SPECTRUM FINDS ITSELF AT FULL STRETCH

Sinclair has been overtaken by other suppliers of upgrades. Stephen Adams reports.

The Spectrum is in four basic forms. Model 1s which have two IC-type sockets into which a printed circuit board is plugged and model 2s which have all the RAM fitted on to the main printed circuit board. There are, of course, two types in each category, the 48K and the 16K.

The 48K cannot be expanded, as all the existing memory space is covered with either ROM or RAM - all 64K of it. The ROM can be switched-out externally to add different ROMs using the ROMCS but the RAM cannot as there is no equivalent RAMCS.

Therefore all memory expansions can be done only to the 16K models. As the computer already contains 16K of RAM, the top 32K of memory area - 32K-64K - is the only space to put it. Most memory expansions fill the space with 32K worth of RAM chips but the East London Robotics 64K add-on - the SP80 - has two sets of 32K RAM which can be switched in and out under a program instruction or from the keyboard.

The kits consist of four memory-decoding chips, except model 1 versions where all the chips are soldered to a PCB, and eight 32K by one-bit chips. Those RAM chips are very sensitive to static electricity and warnings are included in all the instruction sheets. The way to handle them properly is not to remove them from their protective packaging until needed and to keep touching an earthed object such as a radiator or gas pipe occasionally to release the static charge. The static can be caused by nylon or wool in your clothing being rubbed.

Putting-in the chips can be a little difficult and it is recommended that you check that the pins are straight before you insert them. The Fox Electronics kit has the pins already straightened. Also check that none of the pins is bent outside the socket or underneath the chip when you have finished.

The best technique to use is to put all the pins on one side into the socket and then to pull the pins on the other side over the holes in the other side of the socket. Once both sets of pins are resting in the socket holes you can push down gently on the chip to push it into its socket.

The instructions vary from a four-page, step-by-step meticulous description by Delta Research to one page just listing where the chips go by Fuller. Apart from the Fuller instructions all provided sufficient detail to allow you to know where each chip goes and what precautions to take.

As part of its instructions Fox Electronics also includes a sheet showing how to tune the colour on a Spectrum to give better results. It also shows you how to tell whether it is the Spectrum or the TV set causing a problem. Sheets normally cost £1 from Fountain Electronics but are free with its RAM kit, along with a small Basic program to demonstrate the usefulness of 48K.

The fitting of the Fox kit was the easiest but if you have problems you can send back the kit with the details of the Spectrum at any time in the following 12 months. East London Robotics will fit the chips at an extra cost of £7 by post or £3 by personal visit.

Delta sends a memory test tape which checks all the memory by using a machine code program going through at least all the manufacturer's specifications. The tape can be used to keep an eye on suspect memory faults as it stops with an error which can then be sent back to Delta or Sinclair. The tape normally would cost £3.50 and is a really comprehensive test taking at least eight minutes.

East London Robotics and Delta were the only model 1 boards we could test and both could be fitted easily with less trouble than the model 2.

East London Robotics also does an SP80 kit which can provide 64K of memory in the same sockets as the SP48 (48K) fitted. That is achieved by having two separate banks of 32K, switched by an OUT instruction.

That is possible only because of the 64K RAM chips which are used instead of the 32K RAMs and a massive modification of the decoding chips which plug into the Spectrum. No soldering is required but some care needs to be taken inserting the chips, as three of them are wired together using twisted insulated wire.

A LED is also soldered on to one of the chips to indicate which bank is being used. The only problem is that you can see it only with the top off or looking through the edge-connector hole. The LED lights when it is in bank two and when the machine is turned on the light shows on bank one.

The only problem with the SP80 is that the stack and any program running in it must be in the 16K of memory provided by Sinclair. If it was allowed to go into the top 32K it would be switched-out on the first OUT instruction and the program would have nowhere to go.

Also the machine code stack for return addresses would have to be in the lower 16K area for the same reason. That leaves the user to develop a program which will be able to use banks of memory without having the convenience of Sinclair Basic to cope with it.

Prices of the various kits are detailed, along with an indication of how good the instructions were, guarantee period and number of tests performed on memory after fitting.

It is also possible to add a RAM pack on the back of the Spectrum. A Spectrum-type 32K RAM pack has been produced by Cheetah Marketing Ltd. It fits very snugly on the back of the Spectrum and because it is outside the case it does not matter if it is model 1 or model 2.

It also has an extension piece on the hack so that you can plug in Microdrives when they arrive. The RAM pack has no known wobble in use and can be fitted very easily by plugging it into the expansion port. It costs £39.95.

The alternative is to use a ZX-81-type RAM pack with an adaptor to give you another 16K or 32K. To use it you will require an adaptor.

EPROM Services and myself both make adaptors for the 16K RAM pack. Mine can also cope with a 64K RAM pack to give a full 32K by changing a soldered strap on the board or ordering a 64K version. I also produce an Adam II which lets you have a 16K RAM pack on the back of the Spectrum but which also allows devices which used to work in the popular 8K-16K region to work in the 56-64K region of the Spectrum. All the adaptors mentioned cost £9.

Of the RAM packs and kits reviewed. Fox Electronics for kits and Cheetah for RAM packs stand out as good value for money.

Fox Electronics. 141 Abbey Road, Basingstoke, Hampshire. Tel: 0256-20671

Cheetah Marketing, 359 The Strand, London WC2 0HS. Tel. 01-240-7939.

East London Robotics, No. 11 Gate, Royal Albert Docks, London E16. Tel: 01-471-3308.

Delta Research - cheques to Servodata Ltd - 15 Church Street, Basingstoke, Hampshire. Tel: 0635-45373.

Fuller Micro System, 71 Dale Street. Liverpool 2.

Eprom Services, 3 Wedgewood Drive, Leeds LS8 1EF Tel: 0532 667183

Stephen Adams, 1 Leswin Road, London N16 7NL.

IMPROVED MEMORY FOR UPGRADING SPECTRUMS

East London Robotics has improved its SP48 kit which upgrades issue 2 and issue 3 Spectrums from 16K to 48K. The new kit, SP48b, has been introduced because Issue 3 Spectrums need an additional link to be made on the PCB. The kit includes a small metal clip which solves that problem.

The instructions supplied with the kit are clear and straightforward, most useful being a photocopy of the inside of a Spectrum with the positions of the chips marked and also showing the way they go.

If care is taken, fitting the kit can be attempted by anyone, whether having electrical knowledge or not.

To test the kit fully we obtained a 16K Issue 3 Spectrum and fitted it and, as always seems to happen when a number of people are watching, it did not work. We telephoned the ELR panic number and the problem was easily pin-pointed and a replacement chip sent.

It should be pointed out that the error was not due to ELR but a mismatch between two of the chips.

The offending chip was swapped temporarily with one from another piece of equipment and both worked after the transplant.

Also included with the kit is a free software tape entitled Beyond Horizons. It is a very basic program giving a few pointers on how the Spectrum works.

The SP48b costs £23, the kit for Issue One Spectrums is £35 plus 65p p&p, and is available by mail order from East London Robotics Ltd, Gate 11, Royal Albert Docks, London E11. Tel: 01-474 4430.

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.

EXPANSION FOR THE SPECTRUM

East London Robotics has produced a 64K add-on RAM board for a 16K Spectrum costing £50. It fits inside the Spectrum in the sockets provided for the Sinclair 32K board. The RAM is in two banks of 32K and is switched over by an OUT instruction. LEDs indicate which block is in use.

Contact East London Robotics, Finlandia House, 14 Darwell Close, East Ham, London, for your 80K Spectrum. Tel: 01-471-3308.