EP0447274B1 - Display method and device for dot matrix screen - Google Patents

Description

The present invention relates to the method and to the electronic display device implementing a dot matrix screen. Among the dot matrix screens, the best known are liquid crystal screens also called LCD screens (from the initials of the English words Liquid Crystal Display), and in particular screens of the thin film transistor or TFT type (d 'after the initials of the English words Thin film transistor) and molecules of the nematic helical type generally called TN type (after the initials of the English words Twisted nematic).

It is known, from US Pat. No. 4,414,545, to keep in memory standard or special characters, all of the same size, for example 5 by 7 dots, in order to have a display on the screen at predetermined locations. corresponding to a grid of 5 by 7 when the characters are in this format. However, such a display is not flexible, since the character locations are predetermined and only one character format can be used.

The present invention aims to avoid or at least reduce these drawbacks.

This is achieved by allowing the characters to occupy any position on the screen and, for this, to define a primary position which determines where a character should be displayed on the screen.

According to the invention, there is in particular proposed a method of displaying on a dot matrix screen, consisting of: - preprogramming, in a first memory, at known addresses, which are called character codes, the points to be excited of an elementary surface, of predetermined dimensions and of any position on the screen, so that the characters displayed appear on the screen - to be stored in a second memory, line of characters by line of characters, the character codes of the successive characters to be displayed on the screen, the characters all require the same number of lines, y, of points on the screen - to command the reading of the first memory by the second memory, according to '' a regular line by line scan of the screen, so as to display on the screen, the position of a character code in the second memory defining the position, called the primary position, from which the character corresponding to this character code must be displayed on the screen - to read a line y second time from the second memory whose characters require y lines of dots on the screen - and, for this to write a character on the screen when the regular scanning goes through lines a to a + y- 1, at the intersection with columns b to b + x-1, where a, b define the primary position, in line and column, of the character to be written and where x is the number of columns of points of the elementary surface occupied by the character to be written.

According to the invention there is also proposed a display device on a dot matrix screen, characterized in that it comprises n first memories with n positive integer, in which are preprogrammed, at known addresses, which are called character codes , characters, that is to say the points to be excited of elementary surfaces of predetermined dimensions of the screen, so that these characters are displayed on the screen, at least n second memories associated respectively with the n first memories for contain character codes in positions presenting a one-to-one correspondence with the points on the screen, and means for writing character codes in the n second memories, for reading the stored characters, corresponding to these character codes, in the first associated memories in the second memories where these codes are written and to display a character read with the dots on the screen having a match one-to-one weighting with the position of the character code that determined the reading.

• la figure 1, un schéma d'éléments d'un dispositif d'affichage selon l'invention,
• la figure 2, un circuit de base de temps,
• la figure 3, un dispositif d'affichage selon l'invention,
• la figure 4, un schéma destiné à expliquer un dispositif d'affichage selon l'invention,
• la figure 5, un autre dispositif d'affichage selon l'invention.

The present invention will be better understood and other characteristics will appear from the following description and the figures relating thereto which represent:

• FIG. 1, a diagram of elements of a display device according to the invention,
• FIG. 2, a time base circuit,
• FIG. 3, a display device according to the invention,
• FIG. 4, a diagram intended to explain a display device according to the invention,
• Figure 5, another display device according to the invention.

In the various figures, the corresponding elements are designated by the same references. In the various electronic diagrams, the precise synchronization devices, which are part of current technology, have not been shown in order to make the drawings clearer and to simplify the description.

Figure 1 is a simplified diagram intended to facilitate the explanation of the operation of a display device according to the invention.

A liquid crystal screen, 1, is assumed to be able to display n = 4 lines of m = 4 characters each, CANE, DEFI, LIME and BAIL, these words being arranged one above the other; each character is arranged in an elementary surface equal to 1 / m.n = 1/16 of the useful surface of the screen. This elementary surface is a rectangle which has x points per line and y lines of points.

A PROM memory, 2, called character memory, is preprogrammed by rectangular areas of x boxes per line and of y lines; these memory areas therefore have a distribution of boxes identical to the distribution of the points in an elementary screen surface; that is to say that there is a one-to-one correspondence between the boxes of a memory area and the points of an elementary surface of the screen on which the character of the considered memory area is displayed. The preprogramming of the memory 2 consists of a preprogramming of one character per memory area, the binary elements 1 and 0 being arranged in the boxes whose positions correspond respectively to the points to be lit and to the points to be left off in an elementary surface of screen to obtain a given character. Thus, for example, memory 2 contains, among other things, the capital letters A to N of blue color; to facilitate understanding, it was not 1s and 0s that were represented in the memory areas of memory 2 but the characters defined by these 1 and these 0. Each memory area containing a character is identified by an address code consisting of the address of the first of its boxes which is read during a reading by horizontal scanning from left to right with movement of the reading line up and down; thus the letter A is at the address 0,0 and the letter L at the address y + 5x.

A RAM memory, 3, called code memory, contains the addresses where the characters to be displayed on the screen are found in memory 2; thus, to display the word CANE in blue capital letters on the first line of characters in screen 1, the first line of addresses in memory 3 comprises the following successive address codes: 0.2 × 0.0 2y, x 0.4x, likewise, to display the word DEFI in blue capital letters on the second line of characters on the screen, the character codes 0.3x 0.4x 0.5x and y, 2x are contained next in the second address line of memory 3. There is therefore a one-to-one correspondence between the character lines of screen 1 and the address lines of memory 3 and, in other words, the position of a character code in memory 3 defines the position, called primary position, from which the character corresponding to this character code must be displayed on screen 1.

To display on screen 1, the addresses of the same line of memory 3 are read y in succession.

When the ith address of a jth line of memory 3, with i and j respectively between 1 and m and between 1 and n, limits included, is read for the qth time, with q included between 1 and y limits included, the contents of the qth line of the memory area, of memory 2, corresponding to the address considered, is read and the 1s and 0s thus read serve respectively to switch on and leave off the x points of the qth line of that elementary surfaces of screen 1 which is located at the intersection of the ith column of elementary surfaces with the jth row of elementary surfaces.

When the addresses of the same address line from memory 3 have been read for the yth consecutive time, the reading from memory 3 is continued on the next line which is also read y there in succession and the reading is thus continued until the last line of memory 3, that is to say until the nth line, which is also read there times. Reading of the address lines from memory 3 then resumes from the first address line, in order to display again on screen 1 and this new display is identical to the previous one as long as the content of the memory 3 is not changed.

Thus, the device designed to carry out the electronic display on a liquid crystal screen, as it has been produced, comprises a set of counters which is shown in FIG. 2.

FIG. 2 shows a set of four counters Cx, Cm, Cy and Cn connected in series in this order to constitute a time base circuit. The first counter, Cx, is a modulo x counter which counts the display synchronization pulses of the points on the screen; when the counter Cx goes through zero it provides a counting pulse to the counter Cm; in addition, each of these counting pulses constitutes a reading pulse of a new address in the memory 3 and a command to transfer a parallel-serial shift register, 7, which will be represented in FIG. 3 and which serves the transfer to the screen 1 of the information stored in the memory 2 already described with the aid of FIG. 1. The counter Cm is a counter modulo m; when it goes through zero it provides a command pulse to read a line of characters from memory 3. It has been seen that each line of characters from memory 3 is read there in succession, this is why the pulses supplied by the meter Cm are counted in the counter Cy which is a modulo y counter and which therefore provides, at each of its zero crossings, a pulse for reading the next line of characters in the memory 3. The set of addresses in the memory 3 is content on n address lines; the counter Cn, which is a modulo n counter supplied by the next line reading pulses delivered by the counter Cy, therefore supplies, at each of its zero crossings, a pulse which means that a complete reading of the memory 3 comes to be performed.

The preliminary explanations given with the aid of FIGS. 1 and 2 will facilitate understanding of FIG. 3 which is an overall diagram of an electronic display device on a liquid crystal screen according to the invention.

FIG. 3 shows the screen 1, the character memory, 2, and the code memory, 3, which has already been mentioned during the description of FIG. 3. The memory 3 operates in association with a memory 3 ′ identical to memory 3. A multiplexing circuit, 6, symbolized by two switches controlled by a microcomputer 4, makes it possible to use one of the memories in working phase while the other is used in tracing phase; this solution of the two code memories is little used; the device being fast, it is useful only if the microcomputer is slow or risks being occupied with other tasks, in timeshare. In the positions occupied, in FIG. 3, by the switches of circuit 6, it is memory 3 which is in the tracing phase and memory 3 which is in the working phase; that is to say that the memory 3 ′ is connected to the microcomputer 4 which, according to information to be displayed on the screen 1, supplies it with the address codes corresponding to the next information to be displayed. The memory 3 is in the tracing phase, that is to say that a screen controller 5, controlled by the microcomputer 4, scans the memory 3 line by line to read the address codes according to the reading mode explained to using figure 2: reading address lines y times in succession.

The role of the screen controller is therefore to read that of the two memories 3, 3 ′ which is in the tracing phase; for this, the screen controller comprises the time base circuit according to FIG. 2. The role of the screen controller is also to ensure the transfer, to screen 1, of information corresponding to these read character codes; this information is extracted from the character memory, 2, as explained with the aid of FIG. 1 and the synchronization signals which serve for this transfer are supplied by the set of counters according to FIG. 2; the transfer between memory 2 and screen 1 is carried out by means of a parallel-series register, 7, with x positions, that is to say at as many positions as there are points in a line of an elementary surface of the screen 1 and of boxes per line in a memory zone of the character memory, 2, where a character is programmed.

$$\text{m = n = 60}$$

ce qui correspond à un écran de 480.480 points et à des mémoires de codes 3, 3′ capables de contenir 60.60 codes adresses.The above description has been implemented with the following values for the various parameters. $$\text{x = y = 8}$$

$$\text{m = n = 60}$$

which corresponds to a screen of 480,480 points and to memories of codes 3, 3 ′ capable of containing 60.60 address codes.

In the above, the elementary surfaces of the screen all had the same dimensions: x.y points. It is also possible, as will be shown below, to produce a display device where the elementary surfaces have different values according to the information to be displayed. Figures 4 and 5 are diagrams relating to an exemplary embodiment of such a display device.

FIG. 4 shows three distinct images EO, E1, E2, the superposition of which is represented by a circle with a + sign, in which three arrows arrive and from which an arrow starts again; this superimposition gives an image E which is the image to be obtained on a liquid crystal screen using a display device of the type which has been described with the aid of FIGS. 1, 2 and 3. The image EO corresponds to the background of the image E, the image E1 corresponds to information of the image E which are little modified and the image E2 corresponds to information of the image E which is often modified; in the images E1 and E2 broken lines indicate on the one hand the limits of the image E on the other hand the limits of the elementary surfaces occupied by each of the characters which constitute the information in these images.

FIG. 5 represents a display device designed to display on a screen, 1, an image of the type of image E of FIG. 4, from three signals which, taken in isolation, would give, respectively on the screen, the images E1, E2 and E3. This is why the display device according to FIG. 5 differs from that according to FIG. 3 by three circuits for memorizing codes and for memorizing characters and by summing, using a circuit addition 8, signals extracted from character storage circuits.

The display device according to FIG. 5 comprises a microcomputer 4 which defines in the surface of the screen 1 three distinct zones corresponding respectively to the zones occupied on the screen by the images EO, E1 and E2 of FIG. 4; each of these zones is treated as the entire image is processed in the display device according to FIG. 3. That is to say, in order to obtain the image E1 on the screen 1, the device comprises, d firstly, two code memories 31, 31 ′ and a multiplexing circuit 61 connected between the microcomputer 4 and a screen controller 5, in the same way as circuits 3, 3 ′ and 6 in the device according to fig 3 and, on the other hand, a character memory 21 and a parallel-series shift register connected between the screen controller 5 and an input of the addition circuit 8 whose output is connected to the input of video signal from screen 1. To obtain the image E2 on screen 1, the display device according to FIG. 5 has circuits 32, 32 ′, 62, 22 and 72 respectively similar to circuits 31, 31 ′, 61, 21 and 71 and connected identically. To obtain the EO image of FIG. 4 on the screen 1, the display device according to FIG. 5 does not have two but a single code memory, 30, connected between the microcomputer 4 and the controller. screen 5 because it is expected that the address codes contained in this memory will only very rarely be modified; to obtain the EO image there is therefore no multiplexing circuit, on the other hand there is a character memory 20 and a parallel-series shift register 70 connected in the same way as the circuits 21 and 71.

It should be noted that the processing in three parts of the image to be displayed on the screen 1 is intended to simplify the programming of the code memories; in fact when, for example, only the content of the information of the kind of that of the part E2 of the image E of FIG. 3 has to be modified, this avoids having to redo all the programming which relates to the background of the image and the little modified part of the image, that is to say which relate to the information of the kind of that of the parts EO and E1 of the image E of FIG. 3.

It should also be noted that, in the example according to FIGS. 4 and 5, the elementary surfaces on the screen are not the same depending on whether they are used to display the EO image, the E1 image or the image E2; for the image EO the elementary surface is one of square of dimensions a.a, for the image E1 it is a rectangle of dimensions 1.5.3a and for the image E2 it is a rectangle of dimensions 2a. 3a.

In the foregoing, the information to be displayed was limited to numbers, letters and a screen background, and, for the sake of simplicity, they have been called characters; more generally, these characters can consist of any drawing provided that the precision necessary for the representation of this drawing on the screen does not exceed the line precision that it is possible to obtain with the screen.

The examples described above are intended to make quickly understand how the invention works and, for simplicity, describe a display where the characters are always regularly distributed on the screen. In reality, this is only a special case because, according to the invention, the code memory or memories comprise as many lines and boxes as the screen comprises lines and dots per line, so that any point screen can be used as primary position; this leads in the circuits, to some modifications relating to current technology and which have not been described in order to make the drawings clearer and to simplify the presentation.

It should be noted that it is possible to represent animated characters, that is to say whose representation moves on the screen; a movement in the plane of the screen can always be reduced to the sum of a translation and a rotation, to represent an animated character it is necessary to modify the position of the character code in the code memory as a function of the translation at perform, and modify the value of the code to take account of rotation. This is only possible because, according to the invention, the code memory or memories comprise as many lines and boxes as the screen comprises lines and dots so that any point on the screen can serve as primary position. In addition, when an animated character is made up of identical patterns, regularly distributed over a circle, and when the density, on the screen, of the points used to represent this animated character is such that, in a rotation, a pattern takes instead of the following after a sequence of p images on the screen, it suffices to keep in the character memory only p different characters corresponding to this sequence of p images. So to represent the movement of rotation of a watch dial made of a large line for each hour, it suffices to keep in character memory only thirty different characters insofar as for a line to take the place of the following, there are thirty successive images, that is to say one image per degree of rotation. It should also be noted, when representing an animated dial on a screen, that, if the dial includes, for example, figures, it is possible to rotate these figures with the dial but keeping their orientation , that is to say that the top and the bottom of the figure remain respectively turned up and down of the screen in order to facilitate the reading of these figures; for this the graduations of the screen will be treated as a first animated character and the figures as other characters which will follow the movement of the graduations.

The present invention is not limited to the examples described, this is how the elementary surfaces may not all be of the same dimensions for the characters stored in the same character matrix, but it is then necessary for the screen controller to take them into account. counts for the number of successive times that a character must be read in a character memory.

It is also possible, instead of scanning the screen line by line, to control the screen scan so as to display character after character.

Claims (6)

1. Method of displaying on a dot-matrix screen (1), consisting: - in preprogramming, in a first memory (2; 20, 21, 22), at known addresses, which are called character codes, the dots to be excited of an elementary surface, of predetermined dimensions (x, y) and at any position on the screen, so that given characters are displayed on the screen - in storing, in a second memory (3, 3′; 30, 31, 31′, 32, 32′), row of characters by row of characters, the character codes of the successive characters to be displayed on the screen, the characters all requiring the same number of rows, y, of dots on the screen - in causing the first memory (2; 20, 21, 22) to be read by the second memory (3, 3′; 31, 31′, 32, 32′), on the basis of a regular row-by-row scanning of the screen (1), so as to form a display on the screen (1), the position of a character code in the second memory defining the position, called primary position, from which the character corresponding to this character code is to be displayed on the screen (1) - in reading, y times over, a row of the second memory the characters of which require y rows of dots on the screen - and, in order to do that, in writing a character on the screen when the regular scanning passes through the rows a to a + y-1, at the intersection with the columns b to b + x-1, where a, b define the primary position, in terms of row and column, of the character to be written and where x is the number of columns of dots of the elementary surface occupied by the character to be written.
2. Method according to Claim 1, characterized in that it consists in employing elementary surfaces all having the same dimensions.
3. Method according to Claim 1, characterized in that it consists in employing elementary surfaces of at least two types of different dimensions.
4. Dot-matrix screen display device (1), characterized in that it includes n first memories (2; 20, 21, 22) with n a positive integer, in which there preprogrammed, at known addresses, which are called character codes, characters, that is to say the dots to be excited of elementary surfaces of predetermined dimensions (x, y) of the screen, so that these characters are displayed on the screen, at least n second memories (3, 3′; 30, 31, 31′, 32, 32′) associated respectively with the n first memories in order to contain character codes in positions having a one-to-one correspondence with the dots of the screen (1), and means (4, 5) for writing character codes into the n second memories, for reading the memory-stored characters, corresponding to these character codes, in the first memories associated with the second memories where these codes are written and for displaying a character read with the dots of the screen having a one-to-one correspondence with the position of the character code which determined the reading.
5. Device according to Claim 4, characterized in that the second memories (3; 30, 31, 31′, 32, 32′) are m in number, with m an integer greater than n and equal at most to 2n, in that 2(m-n) of the second memories (3, 3′; 31, 31′, 32, 32′) constitute pairs, the two second memories of a pair being coupled to a two-state multiplexing circuit (6; 61, 62), one of the memories of the pair being capable of being written to and the other read for one of the states and conversely for the other state.
6. Device according to Claim 4, characterized in that the characters preprogrammed into one of the n first memories (2; 20, 21, 22) relate to elementary surfaces all having the same dimensions.

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