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ComputerAnswers Column 21


COMPUTER ANSWERS SEPTEMBER 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.



THE ORIC'S INARDS

Where can I find hardware information about the Oric-1 micro? I can identify some 85 per cent of the integrated circuits present, mainly thanks to Radio Spares and Maplin catalogues. Two main problems now exist. I need to identify the remaining IC's and trace the system bus. I would be very grateful if you could point me in the right direction.
G.A Channell, Rushden, Northants.

You need a copy of the Oric Advanced User Guide, published by Adder (0223 861912). It costs £9.95, and you should be able to order a copy at any competent bookseller. The book explains the inner workings of the Oric's hardware and software; it includes a full circuit diagram which should save you the problem of tracing the system bus from the circuit board. Most of the information in the guide refers specifically to the Oric Atmos, a 'cleaned up' version of the Oric 1, but the differences - listed in the guide - are relatively few.



SUPERBASIC AND THE BROTHER EP44

I am using a QL with a Brother EP44 printer. It works reasonably well with Quill and Archive, the word-processor and database packages, but I am unable to install the printer to work in SuperBasic, either for printing or listing. Simply nothing happens.

Secondly, with both Quill and Archive, the EP44 will not print the exclamation mark or the less than and greater than signs. Finally, I experience problems with the addressing of envelopes. On ordinary white envelopes the print from the thermal ribbon just isn't good enough. I don't seem to be able to locate special envelopes, or even labels, with the necessary shiny surface. Can you help?
Leslie Fahidy, Horley, Surrey.

Two possible problems are suggested. Your EP44 expects information to be sent at a rate of 1200 baud. Quill and Archive read the rate of transmission from the 'installation' file, but you must set it yourself in SuperBasic, using the BAUD command.

When you turn on the QL SuperBasic assumes a speed of 9600 baud. This is eight times too quick for your printer, so you'll need to type the command BAUD 1200 to slow things down before the printer can be used.

Secondly, your printer expects two 'invisible' character-codes at the end of each line. These are called Carriage Return, or CR, and Line Feed, LF. As the names suggest, one is meant to cause the return of the printing 'carriage' to the left margin, while the other causes the printer to wind the paper on a line. These operations are usually performed together by a computer printer, so some computers only transmit the CR at the end of a line; if you change the setting of the 'New Line' switch inside the printer you can get an automatic LF whenever a CR is received. Most printers print a line at a time (for extra speed), so you won't get any results unless the correct codes are sent at the end of a line.

QL SuperBasic is unusual in that it transmits just a Line Feed at the end of each line. This confuses many printers, so you can tell the computer to convert the LFs into CR codes, automatically. You do this by opening your SuperBasic printer channel to the device SER1 C rather than SER1. Of course, your printer expects a CR and a LF, so you'll need to adjust the 'New Line' switch so that it can get by with just a CR.

This change should get SuperBasic printing happily, but you'll have to re-install Quill and Archive to send just a CR - not CR,LF - at the end of each line, or they'll print double-spaced results. You must specify CR on its own in response to the question 'End of Line Code?' when you run the relevant installation program.

You can get exclamation marks out of the EP44 with another installation trick. Use the 'Translate 2' facility to convert each exclamation mark into a full stop, a back space code and an apostrophe. The printer will then produce exclamation marks by superimposing two 'normal' characters, just as you would if you had a portable typewriter with no exclamation-mark key. The character code 8 tells the printer to step back a space, so the entire translation option would look like this:

Translate2: "!,".,8,"'

The characters that are explicitly specified must be preceeded by inverted commas, to distingush them from ASCII codes such as 8, the code for back space. I don't believe the EP44 can produce greater and less than signs directly, but you may be able to build them up from other characters in a similar way.

The envelope problem is baffling. I'd like to hear from any readers have found glossy envelopes that work well with thermal printers; I'll then print the details in a future column. In the meantime I can only suggest you resort to hand-written envelopes, and console yourself with the fact that people usually open machine-addressed letters last!

COLOUR BY NUMBERS

I am puzzled by frequent references in reviews of new hardware to colour palettes of 4096 different 'shades' generated from the three primary colours red, green and blue. I can see that 4096 is the cube of 16, which implies that each colour may be included in the mixture in 16 different ways, but it is difficult to see how anything like as many as 4096 different shades could be created.

If we represent the intensity of red, green and blue on a scale from 0 to 15 as (R,G,B) then certain consequences follow. (0,0,0) would of course be black, but what is the difference in 'colour' (as opposed to brightness) between (1,1,1), (8,8,8) and (15,15,15)? Surely all three would just be plain white, because they contain equal proportions of all three primary colours. Am I missing some vital distinction?
Keith Matthews, Peterston, Cardiff.

Each spot on a TV or monitor display has two different properties - colour and brightness, or 'chrominance' and 'luminance' in the jargon. A 'black and white' TV set ignores the chrominance information, and uses the luminance data to produce a varying pattern of black, white and shades of grey. In your example, (1,1,1) would give a very dark grey picture, (8,8,8) would give a medium grey and (15,15,15) would give bright white.

A black and white display can only work in shades of grey, but a colour display can independently vary the intensity of each primary colour at every point on the screen. Even with a single, primary 'colour', different intensities appear to the eye to have different 'colours'. When you mix colours together this is even more evident.

For instance, a low-intensity combination of green and red primary colours appears brown, while higher intensities appear buttercup-yellow. Add a little blue, and the colour you see becomes paler and more like the yellow of a lemon.

What we call 'colour' is really a combination of the effect of luminance and chrominance - which is why the special terms exist. The eye uses separate sensors ('rods' and 'cones') to perceive each component, but the brain muddles the results together to give a composite 'colour'.

In passing, it's worth bearing in mind that most systems offering 4096 colours restrict you to a smaller range - typically 256 colours, chosen from the 4096 - on any given display. The reason is that 12 bits are needed to store a colour chosen from 4096 (four bits for each primary colour). If you only use eight bits - in effect, a code for one of 256 colours chosen from the full range - you reduce the amount of memory needed to store a picture and speed up access to the display memory; most computers are happier working with 8 bit values than they are with 12 bits.

Special timing tricks can be used to change the palette of colours part way down the screen (giving several areas, each with an independent range of 256 colours) but in practice just 256 well-chosen colours can give results comparable to a TV picture, as long as you use a fine enough resolution.

Extra colours have two main uses in computer graphics. They allow subtle 'shading' effects which give a picture an illusion of depth and make it appear to be lit from outside. They also allow 'anti-aliasing' - intermediate colours can be used at the junction between one component of a picture and its background, blurring diagonal edges slightly and hiding the jagged 'step' pattern which would otherwise appear.



PRINTER INTERFACING

I have recently purchased a second-hand Anadex DP 8000 printer, which I wish to use with my Spectrum computer. I realise I shall have to purchase an interface, and am considering buying a Centronics which could also be of use if I obtain a different computer in the future. What are the likely snags? What do I need?
W. Briggs, Cheylesmore, Coventry.

In general, you can't use a Spectrum Centronics interface with any other computer. Each brand of computer has its own set of signals, on a specific type of connector with an individual pattern of connections. There are only two common types of printer. Serial printers expect characters to be transmitted down a few wires, one bit at a time, while parallel printers use more wires - generally arranged in a 'ribbon' - and transmit seven or eight bits simultaneously.

Parallel connections are faster and more reliable; they're also usually cheaper for the maker of the printer. However, they're basically one-way links. Serial connections are two-way, so an interface designed to transmit characters to a printer can also be used to read information into a computer from a modem (telephone interface) or another computer. Serial interfaces can run at many different speeds, while parallel ones just send characters as requested by the recipient.

You can also buy interfaces dedicated to converting serial information to parallel form or vice versa. You don't say whether your printer expects serial or parallel data, but you should obviously buy an appropriate interface. Parallel interfaces are generally much easier to wire up, especially one type of plug is almost universal at the printer end - an 'amphenol' type. Serial printers usually expect a 25-way 'D-type' plug, but arrangements vary, especially on cheap models.

If you need a serial interface the ZX Interface 1 is a good bet; it uses a 9 pin D-type plug at the computer end, but leads for this are widely available. The Interface 1 also contains a fast network handler and a microdrive controller, but not the drive.

There are two sorts of Spectrum parallel interface. The computer uses non-standard internal codes to represent keywords and colour information, so you need special software to convert or ignore the codes.

Cheap interfaces, such as the Tasman (0532 438301) and Kempston 'S' (0234 856633) require you to load a short routine from cassette before you use the interface; this is inconvenient and may make it hard to use the interface with commercial software.

For an extra £10 or so you can buy the software in ROM, built into the interface so that you can access it at any time. Euroelectronics (01 658 6350) were the first on the market with one of these - the ZX LPRINT, now in its third incarnation - and Kempston followed suit with their interface 'E', reportedly designed by the same engineer.

All of these systems will divert the Spectrum's LLIST and LPRINT commands to your new printer, but you will probably have trouble getting COPY to work. Each type of printer uses different codes to indicate high resolution graphics, and I know of no device specifically compatible with the Anadex DP-8000. If you need COPY you should bear this in mind before choosing a printer - non-standard codes make many obscure brands of hardware less of a bargain than they might seem.



ELECTRON PLUS 1

I have an Acorn Electron and have just purchased a Plus 1 interface. The ROM cartridge side of it works OK, but I can't seem to get my joystick to work. Is it possible to run a small program to check that the interface works?

Also, I have an Epson RX80 Centronics printer. Can I run this with the Plus 1? Where can I get a made-up lead?
D.A Campbell, Westvale, Kirkby.

The Plus 1 is compatible with BBC Micro analogue joysticks; on that machine you can read values from the joystick with the ADVAL function. This returns a value between 0 and 65520, in steps of 16, depending upon the position of the stick. There are four different inputs, and you select between them by putting a number between 0 and 3 in brackets after the ADVAL function.

Cheap joysticks, such as those for the Spectrum, Commodore and Atari computers, only produce an On or Off signal for each of four directions. These won't work properly with the Plus 1, which expects a graduated range of values.

The Plus 1 uses the same printer connector as the BBC Micro. Leads to connect that machine to the RX-80 are widely available, as the printer has a standard parallel socket.

Appropriate joysticks and leads are available from any Acorn dealer; if you can't find a local supplier contact one of the big dealers, such as Akhter (0279 443521).



AMSTRAD CONNECTIONS

Being the owner of an Amstrad PCW 8256 and a much older Apple II+, both of which run CP/M, I wonder if there isa way of getting the two computers to communicate, so that I can run my Apple CP/M software on the Amstrad. Would I be able to print output from the Apple on the Amstrad printer?
A.J Rozwadowski, Swindon, Wiltshire.

I use an Amstrad PCW 8256 at home for word-processing tasks. However I regularly travel all over the world and would like to write material while I am away from home. The solution would be to use a portable PC and on my return replay the material into the Amstrad. I should welcome your advice.
Dr. Garry Hunt, Raynes Park, London.

I am considering using an Amstrad word processor to facilitate the printing of my PhD thesis. The dot matrix printer will be adequate for the preparation stage, but the final printout will require a daisywheel to achieve the required standard. Is there likely to be a problem with the difference of control characters? What would be the best way to minimise any extra work involved?
M.J Carter, Yeovil, Somerset.

All of these problems can be cured with the Amstrad serial interface card, the CPS-8256. This lets you transfer information to and from Amstrad disks via an RS-232 interface. The text should be in standard ASCII form, without any 'control' characters, as these are unlikely to be interpreted in the same way by machines at both ends of the line.

Only the latest version of the Locoscript software - version 1.2 - will allow you to handle standard ASCII files, so you will need an upgrade if your version predates this. Upgrades are available free from Amstrad: send them your old Locoscript disk with a covering letter.

Daisywheel printers will not allow the range of changes in pitch and emphasis that you can get with Amstrad's own printer. Even if the equivalent function is available, the control codes are almost certain to be different.

The answer is to use an alternative word- processor, such as New Word or Pocket Word Star, to add printer- specific codes. Check that the package supports all of the features of your chosen printer. You'll have to change all the formatting but at least you won't need to re-type the main text. You'd probably have to re-format the document to use a different type-style anyway.

You'll also need an RS-232 interface at the other end of the link; these are available as options on almost all daisywheel printers, and built in to most portable computers. Plug-in RS-232 cards for the Apple II are widely available; input and output can be diverted to use the card with PR and IN, as for any other Apple peripheral card.

Your choice of portable computer will depend mainly upon your budget and the amount of text you need to store; the cheapest, lightest machines will only hold a few thousand words before you have to save the text onto disk or tape. Most have a cassette interface, but you may find that Epson tape cartridges or disks are easier to use and more reliable. Try to get a system that will run on widely- available batteries, so that you're not at the mercy of foreign mains power.

RS-232 links are not simple to set up, unless you've had a little practice and you know the details of both ends of the link. Unless you're sure you know what you're doing I suggest you get the firm that supplies your interface to demonstrate it working as you want it. This may mean shopping around, and you may be forced to buy the other end of the link - printer, computer or another interface - from the same supplier, but it'll probably save you a lot of hassle.



QL CAD

Last year you refered to CAD on the QL computer in your answer to a query headed 'Computers in Architecture'. Can you please tell me who is preparing such software? I would like to write to them and give them some encouragement, since I have been waiting patiently for such machine-code software to appear.
G.T. Morris, Sutton Coldfield, West Mids.

I've had to sit on this question for a while because it has taken a long time for good QL CAD packages to reach the market. The first few programs were really just drawing packages, and restricted you to the 512 by 256 point area of the QL screen - an unacceptable limitation for real CAD work.

This year has seen the arrival of proper CAD packages, allowing 'windowing' over a design larger than the display area, sub-drawings, and scaling. Talent Computer Systems (041 552 2128) produce TechniQL, the best QL draughting system I've seen - not to be confused with GraphicQL, their pixel painting utility. You may also be interested by Design Board 2, from Micr-a-soft (0204 29643) and QCAD, from Strong Computers (0267 231246).

The Independent QL User Group, Quanta, has an interesting 3D package, Scriptula, available at nominal cost to members from their library. They also have packages called Perspective and Autodraw, which I have not seen. For details, phone Quanta secretary Brian Pain on 0908 564271.


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