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Utility: I/O Handling
ZX Spectrum 48K

Chris Bourne


U-MICROCOMPUTERS, an Apple card manufacturer, has decided to do the same thing for the Spectrum. One of the things for which the Apple computer is famous is the internal motherboard-type slots, which allow you to plug-in things like RS232s, parallel ports and disc drives. All are on separate cards, which need only to be plugged into the system. They are also expensive and some have to be put in particular slots.

The same kind of system has been adopted by U-Micro on its Spectrum range. There is a three-slot motherboard which is completely buffered to reduce the load on the Spectrum. An extension is also offered which will extend it up to seven. That, however, must be supplied by separate power supply using a standard - non-standard to Sinclair users - multi-way plug. The power supply must also supply +12 volts, +9 volts and -12 volts for things like RS232s.

There are, however, advantages. One is that a spare unbuffered printed circuit board edge on the right-hand side of the board is provided; all edge connectors and cards are gold-plated as a matter of course. That can take the Interface One happily and would solve a problem for users whose Spectrum is in a case.

The other advantages are complete Spectrum bus compatability, unlike some other systems, and an alternative decoding system for I/O devices which will allow seven boards w be added to one system without clashes.

That is because the motherboard provides for each edge connector, or slot, to have a different chip-select signal on edge connector position 4A.

That is derived from the top three address lines A7- A5. Internal addresses on each card by U-Micro use the upper three address lines A8- A10.

All that, of course, increases the cost, but U-Micro also compensates for that by detailing in a glossy booklet all the information you want to know about the card you have bought. The booklet contains not only details on how to set up and use the card but also a circuit diagram and specifications of the major chip used.

Listings are also given of any software included in the package. Unfortunately it also includes some mistakes which, although minor, tend to take some gloss from the product. Also for some unknown reason all the booklets have identical covers; it is only when you open them that you can tell which is which.

For serious work using a Spectrum the board is ideal; it relieves the Spectrum of power supply problems and loading of the edge connector by too many devices. It also allows you more cards than any other systems which are compatible with Sinclair equipment.

The only problem is that the ideal solution is not inexpensive. An adaptor is required to fit the Spectrum and motherboard printed circuit board edges together costs £6.90, three-slot backplane £35.65, four-slot extension - if required - £25.30. A power supply was not available at the time of writing but a £70 alternative was supplied. The Spectrum one should be half the price, U-Micro says. There should be an additional £1.50 for postage and packing.

Cards available from U-Micro are dual RS232, dual parallel ports - with a Centronics kit as an extra - and a prototyping card. Other producers' Spectrum cards can also be used but may restrict the use of addresses.

All equipment has a 12-month guarantee and can be obtained from U-Microcomputers Ltd, Winstanley Industrial Estate, Long Lane, Warrington, Cheshire WA2 8PR. Tel: 0925-54117.

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