Dragon 32 and it offers an alternative and British-made solution to the home computer buyer. Whether it will succeed in making an impact on the market will probably depend on the general availability of both it and its extras and the effectiveness of the current advertising campaign.
Table 1. The benchmark timings for the Dragon 32. All are in seconds and timed using the internal clock function. Note that BM8 is taken over 100 loops instead of the usual 1,000
Factsheet for Dragon 32
- CPU: 6809
- Clock: 0.89Mhz
- ROM: 16K
- RAM: 32K
- Language: Microsoft Extended Colour Basic
- Keyboard: 53 key standard layout
- Display: 16 lines of 32 characters on TV or monitor. Block mapped graphics on 32 by 64 grid. Dot resolution graphics to 192 by 256. 16 block graphics characters. Eight colours plus black.
- Cassette: 1500 baud with independent motor control.
- I/O: Two joystick ports. Parallel (Centronics) printer port. ROM cartridge slot.
- Options: Joystick Unit (£10.00), ROM cartridges (£20.00), Cassette software (£8.00), 5.25” disc drive (NYA), OS9 operating system (NYA).
- Cost: Dragon 32 (£199.50)
- Manufacturer: Dragon Data Ltd, Queensway, Swansea Industrial Estate, Swansea, SA5 4EH
First published in Computing Today magazine, November 1982