Although nowhere near as profuse as Spectrum software, various add-ons have now appeared to bridge the gaps in the micro's specification. Tim Langdell reviews.

It is almost a truism to say the Spectrum has been pushed to its limits. A great deal of time has been devoted by software houses to creating programs that put more sophisticated machines with less well-thought-out software to shame. Nevertheless, there is scope for peripherals which even up some of the Spectrum's primary hardware inadequacies.

UNDER CONTROL

Following up its success with a controller - that is, a device which allows you to switch between Loading and Saving, disconnecting the computer when saving and vice versa - Abacus has introduced one for the Spectrum. This means more reliable Saving and Loading. Unlike the ZX-81 version, the Spectrum controller also includes an amplifier, a particularly useful feature in view of the Spectrum's own weakness in amplification. Setting up the controller simply requires plugging the Spectrum's power supply into the side of the Abacus box and the power lead from the box into the back of the Spectrum. The Mic and Amp leads are used to connect the Spectrum to the tape recorder.

Kempston's joystick is a standard design with fire button and control stick working on a switching rather than analogue base.

This means that it can be used to simulate the detection of keypresses. The joystick is mapped to Port 31 of the Spectrum, and can be accessed with the IN command.

The value returned by detecting Port 31 in this manner can be between 0 and 26 with the eight directions from forward through NE to E, SE, S and so on being values 1 to 10 - omitting 3 and 7 - and the fire button returning 16. The joystick can be read in machine code too for a faster response and arcade-like action.

The joystick's connector is a small black plastic box with two matt-black TTL chips visible on the outside which plugs straight in to the Spectrum's printed-circuit board. The joystick itself is very responsive. My only quibble is that a spring-back-to-centre mechanism would make the central off position easier to reach when playing fast arcade games. The joystick costs £19.50.

This company has also brought out one of the first 24-line I/O ports for the Spectrum. Simply constructed - a single TTL chip supports the operation of the 8255 PPI chip - the board comes with clear documentation which indicates how one can use the three 16-pin dual in-line sockets or a 24-way edge-connector attached to the back of the printed circuit board. The 8255 chip has several modes of operation: the three I/O ports can be configured in the following ways - setting up one bank as inputs, another as outputs, with the option of "handshaking" on port C.

Using the In and Out commands the port can be accessed from both Basic and machine code. Apart from the back-to-back edge connector the port can be limited to the Spectrum with a stackable edge-connector, or a motherboard. The stackable edge-connector allows an extra device to be attached to the Micro whilst the PPI is attached. The motherboard will take two cards in edge-connector sockets as well as a Printer or a Microdrive. The motherboard is supplied with its own 5V regulator.

The 24-line PPI has been configured in the Spectrum's I/O map so that it will not clash with the Printer Microdrive or RS-232 interface. The PPI costs £16.50, the stackable connector is £5.50, and the two-slot motherboard is £16.95.

ADD ZX-81 HARDWARE

There are three Adam adaptors for the Spectrum; each allows you to add ZX-81 hardware on to your machine. The fundamental adaptor provides a ZX-81-compatible output port at the rear of the Spectrum, but no address conversions. The adaptor comes with a computer printout description which tells you how to attach memory-mapped devices which do not decode the lower five address lines in the I/O map. The next adaptor - the Adam II adaptor - allows the simultaneous use of two sets of peripherals on the rear of a 16K Spectrum. This adaptor allows you to attach a ZX-81 16K RAMpack to a 16K Spectrum.

The Adam II adaptor can interface with any ZX-81 peripheral which was designed to work in the 0 to 16K region of the ZX-81's memory map, by using it in the 48K to 64K region of the Spectrum's map. Thus ZX-81 equipment will require 49152 to be added to its addressing, and for this reason EPROMs designed to work on the ZX-81 will probably not work on the Spectrum.

Finally, there is the more adventurous Eve adaptor, for those with a 48K Spectrum. With a 48K Spectrum all 64K of the address lines on the Z-80A CPU are already accounted for - 16K ROM and 48K RAM - hence adding any device mapped in the RAM area seems impossible; especially as Sinclair did not provide a RAMCS line at the rear which would have allowed us to turn off some, or all, of the internal RAM. By adding this adaptor and making a few soldering connections inside your Spectrum you can turn off 8K of the upper 32K of RAM and map devices into this area. Of course, making the alteration could invalidate your guarantee.

The RZ-1 Tape Controller is another more recent device from Stephen Adams. It provides both Spectrum and ZX-81 owners with a programmable tape control unit for stopping and starting the cassette motor under software control, or disconnecting the load lead when Saving and vice versa. The RZ-1 plugs in via an edge-connector. The rear connector of the machine is duplicated behind the RZ-1, so a peripheral unit can still be attached. The RZ-1 can control two tape recorders and provide a minimum of five latched outputs for controlling external devices.

Furthermore, it does not use any memory locations, either in RAM or in the I/O map. The unit is located in ROM space between 512 and 1024. Poking various locations in this region allows you to turn on any of the tape motors, or to provide an output to one of the ports.

UPGRADE RANGE

East London Robotics provides a range of RAM upgrades for the Spectrum: the SP-48A which adds a further 32K of RAM to the 16K Spectrum Series 1 on a plug-in board; the SP48 for the current Series 2 version of the Spectrum and an SP-80 RAM add-on which gives not only 32K of extra memory but another 32K which can be accessed as well, using Out commands. It is thus possible to use a full 80K of user RAM with this board.

East London Robotics' Slowloader allows you to load ZX-81 programs into a ZX Spectrum.

The Slowloader adapts itself upon loading to whichever type of Spectrum is in use.

CONCLUSIONS

Perhaps if Sinclair had put a little more thought into primary design, devices like the Abacus controller probably would not be necessary. Its boost to the Spectrum's amplification is useful, as is the capability to switch it off when the keyboard bleeper gets on your nerves.

Once Kempston's joystick is fitted, nothing else can be added to the connector. But what sort of peripheral would you use in conjunction with a joystick? By putting a stackable connector between the Spectrum and the stick's connector one could test the joystick with the supplied demonstration program.

The Adam adaptors are extremely useful, but consider whether or not you really want to make hardware alterations.

The Adams tape controller is effectively transparent to the Spectrum or ZX-81, since it does not use any memory location either in RAM or in the I/O map. The relays involved can cope with 1A at 28V dc or 100V ac. They are sufficiently heavy-duty for many purposes like controlling model train layouts.

THE INGENUITY OF THE PERIPHERALS MANUFACTURERS HAS CONTINUED AND SINCLAIR RESEARCH FINALLY LAUNCHED THE MICRODRIVE. STEPHEN ADAMS REVIEWS ANOTHER INTERESTING YEAR FOR SINCLAIR USERS.

INGENUITY BEATS SPECTRUM LIMITS

Stephen Adams summarises the add-ons.

The biggest blow to users of non-Sinclair-produced equipment was the announcement of the Spectrum. It knocked most memory-mapped add-ons on the head, as no provision for those devices had been made. That was because, unlike the ZX-81, there was no way of turning-off the internal RAM from the expansion port. The only thing left was for producers to put things in the input/output map or to supply RAM packs or RAM upgrade kits.

The I/O map was already full of Sinclair devices, allowing the use of only eight separate devices, if they wanted them to be compatible with the Microdrive. Nevertheless, ingenuity brought forward a large number of new devices after the initial shock had worn off.

RAM kits for upgrading the 16K Spectrum to 32K are now readily available for about £21. Fox Electronics, for example, supplies a kit for £20.99 and it has instructions on how to improve your TV display. They are easy to fit and now have simple instructions on what to do, if you can overcome the fear of opening the case. The kits are usually identical to the proposed Sinclair upgrade but will fit only on model 2-type Spectrums. East London Robotics can also supply an extra 64K kit which is paged.

For those with a model 1 Spectrum, identified easily by the grey keys, there is the choice of an add-on board made by Downsway Electronics or the Spectrum 32K RAM pack by Cheetah Marketing. The Spectrum RAM pack will also fit on to any other Spectrum, as it plugs into the expansion port.

Another memory-mapped device available this year was in a surprising place, inside the Spectrum 16K ROM space. It was the Orme Electronics ROM containing RENUMBER, block delete of Basic lines and many other usefiil routines in a 2K ROM. That can be very useful, as it is immediately available on power-up.

Sinclair has also provided new devices in the ROM space, which should please hardware and software users. One is the Microdrive Interface One which not only contains the controlling ULA and hardware to run the RS232/network/highspeed cassette Microdrive but an extra ROM which can be used to write your own Basic commands. The other is the ROM cartridge system available with Interface Two.

The RS232 can handle a printer easily with its limited handshaking ability but Still is limited for input from an RS232 device, as all that is under software control and not a hardware chip. The network is a very simple arrangement which allows you to talk between 64 Spectrums but I have no doubt that someone will write similar software to use it with the ZX-81 through the cassette sockets. Two books which should help in this respect are those by Andrew Pennel and Dr Ian Logan.

The Pennel one also contains an ON ERROR GOTO machine code routine which should trap 90 percent of Basic errors and send them to a program line to deal with them.

Sinclair has also launched the Interface Two, containing two joystick sockets which will operate the first or last set of five number keys. That will mean that software will have to be re-written to use Sinclair joysticks, as the accepted standard at the moment is the one set earlier in the year by the Kempston joystick interface which operates as an I/O device, depending for its decoding on A6 only being low.

Much software has already been converted to use it and I cannot see software writers wanting to do it all again. Programmable joysticks are just starting to reach the market, which will eliminate the need to rewrite the software.

For the Spectrum and soon the ZX-81, the Stonechip one seems to be best. For ZX-81 and Spectrum users, a cheaper hardware-based version, the Pickard controller, can be used as it fits both computers by plugging into the keyboard sockets. The AGF version uses crocodile clips to set up the five keys to be used; it is a little unstable but it plugs into the edge connector and does not require entering the machine.

The Interface Two also has a single ROM socket which allows you to use Sinclair-designed cartridges. It is not known whether software suppliers will want to try to fit normal ROMs to a port like this. That, and the fact that recording Microdrive cartridges is a slow process, will limit the amount of software available from software manufacturers on Sinclair devices. EPROM software for ZX-81s is available from Eprom Services and Audio Computers.

Both, however, concentrate on the machine code user and not the games player. The fall in price of the ZX-81 and the amount of hardware available for it has started to attract the business user as a control processor for a robot or controlling some industrial process.

That is because it contains all the requirements of the development system on one board - Z-80-A, one of the most popular processors, working at 3.25MHz, TV interface, cassette interface for program storage, alphanumeric keyboard, Basic as well as machine code monitor for designing programs, and an expandable memory map and I/O map.

There is also a wide range of machine code assemblers, disassemblers, EPROM cards and blowers, RAM, battery-backed memory already available, costing just a few pounds. That to the industrial process manufacturer is peanuts, as a development kit from a chip manufacturer would cost more than £200 with far fewer facilities. The ZX-81 costs only £45 with a massive 16K memory included.

Plain-paper printer interfaces for the Spectrum abound and Tasword, the word processing program, can work with most of them. Hilderbay and Kempston provide software-driven Centronics versions, while Morex provides both RS232 and Centronics outputs. Deans also introduced its version of the Timex printer, which uses a much better paper than the Sinclair, gives a clearer print in both black and blue ink, and will use Sinclair commands to control it, so there is no need for extra software.

Printers and other hardware devices make the software "come alive" and that combination makes the Spectrum a very powerful business computer.

That is the most important event of the year, as the more software which is written to use the large amount of hardware, the more that hardware will be used. Voice output units, modems - to talk to other users or databases over the telephone - RS232 interfaces and light pens all rely on good software to make use of them.

The Cheetah Marketing Sweet Talker, for instance, works better because it is accompanied by an instruction tape which not only demonstrates how to use the unit but also shows the user how to structure programs to make it easier to use in their programs.

Modems from Maplin, Ambit and Micronet - for Prestel - will allow users of the Spectrum and, in the first two cases, the ZX-81, to talk to many other computers. Some of them will be other types of computers, like the BBC and the Commodore 64. The others will be maintained by public and private companies which maintain large amounts of information and programs on their computers.

Micronet 800 is a database maintained on Prestel computers as a 24-hour-a-day, seven-day-a-week computer club. It has hints and tips on Spectrums - ZX-81s at the moment cannot use the system - as well as news, free programs and a mail box facility. Keyboards and consoles also have been making their presence felt as ZX-81 and Spectrum users want to upgrade their machines. Plastic cases from W H Smith are about the cheapest containers at £3.99 and will take a ZX-81 or Spectrum, as well as a few add-ons. The d'Ktronics keyboard and case or that from Fullers appear to be the most popular but neither will allow the use of the Microdrive interface without taking it out of its case.

The Filesixty button set is a cheap alternative for ZX-81 users which gives the advantage of spring-loaded keyboard the same size as that of Sinclair, but without costing more than £10.

Colour for the ZX~81 is now available in a simple form for all PAL television users - that is, most of Europe. The black box requires only two wires to insert between the modulator and the breaking of tracks and can be re-connected if required. The rest of the box plugs into the back of the ZX-81 to give black characters on a choice of 16 coloured backgrounds or coloured characters on a black background from DDC. It is also more stable than the Spectrum and requires no extra memory to use it. It will work even on a 1K machine.

One device which requires extra memory is the excellent High-res screen - 192 by 256 pixels - and user-definable graphics package made by Nottingdale Technology Centre. It uses the ZX-81 internal 1K RAM for its system variables and 6K of memory for the storage of the screen in the program. No internal wiring is required, as the unit plugs directly on to the back of the ZX-81.

For the Spectrum, a unit has appeared which will be of great delight to children and disabled users. It is the Currah microSpeech unit which plugs into the back of the Spectrum and, on command, will speak the key pressed. That happens during program input as well as INPUT and INKEY$.

It requires no programming of the speech by the user. Speech output can also be programmed by using S$ to contain the allophones - sounds which make up words - which are then spoken immediately. Thus input and output can be spoken rather than read.

Tapes have been causing problems ever since the ZX computers came into existence; the Spectrum is better than the ZX-81 but still can be improved with some extra hardware.

Tape filters and switch-controlled SAVE and LOAD devices are available from several firms, like Abacus and Elinca. There have now been three Spectrums produced by Sinclair. The model is, which can be identified by the grey keys or by looking through the expansion interface and seeing an IC socket on the left-hand side; the model 25 have the large, black, ROM chip there. Those Spectrums need their extra 32K of RAM mounted on a printed circuit board before they can be put into the computer. There are no Sinclair RAM boards available for the machine.

The model 25 were re-designed completely by a computer and the ULA was changed to get rid of an extra 1C which had to be inserted in the model is, due to a design error. The extra 32K of RAM which can be added to 16K machine now requires only chips to be plugged into sockets on the board. Model 1s and model 2s have had to have an extra transistor fitted to prevent a clash between the keyboard and the ULA TV interface.

The latest model 3s have also had their internal circuitry re-arranged and the ULA updated to give a wider tuning range on TV sets. It has also caused some software problems, as the keyboard inputs are no longer held to binary l - + 5 volts - when not in use. That was done to reduce the power 1 requirements of the ULA.