GB1590476A - Display apparatus - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO DISPLAY APPARATUS (71) We, THE ENGLISH ELECTRIC COMPANY LIMITED, of 1 Stanhope Gate, London W1A 1EH, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to electronic display apparatus and more pafticularly to apparatus for the control of information displayed on a television type of display system.

A television type of display system is one in which information is displayed by illumination of one or more areas of a screen by electronic selection.

The information may be received by a television transmission system known generically as a teletext. It may be received over a telephone line by a modem and one example of such an information transmission system is the VIEWDATA system proposed by the British Post Office. Information for display may also be generated by more localised apparatus such as a teleprinter and may be displayed prior to transmission.

A problem which arises in the design of such apparatus is that for a particular application it has heretofore normally been necessary either to design the apparatus to perform one specific function or to include redundant circuitry within such apparatus and provide means for switching in such redundant circuitry when a variation in operation is required. In particular it is envisaged that apparatus will be required which is at least suitable for the display of both teletext and VIEWDATA information.

The present invention provides apparatus for the display of information on a television type display wherein there are provided an information store unit, one or more data input units and a character generator unit, and a bus arrangement interconnectinig the store unit, said one or more data input units and said character generator unit over which pass electric signals representing said information and the destination of said information.

Preferably said bus arrangement comprises a plurality of electric conductors, and electric signals applied to said conductors representing information to be transferred between said units are preceded on some at least of said conductors by electric signals representing a store address or circuit means to which said information is to be transferred.

The data input units may comprise receiver and decoder means responsive to coded data received over a telephone line or modulated on a broadcast television carrier during field blanking intervals, and the character generator may comprise a read only memory or a programmable read only memory and the information store unit may comprise a random access memory.

A store address control module may be connected to the information store unit to control the reading and writing of information into and out of the information store unit, this store address control module being arranged to produce a cursor output to indicate on the display the address in the store unit at which information is being written at any instant. The store address control module may include circuit means for generating a sequence of data memory address for the sequential read out of a page of data to produce a continuous display.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 shows block diagrammatically a data display control system; Figures 2 and 3 show segments of a data display; Figure 4 shows a logic block diagram for the sequential production of extra information for character rounding of the display of Figures 2 and 3; Figure 5 shows a logic block diagram for the simultaneous production of extra information for character rounding of the display of Figures 2 and 3; Figure 6 shows the display of "graphics" characters; Figure 7 illustrates the address format for a combined data and address bus system; Figure 8 shows a Hamming code evaluation circuit for teletext signals; and Figure 9 shows a store and display subsystem according to the present invention.

Referring to Figure 1, the present invention relates to a system in which data is received in digital form from an external source and is stored in a memory module so that it may be continuously displayed on a television type of display. The basic functions of such a system are represented in Figure 1, i.e.

One or more means of acquiring or trans mitting the data which is required to be displayed. (V) A means of storing this data so that it may be used to provide a continuous display. (W) A means of converting this data from the form in which it is stored to a form suitable for providing a picture on a tele vision type display. (X) A means of transferring the data between the functions above. (Y) A means of controlling the flow of data between the various functions. (Z) A particular example of such a system is a teletext and viewdata receiver.

The function of converting the data from the form in which it is stored to a form suitable for display on a television type of display is implemented in stages. The data word received from the store is first used to address a read only memory which produces the information required to form on the television type of display the character or shape which the data word represents.

This information defines the intensities of a matrix of dots which will be produced on the display. A particular case is a matrix of 10 dots vertically by 7 dots horizontally, though others are possible. This information must be selected from the total available and presented to the display in the sequence necessary to display the required character or shape. The information may be modified before being presented ao the display by an interpolation process generally known as character rounding, which provides a display with some of the characteristics of a matrix with four times as many dots as those provided by the read only memory. The principal improvement is an increase in the legibility of characters or symbols containing diagonal lines.

This interpolation process is illustrated by Figures 2 and 3. One row (A) of matrix segments is producted by two TV lines and the next (B) by two more lines. Two possible configurations of segments of a small part of a display are shown in Figure 2 as they would be produced by the information from the basic matrix. Figure 3 shows how the extra information gained by interpolation may be added to the basic information to give a better representation of a diagonal line. The rules for the production of the extra information Z and Y are: - If Al and B2 are present and A2 is not, or if A2 and B1 are present and Al is not then Z is produced.

Similarly: If Al and B2 are present and B1 is not, or if A2 and B1 are pre sent and B2 is not then Y is produced.

This may be implemented by the logic in Figure 4 for sequential production of each piece of extra information, or by the logic in Figure 5 for the simultaneous production of all the extra information associated with one of the rows of segments forming a character. By the appropriate control of the switches selecting the sets of information A+B both interlaced line displays (normal TV type of display) and non-interlaced line displays (e.g. "Video Display Units" or "Video Keyboard Units") may be catered for.

Some applications, e.g. Teletext and VIEWDATA, require the display of characters in which the character rectangle is split into a coarser matrix than the basic one. For example, Teletext requires the display of ' graphics ' characters formed by a 3x2 matrix. If the basic matrix is, for example, lOx 7 the horizontal dimension, 7, cannot be split into two equal segments.

The interpolation logic described above can provide this facility. In this example if segments Al, A2, A3 and A5, A6, A7 are loaded with the 2 graphics segments and A4 is never loaded, while B1, B2, B3, B5, B6, B7 are never loaded and B4 is always loaded then the symbol produced on the display will have a symmetrical horizontal decision.

Figure 6 illustrates this.

The transfer of information between the acquiring or transmitting functions. and the store unit requires the transfer of two sets of information; the data word corresponding to the symbol which needs to be displayed must be transferred, and address information defining its position in the page display must also be available. On relatively complex systems this is best achieved by a bus structure which more than one module can use.

The simplest way of achieving this is to allocate separate lines to the data and addressing information as in U.K. Patent Application No. 36842/76 (Serial No.

1585100). An alternative method is to use time division multiplexing to send the addressing information on the same lines as the data. One way of doing this is to precede any stream of symbol defining data words by one or two data words carrying addressing information. The first of these words would specify the row into which the first symbol specifying word was to be placed and whether a second word of addressing information was to follow. The second word of addressing information, if present, would specify the position within the row of the first symbol specifying word.

If no second word of addressing information is present, the first symbol specifying word will refer to the first symbol of the row.

In both cases, any subsequent data words, will specify symbols in sequential positions with the row. This is illustrated by Figure 7.

The module controlling the flow of data between the other functions has to provide two sets of addressing information. One of these is associated with the display function and makes the correct data word from the store available to the display function at any time. The other set of addressing information is extracted from the acquiring or transmitting functions via the bus, or generated from previous information of this sort if a multiplexed bus is used. The control module normally passes the first of these sets of addressing information to the store to provide a display of the store contents, but switches to the second set when a transfer of data to or from the store is required by an acquiring or transmitting module.

At all times these two sets of addressing information are compared with each other, and an output produced when these match.

This output can be used to cause the display of a cursor in the display position of the character next to be involved in a transfer of data to or from the store.

The modules or units performing the function of acquiring the data to be written into the store will normally perform some check routine to ensure the veracity of the data received. In particular, a module intended to acquire teletext data is required to both detect and correct certain types of error in the incoming data. Those parts of the data to which this process is to be applied are transmitted in what is usually referred to as 'Hamming Code' to make this possible.

This process involves the use of several 'parity' checks and these checks require some circuitry which may be made common to two or more parity checking circuits. One way of making use of this commonality in processing teletext signals is illustrated in Figure 8, which shows circuitry to evaluate the Teletext Hamming codes and to correct certain types of error.

The store and display subsystem can operate in two modes, either displaying the page of information currently in store, or transferring information between the store and display subsystem and the external acquisition and transmission subsystems.

The subsystem is normally operating in the first of these modes, i.e. displaying the information currently in store. The store address control unit (B) produces a sequence of addressing information which causes the store (A) to place on the data address bus the information it contains. This is accepted by the control code and symbol generation ROM(E) which interprets this information and provides either control outputs for use by the Text I Graphics / Picture control Module (D) or Forty bits of segment information defining the shape of a symbol to be displayed for use by the segment selection, interpolation and serialisation module (C).

This module (C) selects from the forty-five segments available those relevant at any particular instant, performs an interpolation process generally known as character rounding on these segments to improve the legibility of the displayed symbol, and produces a serial data stream suitable for producing a display of the symbol on a television type display. Before being passed to the display device, this data stream is modified by the Text I Graphics / Picture control Module (D), which, in response to control signals from module E and user generated controls, may add information on the colour of display required, may blank the symbol or cause it to flash. Module E also provides signals to blank the normal television picture in teletext applications.

Module C also sends information to the store address control (B) to enable it to produce the correct addressing information sequence.

Occasionally the subsystem receives a signal on the data transfer line to indicate that a module external to the subsystem wishes to use the data and address bus to transfer information to or from the subsystem. Two sorts of information are involved in such a transfer of addressing information specifying the location in the store of the symbol or control information involved in the transfer, and the symbol or control information itself. A convention is adopted whereby the first information word placed on the bus after a timing pulse, for instance, the television line flyback pulse, always specifies the display Row Number of the symbol or control information involved in the transfer.This convention eliminates the necessity to provide a separate data line to indicate whether the main bus carries addressing or symbol information at any instant, this first word of addressing information also indicates whether the next word of information to be placed on the bus will specify the position within the row to which the following symbdl information will refer. If this second word of addressing information is not present, then the position at the start of the row is inferred. Once the addressing information has been passed via the bus to the store address module (B), transfers of symbol information take place involving sequential locations in the store, commencing at the location specified by the addressing information. The timing of these transfers is controlled by the 'data true' line.

Page Store (A) consists of conventional memory devices.

The Store Address Control (B) contains four circuit modules. These are: (a) counters and control circuits to generate the address sequence needed for the display function.

(b) counters, latches and controls required to extract and increment addressing information placed on the bus by external units.

(c) circuitry to compare the addresses generated by the above modules and generate a signal suitable for producing a cursor to indicate the position on the display of the symbol to be involved in the next data transfer.

(d) circuitry to correct the addressing data generated by (a) and (b) above in Row/ Position format (11 bits) to a format giving better packing density in the Page Store (10 bits).

The Control Code and Symbol Generation ROM (E) is based on a conventional ROM structure, but is specially configured for this application. The majority of the symbols are generated by a seven by five matrix, since this is all that is required, though for some symbols this expands to a nine by five matrix. Certain inputs from the store are decoded by similar structures to provide control signals, some of which are passed to module D and some are used in module E to change the signals generated by certain inputs.

The segment, selection, interpolation and serialisation module (C) contains circuits to select those outputs of module E which are relevant at any moment, interpolation circuits to enhance the legibility of the displayed symbols, serialisation circuits to present the processed information in a form suitable for creating a television type display and the counters and control circuits needed to control these operations and the generation of the required address sequence in module B.

The Text I Graphics I picture control module (D) contains control circuits which modify the output of module (C) in response to the control outputs of module E and user specified control signals.

The store address control module may also include circuitry for responding to a first signal from the bus indicating a particular row of display and a second signal indicating the position of a particular character in the row such that that particular character is the first character in that row to be involved in a data transfer between the store and a data transfer device.

According to another aspect of the invention in apparatus for the display of information on a television type display there are provided an information store unit and one or more data transfer devices, and a bus arrangement interconnecting the store unit and said data transfer devices, the store unit including a data memory for storage of the information to be displayed, a read only memory responsive to information signals derived from said data memory to provide display element signals for said television type of display, and logic circuit means responsive to predetermined combinations of said display element signals to generate additional display element signals for said display.

The bus structure referred to herein may for example comprise a plurality of electric conductors some at least of which are utilised at respective times both for address and for data transfer.

WHAT WE CLAIM IS:- 1. Apparatus for the display of information on a television type display wherein there are provided an information store unit, one or more data input units and a character generator unit, and a bus arrangement interconnecting the store unit, said one or more data input units and said character generator unit over which pass electric signals representing said information and the destination of said information.

2. Apparatus in accordance with Claim 1 wherein said bus arrangement comprises a plurality of electric conductors, and electric signals applied to said conductors representing information to be transferred between said units are preceded on some at least of said conductors by electric signals representing a store address or circuit means to which said information is to be transferred.

3. Apparatus in accordance with Claim 1 or Claim 2 wherein said data input units comprise receiver and decoder means responsive to coded data received over a telephone line or modulated on a broadcast television carrier during field blanking intervals.

4. Apparatus in accordance with Claim 1 or Claim 2 wherein the character generator comprises a read only memory or a programmable read only memory and the information store unit comprises a random access memory.

5. Apparatus in accordance with any one of Claims 1 to 4 wherein there is provided

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. word of addressing information is not present, then the position at the start of the row is inferred. Once the addressing information has been passed via the bus to the store address module (B), transfers of symbol information take place involving sequential locations in the store, commencing at the location specified by the addressing information. The timing of these transfers is controlled by the 'data true' line. Page Store (A) consists of conventional memory devices. The Store Address Control (B) contains four circuit modules. These are: (a) counters and control circuits to generate the address sequence needed for the display function. (b) counters, latches and controls required to extract and increment addressing information placed on the bus by external units. (c) circuitry to compare the addresses generated by the above modules and generate a signal suitable for producing a cursor to indicate the position on the display of the symbol to be involved in the next data transfer. (d) circuitry to correct the addressing data generated by (a) and (b) above in Row/ Position format (11 bits) to a format giving better packing density in the Page Store (10 bits). The Control Code and Symbol Generation ROM (E) is based on a conventional ROM structure, but is specially configured for this application. The majority of the symbols are generated by a seven by five matrix, since this is all that is required, though for some symbols this expands to a nine by five matrix. Certain inputs from the store are decoded by similar structures to provide control signals, some of which are passed to module D and some are used in module E to change the signals generated by certain inputs. The segment, selection, interpolation and serialisation module (C) contains circuits to select those outputs of module E which are relevant at any moment, interpolation circuits to enhance the legibility of the displayed symbols, serialisation circuits to present the processed information in a form suitable for creating a television type display and the counters and control circuits needed to control these operations and the generation of the required address sequence in module B. The Text I Graphics I picture control module (D) contains control circuits which modify the output of module (C) in response to the control outputs of module E and user specified control signals. The store address control module may also include circuitry for responding to a first signal from the bus indicating a particular row of display and a second signal indicating the position of a particular character in the row such that that particular character is the first character in that row to be involved in a data transfer between the store and a data transfer device. According to another aspect of the invention in apparatus for the display of information on a television type display there are provided an information store unit and one or more data transfer devices, and a bus arrangement interconnecting the store unit and said data transfer devices, the store unit including a data memory for storage of the information to be displayed, a read only memory responsive to information signals derived from said data memory to provide display element signals for said television type of display, and logic circuit means responsive to predetermined combinations of said display element signals to generate additional display element signals for said display. The bus structure referred to herein may for example comprise a plurality of electric conductors some at least of which are utilised at respective times both for address and for data transfer. WHAT WE CLAIM IS:-

1. Apparatus for the display of information on a television type display wherein there are provided an information store unit, one or more data input units and a character generator unit, and a bus arrangement interconnecting the store unit, said one or more data input units and said character generator unit over which pass electric signals representing said information and the destination of said information.

2. Apparatus in accordance with Claim 1 wherein said bus arrangement comprises a plurality of electric conductors, and electric signals applied to said conductors representing information to be transferred between said units are preceded on some at least of said conductors by electric signals representing a store address or circuit means to which said information is to be transferred.

3. Apparatus in accordance with Claim 1 or Claim 2 wherein said data input units comprise receiver and decoder means responsive to coded data received over a telephone line or modulated on a broadcast television carrier during field blanking intervals.

4. Apparatus in accordance with Claim 1 or Claim 2 wherein the character generator comprises a read only memory or a programmable read only memory and the information store unit comprises a random access memory.

5. Apparatus in accordance with any one of Claims 1 to 4 wherein there is provided

a store address control module connected to the information store unit to control the reading and writing of information into and out of the information store unit.

6. Apparatus in accordance with Claim 5 wherin the store address control module is arranged to produce a cursor output to indicate on the display the address in the store unit at which information is being written at any instant.

7. Apparatus in accordance with Claim 5 or Claim 6 wherein the store address control module includes circuit means for generating a sequence of data memory address for the sequential read out of a page of data to produce a continuous display.

8. Apparatus in accordance with any preceding claim wherein the character generator unit includes a read only memory responsive to information signals derived from said information store unit to provide display element signals for said television type of display and logic circuit means responsive to predetermined combinations of said display element signals to generate additional display element signals for said display.

9. Apparatus for the display of information substantially as hereinbefore described with reference to Figure 9 of the accompanying drawings.