Advanced Teletext System User Guide

Advanced 

Teletext System 

USER GUIDE

The Advanced Teletext System User Guide 

WARNING: THE TELETEXT ADAPTOR MUST BE EARTHED 

Important: The wires in the mains lead for the Teletext Adaptor are coloured in accordance with the following 

code: 

Green and yellow Earth 

Blue Neutral 

Brown Live 

As the colours of the wires may not correspond with the coloured markings identifying the terminals in your 

plug, proceed as follows: 

The wire which is coloured green and yellow must be connected to the terminal in the plug which is marked by 

the letter E, or by the safety earth symbol, or coloured green, or green and yellow. 

The wire which is coloured blue must be connected to the terminal which is marked with the letter N, or 

coloured black or blue. 

The wire which is coloured brown must be connected to the terminal which is marked with the letter L, or 

coloured red or brown. 

If the socket outlet is not suitable for the plug supplied, the plug should be cut off and the appropriate plug fitted 

and wired as previously noted. The moulded plug which was cut off should be disposed of as it would be a 

potential shock hazard if it were to be plugged in with the cut off end of the mains cord exposed. The moulded 

plug must be used with the fuse and fuse carrier firmly in place. The fuse carrier is of the same basic colour* as 

the coloured insert in the base of the plug. Different manufacturer's plugs and fuse carriers are not 

interchangeable. In the event of loss of the fuse carrier, the moulded plug MUST NOT be used. Either replace 

the moulded plug with another conventional plug wired as previously described, or obtain a replacement fuse 

carrier from an authorised BBC Microcomputer dealer. In the event of the fuse blowing it should be replaced, 

after clearing any faults, with a 3 amp fuse that is ASTA approved to BS1362. 

* Not necessarily the same shade of that colour. 

Within this manual and associated software, the letters BBC refer to the British Broadcasting Corporation. The 

term 'BBC Micro' refers to the computer manufactured by Acorn Computer PLC under licence from the BBC. ` 

Tube' and 'Econet' are registered trademarks of Acorn Computer PLC. 

All rights reserved. No part of this Manual (except brief passages quoted for critical purposes) or of the 

computer programs to which it relates, may be reproduced or translated in any form or by any means, 

electronic, mechanical or otherwise, without the prior consent of the copyright owner. 

Disclaimer: Because neither the BBC nor Acorn Computer PLC have any control over the circumstances of use 

of the programs, no warranty is given or should be implied as to the suitability of the programs described in this 

manual for any particular application. No liability can be accepted for any consequential loss or damage, 

however caused, arising as a result of the operation of the program. 

©BBC Enterprises Limited 1986 

First published 1986, revised reprint October 1986 

Published by BBC Publications, a division of BBC Enterprises Limited. 

35 Marylebone High Street, London W1M 4AA 

Printed in the United Kingdom by Grange Press Ltd., London. ISBN 0 563 

21310 8 

2

Contents 

Introduction 6 

1 Getting Started 7 

1.1 The Components 7 

1.2 Connecting up the Units 7 

1.3 Tuning the Teletext Adaptor 9 

2 The Teletext Terminal 11 

2.1 Enter the Terminal 11 

2.2 Leave the Terminal 11 

2.3 Select a Page 12 

2.4 Change Channel 12 

2.5 Tune a Channel 13 

2.6 Reveal and Conceal 13 

2.7 Hold and Release a Page 13 

2.8 Select a Sub-Page 13 

2.9 Load a Page 14 

2.10 Save a Page to File 14 

2.11 Kept Pages 14 

2.12 Terminal Status 15 

2.13 Operating System Commands 15 

2.14 Previous Page 15 

2.15 Telesoftware 16 

3 The Telesoftware Terminal 17 

3.1 Introduction 17 

3.2 Ordered and Disordered Files 17 

3.3 Differences Related to Filing Systems 18 

3.4 Downloading a File 18 

Contents 

3


4 Teletext Operating System Commands 21 


4.2 The Commands: 21 

*BBC 22 

*CH 22 

*DATA 23 

*DATE 23 

*DISPLAY 24 

*HOFF 24 

*HON 25 

*ITV 25 

* MAGAZINE 26 

*NOTTX 26 

*PAGE 27 

*S4C 27 

*TELESOFT 28 

*TELETEXT 28 

*TIME 29 

*TRANSFER 29 

*TTX 30 

*TUNE 30 

5 Teletext OSWORD Commands 31 


5.2 The OSWORD Commands 32 

6 Technical Information 41 

6.1 The Teletext Data Format 41 

6.2 The Catalogue File Format 43 

6.3 The Teletext Character Set 45 

6.4 The Teletext Control Codes 46 

A What is Teletext ? 49 

B Hints on Receiving Teletext 50 

C UK Network Identities 52 

4

D CP/M, PANOS, & DOS+ Telesoftware 53 

E The Copyright Position on Telesoftware 54 

F Fitting the Teletext ROM 55 

G Summary of Teletext OS Commands 59 

H Summary of Terminal Keys 60 

IMPORTANT 

Contents 

IF YOU ARE RECEIVING TELETEXT ON AN ORDINARY TELEVISION 

RECEIVER YOU ARE COVERED BY YOUR EXISTING TELEVISION LICENCE, 

WHICH OF COURSE, MUST BE VALID. IF YOU DO NOT HAVE A TELEVISION 

RECEIVER BUT ARE RECEIVING TELETEXT WITH THE AID OF A VIDEO 

MONITOR UNIT, YOU MUST HAVE A COLOUR OR BLACK AND WHITE 

TELEVISION LICENCE DEPENDING ON WHETHER YOUR MONITOR IS 

COLOUR OR BLACK AND WHITE. 

5


Introduction 

This User Guide contains all the information you need to use the BBC Teletext 

Adaptor. 

Chapter 1 explains how to connect up the Teletext Adaptor and tune it in. 

Chapter 2 describes the facilities available with the Teletext Terminal. 

Chapter 3 describes how to download Telesoftware. 

Chapter 4 describes the extra Operating System commands that the Teletext 

ROM provides. 

Chapter 5 gives details of the OSWORD call used by the Teletext software. 

Chapter 6 gives detailed technical information on the data formats and the 

Teletext character set. 

Appendix A explains just what Teletext is. 

Appendix B gives hints and advice on Teletext reception. 

Appendix C is a table of Network Identity Codes for the United Kingdom. 

Appendix D explains about using PANOS, CP/M and DOS+ Telesoftware. 

Appendix E is a statement about copyright of BBC Telesoftware. 

Appendix F explains how to insert the Teletext ROM. 

Appendix G is a summary of the Operating System commands. 

Appendix H is a summary of the Terminal keys. 

6

1 Getting Started 

1.1 The Components 

You should have : 

One Teletext ROM 

A function key strip 

This manual 

A BBC Microcomputer System Teletext Adaptor 

You will not need a new aerial lead as the existing television aerial lead can be 

used. 

The Teletext ROM will operate with any BBC model B, B+, or Master 

Microcomputer which uses Operating System version 1.2 or higher. If you are 

not sure which operating system your computer uses, switch it on, then type 

*FX0 and press RETURN. 

You will see the letters OS plus a number. If this number is 1.20 or higher, you 

can go straight on to the next section. If you see: 

OS0.10 or OS1.00 

your operating system is unsuitable and to use Teletext you must fit a newer 

operating system ROM to your machine (your Acorn dealer will advise you on 

this). 

1.2 Connecting up the Units 

The first thing to do is to ensure that the Teletext ROM is installed correctly ( 

see Appendix F). 

Next, refer to Figure 1 which shows the microcomputer and Teletext Adaptor 

and connect up the system as follows: 

1. Connect the 34-way plug on the Teletext Adaptor 'ribbon' cable to the the 

socket labelled '1MHz BUS' on the underside of the computer. 

Caution: This plug may fit both ways round - the correct way is with the arrow 

at one end of the plug aligned with the arrow next to the '1MHz BUS' label. IF 

THE PLUG WILL NOT FIT, EXAMINE THE SOCKET FOR DAMAGE 

AND OBSTRUCTIONS. DO NOT USE EXCESSIVE FORCE. 

7


2. Disconnect the aerial lead from the back of your television set and reconnect 

it to the standard television aerial socket on the back of the Teletext 

Adaptor. 

Note: Indoor aerials don't generally provide a strong enough signal. You will in 

all probability need a loft or externally mounted aerial. If you don't think your 

aerial is good enough refer to Appendix B, or consult your TV dealer. 

3. Place the key strip under the clear plastic trim at the top of the computer 

keyboard. 

4. Switch on the Teletext Adaptor, then switch on the monitor, microcomputer 

and storage device (e.g. disc drive or cassette machine) if fitted. IT IS 

IMPORTANT THAT THE TELETEXT ADAPTOR IS SWITCHED ON 

BEFORE THE MICROCOMPUTER, otherwise you will have to press 

BREAK on your computer after switching on the Adaptor. 

To check that all is well, type *HELP and then press RETURN. 

A message similar to the following should be displayed : 

ATS 2.50 (BBC1) 

The HELP text for any other ROMs you have in your computer may also be 

displayed. 

If the message 'No TTX Unit' appears, it means that the Teletext ROM cannot ` 

find' the Teletext Adaptor, so check that the Adaptor is connected properly. If 

the message 'No Power' appears, check that the Adaptor is switched on and 

connected to the mains. The message 'No Signal' means that the Adaptor is not 

tuned in, or the aerial is not connected.

1.3 Tuning the Teletext Adaptor 

Getting Started 

The Teletext Adaptor can be tuned to four separate channels, assigned 

numbers one to four. We recommend that you allocate these channels as : 

Channel 1 - BBC1 

Channel 2 - BBC2 

Channel 3 - ITV 

Channel 4 - Ch4 or S4C 

If you tune the channels in a different order, the channel selection commands 

such as *BBC1 may not work properly. 

The procedure for tuning in the system to receive each channel is as follows : 

1. Type in *TELETEXT on the computer then press the RETURN key. The 

message 'BBC1' will appear in the top left of the screen. 

2. Press the SHIFT key together with the red function key f1 (BBC1) to select 

channel 1. 

3. Press the SHIFT and f0 (Tune) keys together. 

Your screen will display a station tuning scale (see Figure 3). A bar indicates 

the strength of the Teletext signal received. Maximum signal strength is 

achieved when this bar is as long as the scale (100%). 

4. Turn the number 1 tuning control on the rear of the Adaptor (Figure 2) to 

one end of its travel (this is indicated by a 'clicking' as you turn the control). 

Now,very slowly turn the control over its full travel. You will see the tuning 

bar suddenly increase in length as you tune into a BBC or IBA Teletext 

channel. This is accompanied by the channel and page numbers at the top of 

the screen. When you have found the longest tuning bar together with the 

messages CEEFAX and BBC1 you are correctly tuned into channel 1. ( 

CEEFAX pages begin with 1 on BBC1, and 2 on BBC2.) REMEMBER, YOU 

CAN RECEIVE ALL FOUR TELETEXT CHANNELS ON EACH TUNING 

CONTROL, SO MAKE SURE YOU GET THE RIGHT CHANNEL. 

5. Press the SPACE-BAR on your keyboard and repeat steps 2 to 4 for 

channels 2, 3, and 4. The only differences are: 

In step 2, you should press the appropriate channel selection button, with 

SHIFT. 

In step 4, you should rotate the appropriate tuning control (number 2, 3, or 4). 

9


6. When you have tuned in all four channels, press the SPACE-BAR. This will 

remove the tuning scale and a Teletext index page will be automatically 

displayed. This is the index page for the channel you tuned last.

2 The Teletext Terminal 

The Teletext Terminal behaves in the same way as the Teletext section of a 

television. However, it also has some extra facilities. Instead of using a remote 

keypad you use the BBC Microcomputer's keyboard and function keys. The 

function key strip should be placed above the red function keys when using the 

Terminal. 

2.1 Enter the Terminal 

To select the Teletext Terminal, type *TELETEXT and press RETURN. BBC1 

CEEFAX is selected by default and the initial page is displayed once it has 

been received. This initial page is usually an index to the service. 

At the top of the screen you will see a line of text which is constantly 

changing. This consists of : 

The channel title, or page number selected 

The name of the Teletext service (e.g. CEEFAX ) 

The page number indicator, which displays the page number of the page 

presently being transmitted 

The date and time 

2.2 Leave the Terminal 

To leave the Terminal, press f9. 

If you are using a co-processor (e.g. 6502 second processor, etc.), this will 

return you to the language or application that you called Teletext from. 

Normally, any programs, or data, will remain intact. If you are not using a coprocessor, 

pressing f9 will start BASIC; any programs, or data, will be lost. 

The BREAK key 

In order to work properly with different co-processors, the Terminal does not 

start up as a language if you are using a co-processor. This means that if you 

press BREAK, you will leave the Terminal and you will return to the previous 

language, or application. On systems without co-processors, pressing BREAK 

will re-initialise the Terminal, and clear any 'kept' pages (see Section 2.11). 

11


2.3 Select a Page 

To select a page, simply enter the page number using the number keys. The 

number you enter will appear at the top left of the screen, preceded by the 

letter 'P' for PAGE. If you make a typing error, or simply want to replace the 

last digit entered, press DELETE. 

When all three page number digits have been entered, the Terminal will start 

looking for the page. The middle section of the top line will turn green to 

indicate that a page is being searched for. When the page is found, the 

Terminal displays it immediately and the top line of the screen turns white, 

signalling that the page has been found. The page number may also change 

colour. Red indicates that the page is corrupted or incomplete, and yellow 

means that the Terminal is unable to determine whether the page is alright or 

not. 

Note that you can instruct the Terminal to look for a new page while it is still 

searching for the one you initially specified. It will automatically start looking 

for the new page when you enter the last digit. 

At the bottom of the screen there may be a series of coloured boxes, followed 

by page numbers, or alternatively, a series of coloured 'keywords'. These 

correspond to the four coloured blocks on the keystrip (f1 to f4). They show 

that the current page has 'links' to other pages. These links tell the Terminal 

that the pages specified are likely to be selected next, so it should capture them 

if they come by. This means that if you select one of these pages, either by 

entering its page number, or by pressing one of the coloured buttons, it will be 

displayed more quickly. If the bottom line contains coloured keywords, this 

means that the Teletext Editors controlling the broadcast have told the 

Terminal what sort of page the links point to. 

Next to the four coloured keys you will find the INDEX button (f0). Normally, 

pressing this will take you back to the index page. This may be the main index 

page, or a sub-index, such as the sport index. 

2.4 Change Channel 

To change channel at any time, press one of the four function keys f1 to f4, 

while holding down the SHIFT key. This will clear any kept pages and the 

Terminal will start to look for the initial page of the channel chosen. 

12

2.5 Tune a Channel 

The Teletext Terminal 

Pressing SHIFT and f0 will display the tuning bar and scale. See `Tuning the 

Teletext Adaptor' (Section 1.3) for more details on tuning channels. 

When you have finished tuning, press the SPACE-BAR to leave the tuning 

routine. 

Note: The Adaptor will resist any attempt to retune a channel unless the system 

is in tuning mode. 

2.6 Reveal and Conceal 

Certain Teletext pages contain 'concealed' information. These include quizzes, 

jokes, etc. They usually contain a phrase such as : 

Press REVEAL for the answers 

To display the concealed information you should press f6. This will `reveal' the 

information and put the page on `hold' (see the following section). Press f6 to 

conceal the information again and release the page. 

2.7 Hold and Release a Page 

Pressing the f7 key will hold the currently displayed page and stop it from 

being updated by subsequent rolling pages. The clock display in the top righthand 

corner will be replaced by the word 'HOLD'. 

To release the page, and allow it to be updated, press f7 again. The clock 

display should re-appear. The page is automatically released when a new page 

number is entered. 

2.8 Select a Sub-Page 

Some Teletext pages consist of more than one screenful of text. The individual 

pages are transmitted in sequence. A good example of this is Newsreel on 

BBC1. This consists of about a dozen 'sub-pages'. Each of these sub-pages has 

a number from one upwards. If you wish to select a particular sub-page, you 

should press f8. The clock display in the top right-hand corner of the screen 

will be replaced by an 'S' followed by four dashes. Any numbers you now type 

will replace the dashes in the same way as they do when entering a page 

number, except this time there are four digits to enter. DELETE works in the 

13


same way as for page numbers. Leading zeros are important and must be 

entered; sub-page twelve, for example, would be entered as 0012, sub-page 

three would be entered as 0003, etc. 

Once four digits have been entered, the Terminal will start searching for the 

sub-page specified. 

To return to entering page numbers rather than sub-page numbers, press f8 . 

2.9 Load a Page 

If you wish to display a Mode 7 screen stored on the current filing system ( 

disc, network, etc.), press the SHIFT and f6 keys. The message 'Load Page : ' 

is displayed, followed by a flashing line. 

Type the filename of the screen you want to load, and press RETURN. 

The screen is then displayed, along with the message 'Press SPACE to continue'. 

When you press the SPACE-BAR, the top line starts to change again and the 

page displayed before you pressed SHIFT f6 re-appears. 

2.10 Save a Page to File 

To save a page of Teletext to the currently selected filing system, such as disc 

or network, press the SHIFT and f7 keys. The message 'Save Page : ' is 

displayed, followed by a flashing line. 

Type in the filename for the page and press RETURN. (See the filing system's 

user guide for more information on filenames.) 

The page is then stored in a file. If an error occurs when saving the page, a 

message is displayed. 

When the page has been saved, the Terminal is ready for another command. 

2.11 Kept Pages 

If you are using Teletext for long periods at a time, you will find there are 

pages which you want to keep returning to, such as news and financial 

headlines, the sports results, or the weather. The Terminal has the ability to ` 

keep' some of these pages for you, updating them when it can, so that when 

you select them, they appear immediately, without your having to wait for 

them to 

14

The Teletext Terminal 

come round. The number of pages that can be kept in this manner is determined 

by the memory available in the computer. It ranges from about 7 to 11 pages. 

To keep a page, select its page number in the usual way and press COPY. The 

message `Kept' will appear at the bottom of the screen and the computer will 

beep. You can now go and select another page to be kept, without having to 

wait for the previous page to be displayed. If you fill up all the available space 

for kept pages, the message `Buffer Full' will be displayed, and the page will 

not be kept. 

To release a kept page, select its page number and press COPY again. The 

message `Released' will appear and the computer will beep. 

To release all the kept pages, press SHIFT and COPY together. The message ` 

All Released' will be displayed, and the computer will beep. 

To see what pages have been kept, use the `Terminal Status' facility (Section 2. 

12). 

2.12 Terminal Status 

To see what pages the Terminal is currently looking for, together with any kept 

pages, press the RETURN key on its own. The screen will display a page 

showing the page numbers. 

To return to the main Terminal mode, press the SPACE-BAR. 

2.13 Operating System Commands 

If you wish to perform an OS command, press the * on the keyboard and enter 

the command, followed by RETURN. The command will then be executed and 

the message 'Press SPACE to continue' will appear. If you wish to perform 

another OS command, press * again. 

2.14 Previous Page 

When you are looking at pages which have more than one sub-page, the page 

is often updated before you have had time to read it. To get round this problem, 

the Terminal has a `previous page' facility. Pressing TAB switches between the 

current page and the previous page, giving you more time to read the pages. If 

another new page arrives, it is automatically displayed and TAB then switches 

between it and the previous page. 

15


2.15 Telesoftware 

If you wish to download a Telesoftware file, you should first select the correct 

channel and then press f5. This starts the Telesoftware Terminal. For more 

information on how to use the Telesoftware Terminal, see the next chapter.

3 The Telesoftware Terminal 

3.1 Introduction 

`Telesoftware' is the name given to any software that is distributed by 

electronic means, e.g. Teletext and Viewdata. 

The Teletext Terminal has a built-in Telesoftware Terminal for downloading 

programs and data files onto your local filing system (e.g. disc or Econet). This 

makes the business of using Telesoftware very easy. 

Telesoftware files are divided into sections, called 'blocks'. Each of these 

blocks occupies one sub-page of a Teletext page. Normally, a block contains 

about 800 bytes of information, encoded in a special format called 'Redefinable 

Telesoftware Format' (RTF). This format is very complex and it is beyond the 

scope of this manual to describe it. 

3.2 Ordered and Disordered Files 

There are two sorts of file in Telesoftware. One is the 'ordered' file and the 

other is a 'disordered' file. 

Ordered files have to be downloaded in strict order, starting from block 1 of 

the file and carrying on until the end of the file. If an error occurs, in the fourth 

block of the file, for example, the Telesoftware Terminal has to wait for the 

fourth block to come round again before it can continue downloading the file. 

This makes ordered files very time-consuming to download, if you do not have 

a perfect signal from you aerial. 

Disordered files can be downloaded in any order. Say the Telesoftware 

Terminal is downloading a file; it downloads the fourth and fifth blocks, but an 

error occurs in the sixth block. Well, it will skip the sixth block and download 

the seventh. It will carry on downloading blocks until the loading cycle comes 

round to the fourth block again. It will then wait for the sixth block, without 

doing any downloading, and attempts to download the block again. This ability 

to load the blocks in any order makes disordered files far more convenient. 

Most files on CEEFAX are disordered. 

17


3.3 Differences Related to Filing Systems 

The operation of the Telesoftware Terminal differs slightly if you are using the 

cassette filing system instead of disc or Econet. 

Normally, when using disc or Econet, each block of a file is saved as it is 

received. This allows the Terminal to download larger files than would 

otherwise fit in memory. 

Cassettes are not fast enough to save each block as it is received, so if you are 

using cassettes to store files, rather than discs or Econet, blocks have to be 

stored in memory until the whole file has been received. This means that 

cassette users cannot download some of the very large files available on 

Telesoftware. 

3.4 Downloading a File 

On Teletext services that carry Telesoftware there is a special page called the ` 

catalogue'. This page contains a Telesoftware file which has details of all the 

programs currently available on the service. The actual position of this page is 

not defined, but the Telesoftware Terminal can find it by using a 'link' from the 

index page. 

To download a file, follow this procedure : 

1. Enter the Teletext Terminal. 

2. If you are using discs you should place a disc with sufficient room to store 

the programs in the drive. ADFS users must use a *MOUNT command to 

inform the computer that they have changed discs. 

3. Press f5 (Telesoftware). 

The computer will now look for the catalogue of Telesoftware. If there is no 

catalogue, an error message will be displayed. It may take the computer several 

seconds to find the catalogue so please be patient. 

Once the catalogue has been found, the first few entries are displayed on the 

screen. Only those entries that say they are suitable for the BBC 

Microcomputer will be displayed. 

4. Scroll through the list using the UP and DOWN cursor keys to move the 

coloured bar. 

5. When you have found the program or file you want to download, press the 

RETURN key. 

18

The Telesoftware Terminal 

Some of the entries may be in colour. If the item above or below an entry is in 

the same colour, this indicates that the files go together and both should be 

downloaded. There may of course be more than two files in a group. 

When you have selected the file you want to download and pressed RETURN, 

the screen will clear and the name of the file, along with its load and execution 

addresses, will be displayed. 

The computer now waits for the page containing the file to arrive. 

When it finds the file, a display of all the blocks in the file appears - this is 

initially in white. As each page of a file is found, the appropriate block turns 

green, unless an error is detected, in which case the block turns red. If there are 

more than eighty blocks, a text message is displayed instead. 

When all the blocks are green, the complete file has been downloaded. If you 

are using a cassette system, the Terminal will now save the file, so place a 

cassette in the recorder and follow the standard SAVE instructions. 

Once the file has been saved, the Telesoftware Terminal will again look for the 

catalogue and display it. If you have finished downloading Telesoftware, press 

ESCAPE to return to the main Terminal. 

If, while you are downloading a file, the message 'Different File' appears, the 

Terminal has encountered another file on the same page. It is quite possible to 

put several files on one page and thereby reduce the amount of space taken up 

on the normal Teletext service. 

If you are downloading a group of related files, you should start by 

downloading the first file, and carry on downloading each file in turn until all 

of them have been downloaded. Occasionally a special 'loader' will be supplied 

to download a group of files. If this is the case it will be the first file in the 

group and have the word 'Loader' beside it. Download the loader in the normal 

way, return to BASIC, and *RUN the loader. 

Hint for Disc Users: If you are going to download a large Telesoftware file, it 

is a good idea to COMPACT the disc before you start to make sure there is 

sufficient room on your disc. (See the Disc System User Guide for information 

on compacting discs.) As the Terminal uses OPENOUT, the filing system will 

need at least 16K free to open any Telesoftware file. 

19

The Advanced Teletext System User Guide

4 Teletext Operating System Commands 


This chapter is only of interest if you intend to write your own programs to 

handle Teletext data. 

The Teletext Operating System (OS) commands allow you access to the 

facilities of Teletext from your own programs. Some of the commands should 

be used with care because they copy Teletext data into the computer's 

memory and if used incorrectly could corrupt your program. Certain of the 

Terminal's facilities, such as REVEAL, are not available as OS commands. 

These have to be implemented by your program if you wish to use them. 

Important: Before you use the Teletext OS commands you must issue a 

*TTXON command (see below) to tell the Teletext Adaptor to start accepting 

Teletext data. When you have finished with Teletext, issue a *TTXOFF 

command to turn of the Adaptor's Teletext reception. This is important, as the 

computer's memory may be corrupted by unexpected data arriving from the 

Adaptor. 

4.2 The Commands 

All the commands can be typed in from the keyboard or included in a BASIC 

program. Each command is described separately under the following 

headings: 

Description What the command does in functional terms. 

Syntax The actual command words and the order in which commands 

and data are arranged. 

Example An example of a string of commands including the one described. 

Note Additional information. 

As with any other BBC Microcomputer OS command, Teletext allows you to 

type abbreviations for its commands, such as *TE. for *TELETEXT, or 

*MAG. for *MAGAZINE. 

To avoid clashes of OS command names, the Teletext system allows an extra ' 

T' to be placed before a command, e.g. *TTIME for *TIME, or *TPAGE for 

*PAGE. 

21


*BBC 

Description 

This command is used to select channels 1,2,3 or 4 for Teletext reception. 

Syntax 

*BBC 

where is 1,2,3 or 4. If no channel is specified, 1 is assumed. 

Example 

*TTXON 

*BBC1 

This will select channel 1. 

Notes 

It is up to you to ensure that channel 1 is tuned to BBC1 and channel 2 is tuned 

to BBC2 for this command to produce the expected results. 

*CH 

Description 

This command is identical to *BBC and is for use in countries other than the 

UK. It can also be used to select Channel 4. 

Syntax 

*CH 

where is 1,2,3 or 4. If no channel is specified, channel 1 is assumed. 

Example 

*TTXON 

*CH4 

This will select Channel 4 for Teletext reception. 

22

*DATA 

The Teletext Operating System Commands 

Description 

This command transfers the full data for the current page to a given memory 

location. For details of the data format, see Chapter 6. 

Syntax 

*DATA 

where is an area of memory reserved for the data. The memory of the 

current language processor is used, unless an address in the form FFFFxxxx is 

used. 

Example 

*TTXON 

*S4C 

*PAGE 400 

OSCLI("DATA"+STR$~(Buffer)) 

Notes 

This command will wait forever if the current page cannot be found. ESCAPE 

will exit the command if ESCAPE is enabled. 

The area of memory reserved for the data must be 2K long, i.e. 2048 bytes. 

*DATE 

Description 

This command causes the date, as transmitted in the television data packet to be 

displayed. 

Syntax 

*DATE 

Example 

*TTXON 

*BBC1 

*DATE 

Notes 

In order to give the Adaptor time to grab the date, which is only transmitted once 

a second, you must leave a gap of at least 1.5 seconds between changing channel 

and asking for the date. 

If the Television Service Data Packet (TSDP) is not transmitted, an error 

message is displayed instead of the date. 

23


*DISPLAY 

Description 

This command is used to display any Teletext page which has previously been 

transferred into memory with a *TRANSFER command. It decodes the page 

from the internal form used by the Teletext system into the form required for 

screen display. The computer must be in Mode 7 or 135 (shadow) for this 

command to work properly. 

Syntax 

*DISPLAY 

where is the hexadecimal address used in the *TRANSFER or 

*DATA commands. If the address is eight digits long and the first four are ' 

FFFF', the memory used will be that of the I/O processor, regardless of 

whether a co-processor is attached or not. 

Example 

MODE 7 

*TTXON 

*BBC2 

*PAGE 200 

*TRANSFER 7000 

*DISPLAY 7000 

This will display BBC2 CEEFAX page 200 on the screen. 

*HOFF 

Description 

This command switches off the top line display (Header) of the Teletext system. 

Syntax 

*HOFF 

24


*HON 

Description 

This command controls the top line display (Header) of the Teletext system. It 

allows the top line to be displayed, with or without the clock. It also sets the 

display to any magazine (see *MAGAZINE). 

Syntax 

*HON [0] Switch on the Header line with the clock display. 

*HON 1 Switch on the Header line without the clock display. 

The square brackets mean that the zero is optional. 

Example 

*TTXON 

*BBC1 

*HON 1 

PRINT TAB(32,0);CHR$(130);"HOLD"; 

This will switch on the Header for BBC1, and print the word 'HOLD' where 

the clock display normally goes. 

Notes 

This command only works if the screen display is currently Mode 7 (without 

shadow) and the screen has not been scrolled since the last CLS. Scrolling 

within a window does not matter. The Headers of certain services appear to 

flicker; to stop the flicker, use the *MAGAZINE command. 

*ITV 

Description 

This command selects channel 3 or 4 for Teletext reception. If no number is 

given after the command, channel 3 is used. 

Syntax 

*ITV 

*ITV 1 

*ITV2 

Example 

*TTXON 

*ITV 

*PAGE 100 

This will make page 100 of ORACLE the currently selected page. 

25


*MAGAZINE 

Description 

This command controls which magazine's Headers are displayed. 

In Teletext, the pages are grouped together in 'magazines'. These consist of up 

to 100 pages. The initial page digit signifies which magazine the page is in; 

103,156, and 175 are all in Magazine 1, and 704 is in Magazine 7, etc. 

There are two ways of transmitting Magazines in Teletext. In one the 

magazines are sent in numeric order, e.g. Magazine 1, Magazine 2, etc. This is 

called 'serial' transmission. In this case, all the Headers for all the magazines 

are displayed and the *MAGAZINE command has no effect. The other method 

is to send the magazines in 'parallel' . An example page sequence might be 100, 

200,101,201,102,202,etc. In this case the Headers appear to flicker. 

Syntax 

*MAGAZINE 

where is the first digit of the page numbers to be displayed. 

Example 

*TTXON 

*ITV 

*HON 

*MAGAZINE 1 

This will display only those Headers whose page number begins with 1. 

*NOTTX 

Description 

This command 'removes' the Teletext ROM from the Operating System's view. 

It produces the message 'Press CTRL-BREAK...'. Once 'removed' in this way, 

Teletext no longer takes up any of the computer's memory and the Teletext 

commands become inoperative. The only way to 'replace' the ROM is to switch 

the computer off and on again. 

A less drastic, but non-software method of switching off the Teletext system is 

to switch off the Adaptor, and press BREAK on the computer keyboard. The 

Teletext system can then be switched on again by switching on the Adaptor 

and pressing BREAK. 

Syntax 

*NOTTX 

26


Notes 

Switching the Teletext system on and off will alter PAGE in a Model B or B+ 

computer. You should therefore save any programs you are working on before 

issuing this command. This is NOT the case with *TTX. 

*PAGE 

Description 

This command sets the specified Teletext page as the current page. 

Syntax 

*PAGE [S


*TELESOFT 

Description 

This command provides a degree of compatability with the old TFS. When 

issued it has the same effect as a *TTXON command, except when 

*TRANSFER or *DISPLAY is used. When in TFS emulation mode 

*TRANSFER returns the teletext data in the form of a 960 byte block, 

consisting of 24 rows of 40 characters each. The data has the top bit set on 

every character, and is suitable for immediate display. This means that 

*TRANSFER 7C00 will produce the correct screen display. 

Syntax 

*TELESOFT 

Example 

*TELESOFT 

*TRANSFER FFFF7C00 

*SAVE MODE7 FFFF7C00+400 

This will save a file called MODE7 which will be a normal MODE 7 screen. 

Notes 

If you are going to use some of the more advanced features of the ATS, which 

are not available in the old TFS, there is no point in using this command as the 

programs will not work with TFS anyway. Use *TTXON instead and make use 

of the more powerful data format. 

*TELETEXT 

Description 

This command starts the Teletext Terminal. If a co-processor is in use, the 

Terminal is started as an OS command and is exited if BREAK is pressed. 

Otherwise, the Terminal is started as a normal language. 

Syntax 

*TELETEXT 

28

*TIME 


Description 

This command displays the local time, as transmitted by the Television 

Service Data Packet. 

Syntax 

*TIME 

Example 

*TTXON 

*BBC1 

*TIME 

Notes 

Time information is extracted from the television service data packet (TSDP). 

If the TSDP is not transmitted, an error message is displayed instead of the 

time. 

*TRANSFER 

Description 

This command transfers the display data, for the current page to a given 

memory location. For details of the data format, see Chapter 6. 

Syntax 

*TRANSFER 

where is an area of memory reserved for the data. The memory of 

the current language processor will be used unless an address in the form 

FFFFxxxx is used. 

Example 

*TTXON 

*BBC1 

*PAGE 700 

*TRANSFER 7000 

Notes 

This command will wait indefinitely if the current page cannot be. found. 

ESCAPE will exit the command if ESCAPE is enabled. 

The area of memory reserved for the data must be at least 1K long, i.e. 1024 

bytes. 

29


*TTX 

Description 

This command controls the Teletext Adaptor. If you wish to use Teletext, you 

must first issue a *TTXON command. When you have finished, you should 

issue a *TTXOFF command to switch off the Teletext Adaptor. 

Syntax 

*TTXON 

*TTXOFF 

Example 

*TTXON 

*TIME 

Notes 

The *TTXON and *TTXOFF commands are not necessary if you are using the 

Teletext Terminal, which automatically switches the Adaptor on and off. 

*TUNE 

Description 

This command invokes the tuning routine for the currently selected channel. 

For more details see Section 1.3. 

Syntax 

*TUNE 

30

5 Teletext OSWORD Calls 


Teletext OSWORD calls allow you access to the facilities of Teletext from 

your own assembly language programs, and to access some of the lower level 

facilities available with the Teletext system. 

The basis of the Teletext system is the 'page grabber'. This is a piece of 

machine code which constantly looks for Teletext pages. It can look for up to 

20 pages, automatically storing them in the designated area of memory when it 

finds them. It also looks for, and stores, the TSDP. The Teletext OS commands 

only use one of the page grabber's 20 records to grab pages requested with 

*PAGE. From assembly language however it is possible to use all 20, as the 

Terminal does. 

All the facilities of the Teletext system are controlled by one OSWORD call 

&7A. The first byte of the parameter block for an OSWORD &7A is a 

command code. The commands are described in Section 5.2. 

Teletext System Control 

OSWORD with A = &7A 

The call address is &FFF1 

On entry, X (lo-byte) and Y (hi-byte) point to the parameter block: 

Important: Before you use the Teletext OSWORD call, you must issue a 

*TTXON command, or an OSWORD &7A with command = 13, to tell the 

Teletext Adaptor to start accepting Teletext data. When you have finished with 

Teletext, issue a *TTXOFF command, or OSWORD &7A with command = 12, 

and command = 14, to switch off the Adaptor's Teletext reception. 

31


5.2 The OSWORD Commands 

For each call a list of parameters is given, along with the offset within the 

parameter block at which they reside. 

0 Read Channel 

Read the channel which is currently being used for Teletext reception. 

Parameters: 

0 0 

1 Returned channel number (0 to 3 ; 0: BBC1) 

1 Set Channel 

Set the channel to be used for Teletext reception. 

Parameters: 

0 1 

1 The channel to be used (0 to 3). 

2 Read a Record Flag 

For each record in the page grabber there is an associated flag byte. This 

contains information such as whether the page has arrived yet, and if it is being 

updated at the moment. It also controls whether the page is on hold or not. The 

format of the flag is : 

Bit 0 HOLD (0: No, 1: Yes) 

Bit 1 Page received (0: No, 1: Yes) 

Bit 2 Page being updated (0: No, 1: Yes) 

Other bits undefined. 

Parameters: 

0 2 

1 Record number (0 to 19) 

2 Flag for record requested 

3 Record currently being grabbed (or &FF if none) 

32

3 Set a Record Flag 

The Teletext OSWORD Commands 

This command allows you to alter the flag for a particular record. This is done 

to HOLD or RELEASE a page and also to clear the 'page received' bit so that a 

new copy of the page can be detected. 

Parameters: 

0 3 


2 New value for flag 

4 Read a Page Grabber Record 

This command returns one of the page grabber's records. 

Parameters: 

0 4 


2 Magazine number of page being looked for 

3 Page number of page (in BCD, i.e. &23 means page 23) 

4 Sub-page number (hi-byte) &3F means any sub-page 

5 Sub-page number (lo-byte) &7F means any sub-page 

6 Address to put page (lo-byte) 

7 Address to put page (hi-byte) 

Note: The address is always in the I/O processor 

5 Set a Page Grabber Record 

This command allows you to specify which page should be grabbed by a 

particular record. If you specify the same page in different records, only the 

first record will ever get it. 

Note: The page grabber always stores pages in the I/0 processor memory. If 

you wish to store the pages in the co-processor, you must use the Teletext OS 

commands which will copy them across for you. 

33


Parameters: 

0 5 


2 Magazine number of page to be looked for 

3 Page number of page (in BCD, i.e. &23 means page 23) 

4 Sub-page number (hi-byte) &3F means any sub-page 

5 Sub-page number (lo-byte) &7F means any sub-page 

6 Address to put page data (lo-byte) 

7 Address to put page data (hi-byte) 

6 Read the No. of Rows to be Captured 

This command returns the number of rows that are being grabbed for each page. 

Parameters: 

0 6 

1 Number of rows being grabbed 

7 Set the No. of Rows to be Captured 

This command allows you to specify the number of rows that are stored for each 

page. If you only want to store the displayed part of a page, set the number of 

rows to 24. This will require 1024 bytes of memory per page. If you want to 

store non-display rows in addition to display rows, you should set the number of 

rows to 30. This will require 1260 bytes per page. 

Parameters: 

0 7 

1 Number of rows 

8 Read the Header Line Status 

This command returns the current status of the Header line. 

Parameters: 

0 8 

1 Header status 

34

Status values are : 

&00 Header off 

&01 Header on with clock 

&FF Header on without clock. 

9 Set the Header Line Status 


This command sets the current status of the Header line (*HON). 

Parameters: 

0 9 

0 Header status 

See the previous call for the status values. 

10 Read the Magazine for Header Display 

This command returns the magazine whose Headers are currently displayed. 

Parameters: 

0 10 

1 Magazine 

Note: Magazine 8 is returned as zero. &FF means that all Headers are displayed. 

11 Set the Magazine for Header Display 

This command sets the magazine whose Headers are to be displayed ( 

*MAGAZINE). 

Parameters: 

0 11 

1 Magazine 

Note: Magazine 8 should be entered as zero. &FF means that all Headers are to 

be displayed. 

35


12 Switch Off Teletext Interrupts 

This command disables the Teletext Adaptor interrupts (*TTXOFF). 

Parameter: 

0 12 

13 Switch On Teletext Interrupts 

This command enables the Teletext Adaptor interrupts (*TTXON). 

Parameter: 

0 13 

14 Clear All Page Grabber Records 

This command clears all page grabber records. It should be issued before 

turning off Teletext interrupts if you are not going to re-enable them soon. 

Parameter: 

0 14 

15 Read Television Service Data Packet 

This command returns the TSDP, except for the 'status message' (which is not 

connected with Teletext). 

Parameters: 

0 15 

1 TSDP 

to 

13 

The Television Service Data Packet: 

Byte Meaning 

1 Magazine for initial page 

2 Page number for initial page (&FF : Not Specified) 

3 Page sub-code for initial page (hi-byte) 

4 Page sub-code for initial page (lo-byte) 

5 Network Identity Group (hi-byte) 

6 Network Identity Group (lo-byte) 

36


7 Time offset from Universal Co-ordinated Time (UTC) 

8 Modified Julian Date (10,000's) (BCD) 

9 (1000's and 100's) (BCD) 

10 (10's and 1's) (BCD) 

11 Universal Co-ord. Time (Hours) (BCD) 

12 (Minutes) (BCD) 

13 (Seconds) (BCD) 

The Network Identity Group is a 16 bit number, unique to each television 

channel. A list of the numbers used in the UK is given in Appendix C. You 

will see that each IBA company has its own identity number. 

The time offset allows the local time to be calculated from UTC. In the UK 

therefore, the time offset is normally &81, but in British Summer Time it 

becomes &85 to indicate that one hour should be added to UTC. Note that 

UTC is the international name for Greenwich Mean Time (GMT). 

The format of the offset is as follows: 

Bit Meaning 

0 Always 1 

1 Half-hour 

2 1 Hour 

3 2 Hours 

4 4 Hours 

5 8 Hours 

6 0: Add offset, 1: Subtract offset 

7 Always 1 

16 Clear Page Grabber Status 

This command halts the page grabber, even if it is half way through grabbing 

a page. If you wish to change a record it is advisable to check if it is currently 

being updated. If so, call this command to stop the update before changing the 

record. 

Parameter: 

0 16 

37


17 Read Teletext Adaptor Status 

This command returns the status of the Teletext Adaptor. 

Parameters: 

0 17 

1 Adaptor status 

Status: &00: On and connected 

&01: On, but no TV signal 

&02: Off, but connected 

&FF: No Adaptor connected 

18 Set the Subtitle Enable Flag 

This command allows you to turn subtitle reception on and off. Subtitles are 

NOT stored, but displayed immediately upon reception. This allows them to 

remain synchronised with the TV program. 

Parameters: 

0 18 

1 Subtitle enable (&00: enable, &FF: disable) 

2 Subtitle magazine (normally 0) 

3 Subtitle page (normally &88) 

19 Set Interrupt Handling Flag 

This command allows you to control whether the Teletext ROM handles the 

interrupts from the Adaptor, or whether they are passed on to other software. 

This can be used to allow very low level control of the Teletext Adaptor. 

Parameters: 

0 19 

1 Interrupt enable (&00:enable, &FF: disable) 

20 Tuning Routine 

This command calls the tuning routine for the current channel. The call is 

terminated by pressing the SPACE-BAR. 

Parameter: 

38 

0 20

21 Return Time from TSDP 

This command returns the local time in ASCII form. 

Parameters: 

0 21 

1 'HH:MM:SS' time string 

10 Error flag (&00: time OK, &FF: time not found) 

22 Return Date from TSDP 

This command returns the local date in ASCII form. 

Parameters: 

0 22 

1 DD/MM/YYYY' date string 

12 Error flag (&00: date OK, &FF: date not found) 

23 Check CRC 


This command checks the CRC of the page pointed to. It allows you to check 

that the data collected by the Teletext Adaptor has not been corrupted. This 

could be very important if the data being collected is of a financial nature. 

Parameters: 

0 23 

1 Pointer to page data (lo-byte) 

2 Pointer to page data (hi-byte) 

3 Returned flag (0: No CRC, 1:CRC OK, &FF: CRC Failed) 

Note: The page data must be in the I/0 processor. 

39


24 Download a File from Teletext 

This command downloads a file from the current channel. 

Parameters: 

0 24 

1 Pointer to filename (lo-byte) (terminated by &OD) 

2 Pointer to filename (hi-byte) 

3 Load address (lo-byte) (32 bits) 

: 

6 Load address (hi-byte) 

7 Exec address (lo-byte) (32 bits) 

: 

10 Exec address (hi-byte) 

11 Magazine number (0 to 7) 

12 Page number (&00 to &FF) 

13 Load to memory/file (&00: memory, &01: file) 

14 Reset default tables (&00: yes, &01: no) 

Notes: The filename must be in the I/O processor and be in upper case only. 

The load address must agree with the load address in the file being 

downloaded. This is normally held in Block 1 of a file, or is available from the 

catalogue file (see Chapters 3 and 6). 

When downloading to memory, the file is always stored at OSHWM onwards, 

regardless of the load address. When downloading to file, the load and exec 

addresses are set to those given in the telesoftware file. 

Normally, the default tables SHOULD be reset. 

The progress of downloading is shown by a graphical display representing the 

blocks received. 

25 De-Ham a Byte 

This command will translate an 8 bit hammed byte into a 4 bit decoded value. 

Parameters: 

0 25 

1 Byte to be decoded 

2 Decoded byte (&FF: unrecoverable error) 

Note: If bit 6 is set, but bit 7 is not, then an error occured in the transmission, 

but was recoverable, thanks to the hamming protection. The value returned 

should normally be ANDed with &OF before being used. 

40

6 Technical Information 

6.1 The Teletext Data Format 

Each row of Teletext data (normally equivalent to a single row of the screen 

display) takes up 42 bytes. The first byte contains the magazine number of the 

page, and the second byte is a 'row address'. The row address is a number 

between 0 and 29. The first row is always row address 0. The following rows 

can be in ANY order. The maximum number of rows captured is controlled by 

OSWORD &7A:7. For *TRANSFER, 24 rows are captured, and for *DATA, 

48 rows. Unused rows have both the magazine and row address set to zero. 

Row 0 is the Header row and contains the full information on the Teletext 

page. The first byte after the two initial bytes is the page number. This is a 

hexadecimal number, so page 119 would have a page number &19. The next 

two bytes are the sub-page number, high byte first. If this is &0000 there is 

only one sub-page, otherwise it is the number of the rolling page received. The 

next two bytes contain the control bits for the page (see later). 

The next three bytes are all zero and have no meaning. Finally, there are 32 

bytes which are suitable for display and contain the displayed part of the 

Header, complete with the clock display. Each byte should be OR'ed with &80 

before being displayed. 

The following diagram shows the general format of the data, and the specific 

formats for rows 0 and 27 :


The control bits contain information such as whether the Page Header should 

be displayed, whether the page a newsflash, etc. The meaning of each bit is 

given below: 

Rows 1 to 24 are suitable for display, except that each of the next 40 bytes 

should be OR'ed with &80 before being displayed. Not all the Rows 1 to 24 

need necessarily be present and those that are not should be assumed to contain 

40 spaces. 

Row 25 is not intended for display, but may contain 40 bytes of encoded telesoftware. 

Row 27 contains the links to other pages and the Cyclic Redundancy Check ( 

CRC). There can be up to four row 27s and they are distinguished by the first 

of the 40 data bytes. Once this byte has been de-hammed (see OSWORD &7A: 

25) it contains a value of 0 to 3. Only row 27/0 contains the CRC. Bytes 2 to 

37 of the data contain six links, each six bytes long. These six bytes must be 

de-hammed before use. The format of a link group is given below : 

The three bits, C3 (bit 3 of the fifth byte), C4, and C5 (bits 2 and 3, 

respectively, of the sixth byte) form a 3 bit number (C3 is the least significant 

bit of this number). This three bit number is EOR'ed with the magazine number 

of the current page to get the magazine number of the page pointed to by the 

link. Sub-code &3F7F indicates that the sub-code does not matter. Page number 

&FF means that the link is not being used. 

42

Technical Information 

The 38th byte of the data contains the Link Control. This byte must be dehammed 

to give a four bits. The meaning of these bits is given below: 

The 39th and 40th bytes contain the 16 bit CRC. The algorithm used to 

calculate CRC's is too complex to discuss here. Use OSWORD &7A:23 to 

check the CRC of any Teletext data. 

Rows 26, 28 and 29 are not transmitted in Level 1 Teletext. 

6.2 The Catalogue File Format 

The catalogue file contains a list of all the programs and files currently 

available on the telesoftware service of the selected channel. The format is as 

follows : 

The file begins with two strings, each intended for direct display and 

containing teletext colour codes. Each byte must be OR'ed with &80 before 

being displayed. The first byte of any string in the catalogue contains its length 

(not including the length byte itself). There then follow n entries, one for each 

file. Each entry consists of eight fields. 

Field one refers to the type of computer that the file is intended for and is a 

string. The computer types defined so far are : 

ANY : Any computer 

AMIGA : Commodore Amiga computers 

AMSTRAD : Amstrad computers 

ATARIST : Atari ST computers 

BBC : BBC Microcomputer System (B, B+, Master) 

CBM64 : Commodore 64 computers 

CBM128 : Commodore 128 computers 

CPM : Any CPM computer 

IBM : IBM Computers 

MSDOS : Any MSDOS computer 

SPECTRUM : Sinclair Spectrum computers 

*** : End of catalogue - no more data 

43


Field two is the filename, as a string, plus a single colour-code at the beginning 

of the filename. This colour-code is NOT part of the filename and is for 

display purposes only. 

Field three is a string, defining the type of file. This is completely free-format, 

but some examples of entries that might be included are given below : 

TEXT : Text only files (ASCII) 

BASIC : A BASIC program (tokenised if necessary) 

EXEC : An EXEC file, possibly a BASIC program in text form 

M/C : Machine Code 

SCREEN : Screen picture 

LOADER : Multiple file downloader (always M/C for BBC) 

FORTRAN : Fortran source code 

PASCAL : Pascal source code 

Field four is a string, giving the size of the file. This is also completely freeformat, 

but some examples of possible entries are given below : 

12 Pages 

&3453 Bytes 

8K 

Field five is the LOAD address of the file and is four bytes long (32 bits), with 

the most significant byte first (unlike 6502 format). 

Field six is the EXEC address of the file and is four bytes long, with the most 

significant byte first. 

Field seven is the magazine in which the file can be found. This is a single byte 

with values from 0 to 7. 

Field eight is the page number on which the file can be found. This is a single 

byte with values from 0 to 255. 

44

6.3 The Teletext. Character Set 


Here is the Teletext Character set for the BBC Microcomputer. Note that it 

starts at &80 (128), NOT at &00. The characters in columns &CO, and &DO 

are always shown, regardless of whether they are preceded by a graphic colour 

or not. 

* These control characters are presumed before each screen row begins. 

t These control characters have no action on the BBC Microcomputer but may be contained in 

some Teletext pages. 

45


6.4 The Teletext Control Codes 

The previous table shows the available characters, their codes and also the 

control codes. The control codes can be sent in place of any character code 

anywhere in a row. The control codes are normally displayed as spaces (but 

see the section below on the hold graphics control). The fact that they can be 

used within a row enables you to change some aspects of the display part way 

through a row (e.g. the display colour). 

Display Modes 

There are three modes of display in the Teletext system - one alphanumeric 

mode and two graphics modes. The two graphic modes are called contiguous 

and separated. The difference is best shown by illustration : 

Colour 

Seven different display colours are provided (red, green, yellow, blue, 

magenta, cyan, and white). Fourteen control codes are available to select 

alphanumerics or graphics and the required colour simultaneously. This 

provides a change of colour and mode in one step. 

The background colour can be any of the seven colours listed above, or black. 

Coloured background is selected by using the 'new background' control code. 

After this code appears, the new background colour will be the display colour 

in use when the 'new background' control was used. 

Flashing and Concealed Characters 

Two modes are provided in which the display characters appear as spaces 

some of the time. In flashing mode, a character appears alternately as a space 

and as the character at a rate determined by a clock in the computer. In conceal 

mode, the character appears as a space until revealed. The character is revealed 

by pressing 'Reveal' (f6 on the BBC Microcomputer). 

46

Double Height 


Characters may be displayed in double height, in which case they take two 

rows. Therefore the information sent in row n also applies to row n+1 in this 

mode. The decoder ignores row n+1 if it is sent. It is possible to mix single and 

double height characters, but single height characters can only appear on the 

top line of the two. 

Hold Graphics Control 

The hold graphics control code allows a limited number of abrupt display 

colour changes. A control code is normally displayed as a space which 

therefore causes a break in the display. In hold graphics mode, the character 

rectangle occupied by the control code is filled with a held graphics character. 

This can be used with any control code issued in the graphics mode. The held 

graphics character will be the most recent character with bit 6 equal to 1 in its 

code, provided that there has been no intervening change in either the 

alphanumeric/graphics modes or the normal/double height modes. In the 

absence of a suitable character, a space is displayed. 

47


48 

Figure 8 A Page from CEEFAX

A What is Teletext? 

Teletext is a service provided by the BBC and the IBA which makes available 

a wide variety of information through the medium of television. This 

information could be share prices on the stock market or the latest football 

results; the possibilities are almost endless. 

Teletext information is transmitted from BBC and IBA television transmitters 

and can be received on a commercial television receiver suitably equipped with 

a Teletext decoder. The transmitted signal, however, unlike a normal television 

signal, is in digital form which makes it additionally suitable for use with 

computers. 

The total amount of Teletext information is too large to be displayed on a 

television screen at any one instant and for this reason it is transmitted in ' 

pages' rather like the pages of a book. Only one page can be displayed on the 

screen at a time. 

A page of information may contain text, symbols, or a mixture of both; it 

depends on the type of information and how the broadcasters decide to present 

it. 

Because of the amount and variety of information available, transmitted 

Teletext pages are organised and numbered in such a manner as to enable you 

to locate and display specific items of information both quickly and easily. 

The service broadcast by the different channels usually consists of one or more 

'magazines'. These magazines can incorporate up to 255 pages. Page references 

consist of three digits. The first digit always refers to the magazine number and 

as there is a maximum of eight magazines, can be any number from 1 to 8 (for 

OSWORD calls, 8 is represented as 0). 

The magazine number is followed by a two digit hexadecimal number. Page 

&00 normally contains an index to the magazine. Only those pages whose 

number is entirely numeric (i.e. no letters) are used for information that is 

meant to be displayed. The other page numbers are used for computer-readable 

information. 

Each page may contain more than one screen of information. Each of these 

screens is given a sub-page number, which is a four digit hexadecimal number. 

The sub-pages are sent in cycles, so when the last sub-page has been sent, the 

broadcast returns to the beginning of the cycle and re-transmits the first subpage. 

The cycle continues until a new page is selected. 

49


B Hints on Teletext Reception 

Generally, a good receiving system is as important for correctly-decoded 

Teletext as it is for receiving ordinary television broadcasts but, because of the 

digital nature of the Teletext signal, good reception is even more critical in 

certain situations. To display pages of text,Teletext relies on instructions 

received with the television signal. Depending on the quality of reception these 

can produce anything from a perfect or near perfect display to just a hopeless 

jumble of characters. Unfortunately, such jumbled characters can often arise 

even though the ordinary television picture appears satisfactory. The main 

cause of the problem is delayed signals. These can come from two sources: 

reflected signals picked up by the aerial from nearby hills or tall structures; 

reflections within the aerial and distribution system itself. 

Reflections External to the Aerial 

Reflections received by the aerial are normally visible on television pictures as 

ghosting (faint extra images). A suitable receiving aerial will usually reduce 

the ghosting to a level which is not disturbing on pictures and also does not 

affect Teletext signals. As the viewer is not normally able to try a selection of 

aerials it is best to use the services of an aerial contractor and to specifying that 

good Teletext reception is required, of course. 

Reflections in the Aerial System 

Reflections in the aerial system can be particularly troublesome since they can 

rarely be seen on normal television pictures except, perhaps, as an apparent 

sharpening of the picture or slight double-edging on vertical detail (not to be 

confused with 'ringing', a regular pattern of diminishing after-images caused by 

deficiencies of the receiver). 

The problem rarely arises where an aerial feeds a single receiver but is 

commonly found with incorrectly installed multiple-outlet systems where a 

single aerial feed is split between several receivers or aerial sockets. Multiple 

outlet systems are commonplace in blocks of flats but simpler, smaller scale 

versions are increasingly used in households. The general rule is that in order 

to split the signal it is not permissible to simply join an extra cable into an 

existing one, since this creates an impedance mis-match and sets up the 

reflections in the cables. 

50

1. Household Installations 

Hints on Receiving Teletext 

In a household installation the simplest device to split the signal is a 'passive 

splitter' which, because of an inherent power loss, should be used only if the 

signal is strong enough in the first place. In order to prevent reflections 

appearing in the system, a television must be connected to each outlet at all 

times. If you have only one television and move it from room to room then a 

75Ohm termination plug should be fitted to the spare outlets when not in use. 

Suitable attenuators and termination plugs are available from aerial suppliers 

and television retailers. 

If the received signal is too low to allow passive splitting, a 'distribution 

amplifier' should be fitted. These have between two and eight outlets 

depending on the make and model. The two outlet versions are frequently 

called 'second set amplifiers'. Although it is good engineering practice to 

terminate unused amplifier outlets, Teletext reception should generally not 

suffer if they are left unterminated, unless there is a length of unterminated 

cable connected to the outlet. Amplifiers of this type are useful since they 

usually provide a slight increase in the signal level which will compensate for 

losses in long cable runs. 

2. Communal Systems 

In large distribution systems as in blocks of flats or hotels where there are 

many amplifiers and long cable runs, the problem of 'pre-imaging' may arise. 

In this case, the television set not only receives the signal through the cable but 

also receives a direct signal because the receiver and cable act as an aerial. The 

main symptom is noticeable ghosting on the picture caused by the delay 

between the cable-fed signal and the direct signal reaching the television 

receiver. To minimise the problem care should be taken with the lead 

connecting the wall outlet to the television: ensure that 'double-screened' cable 

is used, that it is as short as possible, and that the connections are electrically 

sound. If this does not cure the fault, then the system may need adjusting to 

provide a higher output signal or a translating device should be used to 

distribute the television channels on different frequencies. Once again, these 

items are available from aerial suppliers and television retailers. 

This information was provided by BBC Engineering Information Department. 

For more information on Teletext and Television reception contact : 

Engineering Information Department, 

BBC Broadcasting House, 

LONDON, 

W1A IAA 

Telephone 01-927 5040 

51


C United Kingdom Network Identities 

A Table of the Network Identities for the United Kingdom 

The table above gives a 16 bit number for each TV station transmitting in the 

UK. To find the identity of the station being received you must compare the 

identity contained in the TSDP with the table entries. The following extract 

from a BASIC program includes a function to return the identity: 

10 DIM Buffer 20 

: 

100 IF FNidentity = &5FF6 THEN PRINT "BBC1" 

: 

1000 DEF FNidentity 

1005 Buffer?0=15 

1010 X%= Buffer : Y% = X% DIV 256 : A% = &7A : CALL &FFF1 

1020 = (Buffer?5)*256 + Buffer?6 

52

D CP/M, PANOS, & DOS+ Telesoftware 

When using the Telesoftware Terminal, the files are saved to the current I/O 

processor filing system (i.e. DFS, ADFS, NFS, or ANFS) and not to the coprocessor's 

filing system. 

This does not matter if the co-processor is a 6502 or Turbo, as these use the 

same filing systems as the I/O processor. 

Similarly, if you are using PANOS t , you can access the files directly, because 

PANOS also uses the I/O processor filing system, although the filenames may 

appear slightly different, e.g. the file "_F77.FORPROG" appears in PANOS as " 

FORPROG F77". 

With CP/M* and DOS+* the situation is different. These co-processor filing 

systems do not use the same format as the I/O processor filing systems. To get 

round this a convert program is supplied with each one to allow files to be 

copied from the I/O processor filing system into CP/M or DOS+. 

Caution: Care should be taken when using Teletext from the Z80 co-processor 

as CP/M uses the I/O processor's memory to store the disc catalogue, and this 

will be corrupted if Teletext is used. 

t PANOS is a trademark of Acorn Computer PLC. 

* CP/M and DOS+ are trademarks of Digital Research. 

53


E Copyright Position on Telesoftware 

The copyright situation on Telesoftware programs broadcast by the BBC is as 

follows: 

(i) Domestic users of a program broadcast on CEEFAX may: 

- Make two copies only for private purposes. 

- Adapt or modify it for private purposes but not for sale. 

(ii) Educational and training institutions and agencies may: 

- Record and use the program for their own educational training purposes 

but nor for sale. 

- Adapt, modify, and distribute a program for their own educational and 

training purposes but not for sale. 

(iii) No part of a program may otherwise be reproduced, stored in a retrieval 

system or transmitted in any form or by any means, without the prior 

permission of the BBC, except in accordance with the 1956 copyright act. 

Different concessions apply, and are set out in detail in 'Recording BBC 

Educational Programmes', with respect to those BBC programmes listed in ' 

The Annual Programme for Schools and Colleges' and/or 'The Annual 

Programme for Continuing Education'. 

All other BBC programmes may not be recorded without the prior consent of 

the BBC and the holders of the copyright and performing rights in the 

component parts of the programmes concerned. 

54

F Fitting the Teletext ROM 

Before installing any ROMs you should switch off your computer and unplug 

it from the mains. 

Model B 

1 Remove the top cover. To do this: 

a Remove the two fixing screws from the underside, they are large crosshead 

screws marked 'FIX'. 

b Remove the two fixing screws at the back of the machine. 

c Lift the top cover upwards. 

2 Loosen the keyboard. To do this: 

a Undo and remove the two fixing nuts and bolts at the sides of the 

keyboard. (Don't forget to remove the washers.) 

b Move the keyboard carefully to reveal the ROM sockets at the front right 

of the circuit board. (The keyboard is connected to the circuit board by 

a red and black twisted wire and a flat grey cable. If you wish you can 

unplug these from the circuit board so as to remove the keyboard 

completely. Before removing them notice carefully how they plug into 

the circuit board so that you can replace them correctly.) 

3 Plug the ROM into one of the sockets marked by the arrows in the diagram 

below. The ROM should be inserted with the dimple at the top facing the 

rear of the machine. The BASIC and filing system chips may be in different 

sockets on your computer. This does not matter but normally the ROM you 

are inserting should go to the left of BASIC. If there is no empty socket to 

the left of BASIC, you may have to move the ROMs. If you wish Teletext 

to start when you switch on the computer, you should insert it to the right 

of BASIC, and any other language ROMs you have.


CAUTION: Handle the ROM with care and do not touch the pins. 

Make sure that the ROM is correctly aligned with the socket. 

Each pin should fit into a hole, and there should be none hanging over the edge 

of the socket. Make sure that all the pins are correctly seated before pushing the 

ROM home. 

DO NOT USE EXCESSIVE FORCE. If a pin is not correctly seated it is easy to 

bend it up under the ROM if you push too hard. 

4 Replace the keyboard. 

a If you have unplugged the wire and cable, carefully plug them back into 

the the circuit board. 

b Replace the nuts and bolts securing the keyboard. Do not forget the 

washers, which go between the nuts and the keyboard base. 

5 Replace the top cover. 

a Place the cover in position. 

b Replace the two fixing screws in the base and the two at the back and 

tighten. 

6 Replace the mains power plug and switch on the computer. 

Model B+ 


a Remove the two fixing screws from the underside, they are large crosshead 


b Remove the two fixing screws at the back of the machine. 

c Lift the top cover upwards. 

2 The ROM sockets on the Model B+ are located in the top left hand area of the 

circuit board (near the large copper-coloured power supply, towards the 

back of the computer). There are six sockets arranged in two rows of three. 

Nearer the keyboard are two very similar sockets for the speech system. 

Under no circumstances should a ROM be placed in these speech 

sockets. Some of the six ROM sockets will already contain ROM's and the 

top-right ROM should not be moved, as this contains the operating system. 

The diagram below shows the ROM sockets on the Model B+, along with 

the two speech sockets. 

56

The ROM Sockets on the Model B+ 

CAUTION: Handle the ROM with care and do not touch the pins. 

Make sure that the ROM is correctly aligned with the socket. 

Each pin should fit into a hole, and there should be none hanging over the edge 

of the socket. Make sure that all the pins are correctly seated before pushing 

the ROM home. 

DO NOT USE EXCESSIVE FORCE. If a pin is not correctly seated it is easy 

to bend it up under the ROM if you push too hard. 



b Replace the two fixing screws in the base and the two at the back and 

tighten. 


57


Master Series 

The simplest way to use the ROM with a Master, is to use the EPROM 

cartridge (ADF13), available from your Acorn Dealer. Otherwise you will 

have to insert the ROM into one of the three internal ROM sockets. 


a Remove the four fixing screws from the underside, they are large crosshead 


b Lift the top cover upwards. 

2 The ROM sockets on the Master are located on the far right hand side of the 

circuit board, just above the cartridge slots. There are four, arranged one 

above the other. The top socket contains the 128K Operating System ROM. 

Of the remaining three, the middle one is the easiest to use. Insert the ROM 

as before, making sure the dimple at the top of the ROM goes on the left. 

If the middle socket is occupied you will have to change two links on the 

circuit board. If you want to use the top socket, i.e. the one below the 128K 

ROM, you should change link 19 so that the two right-most pins are 

connected. This will disable banks 6 and 7 of the sideways RAM, and 

replace them by the ROM. To use the bottom-most ROM socket you should 

change link 18 so that the two right-most pins are connected. This will 

disable banks 4 and 5 of the sideways ROM, and incidently, stop the ' 

Convert' program from working. 

The ROM Sockets on the Master Series 



b Replace the four fixing screws in the base and tighten. 


58

G Summary of OS Commands 

*BBC Select channels 1,2,3 or 4. 

*CH Select channels 1,2,3 or 4. 

*DATA Transfer 2K of Teletext data into memory. 

*DATE Display the local date (from TSDP). 

*DISPLAY Display Teletext data held in memory. 

*HOFF Turn off the changing top line. 

*HON [1] Turn on the changing top line. 

*ITV Select channels 3 or 4. 

*MAGAZINE Select magazine whose top lines will be 

displayed. 

*NOTTX 'Unplug' the Teletext ROM. 

*PAGE Select the page to be captured. 

*S4C Dewiswch Sianel Pedwar Cymru. (Select 

Channel 4 Wales.) 

*TELESOFT TFS emulation mode 

*TELETEXT Enter the Teletext terminal. 

*TIME Display the local time (from TSDP). 

*TRANSFER Transfer 1K of Teletext data into memory. 

*TTX ON/OFF Turn the Teletext system on or off. 

*TUNE Tune the current TV channel. 

59

H Summary of Terminal Keys

Advanced Teletext System User Guide

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