The BBC Microcomputer Teletext System User Guide

The BBC Microcomputer 

Teletext System 

User Guide 

Part no 404000 

Issue no 1 

Date June 1983

WARNING: THE TELETEXT ADAPTER MUST BE EARTHED 

Important: The wires in the mains lead for the Teletext Adapter 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. 

The wire which is coloured brown must be connected to the terminal which is marked with the 

letter L, or coloured red. 

If the socket outlet available 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 manufacturers' 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. 

© Copyright Arnie Computers Limited 198:1 

Neither the whole or any part of the information contained in, or the product described in, this manual may be adapted or 

reproduced in any material form except with the prior written approval of Acorn Computers Limited (Acorn Computers). 

The product described in this manual and products for use with it. are subject to continuous development and improvement. All 

information of a technical nature and particulars of the product and its use (including the information and particulars in this 

manual) are given by Acorn Computers in good faith. However, it is acknowledged that there may be errors or omissions in this 

manual. A list of details of any amendments or revisions to this manual can be obtained upon request from Acorn Computers 

Technical Enquiries. Acorn Computers welcome comments and suggestions relating to the product and this manual. 

All correspondence should be addressed to: 

Technical Enquiries 

Acorn Computers Limited 

Fulbourn Road 

Cherry Hinton 

Cain Midge CB1 4JN 

All maintenance and service on the product must be carried out by Acorn Computes' authorised dealers. Acorn Computers can 

accept no liability whatsoever for any loss or damage caused by service or maintenance by unauthorised personnel. This manual in 

intended only to assist the reader in the use of the product, and therefore Acorn Computers shall not be liable for any loss or 

damage whatsoever arising from the use of any information or particulars in, or any error or omission in, this manual, or any 

incorrect use of the product. 

First published 198:1 

Published by Acorn Computers Limited, Fulbourn Road, Cherry Hinton. Cambridge CB1 4JN 

Typeset by Bateman Typesetters. Cambridge 

Printed by Saunders & Williams, Croydon

Contents 

1 About this User Guide 1 

2 What is Teletext? 

3 What does the BBC Microcomputer 

Teletext System do? 3 

3.1 Introduction 3 

3.2 Terminal mode 3 

3.3 Telesoft mode 4 

3.4 Assembler level 4 

4 Getting started 5 

4.1 Connecting up the units 5 

4.2 General information on the format of commands 8 

4.3 Tuning in the Teletext Adapter 8 

4.4 A first attempt at Telesoftware 11 

Downloading a disordered program 12 

Downloading an ordered program 13 

5 Using the system in Terminal mode 14 


5.2 Terminal mode commands 14 

Selecting a channel 14 

Fine tune 15 

Select a page 15 

Keep a page 15 

Release a kept page 16 

Select the last explicit page 16 

Select index page 16 

Reveal and conceal 16 

Save a page to file 17 

Load a page from file 17 

Hold page 18 

Enter * command 18 

Exit to previous language 18

Exit to Telesoft mode 19 

Select wild card 19 

5.3 Accessing linked pages 20 

6 Using the system in Telesoft mode 23 


6.2 Telesoft mode commands 25 

*BBC1, *BBC2 25 

*CH1, *CH2, *CH3, *CH4 26 

*DATE 27 

*DISPLAY 27 

*EXEC 28 

*HELP 29 

*ITV1, *ITV2 29 

*OPT0 30 

*OPT1 30 

*OPT2 31 

*OPT3 32 

*PAGE 33 

*TIME 34 

*TRANSFER 34 

*TUNE 35 

7 Using the Teletext system at assembly level 36 

7.1 Teletext assembly level interface 36 

7.2 Teletext OSWORD calls 38 

8 Changing the filing system 41 

9 Technical information 42 

9.1 The structure and numbering of Teletext pages 42 

9.2 Teletext signals 44 

Rows 1 to 23 45 

Row 0 45 

Rows 24 to 31 46 

Page check word (row 27) 46 

9.3 Character codes 48 

Display modes 48 

Colour 48 

Flashing and concealed characters 49

Double height 49 

Hold graphics control 49 

9.4 Reference 49 

9.5 The television service data packet 49 

Byte structure of the television service data packet 50 

Bytes 1 to 6 – decoder information 50 

Bytes 7 to 12 51 

Bytes 13 and 14 – channel identification 51 

Byte 15 – time offset 51 

Bytes 16 to 18 – modified Julian date 51 

Bytes 19 to 21 – coordinated universal time 52 

Bytes 26 to 45 – status display message 52 

9.6 The Telesoftware format 52 

Names 52 

Command subroutines 57 

Start block and medium description commands 59 

Start block 59 

Teletext 60 

End block 60 

File and segment information commands 60 

End of file 60 

Title of file 61 

Comment 61 

Ignore 61 

Load address (absolute) 62 

Load address (relative) 62 

Execution address (absolute) 62 

Execution address (relative) 62 

Inhibit run 63 

Define data type 63 

Format redefinition commands 63 

Change escaped-name's meaning (decoded string) 63 

Change escaped-name's meaning (command) 63 

Change lone-name's meaning (decoded string) 64 

Change lone-name's meaning (command) 64 

No reversion to default format before next file 64 

Revert to default format 64 

The escape operator 64 

Eight-bit byte adjustment 65 

Eight-bit byte adjustment (lower) 65 

Eight-bit byte adjustment (raise) 65

Figures 

Error in transmission 65 

4.1 Connecting the Teletext Adapter 7 

4.2 Rear view of the Teletext Adapter 10 

4.3 Tuning picture format 10 

5.1 Linked pages 21 

9.1 Byte structure of Teletext rows 1 to 23 45 

9.2 Contiguous and separated graphics modes 48 

Tables 

9.1 Teletext character codes 47 

9.2 Name tables — default entries 54 

9.3 The command subroutines 59 

Appendices 

Appendix 1 

Installing the TELEROM into the BBC Microcomputer 66 

Appendix 2 

Teletext reception 69 

Appendix 3 

Summary of Terminal mode commands 71 

Appendix 4 

A statement about Telesoftware by the BBC 72 

IMPORTANT 

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.

1 About this User 

Guide 

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

Teletext System. Whilst it is essentially an operating manual, the User Guide contains 

certain technical information which will help you to understand generally what 

Teletext is all about and gain some appreciation of the future potential offered by this 

system. 

Chapters 2 and 3 are introductory. Chapter 2 explains briefly what Teletext is all about 

and chapter 3 deals briefly with the various ways in which you can use your BBC 

Microcomputer with the Teletext service. 

Chapter 4, as its title suggests, gets you started. It explains how to connect up the 

system, tune into Teletext and quickly run a Telesoftware program. 

Chapters 5, 6 and 7 contain the detailed instructions for using the system in the three 

modes of operation: Terminal, Telesoft and assembly level. 

Chapter 8 explains how to select, as the current system, the various filing systems ( 

including Telesoft) which may be available on your computer. 

Chapter 9 contains information which will probably be of interest to the more 

technically minded user, but which is not essential for using the system.

2 What is Teletext? 

Teletext is a service offered by the BBC and 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 

Adapter unit. The transmitted signal however, unlike a normal television signal, is in 

digital form which makes it additionally suitable for use with the BBC Microcomputer. 

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 at a time can be displayed on a television screen. 

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 so as to enable you quickly and easily to 

locate and display specific items of information.

3 What does the 

BBC Microcomputer 

Teletext System do? 

3.1 Introduction 

The BBC Microcomputer Teletext System gives you most of the facilities of an 

ordinary Teletext receiver and, in addition, the service known as Telesoftware. 

Telesoftware is a service similar to Teletext and is transmitted in the same 

manner, that is, in pages. However, these pages contain computer programs. A 

program will consist of one or more pages, depending on the program length, 

and each program has its own file name by which it is identified. These 

programs, once received, are decoded by the Teletext Adapter and thereafter 

are available to the computer for display, storage on disc/tape or immediate 

execution. 

It is emphasised that your television set does not require a Teletext decoder. 

This function amongst others is performed by the Teletext Adapter. 

There are three main ways in which you can use the system: in Terminal mode, 

in Telesoft mode or at assembler level. The following is a brief description of 

the facilities offered by each. 

3.2 Terminal mode 

`Terminal mode' is a program which Acorn has supplied to give you easy 

access to Teletext pages. It also lets you use some more sophisticated features 

which only an 'intelligent' receiver can offer. These features include asking for 

pages in advance, having pages stored by the system before you ask for them ( 

see the section on linked pages), and being able to save pages onto any 

available filing system for later examination. 

You can also use Terminal mode as an easy way of finding and loading ` 

Telesoftware' computer programs. 

You cannot write programs whilst in Terminal mode. In addition, if you are 

using a television receiver, you cannot display Teletext pages and television 

programmes simultaneously.

4 What does the BBC Microcomputer Teletext System do? 

3.3 Telesoft mode 

An important feature of Teletext transmissions is the ability to send programs, or ' 

software', with the Teletext service. In keeping with the philosophy of BBC 

Microcomputer products, Acorn has produced a filing system interface as the means of 

accessing Telesoftware files. 

IT IS IMPORTANT that you appreciate that Telesoft is a filing system, and not an 

applications program such as Terminal mode. With Telesoft selected you will not be 

able to save programs as the system thinks you are trying to save data to the television 

channel! 

You may think of Telesoft as a 'read-only' tape; it is quite a good analogy. 

In addition to Telesoftware, you can also display and store Teletext pages. However the 

full range of Terminal mode commands is not available and it is therefore probably 

more convenient to return to Terminal mode should you wish to handle Teletext pages. 

You can write and run your own programs whilst in Telesoft mode, but to store these 

programs you should select the appropriate filing system, ie disc or tape. See section 8. 

3.4 Assembler level 

Assembly code level allows you to control the Teletext system using programs written 

in Assembly Language. You can enter these into the computer from the keyboard or 

from file. There are two main areas of control: one is concerned with the filing system, 

and the other with the Teletext Adapter. 

The filing system function allows the storage and retrieval of Telesoftware files. You 

can control this by the standard interfaces to the Machine Operating System, which are 

independent of the filing system. 

The Teletext Adapter functions, which control the conditions under which a file is 

stored and executed, can be accessed via the general purpose Machine Operating 

System calls.

4 Getting started 

Before proceeding further, check that you have the following items: 

– A Model B BBC Microcomputer fitted with a BASIC ROM. 

– A Teletext Adapter with the following items attached: 

A power cable with a 13A 3-pin plug fitted to it. 

A 'ribbon' cable terminating in a 34-way plug. 

– A coax cable fitted with a phono plug and a UHF plug as supplied with the 

BBC Microcomputer (if you're using a normal television receiver), or a 

coax cable fitted with the appropriate connectors (if you're using a video 

monitor). 

– A Teletext ROM (TELEROM). 

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

be used. 

If any of the above are missing, contact your local supplier quoting the order 

number which was given to you when you first placed your order. This number 

also appears on the dispatch label on the outside of the packing case. 

4.1 Connecting up the units 

The first thing to do is to make sure that the ROMs are correctly positioned on 

the microcomputer circuit board and then to fit the TELEROM. The 

instructions for doing this are in Appendix 1, however if you do not feel 

sufficiently confident, take your microcomputer and TELEROM to an 

authorised dealer who will do it for you. 

Next, refer to Fig 4.1 which shows the microcomputer and Teletext Adapter 

connected together and connect up the system as follows: 

1. Connect the 34-way socket on the Teletext Adapter 'ribbon' cable to the 

plug labelled 1 MHz BUS on the computer. 

Caution: This socket may fit both ways round–the correct way is with the 

arrow at one end of the socket aligned with the arrow next to the '1 MHz BUS' 

label. IF THE SOCKET WILL NOT GO RIGHT IN EXAMINE THE PLUG 

AND SOCKET FOR DAMAGE AND OBSTRUCTIONS. DO NOT USE 

EXCESSIVE FORCE.


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 

Adapter. 

Note: An aerial which stands on top of your television set does not generally 

provide a strong enough signal. You will in all probability need a loft or 

externally mounted aerial. If you think your aerial may not be good enough 

refer to Appendix 2 which may assist you, or consult your dealer. 

3. Connect up whatever storage units you are using (ie disc or cassette) to the 

computer. 

4. Connect the computer UHF OUTPUT socket to the aerial socket on your 

television set using the phono plug/UHF plug cable, or connect the computer 

VIDEO OUT or RGB OUT socket to the input socket on the video monitor. 

5. Connect the television, storage unit, microcomputer and Teletext Adapter to 

the mains supply, if possible using adjacent sockets for Teletext Adapter and 

computer. 

6. Switch on television/video monitor, Teletext Adapter unit, microcomputer 

and storage device (disc or cassette) if fitted. IT IS IMPORTANT THAT 

THE TELETEXT ADAPTER IS SWITCHED ON BEFORE THE 

MICROCOMPUTER. Your television screen should now display the 

following message: 

BBC Computer 32K 

Acorn TFS 

BASIC 

>_ 

The current filing system is Telesoft (TFS). 

Note 1: If Acorn TFS no power appears, check that you have connected the 

adapter correctly and that it is switched on at the rear. Press BREAK before 

continuing. If this still fails to produce the start-up message, check the 

position of the ROMs on the microcomputer circuit board (see Appendix 1). 

Note 2: The Teletext software incorporates a 'power-down' mode so that if, 

when you switch on the microcomputer, the Teletext Adapter is switched

Getting started 7 

off, the message Acorn TFS no power will be displayed. This means that the 

Teletext software is inactive and therefore the memory space it would normally 

occupy is free to be used for running large programs. 

If you switch on the Teletext Adapter after the microcomputer, the Teletext 

software is not automatically activated; you must press the BREAK key first. 

If you switch off the Teletext Adapter whilst the microcomputer is 'on', the 

Teletext software is not automatically de-activated; you must press the BREAK 

key first. 

Note 3: If the positioning of the ROMs is such that Telesoft is not the default 

filing system, press the T key, hold it down and press BREAK , then release 

BREAK then T This will cause the correct start-up message to be displayed 

without re-positioning the ROMs as detailed in Appendix 1. 

Once the correct start-up message is displayed you can now go ahead and tune 

the Teletext Adapter. 

Fig 4.1 Connecting the Teletext Adapter


4.2 General information on the format of commands 

Note 1: Most of the commands are put into the computer by pressing one of 

the ten red keys labelled f0 to f9, either on its own or together with the SHIFT 

key. In the latter case it is important that you press the keys in the following 

manner otherwise the command will never go into the computer: 

— Press the SHIFT key, keep it held down and press the red function key. 

— Release the f key, then release the SHIFT key. 

If you do attempt to input a faulty command the computer will usually tell 

you, with a message on the screen, what to do and how to get back to a normal 

situation. 

Note 2: Throughout the guide there are many instructions on how to type in 

commands to the computer and what the correct response is. The following 

applies to these instructions: 

— Where you see a word in brackets thus, , this is describing what 

you have to type in, eg means you have to type in the name of 

a file. Do not type in the brackets. 

— Where you see a word 'reversed out' this means you have to press a 

specific key, eg TAB means press the TAB key. 

— Where the text is an actual message displayed on your monitor screen it is 

shown in computer typeface, eg the message ***Waiting is displayed. 

Likewise in a command the characters in computer typeface are to be 

typed in exactly as shown, eg type in *EXEC. 

4.3 Tuning in the Teletext Adapter 

There are four channels built into the Teletext Adapter and assigned numbers 

1 to 4. We recommend that you allocate these channels as follows: 

Channel 1 — BBC1 

Channel 2 — BBC 2 

Channel 3 — ITV1 

Channel 4 — ITV2 

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

1. Type in *TELETEXT then press the RETURN key. 

The message ***Waiting for page is displayed. 

2. Press the f4 key. 

The prompt Channel should now appear on the screen. 

3. Type in 1 (to select channel 1), then press the RETURN key. 

The message ***Waiting for page is again displayed. 


4. Press the SHIFT and f4 keys together. 

Your screen will display a station tuning scale (see Fig 4.3). On top of the 

tuning scale sits a tuning bar which indicates the strength of received 

Teletext. Maximum signal strength is when the tuning bar is as long as the 

scale (100 

5. Turn the number 1 tuning control on the rear of the Adapter (Fig 4.2) 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 in to a BBC or ITV 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 CH1 you are correctly tuned in to channel 1. 

REMEMBER YOU CAN RECEIVE ALL FOUR TELETEXT CHANNELS 

ON EACH TUNING CONTROL SO MAKE SURE YOU GET THE RIGHT 

CHANNEL. 

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

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

— In step 3, type in the appropriate channel number (2, 3 or 4). 

— In step 5, rotate the appropriate control number (2, 3 or 4). 

7. 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 default page and is discussed in section 5.2. 

Now that your system is working we suggest that you have a go at running 

one of the Telesoftware programs being transmitted, the procedure for which 

is given in the next section (4.4). You will need to use only a few Terminal 

mode commands and it should give you confidence to use the full range of 

features which are explained later in the guide.


Fig 4.2 Rear view of the Teletext Adapter 

Fig 4.3 Tuning picture format


4.4 A first attempt at Telesoftware 

Assuming that you're carrying on from the previous section your screen 

should be displaying an index page. If on the other hand you've just switched 

on the equipment then you must enter Teletext by typing in *TELETEXT then 

pressing the RETURN key. The CEEFAX channel 1 index page will be 

displayed. 

Next select a channel (any channel) by first pressing the f4 key. This results in 

the message Channel being displayed. Then type in the channel number (1, 

2, 3 or 4) and finally press RETURN . The message ***Waiting for page 

will be displayed until it is replaced by the index page for the channel you've 

selected. 

Do this a few times to get the idea, then try selecting a page. 

You can select a page by pressing the f0 key, then typing in the page number 

you want (three digits) then pressing RETURN . You may have to wait a 

short while before the page you have selected appears. Again we suggest you 

try this a few times to get the idea. 

When you feel confident, select channel 1 then page 700. This will display a 

list of the currently transmitted Telesoftware programs and the page on which 

each can be found. Decide which program you want, then select the page it is 

stored on. 

The next thing to do is to download the program, that is, load it into the 

computer ready to be run. To download the program, press the SHIFT and f9 

keys together. What happens next may not make a great deal of sense and so 

deserves some explanation. 

As you are probably aware programs can be structured in two very different 

ways and this affects what happens when they are downloaded. 

Programs structured in numbered lines can be loaded in any order since the 

computer will organise the lines into the correct numerical sequence prior to 

running the program. A program structured in such a way is said to be a 

disordered file. 

A program structured as merely a series of statements (with no numbered 

lines) must be loaded into the computer starting at the first statement and 

exactly in the order in which it has been written. This is because there are no 

numbered lines for the computer to organise as there are for disordered files. 

Such a program is said to be an ordered file.


Another point to bear in mind is that whilst programs are listed as being on 

consecutively numbered pages, almost always a program will be longer than 

one page. For example there are currently several programs being transmitted 

on page 702 onwards, however they are all longer than one page. 

Let's assume that the program listed under page 704 is in fact 12 pages long. 

This means that it will take 12 transmissions of page 704 to get the entire 

program into the computer and this can take quite a long time. It follows 

therefore that the earlier in the transmission sequence you try to download the 

program, the longer it takes to get round to page one again and this can 

significantly affect how long you have to wait before an ordered program is 

loaded (see below). 

What happens during downloading depends on whether the program is 

ordered or disordered and is explained in the following: 

Downloading a disordered program 

As soon as the SHIFT and f9 keys have been pressed, the message 

Searching is displayed. This tells you that the system is looking for a page in 

the program. 

Immediately a page (any page) in the program is received, the message 

disappears and the contents of the page 'scroll' up the screen as they are loaded 

into computer memory. 

When the page has been completely loaded, the message Searching is again 

displayed until another page in the program is found. 

This process continues until the program is completely loaded, whereupon the 

message Loaded is displayed and an audible 'bleep' sounds. 

During downloading the normal transmitted Teletext page headers are 

displayed to indicate (during waiting) that your Teletext Adapter is still 

functioning. 

When the decoder is loading Telesoftware, it checks the validity of data on 

each page it receives. If this check shows up an error, you will see the 

message Bad data. Retrying. . . 

This usually means you will have to wait until this page comes round again in 

the transmission cycle, but you may be lucky if the bad page was one you 

have already received or if it was a title page with no software on it. If you 

wait long enough you will always be able to load a Telesoftware program, 

unless your reception is particularly bad.

5 Using the system in 

Terminal mode 


We recommend that you spend a few minutes using the select a page and 

select a channel commands, before going on to the rest of the commands. 

You may find it a good idea to read first section 9.1 which explains in some 

detail how Teletext pages are numbered and how the entire Teletext 

transmission is structured. This may help you to understand the various 

commands you are about to use. 

5.2 Terminal mode commands 

First enter Terminal mode by typing in *TELETEXT and pressing the 

RETURN key. A default channel, BBC1 CEEFAX, is selected and a default 

index page is displayed. In addition to news and information, the following 

standard items are usually displayed on your screen: 

– Channel title and page number (header), eg CEEFAX XXX, at the top left. 

– The page number you have selected at the top far left. 

– The changing page number at the left of centre. 

– The date and time at the far right. 

Selecting a channel 

Press the f4 key. 

The prompt Channel is displayed. 

Type in 1, 2, 3 or 4. 

This number appears after Channel. 

Press RETURN (to select the channel). 

The only thing which happens immediately on the screen is that the channel 

title and changing page header now correspond to the newly-selected channel. 

A default index page for the new channel is displayed as soon as it is received.

Fine tune 

Using the system in Terminal mode 15 

This is the same function you used when tuning the Teletext Adapter (see 4.3). 

You can use it anytime to display the tuning scale if the quality of the 

displayed Teletext page deteriorates. 

Press the f4 and SHIFT keys together. 

When you have finished tuning, press the SPACE BAR to inhibit the tuning 

routine and display the page. 

Select a page 

To display a transmitted page: 


Type in the page number which can be three digits or seven digits (see section 

9.1 on page numbering). 

Press the RETURN key. 

Note: Make sure you have selected a page which is being transmitted. 

Until the selected page is reached, the previous page and the message 

***Waiting for page is displayed. 

Keep a page 

This function allows you to store the displayed page in computer memory. 

Thereafter, every time this particular page is received, it updates the stored 

page. In this manner, a 'kept' page is continuously updated and can be 

displayed immediately by using the normal 'select a page' command. You can ' 

keep' a page before it has actually arrived and select another page while you 

are waiting. In this way you can ask for more than one page at a time. To keep 

a page: 


The message Page kept is displayed at the bottom of the screen. 

Note: When you attempt this command, the message Buffer full — please 

release a page may appear. This means that all available memory for 

keeping pages is used up and you must first release a page, before trying to 

keep a page. The following explains how to release a kept page.

16 Using the system in Terminal mode 

Release a kept page 

This function causes the displayed page to be lost provided it is a kept page. 

To release the kept page: 

Press the SHIFT and f3 keys. 

The message Page released is displayed. 

Select the last explicit page 

If you are displaying linked pages (see 5.3) you can quickly return to the last 

page which was displayed by the explicit typing in of its number. This is 

usually the first page in the linked structure. 


The last explicitly selected page is displayed. 

Select index page 

You can return to the default index page which was automatically displayed 

when you first entered the current channel. 

Press the f1 and SHIFT keys together. 

Note: If no default index page number is being transmitted on your current 

channel, then page #00 will be selected instead (see 'Select wild card'). 

Reveal and conceal 

Some pages are transmitted with certain text 'hidden', ie concealed as spaces. 

For example, the answers to a quiz. Any page with hidden data will display a 

message something like Press the REVEAL key. To reveal this hidden text: 


The hidden text appears, and the page itself is 'held' so that it cannot be 

updated by subsequent transmitted pages. 

To conceal the text and cancel the 'hold' state: Press 

the SPACE BAR . 

To conceal the text but retain the page 'hold' state: Press 

the SHIFT and f2 keys together.

Save a page to file 


This function allows you to store the displayed page under any file name onto 

the currently selected filing system, such as cassette or disc. 


The message Save file is displayed. 

Type in and press RETURN . 

The page is stored in a file. When storage is complete, the page is displayed 

with the file name under which you have just stored it, together with the 

message Press space to continue. 

When you press the SPACE BAR , the same page continues to be displayed, 

but the file name is removed, and the changing headers are again displayed. 

If you attempt this with Telesoft as your currently selected filing system, the 

message Illegal operation will be displayed. (This is due to the fact that 

Telesoft is a 'read only' filing system, therefore you cannot save anything to 

this filing system.) 

To recover from this situation, press the ESCAPE key. Now select another 

filing system such as disc or tape by using the Enter * command facility 

described below. You can now save the data to this filing system as described 

immediately above ('Save a page to file'). 

Load a page from file 

This function allows you to display any page which is currently stored under 

a file name. 


The message Load file is displayed. 

Type the file name of the page for display, then press RETURN . 

The page is then displayed, together with its file name. 

Note that the page headers stop changing and the message Press space to 

continue is displayed. 

When you press the SPACE BAR , the file name disappears and the page 

headers again start to change.


Hold page 

This function holds any displayed page and prevents it from changing. This is 

a useful function to have if you are saving or loading rolling pages or wild 

card pages (which are likely to change very quickly). To hold a page: 


The displayed page is held in its current state. 

To cancel the 'hold' state: 

Press the SPACE BAR . 

The page is now free to be updated. 

Enter * command 

This allows you to remain in Terminal mode and at the same time use those * 

commands which relate to the operating system. These commands are shown 

on page 416 of the BBC Microcomputer System User Guide. In addition, you 

have available for use all commands associated with the particular ROMs 

fitted to your microcomputer, eg the disc filing system.To enter a command: 

Press key f5 

The prompt * is displayed at the bottom of your screen. 

Type in the appropriate command and press RETURN . 

The message Press space to continue is displayed. 

if you wish to enter other * commands, ignore the Press space to 

continue message and repeat as above. 

To return to the last displayed page press the SPACE BAR . 

Exit to previous language 


The start-up message for the language previously selected (from which 

Teletext was entered) is displayed and the system is now controlled by this 

language ROM.


Note: If you have pressed the BREAK key whilst in Terminal mode, your 

previous language will be Teletext Terminal mode and the f9 key will cause 

this to be re-entered. 

Exit to Telesoft mode 

If you select a page containing a Telesoftware program, this function puts the 

system automatically into Telesoft mode and causes the program to be loaded 

into computer memory page by page. You can then go ahead and run the 

program. To exit to the Telesoft filing system and execute a program: 

Press the SHIFT and f9 keys together. 

The program will start to load into computer memory as soon as the first page 

is received. If you start this function say halfway through the program 

transmission then it may be a few minutes before the program starts to load ( 

see section on ordered/disordered loading). 

Select wild card 

This enables you to select specified sequences of numbered pages for display ( 

including their sub-pages, if any). We know that each page has a three-digit 

number. The function allows you to specify any combination of one or two of 

these three digits as part of a page number to be displayed. The unspecified 

digit(s) can be any number, ie completely `wild'. For example, if you specified 

34#, all page numbers whose first digit is 3 and whose second digit is 4 will be 

displayed. Theoretically this would be 340, 341, 342 etc to 349. But bear in 

mind that not all pages are transmitted. 

To select a wild card press the f0 key (as you would do when normally 

selecting a page) then type in three characters (which may be any combination 

of digits and #s), then press RETURN . 

The specified wild card pages will be displayed as and when they are received, 

with a small built-in delay between consecutive pages to give you time to hold 

a page.


5.3 Accessing linked pages 

Now that you know how to display any transmitted page of Teletext, we will 

explain how you can display pages which, because of their information 

content, are related to each other. These are known as linked pages. 

A Teletext page displays 24 rows of text or graphic information. However 

more rows may be transmitted which are not displayed on the screen but 

which contain information for the Teletext decoder. In particular, row 27 

contains information in the form of numbers which point to related (linked) 

pages. These numbers are called links. 

Take a look at Fig 5.1. The headlines page has four links, each pointing to a 

lead page. In this case row 27 of the headlines page would contain four link 

numbers, link 1 pointing to lead page 1 and so on. You will see also that each 

lead page has links, each of which points to page 1 of a related story. For 

example, lead 3 has three links pointing to page 1 of stories 3A, 3B and 3C, so 

row 27 of lead 3 would contain link numbers 1, 2 and 3. This system of links 

extends to the last page in each story then back round to the first page as is 

shown by stories 3A and 1. 

The microcomputer looks at row 27 of the page, detects the link numbers and 

loads as many of the linked pages as it can fit into memory. Although you 

cannot see these pages, they are being continuously updated. If for example 

you selected the headlines page on Fig 5.1, the microcomputer would load the 

four linked lead pages into its memory and these would then be available for 

display. 

Let's suppose you are currently displaying the headlines page which can be 

done using the 'select a page' method previously discussed. The headlines 

page will show four links. To select one of the linked pages, type in the link 

number (1, 2, 3 or 4). The message Link n (where n is the number you typed) 

will be displayed. Now press the RETURN key. The message Waiting for 

link n will be displayed until it is replaced by the selected linked page. 

Suppose you select lead 3 for display. This has three links pointing to three 

story pages, and again you can select any one. 

Only link numbers 0-23 are valid and the system will reject an invalid number 

by sounding a 'bleep'. If you select a link number which, although valid, is not 

shown on the current page, the message No such link will be displayed 

when you press the RETURN key. If the current page has no links, the 

message No links present will be displayed.

Fig 5.1 Linked pages 

Using the system in Terminal mode 21


Let's assume that by using the links you have arrived at a page with only one 

link. This could be lead 1 or page 1 of story 3A. You can now use the key 

marked v to 'step' forwards through the story, page by page. You can also step 

back one level by using the ^ key, but to return to the top-level index page 

you need to use the 'last explicit page' key f1. 

If we look again at Fig 5.1 there are routes marked *. These connect together 

adjacent pages at the same level in the structure. You can easily display an 

adjacent page at the same level by pressing the keys (whichever is 

appropriate). For example if you are currently displaying lead 3 and you wish 

to display lead 2, simply press the

6 Using the system in 

Telesoft mode 


This mode provides a series of commands for dealing specifically with 

Telesoftware as distinct from Teletext. Some of the commands, eg `select a 

page', are much the same as in Teletext mode, however commands are not 

available in this mode for specifically dealing with normal Teletext pages, 

such as the 'reveal' command and the commands to save pages to another 

filing system and select linked pages. You can if you wish view normal 

Teletext pages in this mode but it is more convenient to do so in the Terminal 

mode. You should only enter Telesoft mode when you wish to deal with 

Telesoftware files. 

You will recall that in chapter 4 we suggested that as a first step, you try to run 

one of the Telesoft programs before going on to use the full range of Terminal 

mode commands. We suggest that you now do something similar before going 

on to use the full range of Telesoftware commands. 

What follows is a simple procedure which tells you how to get a Telesoftware 

program running using some of the Telesoft commands. To the home 

computer user it is quite often unclear just why certain commands are 

necessary at certain times and what they do. In the following simple procedure 

we have attempted to go at least some way to correcting this problem by 

putting in explanations as and where we felt it would help you. 

The first thing to do is get into Telesoft mode. You can do this by typing in: 

*TELESOFT and pressing RETURN . 

The prompt >_ is displayed. 

The Telesoft mode is now the current filing system until another is entered ( 

see chapter 8: Changing the filing system). 

While in Telesoft mode, the computer will understand and respond to the 

commands discussed in this chapter. Apart from these commands, the 

computer will behave in the same way as before entering Telesoft mode: thus 

you can still write programs while in Telesoft mode. 

Now select BBC 1 channel by typing in:

24 Using the system in Telesoft mode 

*BBC1 and pressing RETURN . 

As before the prompt >_ will be displayed. 

Once you have selected the channel you want, you can then go on to select the 

page you want, 700 in this case, by typing in: 

*PAGE 700 and pressing RETURN . 

After typing this command, page 700 will become the currently selected page 

and will be subject to all subsequent commands until a new page is selected ( 

page 700 is currently the Telesoftware index page). 

The next step is to get the page you've just selected into memory. Until this is 

done you can't display it. However, you first need to make sure that you do not 

overwrite a program already in memory. The command you will use to put the 

page in memory is TRANSFER. You will cause the page selected to be loaded 

in an area of 960 bytes immediately before HIMEM (HIMEM defines the start 

of screen memory). Page 414 of the BBC Microcomputer User Guide explains 

how RAM is allocated and 415 shows where spare memory is located. To find 

the address in memory at which you can start loading the page, type in: 

HIMEM = HIMEM - 960 and press RETURN . Then type in PRINT 

~HIMEM and press RETURN (where ~ indicates a hexadecimal value). 

The address displayed (which is in hexadecimal) is the one you will need to 

use in the TRANSFER command (next). 

Next, transfer the page into memory by typing in: 

*TRANSFER and press RETURN . 

When the prompt >_ appears, the page has been captured and stored in 

memory at the address specified. 

Now display the page, by typing: 

*DISPLAY and pressing RETURN 

where is the one used in the *TRANSFER command. 

The page will be immediately displayed, listing the file name of each 

Telesoftware program being transmitted, together with the page number on 

which each can be found. When you have decided which program you want to 

run, select the page using the *PAGE command described previously, then 

type in: 

*EXEC and press RETURN .

Using the system in Telesoft mode 25 

Refer to 4.4 of this manual which explains what happens when you download 

a program. Having downloaded the program, you can now run it by typing in: 

RUN and pressing RETURN . 

The program will now run. 

This completes the introductory procedure. The full range of Telesoft 

commands is in the next section. 

6.2 Telesoft mode commands 

The Telesoft filing system provides a number of commands which allow you 

to control the Teletext Adapter and manipulate the captured program. 

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: As with any other BBC Microcomputer filing system, Telesoft allows 

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

*TELES. for *TELESOFT. 

*BBC1 


Description 

These commands are used to select channels 1 and 2 for Teletext reception. 

Syntax 



Example 

*TELESOFT 

*BBC2

26 Using the system in Tele soft mode 

This will cause channel 2 to be selected. The appearance of >_ confirms 

the selection. 

Notes 

It is up to the user to ensure that channel 1 is tuned to BBC 1 and channel 2 is 

tuned to BBC2 for this command to produce the expected results. 

*CH1 

*CH2 

*CH3 

*CH4 

Description 

These commands are used to select one of the four available channels for 

Teletext reception. 

Syntax 

*CH1 

*CH2 

*CH3 

*CH4 

Example 

*TELE SOFT 

*CH3 

This will cause channel 3 to be selected. 

Notes 

These commands are alternatives to the *BBC and *ITV commands and 

should be used where the channels are not tuned to the recommended stations, 

ie channel 1 to BBC1 etc.

*DATE 


Description 

This command causes the date, as transmitted by the television service data 

packet (see 9.5), to be displayed. 

Syntax 

*DATE 

Example 

*TELE SOFT 


*DATE 

Notes 

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

If the TSDP is not transmitted or the data is corrupt on reception an error 

message is displayed. 

*DISPLAY 

Description 

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

been transferred into memory with a *TRANSFER command. 

Syntax 

*DISPLAY 

where is the hexadecimal address used in the *TRANSFER 

command. 

Example 

*TELE SOFT 


*PAGE 200 

*TRANSFER 7000 

*DISPLAY 7000 

This will cause BBC2 CEEFAX page 200 to be displayed on the screen.


Notes 

The address specified must be in hexadecimal and should correspond exactly 

to an address used for a previous *TRANSFER command. Several pages may 

be transferred to separate memory locations before display. 

*EXEC 

Description 

This command is used to execute a stream of ASCII characters from a 

Telesoftware file as though they have been entered from the keyboard. These 

ASCII characters may be a BASIC program or keyboard commands. 

Syntax 

*EXEC 

*EXEC "" 

Example 

*TELE SOFT 


*PAGE 704 

*EXEC "WELCOME" 

This will cause the Telesoftware program WELCOME on BBC1 CEEFAX 

page 704 to be executed. 

Notes 

If the file name is given as a null string then the first program found on the 

selected page will be executed. 

Beware: If you have specified a non-existent file name the system will wait for 

ever trying to find it.

*HELP 


Description 

This command is used to display useful information about Telesoft mode, 

Terminal mode or the computer system in general. 

Syntax 

*HELP (For general computer system information) *HELP 

TELETEXT (For Terminal mode information) *HELP TELESOFT ( 

For Telesoft mode information) *HELP OPT (For information about 

user-definable options) 

Example 

*HELP TELETEXT 

This will display a list of all Terminal mode commands, together with a short 

description of each and the function keys used to call up the command. 

Notes 

If the Teletext Adapter is not switched on, help on the Teletext system will not 

be available. 

*ITV1 

*ITV2 

Description 

These commands are used to select channels 3 and 4 for Teletext reception. 

Syntax 

*ITV1 

*ITV2 

Example 

*TELE SOFT 

*ITV2 

*PAGE 400


This will cause page 400 of channel 4 to become the currently selected page. 

Notes 

It is up to the user to ensure that channel 3 is tuned to ITV and channel 4 to 

CHANNEL 4 for this command to have the expected results. 

*OPT0 

Description 

This command sets all options to their default values. 

Syntax 

*OPT0 

Example 

*TELESOFT 


*PAGE 220 

*OPT0 

*EXEC "PROG" 

Notes 

The default settings are: 

*OPT1,128 

*OPT2,1 

*OPT3,0 

*OPT1 

Description 

Telesoftware files can include information which is displayed whilst the file is 

being loaded. This displayed information, as well as 'searching' messages, can 

be controlled with the *OPT1 command as follows:


*OPT1,0 No messages displayed 

1,1 Title displayed 

1,2 Language and title displayed 

1,3 Computer type and all above items displayed 

1,4 Date of file publication and all above items displayed 

1,5 Source or author of file and all above items displayed 1,128 

'Searching' messages and all above items displayed 

Syntax *OPT1, 

 

Example 

*TELESOFT 


*PAGE 703 

*OPT1,2 

*EXEC"" 

This will cause a load of the first program transmitted on BBC1 CEEFAX 

page 703 to be executed, and the program language and title to be displayed. 

Notes 

The default setting is *OPT1,128, ie all messages are displayed. 

The title is a concise description of what the file contains. This is not 

necessarily the same as the file name which is merely a label to identify the 

file. 

*OPT2 

Description 

This command controls the steps taken when the system encounters an error 

whilst reading a Telesoftware file. *OPT2,0 causes the system to ignore 

errors, *OPT2,1 causes the system to retry for a page until it has been 

received correctly and *OPT2,2 causes the system to abort the downloading if 

an error is detected. 

Syntax *OPT2, 

32 Lasing the system in Telesoft mode 

Example 

*TELESOFT 


*PAGE 708 

*OPT2,1 

*EXEC "" 

This causes the first Telesoftware file found on page 708 of BBC1 CEEFAX 

to be executed, and in the case of a reception error for the page to be reloaded. 

Notes 

Errors may be encountered in the checkbytes (see section 9.2) of the page 

header, data parity or page CRC checks. In the first instance single bit errors 

are automatically corrected by the system. Parity or CRC errors can not be 

corrected and the system will retry for the page if *OPT2,1 is set. Pressing 

ESCAPE will cause the retries to abort. 

*OPT3 

Description 

When a Telesoftware load is started all previously redefined protocol bytes are 

reset to their original values, but this feature may be suppressed so that a 

format may be learned from loading one program, then re-used for loading a 

second. *OPT3,1 disables this reset feature and *OPT3,0 re-enables it. 

Syntax 

* OPT3, 

Example 

*TELESOFT 


*PAGE 707 

*EXEC "PROG1" 

*OPT3,1 

*EXEC "PROG2"


*TIME 

Description 

This command causes the time of day, as transmitted by the television 

service data packet (see 9.5), to be displayed. 

Syntax 

*TIME 

Example 

*TELESOFT 


*TIME 

Notes 

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

If the TSDP is not transmitted or the data is corrupt on reception, an 

appropriate error message is displayed. 

*TRANSFER 

Description 

This command transfers the current page to a given memory location. 

Syntax 

*TRANSFER 

Example 

*TELE SOFT 


*PAGE 100 

*TRANSFER 6800 

This transfers BBC1 CEEFAX page 100 to memory starting at location &6800. 

Notes 

The page must have been selected with the *PAGE command before issuing 

this command.

*TUNE 


Description 

This command invokes the fine tuning routine for the currently selected 

channel. 

Syntax 

*TUNE 

Example 

*TELESOFT 

*ITV1 

*TUNE 

This will invoke the fine tuning routine for channel 3. 

Notes 

The fine tuning routine is the same as that entered by SHIFT and f4 in 

Terminal mode, as described in section 4.3.

7 Using the Teletext 

system at assembly 

level 

7.1 Teletext assembly level interface 

This section describes the calls available at assembly level which give the 

advanced programmer more control over the Teletext Adapter than is possible 

in Terminal mode. These calls are available from both Assembly Language 

and BASIC. 

The Teletext system is accessed through the general purpose routine '' 

OSWORD' whose entry point is address &FFF1 in the BBC Microcomputer 

Machine Operating System. 

OSWORD calls in which register A contains the value 122 (&7A) are 

Teletext-specific calls – they are obeyed only when the Telesoft filing system 

is selected. A typical example of such a call (first in BASIC then in Assembly 

Language) is given below. This is the call to select the TV channel from which 

Teletext is received, which in this example is BBC1. 

The description in the manual is a cryptic '[&8B, channel]'. This means that 

the parameter to OSWORD is a control block containing the two 1-byte values 

'&8B' and 'channel' respectively. The values of the registers on the call to 

OSWORD have a fixed significance: 

– A is always the 'Teletext OSWORD number', ie &7A. 

– X and Y are always treated as a concatenated value containing the 16-bit 

address of the control block in which the actual parameters are stored. (X 

is the low byte and Y is the high byte.) 

– P is irrelevant (except that the processor should not be in decimal mode). 

Control blocks have various formats – the only fixed slot being the first byte 

which serves a dual purpose: 

– To identify the specific Teletext command wanted. 

– To return the status of the operation (as a success/failure code, typically 0 

meaning OK, or 17 meaning escape). 

To allow for future enhancements of the Teletext system, control blocks 

should be declared as being exactly 16 bytes long.

Please note that the error codes are command dependent. 

Using the Teletext system at assembly level 37 

Example 1: Calling the Teletext system from BASIC 

OSWORD = &FFF1 

DIM parameter 15 

parameter?0 = &8B 

parameter?1 = 0 :REM 0 —> BBC1, 1 —> BBC2 etc. 

A% = &7A 

X% = parameter MOD 256 

Y% = parameter DIV 256 

PYXA% = USR (OSWORD) 

Example 2: Calling the Teletext system from Assembly 

Language 

DIM CodeSpace 100 

OSWORD = &FFF1 

FOR Pass = 0 TO 2 Step 2 

P% = CodeSpace [OPT Pass 

.SelectBBC1 

Lda #&8B 

Sta parameter 

Ida #0 \SelectBBC1 

Sta parameter + 1 

Lda #&7A 

Ldx #parameter MOD 256 

Ldy #parameter DIV 256 

Jsr OSWORD 

Rts 

.parameter NOP:NOP 

NEXT Pass 

CALL SelectBBC1 

The section below on Teletext OSWORD calls describes the calls available to 

you. Some entry points are used for internal Teletext filing-system operations 

and should not be called. Others are 'reserved for future expansion . . .'. 

Further information will be made available by Acorn in the form of a 

software applications note.

38 Using the Teletext system at assembly level 

7.2 Teletext OSWORD calls 

RELOAD PAGE [&80] 

The last page received must be re-fetched. 

FETCH PAGE [&85,p100,p10,p1,s1000,s100,s10,s1] 

Request the page specified by the seven-digit page number given as the 

parameter. The sub-code is the time-code which is used for selecting a 

particular rolling page in a series of rolling pages. If any rolling page is 

acceptable, the sub-code digits should be set to &FF to denote that they are ' 

wild'. Page digits may also be set 'wild', and the page digits can be specified in 

either binary or ASCII hex. This call returns immediately. See TRANSFER for 

details of how to load a page into memory. 

CHAINED PAGE [&86] 

Fetch the next page in the chain of pages of which the current page is part. The 

Telesoftware decoder uses this call to mean 'Get me the next block in the 

encoded Telesoftware file which I am loading sequentially'. If the current page 

is not part of a chain, the next rolling page to arrive is fetched instead. 

HEAD OF CHAIN [&88] 

Follow the chain round until you find the page which is marked as being the 

head of the chain. The Telesoftware decoder uses this call to mean `Find me a 

page in which I can start looking for some encoded Telesoftware to decode' 

and also 'Get me the next block in the encoded Telesoftware file which I am 

loading in random order'. As with CHAINED PAGE, if the current page is not 

part of a chain, the next rolling page to arrive is fetched instead. 

TEST ARRIVED [&89, result] 

Test to see if the last page requested has arrived. 

Test succeeds: result = &FF 

Test fails: result = 0 

The page in question is LOCKED against further update if the test was 

successful. 

UNLOCK PAGE [&8A] 

If the TEST ARRIVED command has shown that a page has been captured by 

the decoder, the page will have been locked against further

Using the Teletext system at assembly level 39 

update. To secure updated versions of the page (or following pages in a 

series of rolling pages), the page must be UNLOCKED. 

Note that reading data from a page using BGET on channel 15 also causes 

the page to be LOCKED. 

SELECT CHANNEL [&8B, channel] 

Select channel 'channel' in the decoder hardware. Channel numbers should 

be given in the range 0 to 3 (binary or ASCII). 

Note: This is different from Terminal mode, where the range 1 to 4 was 

chosen for the benefit of first-time users. 

READ TSDP [&8D, 16-bit address] 

The readable part of the television service data packet (TSDP) is written to 

the area of store defined by the 16-bit address. As usual for the 6502, the 

address is passed in low, high' order. There is no interlock on this operation, 

as the packet is intended for direct display. 

HAMMING DECODE [&8E, encoded byte] 

The 8-bit hamming-encoded byte is decoded, and the result returned in its 

place. A result of &FF means that an uncorrectable (more than 1 bit) error 

has occurred. 

TRANSFER [&8F, 32-bit address] 

The current page is transferred to the address given. The address is 32 bits 

wide in order to allow data to be transferred to a site in the parasite processor. 

The 32-bit address is stored in the form low, high, higher, highest'. The 

transfer waits if necessary until the page has been received. If this is not what 

you want, use the TEST ARRIVED call which lets you perform other 

operations while you are waiting. (This is the mechanism used by Terminal 

mode to poll for pages received.) TRANSFER automatically UNLOCKS a 

page after the data has been transferred. 

HEADERS [&92, 16-bit address] 

The readable portion of all the headers being received will in future be 

written to the address given. This call is expected to be used for positioning 

the headers within the MODE 7 display.

40 Using the Teletext system at assembly level 

WHAT CHANNEL [&93, channel] 

This call READS the currently selected channel number which it returns in the 

slot provided. As with SELECT CHANNEL, the result is in the range 0 to 3 ( 

binary).

8 Changing the filing 

system 

Your computer can have several filing systems available other than the 

Teletext system. The following commands are all used to exit from the current 

filing system into the one named. 

*TAPE 3 300 baud cassette 

*TAPE 12 1200 baud cassette 

*TAPE 1200 baud cassette 

*NET Econet filing system 

*TELE SOFT The Telesoft mode of the Teletext system 

*ROM The cartridge ROM system 

*DISC The disc filing system 

*DISK Alternative spelling for above 

Typing the command to enter the system you are already in has no effect. If 

you type the command to enter a filing system for which your computer is not 

equipped (ie you do not have the relevant filing system ROM) then the 

computer will respond with Bad command since it does not recognise the 

command.

9 Technical 

information 

This is mainly for interest and is not essential to using the Teletext Adapter. 

However, some of the material may prove useful if you wish to make full use 

of the Teletext system at assembler level. The information in this section 

covers the Teletext signals in general and the specific Tele software signals. 

9.1 The structure and numbering of Teletext pages 

A page can stand alone or be linked to another page to form a chain. Also, a 

number of stand-alone pages and/or chains can be accessed at a common level 

known as a branch. In this way a 'family tree' of pages can be formed with 

branching occurring at many levels. An example of this tree structure is given 

in Fig 5.1 which shows one way in which the contents of a newspaper could be 

transmitted. The first page contains the headlines and could be the index page 

with branching occurring at level 1 to four lead pages. 

Lead 1 is the title page of a story covering four pages whilst lead 2 and lead 4 

are stand-alone single page items. Lead 3 could be a sub-index with branching 

occurring at level 2 to three separate stories. 

The reason why Teletext uses such a structure is to enable you, by using 

simple commands, to find your way through the index/sub-index pages, 

branches and linked pages to the information item you wish to see. 

Pages are numbered in groups of 100, called magazines, and a total of eight 

magazines are currently available for each broadcast channel although not 

every magazine and every page is necessarily transmitted. Each page is 

numbered with three digits, the first of which identifies the magazine it 

belongs to, and the second two the page number within that magazine. In 

addition, a further four digits are available for sub-page numbering, thus 

4070006 would be sub-page 0006 of page 07 in magazine 4. 

Each magazine may have an index page which displays the magazine contents. 

This is usually the first page and is numbered 100, 200, 300 etc depending on 

the magazine.

Technical information 43 

Page numbers are not normally reserved for specific items of information, so 

you must first display the index page to locate the correct page or sub-page 

number which can then be displayed. 

If you select page 206, and page 210 is being transmitted at that instant, some 

time may elapse before the transmission sequence cycles back round to page 

206. 

Index pages are, in fact, often transmitted at a faster rate than other data 

pages. This is to minimise the time you must wait before the selected index 

page is displayed. Another point which deserves mentioning is that not all 

pages are necessarily used. For example, it may be that in magazine 4, only 

pages 420 to 450 are transmitted. 

Finally, there are rolling pages. These are pages which contain different 

information but are numbered the same as sub-pages, eg 0001, 0002 etc. A 

different rolling page is transmitted each time, which allows a great deal of 

information to be sent without changing the page number. For example, the 

BBC Newsreel is transmitted on page 199 but on every transmission a 

different rolling page is sent which contains different information (1990001, 

1990002, 1990003 etc). Suppose the rolling page was changed five times. 

This would give a series of five rolling pages numbered 1990001, 1990002, 

1990003, 1990004, 1990005. 

As mentioned previously, Teletext pages are numbered by up to seven digits, 

made up as follows: 

A one-digit magazine number in the range 0 to 7. A 

two-digit page number in the range 00 to 99. 

A four-digit page sub-code in the range 0000 to 3979. 

The magazine number is sent in the form of a single 3-bit binary number. 

The full range possible is thus 0 to 7 as used by the Teletext system. 

The page number is sent in the form of two 4-bit binary numbers. This allows 

a range of 0 to 255, or 00 to FF hexadecimal, but at present the Teletext 

system only uses the range 0 to 99—the numbers being in binary coded 

decimal (BCD). Page numbers outside this range may be used for other 

purposes, as yet undefined. 

The page sub-code is sent in the form of four binary numbers, whose lengths 

are given below:

44 Technical information 

Most significant digit — 2-bit binary number 

Next digit — 4-bit binary number 

Next digit — 3-bit binary number 

Least significant digit — 4-bit binary number 

These binary numbers give a possible range of 8192 pages (0000 to 3F7F 

hexadecimal). At present, the Teletext system only uses sub-codes which have 

their 4-bit binary numbers lying in the range 0 to 9, and thus with the sub-code 

in the range 0000 to 3979. The use of 2- and 3-bit binary numbers explains the 

strange limits to the first and third digits. 

The 2- and 3-bit binary numbers are a result of the fact that the last four digits 

were originally developed as a 'time code' and hence the full 0 to 9 range was 

not needed for these digits. 

The Teletext specification does allow for hexadecimal page numbering with 

the full range of 0000000 to 7FF3F7F, but this is not used for conventional 

pages. 

9.2 Teletext signals 

A conventional Teletext decoder displays pages made up of 24 rows of 40 

characters per row (except for the first row — see below). The BBC 

Microcomputer Teletext System generates a 25th row for displaying system 

information, prompts etc. This 25th row displayed on the screen has nothing to 

do with the Teletext signals sent by the transmitter. The rest of this section 

deals with the general Teletext signals and the presence of this 25th row on the 

screen is ignored. 

Teletext data is sent as a stream of digital bits forming 8-bit bytes. Each row 

consists of 45 bytes. All rows carry a row address or number in the range 0 to 

31. Rows 0 are the first row on any page and some of its 45 bytes are used to 

identify the page and to carry control information. This leaves 32 bytes for 

character codes. Rows 1 to 23 are the remaining 23 rows of 40 characters 

which, with row 0, make up the complete page. Rows 24 to 31 are often not 

transmitted. They are available to carry special information to the decoder. 

The rows of 45 bytes are transmitted on the spare space between television 

picture fields. Four rows are currently sent between each picture field and a 

maximum of 16 is possible. The structure of the rows of bytes is discussed 

below.

Rows 1 to 23 

These 23 rows have a structure as shown in Fig 9.1. 

Fig 9.1 Byte structure of Teletext rows 1 to 23 


The first three bytes, the clock run-in (2 bytes) and framing code (1 byte) are 

used by the decoder for synchronising the row so that it can tell where one 

character byte ends and the next begins. The next two bytes, the magazine and 

row address bytes, give the magazine number (3 bits) and the row number or 

address (5 bits) arranged in such a way with the eight other bits to provide a 

means of error detection and correction. A discussion of the error protection is 

beyond the scope of this guide – it is dealt with in the reference given in 

section 9.4. The remaining 40 bytes are codes for the 40 characters which are 

to be displayed on corresponding rows on the television screen when the page 

is assembled. The codes are given in table 9.1. 

Row 

Rows with address or row number zero have a special status as page-headers. 

They are made up of 45 bytes like any other row, but only 32 bytes are 

available for character codes. The first 13 bytes are information bytes. The 

first five bytes carry the same information as for any other row, that is, the 

clock run-in, framing code, and magazine and row addresses. Bytes 6 and 7 

give the page number, units and tens respectively. Bytes 8 to 11 carry the subcode, 

the four least significant digits of the page number. Bytes 12 and 13 are 

a series of control bits to give information and instructions to the decoder 

about the page. The remaining 32 bytes are the character codes for display on 

row 0. All of the first 13 bytes are error protected as for the first five bytes of 

other rows. 

When the Teletext decoder finds that it is receiving a row zero (by means of 

the information bytes at the start of the row) it interprets this as meaning that 

the previous row it received was the last one for the


preceding page and that the current row it is receiving is the start of a new page 

for that magazine. Each row zero is thus used to determine the start and finish 

of the pages within a magazine. The rows sent between row zeros can be sent 

in any order (for example, row 1, row 15, row 9 ...) since they each have a row 

number or address amongst the first five bytes (see Fig 9.1). Several magazines 

may be transmitted simultaneously in unrelated order of rows. Blank rows need 

not be sent. If the decoder detects the completion of a page (by receiving the 

next page-header, row zero) it assumes that any row numbers not received for 

the previous page are blank rows. 

To select a given page, the decoder examines the incoming rows of data until it 

finds a page-header with the correct page and magazine numbers. It then stores 

this row in its memory. The decoder continues to store each following row in 

the selected magazine until it receives the next page-header. It now has a 

complete page (bar blank rows) in memory and can decode the character codes 

to display the characters on the screen in the right places by making use of the 

row addresses. 

Rows 24 to 31 

These are often not transmitted but are available for sending special 

information to the decoder. In particular, row 27 is used to tell the decoder 

whether or not a page has any branch or chain linked pages connected with it. 

Rows 24 and 25 have the same structure as rows 1 to 23 and may be used so 

that a page can contain 1K or 1024 bytes of information. A normal page can 

only contain 32 + (23*40) = 952 bytes. The extra two rows provide another 80 

bytes which is sufficient to bring the total up to 1024 bytes without having to 

use all the 32 row zero bytes. In fact, eight of the row zero bytes are left free 

and these are currently used for the time information. 

Page check word (row 27) 

Row 27 includes a 16-bit cyclic redundancy check (CRC) on the first 24 

character bytes of row 0 and the 40 character bytes of rows 1-25 inclusive (a 

total of 1K bytes). For the purposes of this check word calculation any row not 

transmitted is assumed to carry 40 'space' bytes (hex 20).

Table 9.1 Teletext character codes 

Technical information 47


9.3 Character codes 

Table 9.1 shows the available characters, their codes and also the control 

codes. These are the same characters which are available in mode 7 of the BBC 

Microcomputer — see chapter 28 of the User Guide for more details. 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 one to change some aspect of the display part way through a row (for 

example, the display colour). 

Display modes 

There are three modes of display on the Teletext system — one alphanumeric 

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

and separated. The difference is best shown by illustration, as in Fig 9.2. 

Fig 9.2 Contiguous and separated graphics modes 

Colour 

Seven different display colours are provided (white, yellow, cyan, magenta, 

red, green and blue). Fourteen control codes are available to select 

alphanumerics or graphics and the required colour simultaneously. This 

enables 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 entering reveal mode which is done when the user issues the 

required command — such as the key f2 command in the Terminal mode of 

the BBC Microcomputer Teletext System. 

Double height 

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

rows. Thus 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. 

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 thus 

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=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. 

9.4 Reference 

Broadcast Teletext Specification, Sept 1976 

published jointly by 

British Broadcasting Corporation 

Independent Broadcasting Authority 

British Radio Equipment Manufacturers' Association 

9.5 The television service data packet 

In addition to the above Teletext pages, a television service data packet is 

sometimes transmitted. If it is sent, it arrives once per second and carries the 

following information:


1. An initial page address which a terminal should select at start-up without 

further user action. This will be the page selected by the BBC Microcomputer 

Teletext System at start-up. (In the absence of a television service data packet, 

page #00 is selected by default.) The contents of this page are controlled by 

the sender. 

2. A program or network label. 

3. An absolute time reference giving the time and date in a machine usable 

form. 

4. A 20-character block of Teletext coded characters which are intended for 

direct display if the user requests a status report. 

Byte structure of the television service data packet 

The television service data packet (TSDP) is made up of 45 8-bit bytes. The 

first six bytes are for control, identification and synchronisation. The next 19 

bytes carry information in machine usable form. The last 20 bytes carry 

information for direct display when a status display is requested by the Teletext 

system. 

In more detail, the 45 bytes are used as follows: 

Bytes Content 

1- 2 Clock run-in 

3 Framing code 

4- 6 TSDP identification code 

7-12 Default Teletext page 

13-14 Channel identification 

15 Time offset 

16-18 Modified Julian date 

19-21 Coordinated universal time (UTC) 

22-25 Television program label 

26-45 Status display message 

Bytes 1 to 6 - decoder information 

These six bytes provide information to enable the decoder to identify the TSDP 

as such and to synchronise the following bytes so that it can tell where one byte 

ends and the next begins.


Bytes 7 to 12 

These six bytes provide the Teletext decoder with the page number which it is 

to use to select a default page. These bytes are in machine readable form. 

Bytes 13 and 14 - channel identification 

These two bytes can be read by the machine to determine which channel is 

being received. 

Byte 15 - time offset 

This byte gives the offset in hours between the local clock time and the 

coordinated universal time (UTC). The first bit is always 1, the second bit gives 

the polarity of the offset. The last bit is also always 1. The other five bits are 

the offset. For example, the following offsets may be encountered in the UK: 

During winter (GMT): 10000001 – no offset 

During summer (BST): 10000101 – add one hour to UTC to get clock time 

The five offset bits have the following weights: 8,4,2,1,1/2. 

Bytes 16 to 18 - modified Julian date 

These three bytes carry the modified Julian date which increments at UTC 

midnight. The first half byte is always 0101. The remaining two and a half 

bytes carry the date. Each 4-bit binary-coded-decimal number (half byte) is 

incremented by one before transmission. For example the three bytes may be: 

55 5A 81 

which would decode to 44970 or 1 January 1982. 

The following notes should enable one to decode the modified Julian date to 

the standard format. BBC BASIC operators have been used. 

Symbols: JD – Julian date 

Y – year from 1900 

M – month (January = 1) 

D – day of month 

W – day of week (Sunday = 0, Monday = 1 etc)


To find calendar date (in range 1/3/1900 to 28/2/2100): 

Y1 = (100*(JD – 15078.2)) DIV 36525 

M1 = INT((JD – 14956.1 – INT(365.25*Y))/30.6001) 

D = JD – 14956 – INT(365.25*Y1) – INT(30.6*M1) 

M = M1 – 1 – 12*K 

Y = Y1 + K 

where K = INT(0.7 + (1/(17 – M1))) ie IF M1


distinct names by means of their classification into two types of names: lonenames 

and escaped-names. The two types of name are told apart by the 

preceding byte sent. If the preceding byte is the name of the escape operator, 

then the name is an escaped-name. If the preceding byte is not the name of the 

escape operator then the name is a lone-name. For example, if the name of the 

escape operator is &1B, and a string of names received is: 

&56 &89 &1B &89 &67 . . . 

the first two bytes are lone-names, the third byte is the name of the escape 

operator and so the fourth byte is an escaped-name. The fifth byte is a lonename. 

When the Telesoftware decoder is first started up, it carries out an initialisation 

routine during which it sets up a table of names and their meanings in memory. 

The table set up contains the default meanings of the names. Entries in the 

table may be modified from time to time by incoming commands. The default 

table is given in table 9.2, the general Telesoftware table. The table set up by 

the BBC Microcomputer Teletext System will be somewhat different. 

When the Telesoftware decoder is receiving Telesoftware, it looks up the 

names in the table and uses this to decode the Telesoftware.


Table 9.2 (i) Name tables - default entries (&00 to &3F) 

Value ASCII Meanings Value ASCII Meanings 

(hex) char Lone Escaped (hex) char Lone Escaped 

00 NUL 00 20 SP 20 

01 SOH 01 21 ! 21 

02 STX 02 22 " 22 

03 ETX 03 23 £ 23 

04 EOT 04 24 $ 24 

05 ENQ 05 25 % 25 

06 ACK 06 26 & 26 

07 BEL 07 27 ' 27 

08 BS 08 28 ( 28 

09 HT 09 29 ) 29 

0A LF 0A 2A * 2A 

0B VT OB 2B + 2B 

0C FF OC 2C , 2C 

0D CR 0D 2D - 2D 

0E SO 0E 2E . 2E 

0F SI OF 2F / 2F 

10 DLE 10 30 0 30 

11 DC1 11 31 1 31 

12 DC2 12 32 2 32 

13 DC3 13 33 3 33 

14 DC4 14 34 4 34 

15 NAK 15 35 5 35 

16 SYN 16 36 6 36 

17 ETB 17 37 7 37 

18 CAN 18 38 8 38 

19 EM 19 39 9 39 

1A SUB 1A 3A : 3A 

1B ESC 1B 3B ; 3B 

1C FS 1C 3C < 3C 

1D GS 1D 3D = 3D 

1E RS 1E 3E > 3E 

1F US 1F 3F ? 3F


Table 9.2 (ii) Name tables - default entries (&40 to &7F) 

Value ASCII Meaning Value ASCII Meaning 


40 @ 40 60 - 60 

41 A 41 61 a 61 

42 B 42 62 b 62 

43 C 43 63 c 63 

44 D 44 64 d 64 

45 E 45 65 e 65 

46 F 46 66 f 66 

47 G 47 67 g 67 

48 H 48 68 h 68 

49 I 49 69 i 69 

4A J 4A 6A j 6A 

4B K 4B 6B k 6B 

4C L 4C 6C 1 6C 

4D M 4D 6D m 6D 

4E N 4E 6E n 6E 

4F 0 4F 6F o 6F 

50 P 50 70 p 70 

51 Q 51 71 q 71 

52 R 52 72 r 72 

53 S 53 73 s 73 

54 T 54 74 t 74 

55 U 55 75 u 75 

56 V 56 76 v 76 

57 W 57 77 w 77 

58 X 58 78 x 78 

59 Y 59 79 y 79 

5A Z 5A 7A z 7A 

5B [ 5B 7B { 7B 

5C \ 5C 7C | 7C 

5D ] 5D 7D } 7D 

5E ^ 5E 7E ~ 7E 

5F _ 5F 7F DEL 7F


Table 9.2 (iii) Name tables - default entries (&80 to &BF) 



80 NUL 80 A0 SP A0 

81 SOH 81 Al ! Al 

82 STX 82 A2 " A2 

83 ETX 83 A3 £ A3 

84 EOT 84 A4 $ A4 

85 ENQ 85 A5 % A5 

86 ACK 86 A6 & A6 

87 BEL 87 A7 ' A7 

88 BS 88 A8 ( A8 

89 HT 89 A9 ) A9 

8A LF 8A AA * AA 

8B VT 8B AB + AB 

8C FF 8C AC , AC 

8D CR 8D AD - AD 

8E SO 8E AE . AE 

8F SI 8F AF / AF 

90 DLE 90 B0 0 B0 

91 DC1 91 B1 1 B1 

92 DC2 92 B2 2 B2 

93 DC3 93 B3 3 B3 

94 DC4 94 B4 4 B4 

95 NAK 95 B5 5 B5 

96 SYN 96 B6 6 B6 

97 ETB 97 B7 7 B7 

98 CAN 98 B8 8 B8 

99 EM 99 B9 9 B9 

9A SUB 9A BA : BA 

9B ESC 9B BB ; BB 

9C FS 9C BC < BC 

9D GS 9D BD = BD 

9E RS 9E BE > BE 

9F US 9F BF ? BF


Table 9.2 (iv) Name tables — default entries (&CO to &FF) 



C0 51 C0 E0 - E0 

C1 A C1 E1 a E1 

C2 B C2 E2 h E2 

C3 C C3 E3 c El 

C4 D C4 E4 d E4 

C5 F C5 E5 e E5 

C6 F C6 E6 f E6 

C7 G C7 E7 g E7 

C8 H C8 E8 h E8 

C9 I C9 E9 i E9 

CA J CA EA j EA 

CB K CB EB k EB 

CC L CC EC 1 EC 

CD M CD ED m ED 

CE N CE EE n EE 

CF 0 CF EF o EF 

D0 P D0 F0 p F0 

D1 Q D1 F1 q F1 

D2 R D2 F2 r F2 

D3 S D3 F3 s F3 

D4 T D4 F4 t F4 

D5 U D5 F5 u F5 

D6 V D6 F6 v F6 

D7 W D7 F7 w F7 

D8 X D8 F8 x F8 

D9 Y D9 F9 y F9 

DA Z DA FA z FA 

DB [ DB FB { FB 

DC \ DC FC | FC 

DD ] DD FD } FD 

DE ^ DE FE ~ FE 

DC _ DF FF DEL FF 

Command subroutines 

Looking at table 9.2, in the escaped-name meanings column you can see some as yet 

unexplained terms, eg escaped-name &41 corresponds to . These strings 

enclosed in angled brackets are names of command subroutines. The subroutines 

required by the Teletext Telesoftware decoder (as in the BBC Microcomputer decoder) 

are contained in the Teletext filing system ROM. Each command subroutine has a 

three-character code (eg ). An instruction to the decoder appears in the form of 

the name of the relevant command subroutine to be executed, followed by the names of 

any operands required along with the number and size of the operands if this is not 

implied by the command subroutine.


Each command subroutine has either a fixed (implied) number of operands or 

a variable number of operands. Each operand consists of either a fixed ( 

implied) number of decoded bytes or a variable number of decoded bytes. Any 

variable quantity (either number of operands or number of bytes in an 

operand) is preceded by a number giving its value on this occasion. For the 

Teletext system, this number is either a single decoded ASCII hexadecimal 

digit (' 0' to '9' and 'A' to 'F') or the decoded ASCII character 'X' followed by 

two decoded ASCII hexadecimal digits (most significant first). The general 

structure of a command before naming is: 

 

 

 

 

 

 

. . . and so on. 

Many of the commands appearing in table 9.2 are not relevant to the Teletext 

system but are used by other systems making use of the general Telesoftware 

format. In general, there are three modes of obeying the commands — those 

which lie outside a block, those obeyed on the first pass and those obeyed on 

the second pass through the data. Any bytes received outside a block are 

ignored unless they are the names of the start block command and its 

operands, or a description of the medium being used. For the purposes of the 

first and second pass through the data, the block runs from after the start block 

command. Some commands are obeyed on the first pass through the block. If 

an end of block command is encountered, then the second pass stops at the 

name before this command. The rest of the commands are obeyed on the 

second pass through the block. 

In the Teletext system, only one pass is made through the data, all the 

commands being obeyed on this pass. 

A complete list of the commands relevant to the Teletext system along with a 

brief description is given in table 9.3. However, it should be noted that the 

table does not show all the commands listed in the name tables as not all of 

these are relevant to Teletext.

Table 9.3 The command subroutines 

Code Command subroutine 

Comment 

Define data type 

End block 

Change escaped-name's meaning (command) 

Revert to default format 

Change escaped-name's meaning (decoded string) 

End of file 

Ignore 

Inhibit run 

Load address (absolute) 

Change lone-name's meaning (command) 

Load address (relative) 

Change lone-name's meaning (decoded string) 

No reversion to default format before next file 

Start block 

Title of file 

Execution address (absolute) 

Execution address (relative) 

The escape operator 

Teletext 

Error in transmission 

Eight-bit byte adjustment (lower) 

Eight-bit byte adjustment (raise) 

These commands relevant to the Teletext system are discussed below. 

Start block and medium description commands 

Start block 

Operands: 0, 1 or 2; each variable in length. 


marks the start of the block of data. The first operand is the number of 

this block. The second operand (which only needs to be present for one of the 

blocks of a file) is the number of blocks in the file. The blocks need not be 

numbered if the end of file command is used. 

Example: '1"2' '1' '0' 

(This is the 16th block of the file.)


Teletext 

Operands: 0, 1 or 2; each of variable length. 

makes the changes to the name table necessary for data with odd 

parity, streamlines the tables for Teletext and then executes the 

subroutine to mark the start of the block. 

Thus, any Telesoftware file for the BBC Microcomputer decoder received 

from CEEFAX will start with the name of this command. 

The changes from the general format which are brought about are: 

In the name tables, all names that would be a parity error if received are set 

to be names of the , error in transmission, subroutine. If they are 

received, the subroutine will alert the decoder that there has been a 

transmission error. All lone-names with correct parity are set to decode to 

themselves after a logical AND with &7F. 

The command subroutine is given the lone-name &E0 and the 

command subroutine is given the lone-name &FE. The escapednames 

&E0 and &FE are set to decode to themselves. The command 

subroutine is given the escaped-name &42. 

The decoder is set to expect numerical information (numbers describing 

variable operands, load addresses etc) to be given in ASCII hexadecimal 

digits. 

Example: '2"1"1"1"4' 

(Teletext: This is the first block of four.) 

End block 

Operands: none 

marks the end of a block of data. If the end of the block is marked by 

the end of a Teletext page then the command is optional. 

File and segment information commands 

End of file 


indicates that this block is the last block in a file. It can be omitted if 

the end of file is indicated by other means.

Title of file 

Operands: 1, 2 or 3; each of variable length. 


The operands of a command describe the title of the Telesoftware file 

(first operand), its version number (optional second operand) and its date of 

issue (optional third operand). The date should be given as the modified Julian 

date (see section 9.5). 

Files whose blocks may only be received in order are arranged on CEEFAX as 

a chain. The first block is marked as the chain-header and should contain a 

command giving details of the file. Other blocks need not. Files whose 

blocks may be received out of order are also arranged on CEEFAX as a chain. 

However, each block is marked as a chain-header and should contain a 

command. 

Example: '2"7"P"r"o"g"r"a"m"1"5' 

(File title is 'Program'; version number 5.) 

Comment 

Operands: variable number; each of variable length. 

Comments are indicated by the command, and may be displayed by 

the decoder whilst Telesoftware is decoded (the display is controlled in the 

BBC Microcomputer Teletext System by the Telesoft mode command *OPT1). 

The recommended layout is: 

1st operand – name of program 

2nd operand – language 

3rd operand – type of computer used 

4th operand – date of publication 

5th operand – source of program 

6th operand – other comments 

Example: '1"9"A" "p"r"o"g"r"a"m' 

(The name of the program is 'A program'.) 

Ignore 

Operands: variable number; each of variable length. 

The decoder will ignore the operands of a command.


Load address (absolute) 

Operands: 1 of variable length. 

The operand of a command is the first absolute address in memory 

that the decoded Telesoftware should be stored at (unless overruled when 

issuing the *LOAD command — see chapter 6 on the Telesoft mode). 

The first decoded byte of the operand represents the most significant byte of 

the address. 

Example: '4"2"0' '0' '0' 

(Store the Telesoftware starting at address &2000.) 

Load address (relative) 

Operands: 0 or 1; of variable length. 

The operand of a command represents the offset from the first address 

that decoded Telesoftware is being stored at. Decoded Telesoftware should 

now be stored from this offset onwards. 

The command allows blocks to be received and decoded out of order. 

If there is no operand, then the data should not be stored in a contiguous block 

of memory, but should be passed to a command line interpreter in whatever 

order the blocks are received and decoded. BASIC programs are loaded in this 

way after using the Telesoft mode command *EXEC. 

Example: '1"3"1' '0' '0' 

(Store any further Telesoftware in memory starting at &2100— assuming that 

the base address is &2000). 

Execution address (absolute) 

Operands: 1 of variable length. 

The operand of a command gives the execution address of the file of 

Tele software. 

Example: '4"2"0' 'F' '0' 

(The execution address is &20F0.) 

Execution address (relative) 

Operands: 1 of variable length.


The operand of a command gives the execution address relative to the 

load address of the file. 

Example: '2"F"0' 

(The execution address is &20F0 — assuming that the base address is &2000.) 

Inhibit run 


The DIR command inhibits execution of the program immediately after its 

reception. 

Define data type 

Operands: 1 or 2; of variable length. 

The command defines the type of data in the file and the hardware at 

which it is directed. The data type applies until superseded by a different 

command. 

Example: '2"4"B"B"B"C"3"1"6"K' 

(The following program is in BBC BASIC for a 16K machine.) 

Format redefinition commands 

Change escaped-name's meaning (decoded string) 

Operands: 2; first of length 1 decoded byte, second of variable length. 

The command changes the entry in the name tables for the escapedname 

given (first operand) to decode to the string given (second operand). 

Example: 00 '4"w"o"r"d' 

(The escaped-name 00 will decode to 'word') 

Change escaped-name's meaning (command) 

Operands: 2; first of length 1 decoded byte, second of length 3 decoded bytes. 

The command changes the entry in the name tables for the escapedname 

given (first operand) to represent the command subroutine given (second 

operand). 

Example: FF 'U"E"R'


(Reception of the escaped-name &FF indicates that there has been a 

transmission error – the command subroutine is executed.) 

Change lone-name's meaning (decoded string) 

Operands: 2; first of length 1 decoded byte, second of variable length. 

The command changes the entry in the name tables for the lone-name 

given (first operand) to decode to the string of bytes given (second operand). 

Example: 00 '4"W"0"R"D' 

(The lone-name 00 will decode to 'WORD') 

Change lone-name's meaning (command) 

Operands: 2; first of length 1 decoded byte, second of length 3 decoded bytes. 

The command changes the entry in the name tables for the lone-name 

given (first operand) to represent the command subroutine given (second 

operand). 

Example: FF 'E"S"C' 

(The lone-name &FF becomes a name of the escape operator.) 

No reversion to default format before the next file 


The command stops the decoder resetting its name tables to their 

default values prior to decoding the next file (see also the Telesoft mode call 

*OPT3). 

Revert to default format 

resets the name tables to their default values (see also the Telesoft 

mode call *OPT3). 

The escape operator 

The function of the escape operator () is to indicate that an escapedname 

follows, rather than a lone-name. Thus it permits 512 distinct names 

rather than 256. The escape operator must have at least one lone-name and 

may have escaped-names.

Eight-bit byte adjustment 


For the Teletext system which only sends odd parity bytes, there are only 

effectively seven bits to the byte. The and commands are 

available to 'add' an eighth bit. 

Eight-bit byte adjustment (lower) 

Operands: 1 of decoded length 1 byte. 

indicates subtract &58 from the next decoded byte (to give a value in 

the range &C8 to &FF or &00 to &27, if only bytes in the range &20 to &7F 

can be transmitted). 

Example: 20 

(Decodes to &C8.) 

Eight-bit byte adjustment (raise) 

Operands: 1 of decoded length 1 byte. 

indicates add &58 to the next decoded byte (to give a value in the 

range &78 to &D7). 

Example: 20 

(Decodes to &78.) 

Error in transmission 

indicates that there has been an error in transmission.

Appendix 1 

Installing the 

TELEROM into the 

BBC Microcomputer 

CAUTION 

STATIC SENSITIVE DEVICES — DO NOT HANDLE 

UNTIL YOU HAVE READ THESE INSTRUCTIONS 

Please read these instructions carefully before attempting this conversion. If 

you are not completely confident of your ability to carry out this conversion 

yourself it will be in your own interests to take your unit to an authorised BBC 

Microcomputer dealer for him to carry out this upgrade. 

First find out whether or not your computer has a series 1 operating system 

installed, by typing in *FX0 RETURN . If a number greater than 1.00 is 

displayed, you have a series 1 system. 

1. Ensure that the computer is not connected to a mains power socket. 

WARNING 

DO NOT REMOVE THE LID OF THE COMPUTER 

WHILST IT IS CONNECTED TO THE MAINS 

2. Unscrew the two large-headed screws on the rear panel of the computer and 

the two large-headed screws on the underside of the computer (near the front). 

Carefully remove the lid. 

3. Unscrew the two (three on some computers) bolts securing the keyboard 

assembly to the lower case and carefully unplug the 17-way ribbon cable 

connecting the keyboard assembly to the main printed circuit board (PCB) by 

pulling the socket away from PL13 on the main PCB. 

4. Move the keyboard away from the main PCB until the loudspeaker plug ( 

PL15) is accessible. Unplug the loudspeaker by carefully removing the socket 

from PL15. Place the keyboard assembly to one side on a flat surface.

5. If your computer already contains a 'series 1' operating system then 

proceed to instruction 8. 

Appendix 1 67 

6. The current Machine Operating System (MOS) is situated in the bottom 

right-hand corner of the main PCB in one of two configurations which are: 

(i) One integrated circuit (IC) in socket IC51 identified by the legend 'B02' 

printed on the top. If you have this format carefully remove the MOS IC from 

IC51 using an IC extractor (a small screwdriver used with extreme care will 

do). Identify the BASIC language IC by the legend `B01' or 'B05' printed on 

it, and if it is not already in socket IC 101 then remove it as before and 

replace it in socket IC101 as described in '7' below. 

(ii) Four ICs in sockets IC52, IC88, IC100 and IC101 (these sockets are all 

next to each other despite the numbering) identified with the legends 'C', 'D', ' 

E' and 'F' respectively printed on the top. If this is the case the BASIC 

language IC (identifiable by the legend 'B01' printed on the top and all four 

MOS ICs should be removed as described in (i) above. Replace the BASIC 

IC in socket IC 101 as described in '7' below. 

7. The new MOS is supplied in a single IC identified by the legend 'B04' 

printed on the top. Insert the ROM carefully into the socket IC51 ensuring 

that all the 'legs' locate properly into the holes and are not 'bent under' upon 

insertion. The IC should be orientated so that the semicircular cutout in the 

top of the IC is at the top, ie away from the keyboard. Avoid touching the IC 

legs with your fingers wherever possible. 

Now set the following links: 

S18 North 

S19 East 

S20 North 

S21 Two off east/west 

S22 North 

S32 West 

S33 West 

NB north is the edge of the PCB nearest to the back of the case and south is 

the edge nearest to the keyboard. East and west follow logically from these.

68 Appendix 1 

8. Insert the TELEROM IC (identifiable by the legend 'TFS') into any free 

socket (IC88, IC100 or IC52) as described in '7' above. 

Note: This User Guide assumes that the Teletext ROM is in the far right 

position of the filing system ICs (nearest the edge of the circuit board). If this 

is the case, then, when the microcomputer is powered up, the Telesoft filing 

system is automatically selected. 

If the Teletext ROM is not in the far right position then the Telesoft filing 

system is not automatically selected on powering up. You can select Telesoft 

either by typing in 

*TELESOFT RETURN 

or by pressing the T and BREAK keys together. 

9. Reassemble the BBC Microcomputer by reversing instructions 1 to 4 above. 

Your computer is now ready for use.

Appendix 2 

Teletext reception 

Teletext information is conveyed from the UHF TV transmitter to UHF 

domestic TV aerials as part of the complete 625 line UHF channel 

transmitted wave form. The pages of Teletext information are contained in a 

digitally coded form on unused blank lines which occur during the frame 

fly-back period and these pages of information are continually refreshed and 

updated. Thus a basic requirement for 'good' Teletext reception is 'good' TV 

reception, ie a 'clean' TV signal of adequate level. 

Generally speaking 'good' Teletext reception should be possible in BBC/IBA 

defined UHF TV service areas with the usual 'line of sight' qualification, but 

may be difficult under fringe conditions. 

A starting point is the reception of good quality, low noise (imperceptible 

snow), colour TV reception, but this alone will not guarantee error-free 

pages of Teletext information. Very close reflections of the received signal ( 

ghosting) can be almost imperceptible on a good colour picture but can still 

result in Teletext reception errors. This effect can vary between the four TV 

channels in use because the channels are of different frequencies and the 

reflections are usually frequency-dependent. 

If problems are experienced a number of questions should be answered 

before condemning the equipment as faulty, or writing to the BBC/IBA 

and/or the equipment manufacturers etc: 

1. Is the aerial of the correct group? (UHF bands are split into different 

groups throughout the country.) Reputable aerial manufacturers conform to 

specific technical standards which are essential for the best possible Teletext, 

and colour television, reception. The final display of Teletext information 

depends in the first instance on the aerial signal —this must be right before 

proceeding any further. 

2. Was the aerial system properly installed externally with good quality UHF 

cable, avoiding kinks or sharp bends in the cable, and terminated in a good 

quality coaxial plug correctly fitted and soldered? 

Note: Indoor aerials are not recommended for television or Teletext 

reception.

70 Appendix 2 

3. Is the aerial of the correct polarisation (horizontal and vertical systems are 

employed in different regions of the UK) and is it directed towards the 

transmitter intended to serve the area? Out of area reception is often employed 

for a number of reasons, including ignorance of the correct transmitter for the 

area. 

4. Will the aerial signals provide a good quality, low noise, colour television 

picture free from all reflections? (The new electronic test card is a valuable 

aid in detecting close reflections.) 

If all of the above criteria are met it may be necessary to adjust the position of 

the aerial especially if Teletext character error rates vary between channels, or 

between pages of information. 

The aerial should be tried in all positions, including variation of height, 

preferably by the use of the 'cranked arm' type of mast. If a satisfactory result 

is not possible by this means, moving the aerial to a different location is 

occasionally the only answer. 

If the TV aerial signal is fed through amplifiers and/or signal splitting devices 

to feed more than one outlet, it may, in cases of Teletext reception difficulties, 

be necessary to feed the signal direct to the Teletext unit in the first instance. 

This will help to reduce any problems caused by the signal distribution 

system. If the Teletext unit is fed from a larger MATV (master aerial TV) 

system further professional advice should be sought from a reputable 

contractor. 

Every effort should be made to ensure the best possible level and quality of 

signal so that the end result will not vary with time, weather conditions etc. 

Expenditure on good quality aerial installations at the outset will prove to be 

an investment in the long term.

Appendix 3 

Summary of Terminal 

mode commands 

The following is a quick reference list of all the Terminal mode commands 

together with the relevant keys, and the order in which they appear: 

Description of command Keys used 

Select a channel f4 

Fine tune a channel f4 and SHIFT 

Select a page f0 

Select last explicit page f1 

Select index page f1 and SHIFT 

Keep a page f3 

Release a kept page f3 and SHIFT 

Reveal page f2 

Conceal page f2 and SHIFT 

Enter an operating system (*) command f5 

Save a page to file f7 

Load a page from file f6 

Hold page f8 

Exit to previous filing system f9 

Exit to Telesoft and execute f9 and SHIFT

The BBC Microcomputer Teletext System User Guide

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