SPDE

ZX Computing

Content 2/5

Presentation 5/5

Documentation 2/5

Loading 4/5

Quirk Free 4/5

Paul Holmes

A LITTLE BUG When you're tired of BASIC, you may turn to machine code. Paul Holmes looks at a number of 'tools' to help you with entering and running machine code. Entering machine code using tedious and slow BASIC loaders is tiresome, and you're likely to start looking for something to lend a hand. Here are the latest machine code monitors for the Spectrum. DISASSEMBLE FUNCTION One thing which every editor needs is a disassemble option. With this the user can check that all the code he entered was actually the code he wanted to enter, and by disassembling his program he can check it against his original listing. All three of the editors reviewed had this facility, some performed it in a more useful manner by calculating the addresses for relative jumps. Both ZX BUG and SPECTRUM Monitor use 'Z' to access the disassemble function. One point about the ZX BUG that was annoying was that to get a printer copy of the disassembly you had to exit (using 'X') then type 'COPY'. This meant that the X command got copied as well, causing a break if a long listing is needed. The SPECTRUM Monitor politely asks 'PRINTER?' in a similar manner to the 'SCROLL?' message used in BASIC. INSTRUCTIONS The best manual by far was for the SPECTRUM Monitor by Picturesque. It was pleasantly written and very thorough, the sort of quality one expects when buying a complex package like this. By contrast the instructions for Artic's ZX BUG were squashed onto the back of the cassette inlay. For the experienced user this is just about acceptable but for a newcomer to machine code this could leave them baffled. The commands on all three are accessed by a single keypress, SPDE also has an optional menu to refer to which can be summoned to the screen at any time. The instructions for SPDE are contained in the program and give details of the program's operation and how to use it. Both ZX BUG and SPECTRUM Monitor, on loading, relocate themselves above RAMTOP and do not depend on a BASIC master program. This gives the user the advantage of being able to write programs in BASIC that use machine code subroutines developed on the editor. With ZX BUG one has to be careful because the machine code is loaded from a dud line (a line with a ridiculously high line number so that it isn't listed) to the top of RAM. That dud line is left behind and so invisibly uses up 4K of your BASIC workspace. To remove it one must first set RAMTOP to 7100 Hex then type NEW. SPDE requires a BASIC master program and so is therefore not quite as versatile. ZX BUG, or is it SPECTRUM BUG? I'm not sure because my review copy had ZX BUG on one part of the inlay, SPECTRUM BUG on another and ZX BUG 2 on another part. Confusing isn't it? ZX SPECTRUM BUG 2 (GLS!!) had the most functions by far comprising of single and double byte searches, breakpoint system, register display, String entry, byte modification, copy, byte print (on screen only), character print and many more. One of the commands is a block SAVE command which saves a block of memory in the usual way but can only be reloaded using the complimentary LOAD command (abbreviated to 'L'). No file names are allowed. One feature which SPECTRUM 2 ZX BUG lacked was a Hex-Decimal/Decimal-Hex conversion function. In my opinion this is a highly useful feature, since at sometime you are likely to want to call your proud piece of code from BASIC using a Decimal number and it is highly frustrating to have to convert it each time for each program or address. Both the other two editors included this feature which I was pleased to see. SPDE seemed to be lacking a comprehensive range of commands and only the actual nitty-gritty seemed to be by machine code subroutines. EDITING AND DEBUGGING Though one would expect the editors for the Spectrum to be an improvement on those for the ZX81 this has not been the case. I used Bug Byte's ZXDB for editing and debugging machine code on my ZX81 and found that editor exceptional, having a single step facility allowing one to monitor everything but the kitchen sink. It was something of a disappointment therefore, when I discovered that none of the three review packages had any such useful features. Being able to trace machine code step by step is immensely useful when bugs arise, so I am waiting with baited breath for Bug Byte's ASPECT Assembler/Disassembler/Editor which will be ready for sale by the time you read this. There is one improvement I have noticed and that is that the Editors are almost idiot proof, or habit proof. For example, my old editor used to crash when I habitually used the RUB OUT key to delete errors. All the editors had a block move command which is very useful when some code has to be relocated. SPECTRUM Monitor also has an insert command which is very useful when a byte has accidentally been missed out or when an instruction must be added. All of the editors have breakpoint systems. A breakpoint system can insert a breakpoint into your program (a point where the program is to be exited), so you can trap errors down to a small part of the program. The breakpoint can be removed and easily relocated elsewhere. A distinctly annoying point about ZX BUG SPECTRUM 2 was that using addresses (on the 16K Version) 71E0 Hex to the top of memory would interfere with ZX BUG and using addresses 4000-6800 Hex or so would interfere with the loader program so that if you typed in some machine code on the earlier mentioned invisible line and then added to, or deleted from the program, your machine code would have moved. This only leaves about 2K of non moving memory for the user even though the invisible line (4K) does absolutely nothing once the program is loaded. None of the Editors had the ability to search for a string more than two characters. SPECTRUM Monitor had no search facilities at all. It surprised me to learn that Dr Ian Logan uses SPDE since it is remarkably short of editing commands. It can basically do: Hex-Decimal/Decimal-Hex, Block move (in BASIC!), List in Hex and Characters, list as mnemonics and Hex and that's all. It has no Breakpoint system, no fills, no searches, nothing in fact but the bare essentials. It is a pity really because the program itself is nicely presented with a touch of colour here and there and a handy menu to help. Slowly I am getting the impression, after re-reading their letter that Ian Logan is more than mildly acquainted with J.A. Campbell. For instance, he has written a quite complimentary review of their FAST ONE, though I must admit it is worth the cheeky title. Makes one suspicious, doesn't it? MIXING COLOURS SPECTRUM Monitor has a blue background which seems fine from both the colour TV owners point of view as well as the Black & White. I say this because our colour TV doesn't like Spectrums and changes white to green and a whole host of colours to pinks, dirty greens etc. This means that I have to use a Black & White (I would probably be ill otherwise), which tends to mix the different colours into an illegible mess. Since each of the editors has its own merits and demerits I have decided to use a rating table to assist conclusion: As you can see, SPECTRUM Monitor has a nice, all round quality and has outstanding documentation which really should be a lesson to other software houses. It's content didn't quite match up to that of SPECTRUM BUG but had sufficient commands to satisfy the average machine code enthusiast. SPECTRUM BUG's documentation was really poor and though SPDE's was better it was still quite sparse. SPECTRUM BUG falls down on the 'Quirk Free' rating because of the floating RAM trouble I explained earlier. All I can say about SPDE is that it is just a pretty face and bad value at £5.95 in comparison with the other two, even if Dr Logan DOES use it. Overall, for ease of use and documentation, the best buy is SPECTRUM Monitor while if you prefer a little more on the commands side then buy SPECTRUM BUG and a magnifying glass. (You'll need it to read the instructions!). SPDE is available from Campbell Systems, [redacted] at £5.95. Spectrum Monitor is available from Picturesque, [redacted], at £7.50. Spectrum Bug is available from Artic Computing, [redacted], at £7.00.

Your Computer

Boris Allan

SURVEY SPECTRUM SOFTWARE Boris Allan examines the first software offerings designed specially for your Spectrum. Although the Spectrum was announced in April the machine has only become available in large numbers recently. For software suppliers it is still early days. We were therefore relieved to find that most of the programs we received worked first time and reasonably well even if some of them lacked originality. Most of the software we sampled was based on ZX-81 or arcade games but we also tried out some educational and utility programs. Loading the Spectrum was far less frustrating than the ZX-81. The machine performed well, producing particularly good colours but disappointing sound. The limitations of the internal speaker can at least be bypassed by taking the cassette out of the recorder, connecting the two Mic sockets and switching on the recorder. Tone and volume can then be controlled with the recorder's own controls. Games programs are strange things. Long complex programs can be much less enjoyable than a short snappy one incorporating a good idea. So long as the programs are relatively bug-free, as most of these Spectrum games were, then evaluation of any particular cassette is bound to be subjective. To give as objective an assessment as possible we tried out the games on all age groups - even a class of five-year olds. Both Bug-Byte's Spectral Invaders and Quicksilva's Space Invaders approach the standard of real arcade games. Spectral invaders is almost an exact copy of Space Invaders, complete with four different colours for invaders, a flying saucer and high score. Some effects are slightly slower than the Atari original but the graphics quality and the use of colour and sound is excellent. Quicksilva's Space Intruders also had a mutant invader that wobbled and was worth extra points and a hold facility to allow you to stop the game at any point. While the invader programs were written in machine code, Alien Command was written in Basic and was too slow and crude for a space game. Winged Avengers from Work Force is a Galaxian-type game in which waves of attackers move down the screen towards the player's missile firer, break formation, circle about and then attack again. Six speeds are offered and the action is fast. But with the exception of a formation of birds, which appear in the second attack phase flapping their wings very effectively, the display is a little dull. Chromasoft's three programs varied from the sublime to the ridiculous. Worm is a simple but clever idea. A worm on the screen has four segments, and the player has to direct the worm around the screen, eating up numbers. Each time a number is eaten, they flash up randomly, the length of the worm increases by that amount. As the worm gets longer, it becomes more difficult to navigate, because you are not allowed to leave the screen or to cross over yourself. One player reached about 125 segments, and could not find any space. The program is as simple as the display but the idea worked. Defined colours and graphics for the segments would be improvements but only cosmeticBomber is an uninspired rendering of Blitz. Golf is not only unexciting but bug-ridden. Amongst other things the game was unwilling to play the right number of holes. AVC's Fortune could be a useful stand-in for the crystal ball at children's parties. The company's Tables has a more educational objective. The tests of multiplication tables are quite competent but the program would be more useful as a means of generating interest and enthusiasm for mathematics rather than for teaching the tables themselves. Whoever designed it has a keen appreciation of the minds of primary school children, although AVC is stretching a point when it claims the program can be used to the age of 16. One clever ploy to generate interest was the use of the ZX-Printer to give each child a permanent record of its achievement. One kid described it as 'space-age paper'. This theme is reinforced by a countdown to the launch of a rocket each time you play. Time Bandits from Newsoft comprises six separate games on side 1 all combined in an Adventure-style game on side 2. Most of the games have pretty graphics but are rather elementary. Minotaur's Labyrinth is a matter of collecting objects in a maze and Napoleon's army is similar - but without the maze. In Titanic you rely on luck to avoid being sunk by an iceberg while Tower of London is at least distinguished by the appearance of random Beefeaters. Combination is just a matter of remembering a number but Castle of Evil is a little more out of the ordinary. You have to work out the best strategy to cross a web with hostiles converging on you - rather like the Adventure game which used to be shown on BBC 2. Most of the games had not been carefully thought out. It was sometimes possible for instance to offer bribes of minus amounts of money, and thus become richer. Backgammon from Keith Archer worked well enough but was easy to beat and again vulnerable to cheating. There was nothing to prevent you putting more than five counters on a point for instance. Richard Altwasser's Cambridge Colour Collection costs £9.90 for a book of 64 pages and a cassette. Though some of the programs are original, in that they use specific features of the Spectrum, many are not: Maze is marred by a poor algorithm. There is also Breakout, Nim, and most others, including a version of King called Kingdom. The cassette was unfortunately unloadable - the company has had to replace many of the cassettes. We reviewed two graphics packages. Phantasmagraphics plots 2D and 3D patterns and allows you to modify the patterns by entering height, width, perspective and distortion variables. The program is written in Basic and takes up to six minutes to draw a shape. The program contains a bug which causes it to be interrupted by an 'integer out of range' error message for large height and width values. Superdraw 16 is an exceptional program. For £5 you are supplied with an instruction booklet, a pad of screen design pads, and a cassette with a spoken commentary on one side, all in a polythene bag. No other program gave such value for money. The program is written in Basic and allows the user to design screens which can then be saved for incorporation in other programs, which make use of high- and low-resolution graphics, text, and user-designed alphabets of large letters. The 'slide-show' option automatically toads successive screens. High-resolution pictures of a bicycle and southern England among others flash up in turn very much like a slide-show for the unemployed. Two simulation games are available from Case Computer Simulations. Autochef allows you to work your way up as manager of a small catering company. At first you have to avoid being taken over by Trust House Forte - later if you survive you can try to take over Forte yourself. Airline is exactly the same as Autochef except that you are running a small airline.- The two assemblers were useful because they save you money by not buying at inflated prices books which disassemble the Spectrum ROM. Of the two the Campbell version is more attractive as it is written in Basic, and one can learn from studying the program listing - warts and all. The Artic version was difficult to follow, as the documentation had not been prepared, but if the Spectrum documentation is as good as the ZX-81 documentation then it will be terrible. Given the incomplete nature of both offerings, the cheaper price, and the ability to convert from hex to dec and vice versa, sometimes with amusing results, the Campbell Systems offering may be better value.