Oracle – Broadcasting the Written Word 

26 March 2018

From IBA Technical Review #3, in 1973

Engineers of the iba have recently developed and demonstrated an experimental data system, Oracle, capable of providing a continuous public information service on conventional television transmitting networks. With this system the public could receive up to 50 different ‘pages’ of information ‘written’ on their television screens, each page containing up to 880 characters, or roughly 120 words. These messages can be displayed or superimposed on the screen of a domestic television receiver without in any way affecting the reception of normal television programmes.

The idea of data broadcasting services is not new, and in various forms they have been proposed many times before; the iba’s Oracle system, however, is believed to be not only more flexible and to offer more facilities than the earlier proposals, but also has already reached a stage of development where its operation can be demonstrated on experimental transmitting and receiving terminals. Experimental Oracle transmissions are being made on the iba’s London television stations to test the experimental receiving unit which has been assembled at the iba’s London headquarters. The system draws heavily on the techniques developed for the iba’s slice system which has been fully field-tested as a means of identifying picture sources.

It is anticipated that if a firm decision was made to start a public data service, British industry would be able to produce suitable Oracle adaptor units, which viewers could use in conjunction with their normal black-and-white or colour television receivers.

The underlying reason for the current interest in public data transmission services – similar work is being pursued by a number of broadcasting authorities throughout the world – is the dramatic reduction in recent years of the cost of complex digital integrated-circuit devices, suitable for data storage. Despite the intense interest in such systems, the iba system is thought to be the most advanced, and the first system to be demonstrated ‘off air’, although the present experimental receiver adaptor would require simplification before it would be suitable for large scale production by industry.

1: The Oracle ‘test card’ displayed on a television receiver with (right) the Oracle push-button control unit.

What Oracle offers

The adoption of Oracle would mean that a viewer would require an adaptor unit which he would use in conjunction with his normal television set and a small pushbutton keyboard control unit. By means of the pushbutton control he could at any time cause to be displayed on his screen any one of 50 ‘pages’ of information. These messages would be displayed in the form of clear electronic letters or numerals or graphical symbols on his screen, either briefly replacing his television picture or even superimposed on top of it. Any type of written information could be sent, one page at a time, with the individual pages updated at regular intervals. Since it takes 1-8 seconds maximum for the transmission of one page of this material, it is possible for the 50 pages – each perhaps representing an entirely different information service – to be updated or rewritten in a period of less than two minutes. The viewer would also have the facility to ‘hold’ indefinitely any page of this information.

The type of information services which could be provided by such a public broadcast data service are almost unlimited, and the system has many other potential applications for home or business use. The type of information services which could be provided in this way includes continuous accurate time checks, weather forecasts, news, traffic, and local news, stock exchange prices, television and radio programme information, recipes, local and national announcements, exhibitions, theatres, shopping information, and advertising messages. One page of information would provide a summary of the services available and the ‘page number’ which would be used by the viewer to ‘call up’ the display on his screen. Other possibilities include the use of the equipment as a home data terminal, the provision of caption material to accompany television programmes for the deaf viewer or for those who do not understand the language of the programme.

2: This is the Oracle data format for one ‘segment’ representing one quarter of a line of written information. Each segment occupies one line of the television signal in the unused vertical intervals. Normally the Oracle signal would be transmitted on Line 16 and the corresponding line in the odd field (that is Line 329). The form of modulation used is known as ‘complemented element’ in which a ‘1’ is represented by a transition from picture white to black and ‘0’ by the reverse transition. This form of modulation is rugged and unlikely to suffer errors during transmission and has been well tested.

The display letters would be formed from a ‘matrix’ using techniques already widely used in computer visual display units and in electronic character generators. Oracle however has sufficient flexibility to contemplate further possibilities such as the use of individually coloured letters or graphical symbols. The possibility also exists of providing ‘electronic newspapers’ transmitted at night and recorded automatically.

Two 64 µs ‘line periods’ repeating at the rate of 25 per second, are more than sufficient to allow the amount of data envisaged in an Oracle service to be transmitted. During each brief Oracle transmission period – that is 64 µs 50 times a second – one ‘segment’ of display information, representing up to 10 characters, is transmitted together with its ‘address code’. This address indicates to the receiving unit the exact position on the screen and for which page the information relates. This signal is in the form of a ‘run-in code’ (five binary digits or bits); a ‘start code’ (eight bits); a ‘line number’ (five bits); the field or ‘page’ number (six bits); and the address (eight bits). The data format is shown in Fig. 2. A ‘message’ of up to ten letters can be transmitted on each line. Each line thus provides a data communications capacity equivalent to a telephone line.

At the sending end, the text of a page is prepared in advance on a computer terminal unit. The various pages are entered and held in the memory of a small general-purpose computer which allows the information to be inserted into the television signal in the correct form at the appropriate time. When the page has been completed it is transmitted in approximately 1.5 seconds, so that the total time for transmitting all 50 pages – in effect a small ‘book’ of written information – does not exceed about 1 min. In the present experimental system the text is restricted to a standard type-face of some 60 characters, but the code used will allow for an extension of this; the text can incorporate non-typographical signs to allow the transmission of drawings or even free-hand writing. As indicated, the text is transmitted in segments of 10 characters with each character represented by an eight-bit code.

3: A block diagram showing the main elements of an Oracle receiving system. The Oracle circuits could be provided either by means of an independent add-on unit used in conjunction with an existing receiver or, rather more cheaply, by modification of the design of a receiver to provide built-in Oracle circuits. British industry has already shown keen interest in the development of a public data system based on the Oracle principles.

At the receiving end, the domestic television set requires adaption for Oracle either by means of an independent add-on unit or, more cheaply, by an internal modification. The system now undergoing test allows for 50 pages of text, each consisting of 22 lines of 40 characters, and the experimental receiver adaptor enables the user to select any page for display. The equipment at the receiver, Fig. 3, is in principle simple. The data is extracted from the television; checked to see whether it is Oracle data; if it is, the page number is read and when this coincides with the number selected by the viewer, data is fed into an intermediate store capable of storing the ten characters transmitted in the single field interval. Subsequently, at the appropriate moment, the data is fed out of this store into the main recirculating store capable of storing a complete ‘page’ of Oracle information, that is to say 880 characters in 88 segments, or 5,280 bits. A third store completes the sequence, holding a complete line of 40 characters, that is four segments of information, and is up-dated by the recirculating store. The signal from the third store is presented to the character generator one character at a time. Each character is based on the 7 by 5 dot-matrix. On the television picture the characters are built up line by line by demodulating the scanning beam in the appropriate way, i.e. the scanning beam is modulated in rapid succession by the first row of squares for each of the letters in a line of text, followed by the second row and so on until the complete text has been displayed. To achieve this the information from the third store is presented character by character in rapid succession seven times. The line of text is followed by a space four television lines wide. Before these are scanned the third store is reloaded from the main recirculating store.

On switching to a different ‘Oracle’ page, the recirculating store is emptied and then waits until the first segment of the new page is available, the new segment being written in to the recirculating store in precisely the same place as the first segment of the old page. Further segments are entered as they become available and in a period of approximately 1.5 seconds a complete new page is transferred to the recirculating store.

At the receiver the timing sequences needed to display the segments of information at the right time are controlled from the line timebase pulses of the television set which are kept in accurate step with the transmission by means of the line synchronizing pulses. The Oracle adaptor separates the data signal from the television signal and passes the data, in 64 µs packets, into an intermediate store. The address code is then used to insert the information at the precisely right moment into the main store where the complete ‘page’ of information is held ready for display. Each character is based on a matrix of 7 x 5 dots. The main store has to be capable of holding 5,280 bits of information, and in practice this store consists of a recirculating shift register in integrated circuit form.

4: Example Oracle characters based on a 5×7 grid.

At the studios, the various Oracle pages would be kept updated by an editorial team working within a communications complex and using visual display units and keyboards in conjunction with a central computer which would be needed to collate the information so that it can be inserted into the television waveform at the appropriate moments and distributed along with the normal television signals to the transmitting stations. The first line of each page would carry an identification, date and time so that every viewer, no matter which of the Oracle services he was watching, would have the equivalent of a highly accurate digital clock always available. For example the first line might read: ORACLE 33 PAGE 22 21 APR 17:21:07. This would identify the page being transmitted as 33, the page of information displayed (22), the date (21 April) and the time 1 7 hours, 21 minutes, 7 seconds.

The experimental receiving unit developed and demonstrated by the iba is significantly larger and more complex than would be necessary for a domestic Oracle adaptor. Furthermore, advances in large scale integration of the memory devices would drastically cut down the number of devices required in the main store. It is possible that this might in future consist of just a single integrated circuit for the store, with a second chip containing virtually the entire control electronics.

It is hoped that the experience gained with this experimental system will allow the iba, in co-operation with the receiver industry and others, to specify the optimum subjective and technical characteristics of the system, making it possible to contemplate the start of a pilot public data service.

The latest version of Oracle uses two data lines per field so that the maximum time for transmitting 50 pages is only approximately 30 seconds, representing a mean ‘waiting time’ of only 15 seconds. A number of British receiver manufacturers are actively developing prototype Oracle receiving units. The Oracle test card has been transmitted in the London region since April 1973.

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