IF YOU'RE planning to upgrade your Spectrum, the new Plus D interface from Miles Gordon Technology - MGT - is definitely worth a look. It's well-designed and amazing
value for money.
For £50 you get a disk interface, parallel printer port, sophisticated software to control both these, and a simple snapshot device that lets you print screens or save
programs of any size to disk.
A 780K 3.5-inch disk drive costs an extra £80 if you buy it at the same time as the interface. You can use any standard 40-track or 80-track drive, but you'd have to
be very well-connected to beat the price of the MGT drive.
The Plus D was designed by Bruce Gordon, who invented the popular Disciple interface two years ago. That was a competitor for the grandfather of all Spectrum
interfaces, Sinclair's aptly-named Interface One. The £90 Disciple is still available from Rockfort Products.
The Plus D might be viewed as a cut-down version of the Disciple, but that would be unjust. The Plus D is a complete, coherent product. It lacks the Disciple's
through-port, joystick and network connections, but still works with the many programs that have been converted to use the Disciple's disk and printer interfaces.
FITS ANY SPECTRUM
£49.95 buys you a plain black metal box, not much bigger than a single cassette case. An edge connector protrudes from one end of the box, and plugs into the back of
your computer. Two ITC (bed-of-nails) sockets are flush with the other end of the box: one connects to the printer, the other to one or two disk drives. A red light
and a small reassuringly rubbery button garnish the top of the box. That's it.
The Plus D fits any type of Spectrum, as it pokes out from the back of the computer rather than vertically upwards. You need about 12cm of clearance at the back of the
computer; it's best not to use the legs at the back of a Spectrum + or 128K, as they would leave the Plus D hanging precariously by its connections.
The metal box isn't just there to make the unit feel chunky - it also acts as a heat sank, keeping the Plus D cool and shielding it from radiated interference.
Inside, there's a neat double-sided circuit board holding a custom PAL chip, a standard 1772 disk controller, 8K of ROM and 8K of RAM. a latch for data being sent to
the printer, and eight 'glue' chips to tie the rest together. Two of these chips have been soldered piggy-back style on top of other components - this looks ugly but
shouldn't cause any problems.
The RAM holds part of the disk-control and printer-control code, and is loaded from disk or cassette when you turn on the system and type RUN. This arrangement makes
the Plus D flexible, though arguably it's unnecessary. You don't need to reload after a reset, unless the system has crashed or been turned off since the last load.
Clever hackers can even run short routines in the Plus D's internal memory without disturbing the main programs.
MANUAL AND MAGAZINE
The Plus D comes with two A5 leaflets - a user's manual and a 'free introductory issue' of FORMAT, the magazine of the Disciple and Plus D users' group. The main
manual is 24 pages of daisywheel type, stuffed with useful information, readable but very dense. There's no index.
This manual is filled with useful practical tips that stem from experience, but it does not document the Plus D completely - some of the error messages are not listed,
and several technical features are only mentioned in passing. It's a good manual, but would nevertheless benefit from a rewrite.
The magazine FORMAT is a gas, with a great mixture of technical articles, advice and gossip. Subscriptions cost £10 a year, and if I were buying a Plus D as a present
I'd be sure to include a subscription. User groups like this one make the purchase of add-ons fun, rather than a risk.
GETTING STARTED WITH CLIFF RICHARD
When you first get your Plus D you must load a cassette to tell the interface about your set-up. The program loads after about three minutes, displays a neat animated
screen and BEEPs out Cliff Richard's sixties Eurovision hit Congratulations! Three tidy screens of text follow, and you're then asked to specify the details of your
disk drive and printer, in a nonthreatening question-and-answer sequence.
There are some memorable printer options, like a facility to print Spectrum user-defined and block graphics. There's a fast screen COPY option, and a slower shaded
printout. The program initially assumes you've got an Epson printer; it's easy to customise the control codes sent, as long as you've got something similar and can
find your way around its manual.
When all the questions have been answered you are invited to put a blank disk in the drive so that the machine can format it and stash away the system details. After
making extremely sure you've put the right disk in, the little light on top of the Plus D goes out, to show that the disk is busy. It takes about a minute and 40
seconds to initialise a 780K disk.
THE MAGIC BUTTON
The easiest way to use the Plus D is via the magic button on the top. You can load games or other programs as normal, and then press the button at the point at which
you want to SAVE them. The button freezes the program temporarily and fills the border with a pattern, while the system waits for you to press a key.
The digits 1 and 2 print the screen out, in either format. Key 3 saves the screen as a disk file, 4 saves an entire 48K program, including the screen, 5 saves 128K,
and X restarts the program.
This snapshot mode is relatively simple. You cant choose file names, enter POKEs or check if a disk is full. Beware, even if you think there's enough free storage to
hold a program - the Plus D can fit no more than 80 files on a disk, and it this limit is exceeded attempts to save will fail and give no message.
When saving a 128K program, you must tell the interface which of the two possible screen displays the program was using, so the right one is picked when the snapshot
reloads. If the picture changes part way through the SAVE, you must enter Y to tell the Plus D to choose the other screen; otherwise, type N.
The manual says that a 48K program saves in 'just over three seconds' -in fact I measured the time, including a period of directory-searching that precedes most file
actions, at about eight seconds, or 16 for a 128K file. Loading takes about half this time. Speeds vary a bit depending upon your drive and what's already on the disk,
but Plus D Snapshots should be fast enough for almost anyone!
Snapshot files are not compressed as they would be by the Multiface, but you can still fit 16 48K snapshots, or six 128K ones, on a single disk. I couldn't find any
programs that could not be saved at the press of the button, but programmers and hardware-designers compete constantly in this area, so there are probably one or two
resistant games around.
The Plus D is fairly compatible with programs designed to work with microdrives. It recognises the same BASIC commands as Sinclair's Interface 1 and also handles the
hook codes that machine-code programmers are supposed to use.
Sadly Sinclair made rather a mess of these codes, so many existing programs jump straight into the microdrive code. This works OK with Interface 1 or with a Swift Disc
as long as you've got their Emulator loaded so the disk code mimics the microdrive very accurately. Unfortunately such jumps usually crash the Plus D.
Beta BASIC and all the HiSoft compilers are among the programs which work without problems. I found that Laser Genius and Cheetah's Sound Sampler were painlessly
converted to run from disk by their microdrive loaders, but the Sound Sampler couldn't LOAD or SAVE to disk. Laser Genius would SAVE and LOAD files, but the CAT
command crashed the system, as did references to microdrive 2. If you want to use software designed to work from microdrive with a Plus D you ought to ask MGT or the
user group about it first.
The Plus D recognises Interface 1 commands, and many useful variations of its own. It allows microdrive syntax, to suit existing microdrives and the Plus D at the same
time. Alternatively, you can use MGT's own simplified syntax.
LOAD and SAVE work with all the usual file types, and SAVE D1 "namel" TO D1 "name2" lets you copy files around a disk, or from one drive to another. Unfortunately this
won't copy snapshots or files created with the OPEN command. Copying is quite fast, even with a single drive, but it overwrites the program in memory, so you should
SAVE that first.
There are two types of CATalogue: one lists disk filenames in three columns, while the other gives full details of each file including its number size and location,
line by line.
If you're after a quick getaway you can load any snapshot by just typing LOAD, followed by P, followed by the catalogue number of the file. This trick doesn't work for
ERASE, the command to delete a file, because that would make it too easy to delete a file by accident.
You don't have to supply full filenames, even so. Most commands work with wild-card symbols - for instance, a question mark stands for any letter, and an asterisk
stands for any sequence of character, so
ERASE D2 "Snap*'
erases all the files with names starting 'Snap' on drive 2. This will include all the snapshot files, which are given arbitrary names when the system creates them.
Later you should rename them with a command like
ERASE D1 "SnapC1A" TO "TechTips"
OPEN and CLOSE set up files, accessed with PRINT and INPUT or INKEY$. The normal microdrive syntax is extended so you can explicitly say whether you want to read or
write a file, but you can't use random access to skip around a file at will unless you're also using the latest version of Beta BASIC - a fine add-on for serious BASIC
programmers, but £16 extra.
As compensation, everyone gets direct access to the disk surface, in 510-byte lumps, via the hacking commands LOAD@ and SAVE@. POKE@ commands let you change the system
configuration as a BASIC program runs. LLIST and LPRINT send programs and data to the printer port of your choice, and SAVE SCREEN$ copies the display to the printer.
MOVE transfers data from one stream to another. 128 BASIC crashes if you try to MOVE a file to the screen, but 48K BASIC lets you MOVE data to any device.
At its £129.95 total price (including the 780K-capacity 3.5-inch disk drive), the Plus D system is strongly recommended to anyone frustrated by cassette loading. It's
even worth considering just as a printer interface, if there's a possibility you'll want disks in future.
Sixword's £150 Swift Disc system (reviewed in CRASH issue 44) is still competitive, particularly if you're interested in upgrading from a microdrive system. Both the
Swift and the Plus D have unique features, and they're much closer in price than any competitors.
Amstrad's Spectrum + 3 has serious compatibility problems and needs a £45 Multiface 3 before it can even approximate to the performance of an older Spectrum with a
Post-Christmas trade rumour has it that the +2 sold quite well but the +3 bombed, in the absence of much software on the slow and pricy three-inch disk format. It
won't be surprising if there's a further big cut in the price of the +3 soon, following the £50 cut to £199 in September. Even so, I don't think it will tempt many
people who already own Spectrums - in particular 128Ks - away from the Plus D or Swift systems, which are superior upgrades.