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ComputerAnswers Column 17


COMPUTER ANSWERS MAY 1986



Copyright 1984-1989 Simon N Goodwin

Computer Answers is PCW's help column. We offer advice about all kinds of specific hardware and software problem, through the pages of the magazine. We also welcome further information in response to published queries.





COLLECTOR'S CORNER

Having been a regular reader of PCW for some months now, and a computer 'collector' by avocation, I often find myself experiencing salivation at the sight of some of the marvellous micros available in the UK and unavailable here. My only recourse would seem to be to import a few to satisfy my desire.

Given the fact that NTSC and PAL television standards are mutually incompatible, is there any difference in the RGB output of a British computer and a similar American device? Could I hook up a a UK computer to a US monitor and expect to see anything legible?

Assuming that the RGB signal is compatible, what would be the effects of the screen being refreshed some 20 per cent faster than it expects?

The computer I am most interested in is the Enterprise 128, which is continually promised for the US but which now seems unlikely to arrive. I would also be interested to know how the facts would relate to the Sinclair QL, as I am not sure that the lower prices on this unit will carry over to the US.
Lonnie McClure, Memphis, USA.

The mains electricity supply alternates at 60 Hertz in the US, whereas the UK supply alternates at 50 Hertz - this means that the time for each 'frame' of the picture is smaller in America, and the time for each line is also changed. However, the computer's signal includes timing pulses which most US monitors can 'lock on' to.

You may need to 'tweak' the monitor a little, but most UK computers will drive a US RGB display fairly happily. When the Enterprise was shown at the US Consumer Electronics Show it worked fine with 'standard' US linear monitors.

It is unlikely that you'll be able to get a proper TV display, as PAL and NTSC are very different systems. At the moment Enterprise have no plans to produce a NTSC version of their machine, although the 'Nick' graphics chip was designed with compatibility in mind. Sound is not a problem, as the left and right channels are available separately on pins A7 and B7 of the monitor socket; you can connect these signals directly to an amplifier or HiFi. The 'ground' connection can be taken from pins A2 or B2 on the same socket.

You'll need a different mains transformer for the Enterprise, as the US supply is 115 volts rather than 240. The Enterprise uses a separate power unit which delivers up to 2 amps at 9.5 volts. This supply should be rectified (converted to DC) and smoothed, but you don't need to regulate it - the Enterprise contains a built-in regulator. DON'T be tempted to supply more than 9.5 volts, or you'll probably cause the regulator to overheat and shut down. The regulator will probably short-circuit if you get the supply polarity wrong or use AC rather than DC, so be careful.

The Sinclair QL is now available for $299 in the States, so there's not much point importing one from the UK, even though the video chip in a British machine can be persuaded to generate US video (but not vice versa). The ROM in an American QL is slightly different from the UK version. The character set is compressed so that you get the same amount of text in a smaller number of lines in 'TV' mode - British TV sets have more lines than their counterparts in the New World. This change upsets some UK software, so you should start the machine by pressing F1 (monitor mode) if programs otherwise give you a jumbled display.

Another change takes into account the different aspect ratio - shape of each pixel - on a US TV. This means that circles programmed in the UK still look round, rather than oval, on an American machine, even though they need a different number of pixels. You may get confusing results if programs try to overlay windows, specified on a pixel grid, and graphics, which are re-scaled, but you can get around this by using the CURSOR command to set co-ordinates relative to the pixel grid.



MIND YOUR LANGUAGE

I'd like to gain some programming experience on a home computer, with a long term view to employment in the industry. At the moment I am almost completely computer- ignorant, so I'd appreciate the answers to the following questions: Which modestly-priced micros would allow me to programme in both Basic and Cobol (with an option on Pascal)? Is there a book available that will instruct the complete novice in Cobol programming on a micro? Is there a similar book giving instruction in the use of Pascal?
Name and address supplied.

Micros are a very good way of learning programming, so long as you make the effort to plan your work, and have access to more experienced users. Cobol is not a popular language on microcomputers, for good reason, but you can get reasonable Cobol implementations for the larger Amstrad computers, the Apricot range (which includes the low-priced F1E model, discontinued but still available) and Tandy's aging TRS-80 family. Remaindered CP/M machines are also worthy of consideration.

You should not spend too much time comparing hardware prices, as Cobol compilers do not come cheap - you may have to spend more on software than you do on hardware! The cheapest Cobol compiler is RM-Cobol for the TRS-80 model 1, 3 and 4; you should be able to buy this for less than #100 if you shop around.

There's not much demand for Cobol compilers on micros - there are so many better langauages - but there are a few versions available for CP/M and MSDOS machines. You should expect to pay several hundred pounds, plus the cost of conversion to the disk format expected by your machine.

I would not advise anyone to learn Cobol as a first programming language, any more than I would advise them to learn Gothic script as their first handwriting. I have never encountered a good micro-specific tutorial on Cobol, although most implementations come with copious reference documentation.

Cobol is verbose, clumsy and - on most micros - inefficient. Experience on a micro is unlikely to be directly relevant to a larger computer, so you're taking a big gamble if you expect micro Cobol to land you a job in commercial Data Processing. Most Cobol job advertisements demand two years of experience on a specific mainframe system; if anything, there's a glut of inexperienced Cobol programmers, mostly from TOPS courses. Learning Cobol now is not much more sensible than training as a Linotype operator.

If you are determined to get a programming job your initial choice of language is not crucial. Look at good 'structured' versions of BASIC as a relatively painless interactive introduction. Then consider the wide range of other languages such as C (flavour of the decade), Pascal (better to learn than to use), Fortran (losing out to C) and Ada (if you don't mind being responsible for killing people).

Pascal is widely available on micros, though the quality of implementations varies. There is a good, inexpensive book for Basic programmers who wish to change to that language - P.J Brown's 'Basic from Pascal'.

The C language is also quite common, although some micro versions are poor. THE book is 'The C programming language', by Kernighan and Ritchie.

R.E Kaufman's 'Fortran Coloring Book' is a good introduction to the world's first programming language.

Ada has yet to be implemented properly on micros, but it is the military programming language of the future.

Languages like Forth and Pilot appear on micros because they are easily implemented. Avoid them, unless you enjoy learning new languages for their own sake.

Lisp and APL have a solid minority following in industry, but micro implementations of these languages are often slow or incomplete.

The demand for Prolog programmers is predicted to grow. Micro Prolog systems are slow and run out of memory quicly, but those I have seen are well-written, well- documented and cheap.

A professional programmer can express data-structures and problems in a form that is largely independent of language. You may find this easier if you understand a wide range of languages, but don't expect fluency to guarantee you a job. Employers are notoriously conservative and the best guarantee of work is a Computer Science degree or two years' full-time experience. 'Group' programming experience is often important; there's a world of difference between programming on your own and as part of a team.



DAISYWHEEL PRINTER INFO

In PCW February 1986 you state that 'you can pick up a rebadged Juki printer for well under half-price if you want a Commodore interface'. Where can I get hold of one of these machines? What is the model called?
Dr. J Zamler, Cambridge.

The Commodore DPS-1101 is the model in question - it sold for £150-200 in branches of Lasky's, Curry's and other chain stores during the winter, although supplies seem to be drying up now. The printer has the same beautifully-engineered mechanism as a Juki 6100, although the case is grey and blue rather than Juki's usual cream. The DPS-1101 uses a Commodore serial interface, which means that it is difficult to connect to standard micros with RS-232 or Centronics ports - I'd be interested to hear from any reader who has converted one of these printers to use a standard interface.



QL DISPLAY GLITCHES

I bought a QL in November because I needed a word-processor. The five free games are unplayable and amateurishly programmed, but the Psion business package represents superb value for money.

However I have had to return four QLs to the dealer as unsatisfactory All displayed a distracting ripple on the TV screen (colour or monochrome) after they had warmed up for 3/4 hour or so. The worst affected characters were 'm' and 'w'. I have been supplied with versions AH, JM and JS. They all behave the same way.

If I buy a monitor will I get a more stable display? Is the power supply of the QL adequately regulated? The TV screen display is particularly bad while the microdrives are operating.
Ronald Johnson, Bracknell, Berks.

All computers give some flicker, or 'dot crawl', on a TV display, although the problem is usually minor on a black and white set. The QL display is less stable than that of some other machines, partly because of sloppy design and partly because of the unusually high text resolution. Even so, I know many QL owners who get an acceptable TV display, and I use a QL and a Pye TV every day without problems. It sounds as if some aspect of your system is causing 'freak' results.

You can reduce the flicker when using the Psion software if you select a 40 column display rather than the usual 60 column TV layout - change this by selecting the DESIGN option. This will help a lot with lower-case letters, and it will not restrict the format of printed information.

Your power-supply is a likely culprit, given your problems with microdrives and overheating - Sinclair tell you not to return the supply with a faulty machine (to save postage costs) but in this case a replacement unit might help. Since the problem is associated with 'warming up', you might cure it by using a cooler room or directing a fan at the grille behind the microdrives, where most of the QL's heat-sensitive components are located.

The display on a monitor should be much better in any case - the Psion software was really designed to work best that way. Try to get a monitor on loan for a couple of days, so that you can test its performance when your computer is warm. A monochrome monitor is easier on the eyes than a colour unit if you intend to make heavy use of the machine.



THE BROTHER & THE BEEB

I use a BBC B computer with a Brother HR15 computer, and the combination works well. But I would like to be able to use the printer as a typewriter for carrying out minor work such as addressing an envelope. The Brother instruction manual gives no information in this regard and I will be obliged if you can tell me what to key into the computer in order to do so.
G Lowery, London.

It's not easy to make specific recommendations since you don't say how you are driving the printer from the micro at present. If you are using a word-processor you can type addresses into a short file and then print them out like any other text, once you've put the envelope or a label into the printer.

Alternatively you can enter the name and address into a series of PRINT lines, so that they appear in the correct format on the screen when the program is run. Put the command VDU 2 at the start of the program once you've got it working, and VDU 3 after the last PRINT statement. When you next run the program the characters will then be sent to the printer as well as the display. You can edit the PRINT lines for each address required.

You'll need to select the correct kind of printer output format, using *FX statements in the usual way, as explained in the BBC User Guide.



CP/M QUERIES

With the recent purchase of a Commodore 128 computer, I encountered the CP/M operating system. Whilst I understand that this system is for running business programs, I wonder if you could answer these questions: The 128 leaves 59K of memory in the Transient Program Area when running CP/M. This seems to me to be quite a small amount of free memory. Would I be restricted in the number of commercially available CP/M programs that I could use?

I am using a Commodore 1541 disk drive with the 128, and find that I cannot read the directory of a 'CP/M' disk unless I am using CP/M. Is this because the format of the disk differs from the normal Commodore DOS format?

If I wish to write my own programs to use CP/M the computer suggests using 'a language, either high-level or assembler'. Could you give me examples of the programs required?

Until the 1571 drive, dedicated to the 128, becomes available, is there a company who can transfer any CP/M programs I purchase, from the MFM format to the CBM GCR format?

Could you please tell me what CP/M stands for, and what, if aything, is the difference between CP/M 2.2 and CP/M-86. Could I use either system?
R.K Snelling, Newport, Gwent.

CP/M (and CP/M plus) can only handle a maximum of 64K of memory for programs, directly-accessible data and 'hook' code to handle communications with peripherals such as disks, printers and the display. There is therefore little point in having more than 64K of memory on a computer used to run CP/M, as the extra RAM will not be accessible to the program. Virtually all CP/M software will run happily on a system with 59K of Transient Program Area.

The CP/M and Commodore disk formats are different, as you have guessed. It is possible to read either format from the other environment, but you need complex routines and an intimate knowledge of the machine in order to do so.

All compilers or assemblers that run under the CP/M system produce code that also works under CP/M, and has access to the rather sparse facilities of the operating system. Compilers for languages such as Pascal, Fortran, and C are widely available, as are machine-code assemblers.

To use these languages properly you'll need a debugger or machine-code monitor, and an intimate knowledge of 'Z80 code', which is quite different from the 64's '6502 code'. Don't bother unless you want low-level access to the disks or you intend to write software to run on other CP/M machines (such as Amstrads). In either case, you should expect to do a lot of hard work.

Laurie Faulkner & Associates (053 750 305) can convert disks to and from the majority of Commodore formats.

CP/M stands for 'Control Program/Monitor'. It was written at the end of 1973, and became popular in the early days of microcomputing because it was the only operating system that worked on a variety of computers. As you might expect, this meant that it was slow, crude and unfriendly, but it did make the bulk marketing of software possible in the seventies, when models of computer appeared and vanished even more suddenly than they do today.

CP/M only works on computers with the Intel 8080 and 8085 processors, or the Zilog Z80. When the Intel 8088 and 8086 came out, a new similarly-limited version of CP/M was produced, called CP/M-86. CP/M-86 only works with the 8086 family of processors (8088, 8086, 80186 etc). It won't work at all on the Z80, because the instructions recognised by the processor are different in each case. So there's not much in common between CP/M and CP/M-86, apart from the name and a similarly unfriendly attitude to the user.

Various different versions of CP/M have been produced, such as CP/M plus, in an attempt to correct its major weaknesses, but progress has been slow. CP/M-86 never really caught on, and a similar but better-designed product called MSDOS is the most common operating system on machines with newer, 8086-style processors. Another rare version of CP/M, CP/M-68K, works with the 68000 processor family, and forms the rather shaky foundation of Atari's ST system. Again it is incompatible with all the other CP/Ms.





FEEDBACK: FURTHER ADVANCES

Since we published Alan Curtis's letter in the February PCW several people have written in with help or further problems with the Advance computer. The Advance Self Help User Group has 50 members, and is 'growing all the time' - write to Charles Prince, of 125 St. James Avenue, Thorpe Bay, Southend, Essex, SS1 3LW for more information.



GLOBE

Tony Billing has written to ask for advice about hard disk faults on a Globe computer. 'A Globe model 103 has been handed down to me for use in my parts store...please stop laughing', he writes. I've drawn a blank on this micro. Can any readers help?



SHARP PRACTICE

Clive Westwood's enquiry about the Sharp PC 1500 has brought several letters. The 'Status 1500' newsletter is published monthly for Sharp users; write to Ronald Cohen, 62 Blenheim Crescent, London W11 for details. PC 1500 Technical Reference Manuals are no longer available from Sharp themselves, but you can get copies for £20 from Teega Agencies of Martin Street, Burnley, Lancs. BB10 1SH.




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