CRASH - The Online Edition
— Issue 50 Contents|
Tech Niche: Sinclair
Tech Niche: SAM Coupe
ONE of the most popular and versatile Spectrum add-ons is the ‘magic button’ interface, which lets you interrupt the operation of any program, run a routine, and return to the original program later.
All the devices reviewed here work much the same way. They turn off an area of fixed program in the Spectrum’s memory — the ROM that recognises what you type when you turn the machine on — and replace it with memory into which you can load anything you like. Sometimes they also contain their own fixed program.
Lots of firms have made this sort of device. Once-popular devices such as the Mirage Microdriver and Interface 3 are no longer on sale, and the remaining companies spend lots of time developing their products and adding extra bells and whistles.
Most magic-button interfaces provide several extra hardware tricks besides the basic interruption facility. Prices and options vary widely. This article reviews four major models: the Multiface and Multiprint, made by Romantic Robot; Datel’s Snapshot 2; the Swift Disc, made by Sixword; and the Plus D and Disciple interfaces from Miles Gordon Technology (MGT — producer of the Spectrum superclone SAM). (The Disciple is marketed by Rockfort Products.)
There are three main uses for magic button devices: program-copying, screen-printing and hacking, which is best defined as ‘changing the operation of existing programs to make them more interesting’.
First and foremost, magic buttons make it easy to copy games to microdrive, cassette or disk. These devices can save the entire contents of memory — including register values — in a big file, like a photo or snapshot of the state of the machine.
As long as the device saves everything there’s no way the program can tell it’s been interrupted, and the snapshot copy will restart wherever it left off as soon as you reload it.
This is good news if you want to speed up loading of a program, as it makes it easy to save the program on any device. Most commercial disk systems would be useless without such a facility, because programs are usually protected to make it difficult for people to read the tape and write out an identical copy.
Software houses don’t like disk systems, though arguably disks encourage people to play games — they see it as too easy for a gang of people to buy one tape and then use a snapshot device to take lots of copies of it, stripped of the antipirate protection. Unfortunately this attitude lumps honest users of disk systems in with the thieves.
If you’re playing games, or developing something on the screen — text or graphics — you can use the magic button to grab a screen, either saving it on disk or tape to be reloaded later or printing it out.
With this useful facility you can keep print-outs of screens as progress reports, and they’re a wonderful way to make a map of a multiscreen arcade game, a simulation or a text adventure.
Black text on white paper is always the easiest and quickest type of print-out, but some routines can print graphics in shades of grey. (You have to have the right printer — see Choosing A Printer in this supplement.)
The third — and to my mind most interesting — application of the magic button is hacking. You can load all sorts of programs into an interface and call them up any time by pressing the button.
The CRASH Tech Tape contains a program that illustrates this idea very nicely. Three In One, by Khalid Rafiq, is a short, fast-loading program that works with the Multiface One, Multiface 128 and Multiprint. It lets you have three programs on the go on one computer at the same time!
The only restriction is that the programs should fit into 16K of memory, so that there’s room for three in 48K. This is a limitation, but not a serious problem — many good early Spectrum games and utilities were designed to run on 16K systems, because the original entry-level Spectrum had only 16K of memory.
You can run any three programs, BASIC or machine-code, at once. I’ve had no trouble running such classics as Don Priestley’s 3D Tanx as well as Gold Mine and Munchman, two early 16K games written by people with the unlikely names of Simon N Goodwin and Derek Brewster. Good 16K games include Deathchase and JetPac.
Three In One doesn’t give true multitasking, as any one time only the program shown on the screen is running, but it’s fun. Now you can play a game, switch to BASIC whenever you want to work something out, and then go back to the game instantly.
The screen is always kept up to date, but the border colour can take a while to catch up with you. And it takes less than a second to swap programs, but it’s important not to press the button again before the next program restarts, or Three In One may get knotted.
The utility runs in 48K mode on a Spectrum 128K, so it doesn’t use the extra memory. It should be possible to adapt it to run more or larger programs in 128 mode.
Tech Niche regularly carries tips and new information on all Spectrum add-ons
Some magic-button devices contain simple editors with which you can change crucial instructions in the main program to give yourself extra turns in a game, or to change the score or the playing conditions.
These changes, or POKEs, are discovered by keen programmers who analyse commercial software and work out interesting ways to alter them. The Playing Tips section of CRASH is always full of Multiface POKEs which can be used with most magic-button devices.
Some programs try to work out POKEs for you automatically. These don’t always come up with anything useful, and they can easily crash a program by adjusting something that should be left alone, but they’re great fun to play with.
The first such program was The Gamester, featured in CRASH Issue 41. This program runs on the Multiface One, Multiface 128 and Snapshot 2 devices. It will search for POKEs to give you infinite lives in games, and works quite well with some programs. It also lets you run most games at half or quarter speed, which may be useful if you want to cheat or take photographs.
The Gamester sells for £5, and is available direct from author DR Walton [address deleted]. When ordering it, be sure to say which interface you own. CRASH readers who bought the first version are allowed a free upgrade if they return their original tape.
Romantic Robot has recently released its own version of this idea — the £7 Lifeguard program will work out POKEs for you automatically.
Both The Gamester and Lifeguard are rather unpredictable, because they both work by looking blindly through the contents of memory, adjusting parts of the program that appear to keep count of something, in the hope that the change will make the program easier to use.
Lifeguard is a bit less hit-and-miss than The Gamester, but has much the same effects and limitations. It works with three of Romantic Robot’s own interfaces: the Multiface One, Multiface 128 and Multiprint.
The POKEs in magazines are usually sent in by programmers who use a mixture of automatic and manual techniques to analyse a program before they start fiddling with it. This is hard work but has great potential, as in theory a good hacker can make just about any change that the original programmer could have made. Quite significant changes to gameplay are possible...
The problem is that you have very little information when you’re putting in POKEs. Everything in the program — code, graphics, sounds, scores and so on — is muddled together in a stream of 49,152 numbers.
But Romantic Robot sells a £9.95 package called Genie that lets you analyse the contents of memory in detail.
Genie can search for text or other patterns in memory, has good facilities to edit a program, and can automatically translate numbers in memory into assembly-language program instructions.
This process, called disassembly, makes it easy to follow other people’s programs, but you must be able to read assembly language or you won’t be able to tell real programs from the misleading information that you get if you try to disassemble graphics or other data! Genie works with the same gadgets as Lifeguard, but you can’t use the two programs simultaneously.
Genie won’t work with magic-button disk systems, but Sixword is working on its own monitor/disassembler package to run with the Swift Disc.
The company has already produced a microdrive-emulator package that makes its disk drive behave like up to four very fast microdrives. When the £12 emulator is loaded you can run special versions of serious programs that allow microdrive filing but wouldn’t be able to handle the disk unless they were heavily changed.
Normally the magic button on the Swift Disc calls up a new command level. The bottom two thirds of the screen are cleared temporarily, and you can type in a wide range of commands affecting the disk drive and the program in memory.
You can enter POKEs, read the disk directory, save, load, erase and protect files. You can format new disks, load and save sections of memory including the screen, and copy programs from one drive to another. When you’ve finished housekeeping the old display reappears and everything continues as before.
The magic button on the Disciple disk system and the Plus D, both from MGT, is more limited. They let you print the screen display in black-and-white or shades of grey, as long as you’ve got a printer that works something like an Epson. Alternatively you can save the display on disk, or save the entire contents of memory as a 48K or 128K file.
The Multifaces are add-ons, rather than controllers of disks and printers. The £34.95 Multiface One, designed to run on 48K Spectrums, can save and load 48K programs and screens on tape, microdrive, wafadrive and most disk systems. Files are written in a compressed form, to save space and speed up loading.
It also lets you print the screen display if you’ve already got an appropriate printer wired up. You can enter POKEs, and load utilities like The Gamester, Lifeguard and Genie into its 8K RAM. It has one Kempston-standard joystick interface built in.
The Multiface 128 is similar but can save 128K programs as well as 48K ones; it costs an extra £5. Both Multifaces annoy software houses by allowing you to reload files you saved even if the Multiface is not present — in other words, they produce files that can be freely copied.
By far the cheapest snapshot device is the eponymous (LMLWD) Snapshot 2 from Datel, which costs just £25. But this is less of a bargain than seems — the one CRASH tested last year was hard to use and unreliable.
Unlike the Multifaces, the Snapshot 2 does not contain a built-in program, so you must load a file from tape or disc before starting to use it. It is meant to transfer compressed files to cassette files or microdrive.
Readers’ impressions have been mixed — some people find it works OK, but others have had to return it as unusable. The software I received had bugs, the built-in joystick interface wouldn’t work with all sticks and despite hours of trying I was only able to persuade the Snapshot 2 to transfer one old program to microdrive.
I suspect that there is something wrong with the design that stops it working on all Spectrums; sloppy design and assembly do not encourage me to recommend the Snapshot 2.
When Amstrad launched the +3 last year it changed the Spectrum design so that none of the existing magic-button devices would work. And the new design made it almost impossible to transfer programs to the disk drive built into the computer; since very few programs are available on disk, that left a lot of frustrated users.
Romantic Robot has resolved this frustration, at a price, by launching the Multiface 3, a new magic-button device specifically for the +3. The new unit lets you save and load programs or screens, format disks and erase files, from 128K or 48K BASIC. You can also examine memory and enter POKEs.
The Multiface 3 is quite different from its predecessors — there’s no joystick socket, and no room to load current versions of Genie, The Gamester or Lifeguard. In theory +3 programs can be written in such a way that the Multiface can’t copy them, but in practice it seems to be able to cope with just about everything on the market at the moment.
The Multiface 3 costs £39.95, or £44.95 with a through port. It’s so useful to the +3-owner that it’s almost an essential purchase, but it’s important to bear that extra £44.95 in mind if you’re considering buying a +3. You may be better off with an older, more compatible Spectrum and a superior disk system from MGT, Rockfort or Sixword.
Romantic Robot’s Multiprint combines the magic button with a parallel printer interface. You can print out screens or send controls codes to the printer at any time, but it won’t save software for you. The print-out routines assume you have an Epson-compatible printer, though the Multiprint will work with most other parallel printers except for printing graphics. And it works with any Spectrum except the +3.
The Multiprint has 8K of RAM and 8K of ROM, like other Multifaces, so you can use it to run Genie, Three In One and Lifeguard. It also includes the Multiface Toolkit, which lets you examine memory and enter POKEs.
The Multiprint cost £39.95 when it was reviewed last year in CRASH Issue 40, but Romantic Robot couldn’t justify that price after MGT’s Plus D appeared, so it’s now £29.95. That’s good value if you need a printer interface and you’re sure you won’t want a disk drive for your Spectrum. The price goes up by £5 if you need a through port to plug other peripherals, such as joystick interfaces, into the back of the Multiprint and use them at the same time as your printer.