The following is abridged from “IEE Conference Publication 166, pp 273-276, September 1978” and reproduced by kind permission of the Institution of Electrical Engineers, UK

Copyright IEE

TELESOFTWARE: USING TELETEXT TO SUPPORT A HOME COMPUTER

J Hedger

ITCA ORACLE Project at London Weekend Television

SYNOPSIS

Telesoftware represents perhaps the most practical solution yet to a realistic home computer system by using teletext to broadcast software right into the heatr of specially-adapted decoder terminals.

A teletext decoder already contains many of the basic elements of a simple computer: memory, visual display, etc. By careful marriage with an appropriate microprocessor, the result is a small but powerful computer system. Telesoftware, by deriving its software entirely from a repertoire of programs transmitted integrally via teletext, eliminates the need for cumbersome storage peripherals or an expensive hardware link to a distant mainframe, while still offering the user true interactive capabilities. Operation is a simple as selecting the appropriate teletext page, and by its nature, the system will support an infinite number of concurrent users.

The implementation of Telesoftware will have far-reaching benefits not only for the domestic user, but also in the worlds of education, science and business, and may even be applied to helping the handicapped and disabled.

A study project, initiated by the Independent Television Companies Association, has already led to the design and construction of an experimental terminal for demonstration purposes, currently undergoing on-air evaluation using software transmitted via the ORACLE system. The author reviews the progress of this project to date, and examines some of the important and varied applications for this new broadcasting technology.

INTRODUCTION

The word “Telesoftware” was coined by W J G Overington (1), (2) who first proposed the idea; it literally means “software at a distance” and it refers to the transmission of programs for a microprocessor via broadcast teletext. Software bytes are presented to a terminal as pairs of standard teletext characters, thus utilizing an existing and well-proven broadcasting system.

The standard teletext decoder is, in fact, well-suited for adaptation to a small computer. Its character-generator and associated display circuitry can be pressed into service as a visual-display-unit (VDU). It has a page-store which may be used as memory. Even its numeric keypad, normally used to select teletext pages, can be used to enter simple data. With the addition of a suitable microprocessor and some extra memory, the result is quite a powerful stand-alone computer system right inside the television set!

There is, at this stage, no mass-store; but since all the software for such a system is stored on the teletext database, the user needs only to select the required page containing his desired program. Once this has been read-in, it can be loaded into the microprocessor and executed, obviating the need for data lines or expensive input devices.

The limit of separate programs which may be carried by a teletext system at any one time is, of course, subject to the same parameters as are the limits for normal page data; namely, that an increase in the number of pages also increases the maximum access–time to a single page. Programs themselves, however, need not be confined to a single page, and may consist of data carried on a number of separate but sequentially-linked pages in the system, and even with a total capacity limitation, there is a wide variety of uses to which such a system can be put. Some of these are discussed later on.

EARLY DEVELOPMENT

The Independent Television Companies’ Association’s ORACLE teletext systems has been broadcasting a service of news and information since around mid-1975.

After about a year of operation, ITCA were approached by W J G Overington with a proposal for a Telesoftware system system, he himself having invented the concept. At ITCA it was felt that the idea had some exciting possibilities as an extension to ORACLE, and so, in conjunction with Overington, a provisional specification for Telesoftware was prepared, and the first Telesoftware transmission, based on the use of a Signetics 2650 microprocessor, was made during late February 1977. The program was a simple one, designed to show loading and changing of various character on the television screen.

THE ORIGINAL SPECIFICATION

The specification drawn up was somewhat open-ended; deliberately so, since at this stage it was desired simply to show that a Telesoftware system was indeed viable. By setting no hard and fast rules, it was hoped that if the system were eventually adopted by decoder manufacturers, any changes felt to be necessary could easily be incorporated.

The system was designed to utilize a standard Teletext decoder in conjunction with a Signetics 2650 microprocessor, plus extra memory and interfacing.

The MAIN MEMORY used the RAM (Random Access Memory) page-store already to be found in the decoder. This was arranged as two 512 x 7 bit memory blocks, and would allow a program to be entered as 23 rows of 32 columns of Teletext characters.

A SECONDARY MEMORY was also specified; this being 8k bytes of RAM storage.

There was also a TERTIARY MEMORY. This was originally intended to act as a partial or complete replacement for the standard teletext character ROM (Read-only Memory), so as to allow ANY character-set to be defined and transmitted to a terminal.

There was also provision for 8 toggle-switches to be used as a user-controlled register.

An optional control-program, held on PROM (Programmable Read-Only memory) was incouded, although for cheapness, this could be substituted by a software-based control program.

PROGRESS

The first broadcast of Telesoftware was fairly well reported in the technical press, and in March 1977 a further program was included on page 766 of ORACLE where it remained for some months.

Clearly, enthusiasm was by now growing for the project from all areas, but it was still embarrassed by the lack of a terminal on which to demonstrate the viability of the system.

As a means of solving this situation, towards the end of 1977, ITCA initiated a project for the design and construction of a simple experimental Telesoftware terminal, using ORACLE to transmit the experimental software. It was decided to use a simplified and somewhat modified version of the original specification, and work began in late 1977.

The aim of the project was to produce quickly a simple device capable of demonstrating the basic concept of Telesoftware. As such, the resultant design was far from optimum, It was felt that by showing in a very limited way what was POSSIBLE with telesoftware, that this would stimulate the interest of decoder manufacturers and other broadcasters, who in the future, perhaps, would continue the development to a stage where the specification for an “ideal” system could be incorporated as an important extension to Teletext. Figure 1 shows how such an “ideal” terminal might look.

COMPATIBILITY WITH THE TELETEXT SPECIFICATION

It was very soon realized that Telesoftware could in no way interfere with the now-established specification for teletext – indeed, it had to be structured in such a way as to remain compatible with any modifications which might be made to the specification in the future. For this reason, it was decided to base experimental work upon the use of entirely standard teletext transmission techniques, using normal characters and pages. The system was thus configured to use pairs of characters to represent bytes of program, with two characters per single byte, the redundancy being used for protection of the data using the Hamming error-correction technique.

It would, in the future, be possible to use some of the extra 8 rows per teletext page, which are specified as being available although not capable of being displayed by a normal decoder, for the transmission of telesoftware data, thus separating it from the normal editorial output.

Alternatively, if normal pages were to be used, it might be desirable to set a control bit in Row 00, the header row, so as to inhibit (bit C10) the display of what to a normal decoder would seem gibberish text!

THE EXPERIMENTAL TERMINAL

The design consisted of a single add-on board for a teletext decoder, comprising a total of some 45 integrated circuits. This was made up of secondary memory, a temporary store, and a special control program, held on erasable PROM, plus of course the Signetics 2650 microprocessor. The design did not include a tertiary memory since, by this time, a foreign language character-set facility was already available within the confines of teletext.

With large-scale integration, of course, a final design could be reduced to perhaps two or three integrated circuits but at this early stage, discrete components were employed as a matter of practicality.

The teletext keypad, which would normally be used to select pages from the teletext broadcasts, was used for system control and user data-entry.

The MAIN MEMORY was the teletext page-stored, addressed by two bytes of indirect address – the first pointing to a row and the second to a column address. This memory was in the addressing range Hexadecimal 2000 to 3727.

The TEMPORARY STORE, which was used as a buffer between main and secondary memory while data was validated, was 256 bytes of RAM in the addressing range H 1F00 to H 1FFF.

The SECONDARY MEMORY was 2k bytes of RAM in the range H 4000 to H 47FF.

The CONTROL PROGRAM was held on ultra-violet erasable PROM. Its functions were as follows:

1 To accept and interpret commands

2 To validate incoming data, using the Hamming protection system

3 To transfer valid data to secondary memory

4 To re-read data incorrectly received

5 To go to the start of the program when correctly loaded

The decision to opt for a single microprocessor and associated instruction set was basically for convenience in this particular experiment. It may be that when, in future, a final Telesoftware system is specified, it will be desirable to transmit programs in an intermediate language rather than in terms of a specific instruction set. This would allow various different microprocessors to be employed, and enable the system to support simplified versions of BASIC or other high-level languages. The disadvantage of this idea is that it would require considerably more memory in the terminal, and could also increase the coding requirements on the transmission side.

It would, in any event, be unwise to specify one microprocessor device, since this would not allow the system to take advantage of the many developments in microprocessor technology which continue to take place.

EXPERIMENTAL PROGRAMS

Two simple text programs were developed in order to demonstrate and test the basic working of the system.

The first was a simple Video Game; a teletext representation of the well-known “MASTERMIND” game. In this case, the pattern which the player was invited to guess was randomly generated by the microprocessor, and the keypad used to enter the user’s guesses. The program used approximately 1k bytes of storage.

The second program was of the calculation variety, intended as an aid to mortgage computations, involving the calculation of monthly repayments from other given variables.

These programs are now being transmitted via the ORACLE system, together with others, while the experimental terminal is evaluated.

OTHER APPLICATIONS

While technical work continues, other research is taking place at ITCA into other applications for the system. Some of these are now described.

VIDEO GAMES

The Mastermind game program shows a possible usage in this area. The advantage of Telesoftware games is that the user may select from ANY game being broadcast at the time, all of which can be played using the SAME hardware, rather than being limited to specific games built into conventional television games units, or at best, in the case of a programmable games unit, being able to purchase extra cartridges (ROM-based) with alternative games on them. The Telesoftware approach requires no extra cost after the basic hardware has been obtained.

Depending upon the complexity of the terminal, it would be possible to incorporate animated games. In the basic terminal, the user interacts with the system via the teletext keypad, possibly with the keys having cursor-control functions. With a more sophisticated system, however, there would be provision for one or more analogue input channels, to accommodate potentiometer or Joystick controls. These would allow a much wider variety of games to be transmitted.

MATHEMATICAL ROUTINES

The system can be used for many different “calculator” functions, as well as for solving problems requiring more specialized functions, for example, tax calculations, electricity and gas consumption, metric conversions, etc. It would also be possible to add a cassette storage system in order to maintain a local database, and to make use of a low-cost printer or the kind now available for teletext output.

PUBLIC INFORMATION

Telesoftware may be used to provide interactive public information of the kind often required in dealing with Social Security claims, Health Education, etc. For example, the user may with to know if he or she is entitled to claim a certain benefit. By interaction with the appropriate program which would ask a number of structured questions, an assessment may be made by the terminal, which would be output on the television screen. The system, which would employ question-sequences of the “multiple choice” type, could also be used for the assessment of tax-allowances. If a program is too complex to be held in memory as a single block, then the system may be instructed to read-in a new page of program, for example, when the current program reaches the end of a particular branching sequence. This allows a program to be of virtually unlimited size, although in practice, the limits of the teletext system in use will dictate the number of pages available.

Telesoftware offers a proven social advantage over a human “advisor” in many cases, since it seems that people are far more truthful and uninhibited when being “questioned” by a machine. Also, unlike a wired-system, there is no security risk to the user’s responses, since the Telesoftware terminal clearly has no means of storing such data or communicating it to anyone else!

EDUCATION

A very large and important area of Telesoftware application is in the field of automated education techniques. Quite a number of proven systems already exist for Computer Managed Learning, but all of these rely upon quite sophisticated and consequently expensive computer systems and terminals. Such systems are generally owned by a Local Education Authority and used by individual schools on a time-sharing basis, so loading problems can occur at times of peak usage.

With Telesoftware, the techniques can be made available cheaply and easily to any number of concurrent users.

The system is perhaps most suited to the multiple-choice type question and answer technique. It can, in addition, provide complex and possibly animated graphics to illustrate a subject, and can even control a slide projector if the need arises!

Probably the most appealing feature of the system is that fact the programs can be made available at no cost to the user – perhaps once reason why a number of educational establishments, including the University of Surrey, who possess a very large Computer Assisted Learning resource, have already expressed a keen interest in the educational possibilities offered by Telesoftware.

ADULT LITERACY AND VOCAL OUTPUT

Telesoftware could conceivably be used to provide a graded course of literacy for adults, with programs automatically grading the individual and continuously assessing progress. It may be possible, in the future, to add a simple vocal output to the terminal (by the use of synthesized speech) to back up written data in this respect, although the very considerable amounts of local memory require dto achieve this are not yet available at realistic cost.

ASSISTING THE BLIND AND THE DISABLED

It is possible for a terminal to assume control of various domestic peripherals; a handicapped person could, for example, use the system to set up telephone calls, summon assistance, control lights, etc. all by using facilities offered by the microprocessor.

It could even render teletext capable of being read by a blind person, by outputting Braille characters from standard ASCII, via a tactile output device.

FINANCIAL IMPLICATIONS AND THE FUTURE

It is expected that, with mass-production of teletext decoders, the extra cost of incorporating a basic Telesoftware system would be around £50 per unit. Since this is the only charge which one could possible expect a user to pay, the system has clear advantages in terms of cost-effectiveness over a wired system, where line and other charges would apply. However, the areas of usage for telesoftware are far more clearly defined than with a wired system; since its advantage is in its local processing capacity rather than database interaction. It can never, for example, forward a message to another user! For this reason, telesoftware may well prove to be an asset to systems such as VIEWDATA, by providing them with a local processing facility instead of them having to make continuous use of expensive two-way communications with a central computer.

Telesoftware clearly has a number of applications in the business world, such as cataloguing, credit control, insurance quotations, etc. to mention but a few of the ideas yet proposed, but perhaps its major impact will be in the home, where it will allow the television set to provide many interesting and useful facilities, all at low cost.

REFERENCES

1 Overington, W J G, “Telesoftware”, Computing, 12^th. May 1977, Vol.5. No. 19, p18

2 Vivian, R H and Overington, W J G, “Telesoftware makes broadcast teletext interactive”, This publication

ACKNOWLEDGMENTS

The author would like to thank P James, R Eason and M Figuerola of Mullard Applications Laboratory, and N W Green of ITCA for their assistance with this work, and to thank the ORACLE Board for permission to publish it.

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