Previous column ComputerAnswers    Next column ComputerAnswers

Logo

ComputerAnswers Column 6


COMPUTER ANSWERS JUNE 1985



Copyright 1984-1989 Simon N Goodwin

Stuck? If you're tearing out your hair trying to solve a hardware or software problem, and you think other people might have run into the same snag, why not write to P.C.W? Please keep your questions short and relevant to other readers - then Simon Goodwin can try to do the same in his replies!

TRANSATLANTIC POWER STRUGGLE

I have a hardware question concerning power supplies. I am an American currently resident in Britain, looking at personal computers. One I have my eye on (the Wren) runs only on 240v power. If I return to the US, I will have to feed it 120v power. So I have two related questions.

First, is it possible to rig the 240-120v transformers I use for my American appliances here, to use a 240v computer there? Second, is there some single component in the power supply (for example a transformer) which I might be able to replace once I get to the US?
D.E Netherton, London N3

The 'auto-transformers' which you use to convert 240v into 120v should be symmetrical components, and thus work in either direction, but I'd suggest that you check this fact with a competent electrician when you get back to the States. I can't be completely certain without examining the devices concerned.

In theory you can convert most appliances to run on a different supply by changing the internal transformers, but this won't always be a simple one-step modification: modern computers use a variety of supply rails (generally including +12, +5, -5 and -12v), so you may need to replace a number of transformers. Make sure that the replacement components can provide the correct current as well as voltage. At worst, you may find that a specially-made composite transformer is used in the UK machine, to generate a range of different outputs from one mains input. It might be hard to find an exact equivalent in the States.

There are a number of other points to be born in mind when you plan to take a British computer to the USA. You shouldn't use a computer in the States unless it complies with FCC rules for radio interference. British law is much less strict, so most UK machines will need metal or conductive-paint screening around the circuit-board before they're legal.

Some computers derive timing signals from the UK mains, which alternates at 50Hz, so they'll run at a different speed (if at all) when connected to the 60Hz US supply. Likewise, British television sets and monitors refresh the screen 50 times a second, while their American counterparts expect to be refreshed at 60Hz. In many cases the signal is generated using a 'dual standard' component, and only one connection need be changed to convert the display, but some machines need major alterations to cope with a 60Hz supply.

Telephone modems use different tones in Britain and the USA, so you may find that communications equipment purchased here won't talk to Ma Bell. Again, 'dual standard' components are probably in there somewhere, but you'll have to find out how to let them know about their change of environment.

It is certainly possible to make a British computer work in the States, but there are lots of things that could go wrong in the process. You'd be wise to avoid machines that are unknown in the USA, or you could run into maintanance problems after you get the hardware working. Battery portable machines are obviously going to make the crossing most easily, but you could still run into interfacing problems.



COMPUTERS FOR ARABS

Recently you answered a request to provide information on a computer system running in Spanish. Are there any computers or dealers you can recommend for potential users wishing to work in Arabic? The ideal system my contacts require would run at the 220 voltage in the Far East and be capable of presenting both English and Arabic visual displays.
Dr R.P Newton, University College Swansea

Most modern computers are capable of displaying arabic characters, since they allow the character shapes to be redefined at the whim of the user. You draw the characters, dot by dot, with a character design program. Each new definition takes the place of a 'normal' letter or symbol, and you can chop and change between the two sets at will. The exact procedure will vary depending upon your choice of machine - appropriate instructions will come with the character design program.

This doesn't get around the problem of data entry, since you presumably need a kind of 'backwards INPUT' routine to accept data entered from right to left. It shouldn't be much work to implement such a feature, reading characters one by one from a keyboard with appropriate replacement legends.

Ramez Halaby & Co, of P.O. Box 147, Jeddah, Saudi Arabia, specialise in Arabic computer systems. They have advertised various of conversion kits in back issues of P.C.W, including an adaptor and keyboard called 'Arab Ram' for the Sinclair ZX81. This was described as 'the first Arabic Personal Computer in the world' when it appeared a year or so ago. Nearer home, An Arabic conversion kit for the IBM PC is available from Microware, 637 Holloway Rd, London, for 600 pounds. They also offer an 'Arab Word Processor' package at the same price.



HOW TO GET HACKING

Could you please tell me where I can get some information about hacking, such as any books about it, or dealers who specialise in it? What equipment is needed?
D. Trowsdale, Kingswinford, Dudley

'Hacking', or communicating with other computer systems (with or without the consent of their owners) is a difficult hobby to break into. The hacking community is very tight-knit. This is partly because of the strange hours you have to keep if you want to take advantage of the cheapest or least congested connections. Hackers carry out most of their communication - logically enough - by computer, so the best way to contact them is to join them! I don't know of any specialist Hackers' Shops - the hobby is probably too small and widely dispersed to make them economically viable.

The only good book on hacking which I have seen is "The On-line Handbook" by Ray Hammond. It is published by Fontana, and available for under a fiver from most bookshops.

Before you can become a hacker you need three pieces of equipment: a computer, to accept and display messages, a 'modem' (short for MODulator DEModulator) to convert computer signals into a form which can be transmitted by telephone, and a telephone. A printer - of any kind - will also be very useful.

The computer and the modem generally communicate via the infamous RS232 interface. Low cost modems sometimes plug directly into the computer without the need for such an interface, but this generally means a reduction in versatility. Similarly, the cheapest computers contain simplified RS232 interfaces which restrict the flexibility of your system. Look for a machine with an interface capable of sending and receiving simultaneously at two different speeds.

There are two types of modem - the acoustic coupler and the direct-connection type. The accoustic coupler is a simple microphone-and-speaker contraption which you fix to your telephone handset. This transmits and receives bleeps and buzzes down the line. Unfortunately it also relays any other background noises in the room at the time, unless you jam it very carefully onto the handset, so the acoustic coupler can be rather unreliable. Direct-connection modems are more expensive but more reliable. They plug directly into the telephone circuit (so you'll need one of the new rectangular BT sockets) and generate the whistles and bleeps of computer communication electronically.

Computers communicate at a variety of speeds: a serious hacker will need to be able to use 1200/75, 300/300 and 1200/1200 'baud'. The first figure refers to the speed of data reception, the second to the speed of transmission. The 1200/75 speed is used by Prestel. 300/300 is favoured by businesses and 'Bulletin boards'. These are electronic noticeboards, generally run by amateurs, through which hackers send and receive messages. At 1200 baud it takes about seven seconds to transfer a screen-full of information.

To find out more - such as the 'phone numbers of bulletin boards - read the 'Networks' section of PCW. Like so many areas of computing, the only real way to find out about hacking is to try it. Once you have taken the plunge, as in any 'communication' hobby, you will find lots of people eager to advise you further.



ATARI COLOUR COMBINATIONS

I have an Atari 600XL, and very nice graphics it has, for the price. Unfortunately the resolution in 16 colour mode is 80 x 192 - it's like painting with a brick! Graphics mode 7 has a resolution of 160 x 96, which is a lot better, because each dot is a near-perfect square. Unfortunately again, only four colours can be displayed at once. Is it possible to have 16 colours on the screen at the same time, in mode 7 resolution?
Richard Donscombe, Denton, Manchester

The short answer to your question is No. However, since I'm not famous for my short answers, and 'No' doesn't seem very helpful, let's look in a bit more detail at the Atari hardware.

The Atari 600XL is a re-styled version of the Atari 800, launched in 1979. When that machine first appeared it lacked the 16-colour modes - you were stuck with modes 0 to 8, giving five colours in text modes, and two or four colours for graphics. You also had five sprites, or 'player/missiles', and they could each be a different colour, so you could - in practice - get nine colours onto the screen at a time, although the sprites could only occupy a restricted area.

After a while Atari replaced one of the graphics chips in the 400 and 800 with a device called the GTIA, which had the extra 16-colour modes you mention. However, these were grafted onto the original design. For a long time they weren't documented, and their were restrictions on their use. Now they've popped up, officially, as modes 9 to 11 on the XL machines.

The problem is that Atari have only changed the GTIA chip, to give 16 colours in new modes. They haven't changed ANTIC, the other graphics controller in the machine. ANTIC can only read 40 bytes of graphic information in the time needed for the TV display to scan from one edge of the screen to the other. To store 16 colours you need four bits, or half a byte, so you can only get 80 dots onto each line of graphics when using 16 colours. The hardware just can't read the data any faster.

This isn't really a criticism of Atari - every micro design has this problem. Machines like the Memotech and Commodore 64 get around it by restricting the number of changes of colour on a line. On the Sinclair QL the graphics controller can stop and start the processor to give itself more time to scan the display memory. In that case, with 512 dots on each line, each in one of four colours, the processor only gets a look-in forty per cent of the time. Even a 68008 processor finds that something of a handicap! You CAN increase the number of colours on an Atari if you use devious machine-code, but it is quite hard work. A year or so ago I produced some graphics for a Central ITV series, squeezing just over 100 colours out of a standard Atari, with a resolution of 160 x 192 - but it took me three months to do it in a flexible way. The trick is to write a program which changes the colours used by the Atari as the dot flies down the screen. Since the TV draws each line in about 1/20,000 second, your program has to be pretty efficient if you want arbitrary colours on each line, and you are still stuck with just four or five colours on a given line.

After six years the Atari system is well-documented, although some of the books are rather expensive. 'De Re Atari', published by the manufacturer, is indespensable once you've tracked a copy down. 'Compute!' publish a range of tutorial and reference books which explain the hidden intricacies of the machine well. Despite its old age the Atari still has more sophisticated graphics than any other home micro - but that doesn't mean the graphics are easy to use.



MENAGE A TROIS

I wish to use different computers with the same printer (all with Centronics interfaces) without constantly having to plug and unplug connectors. I have been astounded at the cost - nearly 100 pounds - for a commercial switchbox. What are the problems that need such an expensive solution? Having some experience of electronics, is it practicable for me to construct a cable junction box along one of the following lines:

(a) parallel connections throughout, leaving it to common sense to power up only one computer at a time?

(b) a simple diode matrix to to connect lines from each computer to the printer bus?

(c) using multiway wafer switches?

(d) using electronic data selectors and/or bilateral switches to make and break each connection?

Ten active lines need to be switched: STROBE, BUSY and eight data lines. Which system do you recommend?
A.J Clarke, London EC2

I'm impressed - you've all but answered the question yourself. Answer (c) is the briefest and seems to me the most sensible, although the others might work too. Answer (a) is fraught with danger, even if you DO believe in common sense, since even an inactive computer might interfere with the signal on its way to the printer. Answer (b) is nice in theory but might require some trial-and- error to get right. A faulty diode could cause all sorts of problems. The same goes for answer (d), which smacks of complexity for its own sake.

Answer (b) is easy to build (once you've got the right switch) and easy to check by eye if something goes wrong. The only point to watch for is that the switch has contacts which break the first connection before they make the second.

Commercial switchboxes are expensively made by hand - the fairly low demand is spread between many small manufacturers. The price is what the market can bear - so long as a switchbox is cheaper than a second printer it will be seen as economically viable by those who lack the knowledge, or the confidence, to build their own. Remember that many such boxes also incorporate serial-to-parallel converters or buffers.



COBOL ON A MICRO

Please could you tell me which micro computers can run CIS Cobol, as I am using Micro Focus's version for my Computing 'A' level at college and would find it helpful if I could program at home.
A Lake, Edenbridge, Kent

To the best of my knowledge CIS Cobol is only available for machines with disks and an Intel-type processor (8080, Z80, 8088, etc). This rules out a lot of home computers, which use other processors or non-standard disk systems. Any CP/M-80 or CPM-86 machine should run the system, although you might run into problems of lack of memory on a few home computers. A CIS Cobol compiler will set you back about 400 pounds.

Cobol is a standardised language, so it might be worth looking at another 'popular' implementation for microcomputers. RM Cobol for the TRS-80 is cheaper than Micro Focus's version, and seems to work just as well. You can pick up a TRS-80 system for next to nothing nowadays, so it might be worth considering that if you're determined to run Cobol at home.

It disturbs me to hear that you're still being taught Cobol at college. Are they teaching you to write with a quill on parchment as well?

BBC PRINTER PROBLEMS

I run a small business in Jamaica and decided to have it computerised. While I was in London I purchased two BBC Model B computers with disk and printer interfaces, cables, colour monitors and Epson FX80 dot matrix printers.

I am having problems interfacing the computers with the printers. Whenever a print command is to be executed the Caps Lock and Shift Lock lights come on and the computer stops execution.
Orlando Budoo, Gimme Me Bit, Jamaica, West Indes

The BBC micro turns on the two lights whenever it has stopped because a buffer is full. In this case, characters are stored in a buffer before they are printed. Normally the computer puts characters into the buffer and the printer takes them out, by signalling its readiness to the printer interface. In this case, the machine stops because the printer's signal is not getting through.

The fault could be in the hardware of the printer, the cable or the computer. Since you've bought two of each, and report no other faults, this explanation is unlikely. The BBC Micro software is perfectly compatible with the FX80, so we're left with one likely source of error - you.

Printer output on the BBC Micro can be routed to one of two interfaces - the serial (RS423, via a socket at the back of the machine) or the parallel one (Centronics, via a more complicated socket under the keyboard). When you turn on the BBC Micro it expects to send printer output to the parallel port. If you've connected up the serial port, the machine will 'hang up' as you describe, since it will wait for ever for a signal at the parallel port.

You can switch between the two ports with the command *FX 5. Type *FX 5,1 to select the parallel interface, or *FX 5,2 to select the serial one.

If you have a serial printer, you will probably need to select the correct speed for data transmission. Use the command *FX 8,N where N is a value between 1 and 8. Try each value of N until you find one that works. Again, the system will wait for ever unless you use the correct speed.

If neither of these tricks work, you've got a hardware problem. Make sure that you haven't fiddled with the switches inside the printer, which tell it the data format it should expect. Try out the computer with any other printer you can lay your hands on. Test the printer with other computers. You should be able to isolate the fault to the printer, cable or computer.

This goes to show how important it is to have a system fully demonstrated before you buy it. Take note of any special commands used when the machine is set up, and always buy the exact hardware you've seen working.


Link to the top of this document    Link to the main index
Previous column ComputerAnswers    Next column ComputerAnswers