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ComputerAnswers Column 9


COMPUTER ANSWERS SEPTEMBER 1985



Copyright 1984-1989 Simon N Goodwin

TANDY AND APRICOT COBOL

About a year ago I had access to a Tandy Model 4 microomputer. This machine has a Z80 processor and uses the CP/M operating system. I purchased a copy of the RMCOBOL compiler and a 'run-time' diskette.

I have now purchased an Apricot PC. At the time of buying I knew that I would not be able to slot my RMCOBOL compiler diskette into my Apricot PC and use it efficiently, due to the different processors. Programs can be transferred between the different diskette sizes.

Can I use my RMCOBOL compiler to write and run COBOL programs on my Apricot PC? Can I use the programs written with the Tandy machine on the Apricot?
I.M Bawa, Streatham, London.

The disk for the Tandy contains a program which translates from one language - Ryan-McFarland Cobol - into another - Z80 machine code. Your Apricot expects programs written in 8086 machine code, which is very different from Z80 machine code.

Programs to convert Z80 code into 8086 code do exist - Microsoft's BASIC interpreter was translated using such a program - but the task is difficult. Translated programs are generally much slower and longer than those written in the correct code to start with. The translator will not be able to cope if the original program contains references to hardware which is not present in the final machine.

Another problem with machine-translation is that it makes error-diagnosis very difficult. Imagine writing a book in English and then translating it into Greek, armed only with an English-Polish dictionary and a Polish-Greek dictionary. In your case, Z80 code is the equivalent of Polish. Errors multiply and become increasingly hard to correct if you have to go through an intermediate language.

The XLT86 code translator is available, but it is really a product aimed at software houses rather than business users. Give it a miss unless you're VERY familiar with the internal idiosyncracies of both computers.

Rather than buy a translator for compiled programs, I'd advise you to buy a new Cobol compiler for your Apricot, and re-compile your original 'source' programs. A version of RMCOBOL is in the ACT catalogue of 'third party software' for the Apricot, but I have not seen it advertised; you may have to ring around a few dealers to obtain a copy.

ACT recommend two Cobol compilers - Microsoft Cobol and CIS Level 2 Cobol. Both of these are expensive, but widely available. You should not have any major difficulty converting your RMCOBOL programs to suit the other compilers, although it you may have to read the manuals quite carefully if you've used obscure features of the language; in general, RMCOBOL is a pretty good implementation of the 1974 Cobol standard.



A CLEARER VIEW...

I do my journalistic activity with a BBC Micro and the 'View' word-processor. I have a 'standard' 80 column monitor. View has many facilities that I value, but what it lacks is a display of pagination while working on a document. There is a 'screen' facility that can reveal the paging of a document when it has been completed, but it is a very cumbersome command, especially with long documents. What is the answer? Are there any monitors that have an A4 format? I have seen such a monitor but it was integral to a #10,000 system for high-resolution graphics work - beyond my pocket!
D Pickup, Low Fell, Tyne and Wear.

Very few low-cost word-processors display page-breaks as text is entered - they are quite difficult to process properly, since they are affected in subtle ways by alterations to 'headers' and 'footers' at either end of the page, and the insertion and deletion of text. I suspect that Psion's 'Quill' is the cheapest word-processor which allows continuous text entry with automatic display of page-breaks; unfortunately this program uses about 120K of memory on the Sinclair QL, so there's little chance that it will be converted to run on the 32K BBC Micro! If you really need to get page-breaks right first-time you should look at the page-oriented word processors for the BBC Micro. These accept text page by page, rather than in a continuous stream. Such programs encourage you to format your document as you edit it (rather than later) - if you do a lot of creative writing you will probably find this a chore.

I have tracked down three page-oriented word- processors for the BBC Micro: 'Beebpen' (Braintech, 01 997 8986), 'Edword' (Clwyd Technics, 035 283 751) and Scribe (Merlin Computer Products, 0792 467 980). All three are supplied on ROM.

In answer to your second question, it won't help you to connect an A4-sized screen since that won't alter the number of lines which the Beeb's display electronics can generate. You'll still be stuck with 20-odd lines displayed at any one time - with a big margin at the top and bottom of the display! To show the 70 lines of text that make up a full A4 page you need special electronics to generate the extra lines. It's not really feasible to add this electronics to the Beeb. Even if you did so you'd have to make major changes to your software before the extra lines could be used. The page-oriented word-processors I have listed only show you part of a page at a time, although they do indicate page boundaries as text is entered.

Sooner or later someone will produce a reasonably- priced machine with an A4 display, but I've not seen one yet. Remember that A4 is not a standard size outside Europe - in the USA they use Quarto, which is rather shorter than A4.



THE ART OF PROGRAMMING SLOWLY...

Recently I bought the first three volumes in the series 'The Art of Computer Programming', and I have enjoyed them very much. However I can't help wondering what has happened to the other four volumes in the series. One could think, after reading the preface of the first volume, that the author finished writing all the seven volumes in 1967, but the third was published in 1973. Do you know if and when the remaining volumes will be published?
G. R Hjaltson, Reykjavik, Iceland.

The publishers, Addison Wesley, tell me that work on the series is still taking place, and they hope to have volume four some time in 1986. You can be certain that PCW will bring further news when publication becomes imminent.

Donald Knuth, the author, seems to have become the victim of his own success with this series. The first brilliant and exceptionally comprehensive volumes have set a very high standard for the rest.

In 1967 the computer industry was barely 20 years old, and a comprehensive programming guide may have seemed feasible. Since then computing has advanced at such a rate that it is almost impossible to keep a monthly magazine up- to-date, let alone a series of books. It's hard to see how Knuth can encapsulate the rest of computing knowledge in four volumes, but if he can't do it, no one can.

2011 update - still waiting - though some draft chapters from Volume 4 are online on Knuth's home page at Stanford!



ATARI ENQUIRIES

Could you tell me if there is any point in getting a modem for my Atari home computer? There does not seem to be any opportunity for Atari users to access networks like Prestel.

I am considering buying an Atari 520 ST with disk drive and a monitor. I am especially interested in integrated programs, like 'Jazz' on the Apple Macintosh. Will any such programs be included in the price of the ST? Also, will the graphics be up to the standard of the Macintosh?
I Fairbairn, Chislehurst, Kent.

There are several 'bulletin board' services open to Atari users - these are small information services run (mostly) by hobbyists. At least three services cater specifically for Atari users; these are BABBS in Bath (0225 23276) which operates at night (9pm-8am) and at weekends; MBBS in Mitcham (01 640 2617) which can be contacted on Thursdays and Sundays between 10am and 8pm; and WABBS in Worthing (0903 42013), which is a 24-hour 'ring-back' service - let the phone ring once to signal that you want to access the service, and then call again with your modem connected. All of these services work at a speed of 300 baud.

You will obviously need a modem, and some means of connecting it to your Atari. Modems expect an RS-232 signal from the computer, but the Atari does not come with such an interface as standard. If you have one of the rare 850 interface units you can connect a modem to it directly, but this won't give you access to the Prestel service because the 850 can't transmit and receive concurrently at two different speeds.

Miracle Technology recently announced a Prestel/Modem adaptor for Atari users. It costs about #60 (not including the modem); you can get further details from Silica Shop on 01 309 1111 (voice only!).

At present Atari don't plan to include business software with the ST, as Sinclair do with the QL. You get GEM, the 'Graphics Environment Manager', bolted onto TOS, a version of the CP/M 68K operating system, and the languages Logo and Basic, but no applications software. I don't think that the 'Jazz' system would even fit in the memory of early STs, although it should be available once the operating has been copied into ROM. At present much of the ST's 512K of memory is occupied by the operating system.

The 'medium resolution' display of the ST has less dots than that of the Macintosh, but each may be in one of four colours. The 'high resolution' black-and-white display should be marginally better than that of the Mac, but it doesn't seem to work at all on machines delivered up to the time of writing. This problem should have been cleared up by the time you read this...



LINKA FRANCA?

Why doesn't someone come up with a modulator that will let a tape recorder be hung onto the serial port of a micro, either to receive or transmit? All my micros have a serial port of one type or another so I could chuck the data between the machines without having to worry about compatibility. Surely someone could string the electronics together and you could publish it as a project. After all, it would be compatible with all machines.
P Hickman, Kingston, Surrey.

This is a great idea, but sadly it is not practical. You suggest that we design a gadget which can be connected to any computer, capable of reading and writing information. A cheap computer would be just such a device. But this pre-supposes that a single gadget could communicate with the serial ports of every computer.

If there was such compatibility between serial ports, why not dispense with the electronics completely and connect the serial ports together as needed? In theory this is possible, but in practice it is fraught with difficulty. The snag is that there are many ways of wiring so-called 'compatible' equipment together. You must take account of the 'handshaking' - the way machines warn one another that they are busy - and a wide variety of machine-specific quirks. If you make sure that everything is set correctly, you can get two computers to talk to one another. But, if anything is wrong, the system probably won't work at all.

Under these circumstances you need a fair amount of technical information, time, luck, and organisation just to connect a pair of computers. Unfortunately many computers are sold without such technical information. Often this hides the fact that a so-called 'standard RS232' interface is almost totally non-standard - it might drive a printer, just about, but you shouldn't necessarily expect it to do anything else. 'Built-in' RS-232 interfaces on home computers are worst in this respect.

If you want to connect Sinclair computers together you're best advised to ignore the RS-232 and use the built-in network - contrary to other reports it does work; however the Spectrum and QL use different characters to mark the end of lines, so you'll need to convert them - the Spectrum uses the usual CHR$(13) while the QL follows the Unix convention and expects CHR$(10). If you've some programming ability it can often be worth connecting small computers via 'game' ports rather than RS-232, POKEing data back and forth.

In general terms, all I can recommend is (careful) experimentation and perseverance. I've got five computers in my office and they're all on speaking terms, but I've had to experiment to get them to communicate fluently.



THE 5.25 INCH ELECTRON

Is there a disk interface for the Acorn Electron that uses standard 5.25 inch drives? Does Acorn's 'Plus 3' only run 3.5 inch drives? Will the disk interfaces for the BBC Micro work on the Electron? Is there any other fast data drive on the market? Is it possible to swop the 'Atari' style joystick plug so that the 'Quickshot 2' joystick will fit the analogue joystick port on the Acorn 'Plus 1', and work properly?
T Oldreive, Gowdall, N. Humberside.

Phew! Cumana (0483 503 121) have a disk interface compatible with 5.25 and 3.5 inch drives - it costs a hefty #150 (not including the drive) and plugs into the Acorn Plus 1 interface. Unfortunately it doesn't use Acorn's format, though it comes with software to convert unprotected disks of both sizes.

Pace (0274 729 306) are also working on a 5.25 inch disk interface for the Electron, but it is not available as I write (early July), due to a shortage of the infamous 8271 disk controller chips. The Plus 3 is only designed to work with 3.5 inch disks, though it could probably be fooled into using a larger drive via an appropriate cable.

The BBC Micro disk interface is just a collection of chips to fit a space on the micro's circuit-board - you can't use it with the Electron since the requisite sockets and signals don't exist on the Electron circuit-board.

I have seen a few adverts for 'fast drives' for the Electron but I have not seen any working hardware; I'd advise you to get 'proper' disk drives if you can afford them.

Your Quickshot joystick only generates simple digital signals (Up, Down, Left, Right and Fire) whereas Acorn joysticks produce a gradual (up a bit, left a bit) or 'analogue' signal. You could use an adaptor to connect the Quickshot to the analogue port, but you should be aware that that type of joystick will only give crude 'all-or- nothing' control. If you've already got the Plus 1, C-tech Computers (061 366 7794) can help - otherwise you might as well get a proper digital joystick interface. These are available from First Byte Computers (0332 365 280).



SPELLING OUT INSTRUCTIONS TO YOUR SPECTRUM

I have recently purchased an add-on keyboard (not Sinclair's) for my 48K Spectrum computer, and find it very much easier to use than the original rubber keys, especially when I use the word processor (Tasword). However when I use BASIC the original multiple key functions still operate. Is there any way I can change the computer so that commands can be typed in properly, rather than using 'extend mode' etc? Is it possible to simplify the sequence when typing special symbols? At present I have to press four keys just to get a square bracket.
G Sumpter, Rossendale, Lancs.

The Spectrum's 'keyword entry' scheme worked well on the ZX-80, where it first appeared, but it has now grown unweildy - the Spectrum still has 40 keys, like the ZX-80, but more than twice the number of commands are packed onto the keyboard. The idea was to reduce the number of presses needed to get a given character (and to make automatic syntax checking easier), but as you point out it sometimes has the reverse effect on the Spectrum.

The scheme is built in to the computer's ROM, but it is possible to override it with software. A program called MegaBASIC will solve your keyword problem, and add several dozen new commands to ZX BASIC - the only snag is that it occupies about 19K of memory, leaving you with only about 22K for your own programs and data. The program allows user-defined keys, so you should be able to reduce the number of presses needed to get square-brackets to two, as long as you don't mind them appearing somewhere else on the keyboard. MegaBASIC is available from Your Spectrum (01 631 1433).

Alternatively you could dig out an old copy of Your Computer (June 1984), which contained a short machine-code program to allow keywords typed in full. This program is only 230 bytes long, and offers no other features, but it works perfectly well - I've used it myself on occasion.



ZIL0G Z800 REVISITED

In the July PCW I answered a question about the Zilog Z800 processor, pointing out that it was four years late and details were still not forthcoming from the manufacturer. Since then Zilog UK have published a new Data Book which includes seventy pages of notes on the processor. There are still no instruction timings because the chip has not been manufactured yet, but Zilog expect to produce a prototype later this year; if all goes well sample chips should be available in Spring 1986.

The new chip should be compatible with almost all Z80 software (I'm not sure about the undocumented instructions used in the ZX-81, Spectrum and other computers), but you can't just plug it into a Z80 socket since it uses Intel-style multiplexed address and data buses.

The cogniscenti will be interested to hear that the chip will feature fast 'cache' memory, timers, a UART and various 24-bit bus controllers. There are lots of new instructions, including full 16x16 bit multiplication and division. For more gibberish contact Zilog UK on 0628 39200!
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