John Lettice welcomes a centronics interface for the Jupiter Ace and Sinclair Spectrum
ust a few months ago the Sinclair Spectrum and the Jupiter Ace were pretty lonely machines. It was difficult
to link them to a wide range of peripherals because of the dearth of interfaces. While there were some interfaces available for the Spectrum, Ace owners must certainly have been feeling aggrieved at the lack of support their machine was getting.
The Spectrum, of course, has had a run of excellent interfacing devices recently, courtesy of Sinclair Research. The launch of the ADS Centronics Interface also means that the Ace, if not coming in from the cold, has at least been thrown a pair of gloves.
The ADS comes in two versions, the straight interface for the Spectrum, which plugs firmly into the edge connector and will drive any Centronics printer, and the slightly more complicated version for the Ace. Here you first fit an adaptor card to your Ace, then connect the interface and your RAMpack to the card.
A tape with the necessary driver software-Spectrum on one side, Ace on the other comes with the ADS. In the case of the Spectrum, this is a piece of relocatable machine code. This means that it can be shifted around in RAM, and will therefore work with all but the fussiest of programs.
However, it is unlikely to work with software that moves RAMtop.
In the event of your having any difficulty with a particular program, clear instructions are given on moving the code's location.
Things proceed just as smoothly with the Ace, although Ace users are much more likely to be using the ADS to take advantage of the ZX Printer, rather than testing the joys of 80 columns. Using the command PRTON will send all output via the interface to the printer, while PRTOFF switches this off. COPY will get you a screen dump.
It can't be often that a single device can have (apparently) two such widely differing applications. For the Spectrum, the obvious thing to do was to run micro, printer and Tasword 2 as a word processing system, and the three seemed to get on very well together.
Considering the dearth of software for the Ace, the most likely use for the ADS will be to provide a hard copy output for program listings, and again it does this well. It probably would not make sense to run it with anything more expensive than the ZX printer, unless you already had a larger one, but this set up should provide all the
budding Forth programmer is likely to need. Of course there are hazards with any interfacing project of this kind.
The Spectrum's tokenised keywords are a particularly obvious problem. As the letters of the commands are stored as single tokens rather than as separate ASCII codes, just sending them to the printer would not work.
The ADS therefore decodes the tokens and translates them into the ASCII codes that will be understood by the printer. The software assumes that codes above the value of 164 are tokens, but should you need to send data bytes above this value you can.
Using the Spectrum's Basic COPY command also causes problems, so if you wish to use this command you must use a routine (provided on the driver software cassette) which emulates this. You call it by using RANDOMISE USR 23310, which dumps the screen contents to the printer.
The code provided drives a Seikosha GP-250X, but information is provided to allow you to alter it for other graphics printers.
As far as the Ace is concerned, things are rather more DIY. Once you've got over the initial shock of being able to use word processor class printers and graphics plotters, you'll probably start wondering where you're going to get the word processor class software to run with it.
From the point of view of the Ace owner. the ADS interface is undoubtedly a winner. At £34.50 it's a reasonably cheap way to use the ZX Printer to produce hard copy listings, and although it's clearly something of an uphill task, it at least means the hardware for more complicated text and graphics handling is there.
Its position vis-a-vis the Spectrum is a
little more problematical. Granted, it's a cheap and effective Centronics interface, but with Sinclair Research plunging into interfaces in a big way, Spectrum owners may be thinking more in terms of going RS232 with Interface 1.
That said, there will be Spectrum owners who'll want a Centronics interface, and in terms of efficiency and value for money, the ADS is certainly highly competitive.
Item ADS Centronics Interface Machine ZX Spectrum and Jupiter Ace Price
£34,50 Contact Advanced Digital Systems, x Bonchurch Road, Portsmouth, Hants PO4 8RY, tel 1234-123456.