WO1986006195A1

WO1986006195A1 - Display apparatus

Info

Publication number: WO1986006195A1
Application number: PCT/GB1986/000214
Authority: WO
Inventors: John Alan Eggleden; Clive William Warder Read; Carl John Orsbron; Julian Malcolm Coles
Original assignee: Telebeam International Limited
Priority date: 1985-04-16
Filing date: 1986-04-15
Publication date: 1986-10-23
Also published as: EP0221099A1; GB2184280B; GB8622042D0; GB2184280A; AU5696786A

Abstract

A display apparatus capable of displaying a plurality of alpha-numeric characters includes a display device (2) comprising a matrix of picture elements disposed in a plurality of rows and columns and means for activating selected combinations of the elements to display a full range of alpha-numeric characters. All, or substantially all of the characters are each displayed in a sub-matrix occupying only 5 rows and 5 columns of the matrix of picture elements.

Description

Display Apparatus

The present invention relates to a display apparatus including a matrix of picture elements and capable of displaying a full range of alpha-numeric characters as sub-matrices.

In a well known matrix display device alpha¬ numeric characters are each represented by a respective 5 X 7 sub-matrix of square energisable elements. 'Such an arrangement is able to depict the full range of alpha-numeric characters quite satisfactorily. While only a few characters are to be displayed, for example. - if one or two lines only of text are to be shown, then the overall number of elements is not too great nor is the size of display too large. If, however, it is desired to display an entire page of text, then a very large number of picture elements, each of which has to be individually controlled, are required. Provided ^" that cost and space are no object, it is possible to expand the size of such a display, but in practice cost is usually very important and in many applications, for example if the display is to be incorporated in a portable apparatus, size is also important. -Accordingly attempts have been made to display alpha-numeric characters in smaller sub-matrices, it being recognized that this is desirable. US-A-3 872 463 describes two forms of alpha¬ numeric display system. In a first form an array of elements consists of sixteen. icture elements arranged in five rows with four elements in one row and three elements in the other rows. The specification illustrates how numerals can be portrayed by such a display and comments that a substantial number of upper and lower case alphabet letters and/or mathematical and punctuation symbols can be portrayed although how this is to be done is not described. In a second form, an arrayof elements consists of twenty four picture elements arranged in 5 rows with six elements in a bottom row, five elements in the first and fourth row and four elements in the second and third rows. In this case the specification shows how all the upper and lower case alphabet letters can be portrayed.

US-A-3 872 464 describes a cold cathode discharge type display in which letters are said to be displayed by an array of picture elements comprising five rows with four columns in each row. Each array of picture elements is separated from an adjacent array by a further group of discharge cells which store a binary code of a letter subsequently to be displayed. US-A-3 872 464 contains no indication as to the range of alpha-numeric characters that can be displayed and no disclosure as to how those characters could be displayed. - 3 -

It is an object of the invention to provide a display apparatus that is able to display a full range of alpha-numeric characters in sub-matrices having relatively few picture elements. According to the invention there is provided a display apparatus capable of displaying a plurality of alphanumeric characters, the apparatus including a display device comprising a matrix of picture elements disposed in a plurality of rows and columns, and means for activating selected combinations of the elements to display a full range of alphanumeric characters, characterized in that all or substantially all of the characters- are each displayed in a sub-matrix occupying 5 rows and 5 columns of the matrix of picture elements. It is surprising that clear characters can be obtained from a sub-matrix that is only 5 X 5; we have ^• found, however, that this is possible and one particular set of characters even including fractions (1/2, 1/4 and 3/4 in this particular example) is fully described below by way of example with reference to the drawings. The set of characters illustrated are suitable for English speaking countries. We have also devised modified versions of the sets for use in other countries where for example accents may have to be included. In the example described all of the upper case characters are within the 5 X 5 sub-matrix but some of the lower case, characters extend below the 5 X 5 sub-matrix; while there are relatively few such charaters we have found that such an arrangement is satisfactory. An alternative arrangement is to employ upper case characters only.

By using a sub-matrix as small as 5 X 5 the number of picture elements used to generate each charac¬ ter is substantially reduced from that required with a 5 X 7 sub-matrix. Thus for a given si2e of picture element the area required to depict one character is much reduced without affecting the density of connections that have to be made to the matrix of picture elements. It is also possible to make the picture elements of the 5 X 5 sub-matrix bigger without increasing the area occupied by the display beyond that occupied by a display using a 5 X 7 sub-matrix and in this case the density of connections that have to be made to the matrix of picture elements is reduced. The use of a 5 X 5 matrix is of particular advantage in applications where the size of the display device is to be minimised. The rows and columns in which the picture elements are disposed are preferably orthogonal.

The picture elements may be of oblong shape with their minor dimensions extending across the widths of the characters. We have found that a satisfactory character set can be obtained using oblong picture elements. In providing oblong elements whose major axes extend "down" the display, comparatively more space is provided to make connections to the sides of the display. In the embodiment of the invention to be - 5 - described the major dimension of each oblong picture element is about 30 per cent greater than its minor dimension.

Adjacent sub-matrices- for displaying characters are preferably separated from one another by further energisable picture elements. These picture elements may be used in displaying those lower case characters that require a sub-matrix bigger than 5 X 5. Adjacent sub-matrices in the same row may be separated from one another by a single column of picture elements and adjacent rows of sub-matrices may be separated from one another by a single row of picture elements. This arrangement permits the display of contiguous graphics shapes. Adjacent sub-matrices in the same row preferably have a centre-to-centre spacing of 6 columns. Similarly, adjacent sub-matrices in the same column preferably have a centre-to-centre spacing of 6 rows and this applies even when a lower case character that occupies 6 rows is being displayed. By using the normally vacant row that spaces adjacent lines of text to accommodate those lower case letters that benefit from the extra row of picture elements, there is no increase in the overall number of picture elements required in the display over that which would be required if all the characters were depicted within 5 rows of picture elements. At the same time because only a few lower case characters require this extra row the overall clarity of the display is not impaired by what is only an occassional merging of adjacent lines of characters.

The display device preferably has a capacity enabling it to display a page of information rather than merely one or two lines. Thus it is advantageous for the device to be capable of displaying at least ten lines of text information.

The display device may have a capacity of approximately 24 lines, each of approximately 40 characters, this being the capacity required for a standard page of teletext in the United Kingdom. The numbers quoted above are approximate because a very slightly smaller or larger display could provide a workable arrangement and, in the case of the number of characters, also because the first character of each line of a conventional teletext transmission is a control character and that character need not therefore be displayed. A display of the above capacity may occupy an area of less than 100 cm².

The picture elements may be liquid crystal elements.

The picture elements are preferably energised substantially at the same time in more than one region of the display. For example, picture elements in an upper and a lower region of the display may be energised at substantially the same time. Energising more than one region of the display at a given time has the effect of permitting the energisation of each picture element for long enough to provide a display with good contrast (and therefore good legibility) despite the relatively large size of the display.

According to another aspect of the invention there is provided a portable apparatus- including a display apparatus as defined above. The display device is of particular value when used on a portable apparatus because it can occupy less space. The apparatus may be one which is arranged to receive information signals from a remote source and display those signals. In particular the apparatus may be a teletext receiver. One particular form of receiver in which the display apparatus may be incorporated is that described in our co-pending PCT Application filed on the same date as this application and entitled "Text Receiver". The disclosure of that application is incorporated herein by reference. The present invention also provides a method of displaying alphanumeric characters on a display device including a matrix of picture elements disposed in a plurality of rows and columns, the method comprising activating selected combinations of the elements to display a full range of alphanumeric characters, characterized in that all or substantially all of the characters are each displayed in a sub-matrix occupying 5 rows and 5 columns of the matrix of picture elements.

A- hand-held teletext receiver incorporating a display apparatus in accordance with the invention will now be described by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a plan view of the teletext receiver, Fig. 2 is a block diagram representation of a teletext data reception and processing system suitable for operating a ulti- plexed display device to provide the hand-held teletext receiver of Fig. 1, Fig. 3 is a block diagram representation of the timing and display control arrangements of the teletext data processing system represented by Fig. 2,

Figs. 4a to 4d_ illustrate the complete set of characters (excluding graphics) displayed by the receiver by means of a 5 X 5 matrix of picture elements, an "X" denoting an energised picture element, the matrix characters being accompanied by their non-matrix equivalents, Fig. 5a illustrates diagrammatically the display of sample characters on the device, and, Fig. 5b illustrates diagrammetically the arrangement of the display device as a whole. Referring to Fig. 1, the teletext receiver shown is a portable, personal teletext receiver and includes a generally rectangular-sided -enclosure 1 of approximate dimensions 220 mm (length) by 130 mm (width) by 38 mm (depth) having openings in a major surface to accommo- date in one half of the surface, a display device 2 of approximate dimensions 82 mm (height) by 100 mm (width), and, in the other half of the surface, a plurality of push-key members. The size of the teletext receiver is therefore such that it can comfortably be held in an adult person's hand and is truly portable.

The push key members include a power control switch 3, a first group 4 of keys labelled 0 to 9, respectively, a second group of keys 5 labelled HOLD, REVEAL, AUTO PG and LAST PG, respectively, a channel select key 6 labelled CHSELECT, and a SEARCH key 7. The teletext receiver also includes a scale 8 for a bar graph signal strength indicator and a retractable or plug-in aerial 11 (not shown in Fig. 1). The display device 2 is a liquid crystal display device consisting of a matrix of energisable picture elements capable of displaying a full page of teletext information which may include alphanumeric and graphics characters. The display device is described in more detail below.

Referring to Fig. 2, the functional components of the teletext receiver of Fig. 1 include the aerial - lO -

ll, a tuning system 12, a computer 13, a control key¬ board 14^", a data slicer 15, a data acquisition system 16, a timing signals generator and liquid crystal display driver 17, an alterable data store 18, a clock oscillator 20, an analogue-to-digital converter 21, and a power management circuit 22. The teletext receiver makes use of standard batteries.

A front end amplifier is included in the tuning system 12 in order to provide the necessary UHF signal- receiving capability in compact form.

The tuning system 12 is arranged to be tunable by digital commands, and, as shown in Fig. 2, is arranged to receive digital- uning commands from the computer 13. The computer 13 is arranged to carry out the following functions:-

(i) Setting up the tuning synthesiser (part of the tuning system 12) to receive a television signal on a specified channel.

(ii) Setting up the data acquisition system 16 to extract teletext signals from the video signal provided by the tuning system 12.

(iii) Responding to and executing commands entered through the keyboard 14, including the REVEAL operation. (iv) Effecting modification of the contents of the alterable data store 18, as appropriate, to reflect commands entered through the keyboard 14. (v) Clearing the display at certain times. (vi) Checking on the strength of the signal being received by the tuning, system 12 and the condition of the power supply batteries, and causing the display of the results of the checks.

Referring still to Fig. 2, the computer 13 includes a processor, a program memory, a data memory, reset control circuits, address decoding circuits, and input/output-control circuits. The computer 13 uses the clock oscillator 20 as the source of its timing pulses. Some of the component parts of the computer 13 are provided by a 80C49 type microprocessor circuit available from various manufacturers. The computer 13 includes a substantial proportion of CMOS devices as a means of minimising power consumption. Output control circuits of the computer 13 are disabled by a signal from the timing signals generator and display driver 17 when the computer is inactive, in order to ensure that the computer cannot corrupt data by placing data or address signals on to shared data and address buses at times when the computer is not active. The computer 13 also includes a character read only memory (ROM) the use of which is described below.

The data slicer 15, the data acquisition system 16, and the alterable data store 18 are interconnected with each other and with the timing signals generator 17 and the computer 13. The timing signals generator 17 is - 12 -

arranged to repeat a cycle of operations' of 20 milli¬ seconds duration which corresponds to the transmission period of a television field.. Each cycle of operation includes periods for (i) transforming any available teletext signal into lines of teletext data and storing the data in the alterable data store IS, (ii) altering, by the computer 13, the contents of the alterable data store 18 or of registers included in the data acquisi¬ tion system 16 and the timing signals generator and display driver 17 (in accordance with keyboard presses, for example) and (iii) transforming, by means of the timing signals generator and display driver 17, the contents of the alterable data store 18 into signals used to operate the display system. Referring still to Fig. 2, part of the alterable data store 18 is arranged to act as a character read only memory (ROM) and the remainder of the alterable data store 18 is used to store the page of data displayed as teletext information at any time. The alterable data store 18 consists of 2048 X 8 addressable storage elements (nominally 2K X 8), 1024 X 8 elements of which are used as the current page store, that is, as the store for the data being displayed as teletext information. The part of the alterable data store 18 arranged to act as a character ROM is made to receive the full range of ASCII control and display codes from a character and display code ROM located in the computer 13 when the receiver is first switched on. The timing signals generator and display driver 17 is involved in the transfer of the ASCII teletext codes from the character ROM in the computer 13 to the appropriate addresses in the alterable data store 18. The alterable data store 18 is then used by the timing signals generator and display driver 17 as the- source of ASCII codes required to transform the teletext data, held in the remainder of the alterable data store 18, into data suitable for presentation to the liquid crystal display. The sequence in which data is read from the alterable data store 18 is dictated by the structure of the display itself, the display structure being described below with references to Figs. 5a and 5b. Referring still to Fig. 2, the analogue-to- digital converter 21 is arranged, under the control of the computer 13, to sample the voltage level of the batteries in the power supply 22 and to digitise the sampled value for assessment by the computer 13 as to the battery condition.

The analogue-to-digital converter, referred to above, is used also for providing the signal strength indication at the bottom of the liquid crystal display device 2 adjacent the scale 8 as a bar graph. In the presence of a strong input signal to the tuner system 12, the timing signals generator and display driver 17 receives a composite sync signal from the data slicer 15 and derives, from the' composite sync signal, two time slot signals one of which is passed to the data acquisition system .16 and the other of which goes to the computer 13. The data acquisition system 16 and the computer 13 are rendered active at the same time by the timing signals generator and display driver 17 by the application of the time slot signals referred to. The time slot signals are arranged to cover lines 7 to 22, of the odd fields, and lines 320 to 335, of the even fields, of a television transmssion (these being the teletext-carrying lines) . The timing signals generator and display driver 17 provides a short (.5μS) synchronising pulse at the beginning of each of the teletext-carrying lines referred to, and the data slicer 15 and the data acquisition system 16 are arranged to extract data carried in lines "marked" by the synchro¬ nising pulse from the timing signals generator and display driver 17. On receipt of the synchronising^' pulse, the data slicer 15 halts its clock and waits for teletext data from its connection to the tuning system 12. It then passes on received data, with its now regenerated clock signals, to the data acquisition system 16 which examines the run-in sequence that precedes teletext data (alternate l's and 0's trans- mitted at the beginning of each teletext line). The data acquisition system 16 issues a new synchronising pulse to the data slicer 15 to alter the data slicer - 15 -

clock and synchronise it to the teletext^' data pattern. The data acquisition system 16 is partly controlled by the computer 13 which instructs it to select particular pages of a teletext magazine. The data acquisition system 16 transfers, to the alterable data store 18, teletext pages identified to the data acquisition system 16 by the computer 13. When appropriate, time informa¬ tion is copied to the alterable data store 18. The interconnection of the computer 13, the data acquisition system 16, and the alterable data . store 18 is such that the computer 13 may arrange either for the data acquisition system 16 to transfer data to the alterable data store 18 to provide up-to-date information for display or for the data acquisition system 16 to transfer data to a non-existent store, thereby dumping that data and holding the previous data in the alterable data store 18 for display.

The teletext receiver has two modes of operation, one being the tuning mode during which channel selection is achieved, and the other being the teletext mode during which the selection and display of the teletext data available on the selected channel is achieved. The full range of function performed by the timing signals generator and display driver 17 may be understood by referring to Fig. 3, which shows that the timing signals generator includes a video signals generator 71, a character counting and address logic circuit 72, a character decoder 73, and ^"a liquid crystal display control circuit 74. The timing signals generator and display driver 17 includes various input and output multiplexers, associated with a sequence controller 75, required for operation with buses, in known manner.

Referring to Fig. 3, the video signals generator 71 is arranged to receive composite sync television signals and also signals from the clock oscillator 20 (Fig. 2), and to provide, from the composite sync signal, or in the absence of the composite sync signal, from the clock signal, the synchronising pulse and the time slot signal for the data acquisition- system 16 and the data slicer 15 and the time slot signal for the computer 13. The video signals generator 71 also provides the timing pulses for the character counting and address logic circuit 72 and the character decoder 73, which together with the fixed data store 19 (Fig. 2) effect the transformation of the contents of the alter¬ able data store 18 into the signals required to effect, by way of the display control circuit 74, the display of the data stored in the alterable data store 18 by means of a liquid crystal display device.

As explained below, data held in the alterable data store 18 are transformed for display in terms of picture element matrices by means of the character decoder 73, which actually transforms the data from ASCII code to "matrix" code, assisted by the character count and address circuit 72 which supplies addresses for application to the alterable data store 18.

In the teletext data -processing system the timing signals generator and display driver 17 provides control signals for a liquid crystal display (not shown in Fig. 2) having a fully populated matrix of display picture elements. The timing signals generator and display driver 17, as indicated above, controls the overall operation of the system on the basis of a 20 milliseconds cycle time, allocating some 86% of the available time to the display functions, 5% of the time to data acquisition, and the remainer of the time to the computer-related functions". Additionally, the timing signals generator and display driver 17 is capable of operation without the synchronising signals from a television transmission and is arranged to continue to generate the time slot signals for the data acquisition system 16 and the computer 13 in the absence of a television signal. Referring still to Fig. 3, the manner of opera¬ tion of the character count and address circuit 72 and the character decoder 73 is largely dictated by the manner in which the display device is operated. The alterable data store 18 (Fig. 2) includes a IK X 8 bits memory (actually 1024 X 8 bits) which contains a repre¬ sentation of 24 lines of 40 characters of teletext data. The character count and address circuit 72 controls the - 18 -

sequence in which data is read from the alterable data store 18^'and applied to the character decoder 73. The data stored in the alterable data store 18 includes additional information as to the form of each character or group of characters (lower case alphabetical charac¬ ters, upper case alphabetical characters, double height characters, and the like), and the additional informa¬ tion is also presented to the character decoder 73 in order that the specific form of each character is generated and displayed. The period allocated to applying a page of teletext data to the display device exceeds the time required to carry out the display function and the excess time is taken up by allowing ^"the display control system to continue driving beyond the last line of picture elements, that is off the display device.

The timing signals generator and display driver 17 is capable of providing control signals for double height characters, which occupy two adjacent rows, by subtracting 40 from the address applied to the alter¬ able data store 18 in extracting the data for the lower of the two rows. Double height characters may be dis¬ played in either half of the display device, and a double height character which occupies lines 12 (upper half) and 13 (lower half) of the display device is dealt with by noting the double height requirement through the end of page reset. The liquid crystal control circuit 74 is arranged as a 480 stage shift register which is provided with data for display and clock pulses for driving the shift registers. Referring to Fig. 5a, which illustrates in detail a portion of a liquid crystal display device made up of a uniform matrix of picture elements which are selec¬ tively energisable to represent alphanumeric or graphics characters. Each alphanumeric character may be represented by a 5 X 5 sub-matrix of picture elements, adjacent columns of characters being separated by one column of picture elements, and adjacent rows of charac¬ ters being separated by one row of picture elements. The picture elements separating the characters are energisable elements permitting the display of graphics characters including the active separating elements to provide contiguous graphics shapes. The picture elements are of rectangular shape of height about 30 per cent greater than their width (Fig. 5a is not to scale in this respect) . The display device consists of a matrix of 144 lines (lines numbered 0 to 143) of picture elements and 234 columns of picture elements, giving it a capacity of 24 lines each of 39 characters. Each picture element is, in this example, .35 mm wide by .45 mm high.

Referring to Fig. 5b, the display device is divided electrically into an upper and a lower half each of 72 X 234 picture elements. The upper half and the lower half are so connected electrically as to be driven simultaneously line by line.- That is, the data to be displayed is provided for the uppermost row of picture elements (row 0) at the same time as the data for row 72, followed by the data for rows 1 and 73, and so on, until the data has been supplied to all 144 rows (rows numbered 0 to 143).

A 5 X 5 sub-matrix is a relatively small matrix to use in generating a full range of alphanumeric charac¬ ters. We have, however, devised suitable sub-matrices for displaying a full range of upper case and lower case alphanumeric characters ani these are indicated diagram¬ matically in Figs. 4a_ to 4d, where the picture elements that are energised to form each particular character are shown marked by the symbol "X". It will be seen that a few of the lower case letters make use of the picture elements in the row below the 5 X 5 sub-matrix and there¬ fore border directly on letters in the line below. We have found, however, that this does not unduly impair the legibility of the text while there are only a few such characters. In any case, it is not essential to employ lower case letters or those lower case letters that do make use of the picture elements in the row below the 5 X 5 sub-matrix may be shifted upwardly by one row of picture elements in which case they are accommodated wholly within the 5 X 5 sub-matrix. The present teletext receiver is .also capable of executing the HOLD GRAPHICS control command at a colour change in a modified form consistent with a monochrome display. In the execution of the HOLD GRAPHICS command at a colour change, the picture area corresponding to the colour change command is presented with the first four columns energised and the last two columns de-energised, providing a "break" between the two "colours". Further details of the structure and operation of the teletext receiver are given in our co-pending PCT application filed on the same date as this application and entitled "Text Receiver".

Claims

What we claim is:

1. A display apparatus capable of displaying a plurality of alphanumeric characters, the apparatus including a display device comprising a matrix of picture elements disposed in a plurality of rows and columns, and means for activating selected combinations of the elements to display a full range of alphanumeric characters, characterized in that all or substantially all of the characters are each displayed in a sub-matrix occupying 5 rows and 5 columns of the matrix of picture elements.

2. A display apparatus as claimed in claim 1 in which the rows and columns are orthogonal.

3. A display apparatus as claimed in claim 1 or 2 in which the picture elements are of oblong shape with their minor dimensions extending across the widths of the characters.

4. A display apparatus as claimed in claim 3 in which the major dimension of each picture element is about 30 per cent greater than its minor dimension.

5. A display apparatus as claimed in any preceding claim in which adjacent sub-matrices for displaying characters are separated from one another by further energisable picture elements.

6. A display apparatus as claimed in claim 5 in which adjacent sub-matrices in the same row are separated from one another by a single column of picture elements.

7. A display apparatus as claimed in claim 5 or 6 in which adjacent rows of sub-matrices are separated from one another by a single row of picture elements.

8. A display apparatus as claimed in any of claims 5 to 7 in which adjacent sub-matrices in the same row have a centre-to-centre spacing of 6 columns.

9.. A display apparatus as claimed in any of claims 5 to 8 in which adjacent sub-matrices in the same column have a centre-to-centre spacing of 6 rows.

10. A display apparatus as claimed in any preceding claim in which the display device is capable of displaying at least ten lines of text information.

11. A display apparatus as claimed in any preceding claim in which the display device has a capacity of approximately 24 lines, each of approximately 40 characters.

12. A display apparatus as claimed in claim 8 in which the display area is less than 100 cm².

13. A display apparatus as claimed in any preceding claim in which the picture elements are liquid crystal elements.

14. A portable apparatus including a display apparatus as claimed in any preceding claim.

15. A portable apparatus as claimed in claim 14 in which the apparatus is arranged to receive information signals from a remote source and display those signals.

16. An apparatus as claimed in claim 15 which is a teletext receiver.

17. A method of displaying alphanumeric characters on a display device including a matrix of picture elements disposed in a plurality of rows and columns, the method comprising activating selected combinations of the elements to display a full range of alphanumeric characters, characterized in that all or substantially all of the characters are each displayed in a sub-matrix occupying 5 rows and 5 columns of the matrix of picture elements.