EP0021928A1 - Writing device for a television screen and remote writing system comprising such a device - Google Patents

Abstract

The invention relates to devices enabling writing on a television screen using a light pen. It consists in combining with a standard television (1) a device comprising a light pen (3) enabling the drawing of a dot on this television (1), a digitiser (8) furnishing the coordinates of the dot thus drawn, a picture memory (6) enabling all of the dots drawn on the screen to be stored, and a centralised control device (7) enabling monitoring and coordination of the functioning of these units. It enables construction of real-time remote writing devices which function on being connected by a simple telephone line. <IMAGE>

Description

The present invention relates to writing devices on a television screen which make it possible to translate graphic signs into electrical signals as and when these signs are drawn on a screen using a photostyle. It also relates to remote writing systems which make it possible to transmit via a transmission line of any type, in particular telephone, these electrical signals to a distant station on which the graphic signs reproduce at the same time as we trace them to the local post.

It is known to use a device connected to a telephone line, in which a pen is fixed to a pantograph which drives two potentiometers whose output voltages make it possible to define the position of the tip of the pen. These voltages are converted into variable frequencies which are themselves transmitted via the telephone line to a reception station. At the reception station the frequencies are converted into voltages which allow two motors to be actuated which cause a pantograph similar to that of the transmission station to move. This pantograph drives a pen that reproduces the layout that is made on the show. This device is of delicate use, and the transmission by signals of variable frequencies offers a relatively low precision.

We also know how to write on a television screen using a luminous pencil. In fact, it is the pencil in question which receives the light from the screen and which designates for example a specific graphic already present on the screen.

By computer processing done on donations data collected by the pencil on the determined graph, the command to move this graph in the same direction as the pencil is programmed. The processing is important and the possible writing materializing the displacement can be ensured only within the limits of the graph. To write to another location on the screen, you must first move the graphic to the new writing area.

In addition, if the graphic keeps a simple form, the writing is jerky since the movement is controlled only by the passage of the pencil over a line of the graphic different from its center.

Telewriting devices comprising digitizing tablets and a separate television have also been used, but are unpleasant to use because the tablet on which the pencil moves is not superimposed on the screen.

• - un téléviseur comportant un écran parcouru par un spot selon un balayage standard, recevant un signal vidéo, et délivrant des signaux de synchronisation ;
• - un photostyle permettant de désigner un point déterminé sur l'écran du téléviseur, et d'émettre un signal de détection et un premier signal de commande d'inscription ou d'effacement
• - un numériseur permettant à partir des signaux de synchronisation et des signaux émis par le photostyle d'élaborer un premier signal numérique représentant les coordonnées du point désigné par le photostyle ;
• - un dispositif de commande centralisé permettant de recevoir le signal de commande du photostyle et le premier signal numérique, d'émettre pour chaque ligne du balayage un deuxième signal de commande d'inscription ou d'effacement et un deuxième signal numérique représentant un segment à inscrire ou à effacer sur cette ligne de balayage ; et
• - une mémoire d'image permettant de mémoriser les données représentant le signal vidéo reçu par le téléviseur, de générer ce signal vidéo à partir de ces données, et de modifier ces données en fonction du deuxième signal de commande et du deuxième signal numérique émis par le dispositif de commande centralisé.

The object of the invention is a device for writing on a television screen mainly characterized in that it comprises:

• - a television set comprising a screen traversed by a spot according to a standard scan, receiving a video signal, and delivering synchronization signals;
• - a photostyle making it possible to designate a determined point on the screen of the television, and to emit a detection signal and a first recording or erasure control signal
• a digitizer making it possible, from synchronization signals and signals emitted by the photostyle, to develop a first digital signal representing the coordinates of the point designated by the photostyle;
• - a centralized control device making it possible to receive the photostyle control signal and the first digital signal, to transmit for each line of the scan a second recording control signal tion or erasure and a second digital signal representing a segment to be written or deleted on this scan line; and
• - an image memory making it possible to store the data representing the video signal received by the television set, to generate this video signal from this data, and to modify this data according to the second control signal and the second digital signal emitted by the centralized control device.

• - la figure 1 qui représente le schéma synoptique d'un dispositif d'écriture à distance selon l'invention;
• - la figure 2 qui représente le schéma détaillé de l'organe 8 de la figure 1 ;
• - la figure 3 qui représente le schéma détaillé de l'organe 6 de la figure 1 ;
• - la figure 4 qui représente une coupe partielle du photostyle 3 de la figure 1 ;
• - la figure 5 qui représente le schéma de l'organe 9 de la figure 1 ;
• - la figure 6 qui représente le schéma de l'organe 7 de la figure 1 ;
• - les figures 7 à 10 qui représentent les ordinogrammes des programmes permettant de faire fonctionner l'organe 7 de la figure 1.

Other features and advantages of the invention will appear clearly in the following description presented by way of nonlimiting example and made with reference to the following appended figures:

• - Figure 1 which shows the block diagram of a remote writing device according to the invention;
• - Figure 2 which shows the detailed diagram of the member 8 of Figure 1;
• - Figure 3 which shows the detailed diagram of the member 6 of Figure 1;
• - Figure 4 which shows a partial section of the photostyle 3 of Figure 1;
• - Figure 5 which shows the diagram of the member 9 of Figure 1;
• - Figure 6 which shows the diagram of the member 7 of Figure 1;
• FIGS. 7 to 10 which represent the flow charts of the programs making it possible to operate the member 7 of FIG. 1.

The general structure of a remote writing device according to the invention is represented in FIG. 1. The graphic signs to be represented will be displayed on a television set 1 of a standard type and using for example a scan at 25 images per second and 625 lines per image. This television receives a video signal from a picture memory 6, and transmits signals from frame and line synchronization to a digitizer 8 and the memory 6. A photosensitive stylus 3 makes it possible to designate a point on the television screen 1 and is connected to the digitizer 8. The digitizer 8 makes it possible to locate the position of the designated point on the screen by photostyle 3 as a function of the synchronization signals received from the television. It transmits to a interpolation and transfer device 7 the digital data designating this point. The transfer and interpolation device proceeds on the one hand to the calculations making it possible to interpolate the drawing between two successive positions of the photostyle 3, and on the other hand to the formation of blocks of characters which are then transmitted to a modem 9, which is connected to a telephone line L. The results of the interpolation are transmitted to the image memory which is loaded with the coordinates of all the points to be displayed on the television. This image memory works out from these coordinates a video signal retransmitted itself to the television set.

The digitizer 8, the diagram of which is shown in FIG. 2, receives, on the one hand from the television, line synchronization signals SL and frame ST respectively on the connections 802 and 801. It also receives photostyle 3, a detection signal DL light on connection 816, a CI registration control signal on connection 828, and an erase control signal CE on connection 831.

At each start of image, the signal ST is applied to a line counter 803 from which the first stage has been distinguished in the figure and which it resets to zero. It is also applied to a flip-flop 808 which it positions in a state such that its output connected to an AND gate 811 opens the latter. II _\ is finally applied to a register 805, and via an OR gate 806 to a register 807. Both registers are three states respectively rated O, 1 and 2, and are positioned by the signal ST in the state O. The signal SL at each end of line resets to zero a point counter 809 from which the first stage has been distinguished in the figure, by means of the gate 811 opened by the flip-flop 808 An AND gate 812 is also applied which is open by the state O of the register 805 and which applies this signal SL to stage 2 of the line counter 803 which thus counts the line synchronization signals.

When the CI registration command signal arrives, it is applied by connection 828 to the AND gates 814 and 815 which it opens. This signal CI is also applied by the connection 828 to the transfer and interpolation member 7 which, under the control of this signal, sends to the modem 9 a signal for online transmission of the line seizure tone.

When the scanning light spot of the television set 1 is detected by the photodiode contained in the photostyle 3, the signal DL is received on the connection 816. This is applied to a branch circuit 817 symbolized in the figure by a capacitor, and which makes it possible to obtain a first signal corresponding to the leading edge of the signal DL and a second signal corresponding to the trailing edge. These first and second signals are separated by two diodes 818 and 820 connected in opposite directions. The first signal is applied at the output of the diode 818 simultaneously to the AND gates 814 and 819. The gate 814 being opened by the signal CI lets pass the first signal which is then applied to the registers 805 and 807 which advance one step and are positioned in state 1.

The door 812 connected to the first stage of the register 805 therefore closes, which prevents the signal SL from being applied to the second stage of the counter 803. On the other hand, the AND gate 821 connected to the second stage of the register 807 via '' a door OR 822, lets through the signal SL which is applied to the first stage of the counter 803. The latter therefore starts counting the lines at a speed half of the previous speed.

An AND gate with 3 inputs 823 is opened on the one hand by the flip-flop 808 at the same time as the gate 811, and on the other hand by the second stage of the register 805. This gate 823 lets the pulses of a signal d clock H applied by a connection 68. The frequency of this clock signal is such that the scanning precision along the line is substantially equal to the vertical definition given by the number of lines in a frame. This clock H at the output of gate 823 is applied to the second stage of the point counter 809 which therefore starts to count these clock pulses at a determined speed.

At the end of this first line where the signal DL arrives, this counter 809 is reset to O by the signal SL since the door 811 is always open.

At the start of the second line where the DL signal appears, the signal from gate 814 advances the two registers 805 and 807 by one step, which go back into state 3. Gate 823 connected to the second stage of register 805 therefore closes, but an AND gate 825 with 3 inputs connected on the one hand to the third stage of register 805 and on the other hand to flip-flop 808 by the same connection which leads to doors 811 and 823 opens his turn. This gate 825 receives the clock H and then applies it to the first stage of the counter 809 which thus begins to count these clock pulses at a speed half the previous speed.

When the second signal marking the end of the signal DL leaves gate 815, it switches flip-flop 808 via an OR gate 826 and an AND gate 833 which is open because it is connected to the third floor of register 805. Toggle 808 closes then door 825 and counter 809 stop counting.

At the start of the third line where the signal DL exists the signal SL is applied to an AND gate 824 which is opened by the third stage of the register 805. At the output of this gate 824 the signal SL is applied to the register 807. This it can operate as an up-down counter and the output of door 824 is connected to the down-counting input. Under the effect of the signal SL at the start of the third line, the register 807 returns from position 2 to position 1. In the course of the line, the signal leaving door 814 and indicating the start of the light spot will do so. go back from position 1 to position 2. So all the time that the DL signal produced by the light spot is present, register 807 will go from position 2 to position 1 at the start of the line and from position 1 to position 2 at the start of spot detection.

At the start of the first line where the DL signal disappears because the light spot is no longer detected, the register 807 returns to position 1 and since it does not return to position 2 during this line, it returns to position O at the end of it, which corresponds to the start of the next.

The door 821 then closes but the door 812 does not reopen, and the counter 803 stops. An AND gate 826 connected on the one hand to the third stage of the register 805 and on the other hand to the first stage of the register 807 opens and applies to a connection 827 an LC signal for reading the coordinates of the point of the light spot.

These coordinates are contained for the abscissa in the counter 809 and for the ordinate in the counter 803. In these two counters the first stage is not taken into account to define these coordinates because it is only used to count at a speed half when the DL signal exists, which allows to obtain automatically in the counters the coordinates of the center of the light spot.

It can also be noted that the countdown does not start until the line following that on which the DL signal was detected for the first time. This improves the precision of definition of the abscissa.

These coordinates are in the form of two binary words respectively CNP and CNE presented on the multi-wire connections 829 and 830.

When the erase photostyle contact closes, a CE signal appears on a connection 831, while the CI signal disappears from connection 828.

During this erasure, the operation of the digitizing device is the same until the DL signal arrives. At this time, the first signal from the front edge of the DL signal is delivered by the diode 818 to gates 814 and 819; it is blocked by door 814 which is no longer open since the signal CI no longer exists, but passes through door 819 opened by the signal CE. At the output of this door 819, this first signal causes the flip-flop 808 to toggle through the door 826 so that the doors 823 and 825 to which it is connected close; this same signal positions register 805 in state 2, and register 807 in state O via the OR gate 806.

The gate 826 connected to the second stage of the register 805 and to the first stage of the register 807 then transmits on the connection 827 the signal LC which indicates in combination with the signal CE present on the connection 831 that one has in the counters 803 and 809 the coordinates of the point to be deleted. These counters stopped counting as soon as the first signal from the front of signal DL which closed door 812 via the first stage of counter 805, and doors 823 and 825 via flip-flop 808. In fact these coordinates most often indicate a point closer to the start of the line and the top of the frame as that actually displayed since the photostyle detection zone is widened by means which will be seen later in the event of erasure. This is not important since the image memory only contains the coordinates of a single point and it is this which will be deleted. If, however, several light points side by side are lit, they will be erased one after the other as the scans are carried out.

These coordinates, both for writing and for erasing, are transferred to the image memory 6, the diagram of which is shown in FIG. 3.

This transfer takes place via the transfer and interpolation device 7 which carries out the necessary processing.

In the image memory diagram, multiple connections carrying signals in parallel have been systematically represented by simple arrows surmounted by a circle. Likewise, the different sets of doors necessary to make these signals pass in parallel are represented by single doors. Finally the numerical values are given for a single frame and the transposition in the case of two interlaced frames is immediate.

At the start of each image, the frame synchronization signal ST applied to a connection 601 gives O a line counter 602. This rotates under the control of the line synchronization signal SL applied by a connection 603.

The signal SL is also applied to the input of reset to O of a point counter 604 which is therefore reset to O at each start of line. This point counter 604 rotates under the action of the clock signal H applied to a connection 68.

A point memory 605 consists for example of a shift register containing as many stages as there are points used on the surface of an image. To take into account the different tolerances, for example on the image and line return times, as well as to be able to use this device with different standards, this number of written points is deliberately smaller than the maximum number of points usable in an image. For example, a shift register with a capacity limited to 512 x 512 will be used. This register 605 rotates under the control of the clock H which is delivered to it via an AND gate 606. This gate is not open only during the time when the spot on the screen describes the useful portion of a useful line. The shift register 605 is coupled in circulating memory between its output connection 609 and its input connection 610 by an OR gate 608. The output of gate 608 is also applied to a digital-analog converter 611 which delivers on its output a VI video signal directly applied to the TV. 1. Thus when the register 605 delivers a signal 1, the latter via the converter 611 is converted into a voltage which is reflected on the screen of the television by the appearance of a light point.

The line 602 and point 604 counters are provided with decoding devices which deliver respectively on the connections 631 and 632 opening signals to the door 606 for the time corresponding on the one hand for the counter 602 to the useful lines and d on the other hand for the counter 604 with useful segments on each useful line. When door 606 is thus open during this period, which corresponds to the moment when the spot on the screen crosses the useful surface, it delivers the clock H to the register 605.

The signal TU present on connection 631 is also sent to the transfer and interpolation member. It also receives an IT interrupt signal from the combination in an AND gate 640 of the signal on connection 631 and of the signal SL.

On the other hand, the line numbers are transmitted in parallel on a multiple connection 614 in the form of an NL signal from the counter 602.

The transfer and interpolation member 7 receives these signals TU, IT, and NL and in return transmits on the multiple connections 615 and 616 respectively the digital signals DS and FS indicating the start and the end of the segment to be recorded. These abscissas are entered in registers 617 and 618.

The content of these registers 617 and 618 is permanently applied to the AND gates 619 and 622. These gates are also connected to the counter 604 which continuously transmits its state to them, which changes as the spot moves along d 'a line.

When the spot arrives at the start of a segment to be entered, the value contained in the register 617 is equal to the state of the counter 604 and the door 619 opens by positioning a flip-flop 620 in a first state. The output of this flip-flop is connected to an AND gate 621 in such a way that this first state corresponds to an opening signal applied to this gate 621.

This gate 621 also receives the clock signal H and a signal OI ordering the registration and transmitted from the transfer and interpolation device 7. Under the action of this signal OI and the flip-flop 620, the gate 621 therefore allows the clock H to pass. This clock H transmitted by the door 608 is applied by the connection 610 on the register 605 which then positions the memory points intended to represent light points on the screen on a value 1.

When the spot arrives at the end of the segment to be entered, the content of the register 618 is equal to the state of the counter 604 and the door 622 opens. The output of this door 622 is applied to the other input of the flip-flop 620 and the latter is positioned in its second state which closes the door 621, thus stopping the positioning of the memory points of the register 605.

If several segments are to be registered on the same line, registration will be done at the rate of one segment per 'frame under the control of member 7.

When one wishes to erase, one designates with photostyle 3 only one point and it is not possible to predict in advance if this erasing point designates the beginning of a complete segment to be erased. This is the reason why, as we saw above, we only erase point by point. In this case, the transfer and interpolation member 7 sends on the one hand the segment start and end addresses corresponding to two successive points, and on the other hand on a connection 613 an OE signal ordering the erasure on the screen. A NAND gate 624 is connected on the one hand to that of the outputs of the flip-flop 620 which is connected to gate 621, and on the other hand to connection 613. The signal at the output of this gate 624 is always equal to 1 except when there is simultaneously a 1 on the output of the flip-flop 620 and a 1 in input on the connection 613. Outside erasing periods, the gate 623 to which the output of the gate 624 is connected therefore leaves pass the refresh signal from register 605 through connection 609. When on the other hand door 624 closes, its output therefore passing to O, door 623 also closes for the duration of a point and it is therefore no longer refreshed; its indication disappears in register 605 and it goes off on the television screen.

The connections 612 and 613 are moreover connected to the digital analog converter 611 in order on the one hand to improve the functioning of the photostyle and on the other hand to give the operator information on the action which he sets in motion.

• - en dehors de l'inscription et de l'effacement les zones lumineuses ont une brillance réduite et les zones noires ne sont absolument pas excitées, ce qui permet d'éviter de bruler le tube cathodique et donne un contraste moyen ;
• - lors de l'inscription les zones lumineuses gardent la même luminosité que précédemment, mais par contre le fond de l'écran est rendu uniformément lumineux avec une brillance légèrement plus faible que celle des zones lumineuses et juste suffisante pour discerner l'inscription, ce qui permet d'obtenir un signal DL quelque soit l'emplacement du photostyle sur l'écran
• - lors de l'effacement les zones lumineuses sont portées à la brillance maximale et non dangereuse et les zones non inscrites ne sont absolument pas lumineuses, ce qui donne un contraste maximum ; de ce fait la zone de sensibilité du photostyle est beaucoup plus grande et il est possible de pointer des emplacements à effacer avec une précision plus faible.

For this, the signals OE and OI control in the converter 611 the variations in contrast and brightness. Depending on the case, we have the following 3 configurations:

• - apart from writing and erasing, the light zones have a reduced brightness and the black zones are absolutely not excited, which makes it possible to avoid burning the cathode ray tube and gives an average contrast;
• - when registering the light areas keep the same brightness as before, but on the other hand the background of the screen is made uniformly bright with a slightly lower brightness than that of the light areas and just sufficient to discern the inscription, this which allows to obtain a DL signal whatever the location of the photostyle on the screen
• - when erasing the bright areas are brought to the maximum brightness and not dangerous and the areas not listed are absolutely not bright, which gives maximum contrast; therefore the sensitivity area of the photostyle is much larger and it is possible to point to locations to be erased with lower accuracy.

To obtain this result, the gain and the quiescent point of the output amplifier of the converter 611 are controlled for example using the signals QE and 01.

FIG. 4 shows a partial view in section of the photostyle 3. This photostyle comprises a body 3O1 in the end of which slides a transparent cylindrical part 302, made of plastic for example. A photodetector cell 303, for example a photoresistor, is fixed to the end of the cylinder 302 situated inside a cavity dug in the body 301.

This cell is supplied from a voltage source + and it outputs the DL signal.

When the operator presses the external end of the cylinder 302 on the screen of the television 1, it sinks and the rear part of the cell 303 presses on a first part 305 which comes into contact with a central part 304 This part 304 is itself joined to the source +. The contact thus established between the part 304 and the part 305 makes it possible to deliver on a connection joined to the part 305 the registration control signal CI.

When the operator presses more strongly on the photostyle, the cylinder 302 is reduced more deeply into the body 301 and the rear of the part 304 comes to press on a part 306 forming a second contact. This part 306 is therefore supplied from the voltage + and delivers on an external connection the erasure control signal CE. An additional spring 307 allows the operator to feel an appreciable difference in resistance when he presses on the photostyle and thus to tactually detect the transition from writing to erasing.

So that the digitizing member in the example shown sees the CI signal disappear when the CE signal appears, in this case a relay 308 is used which, under the control of the CE signal, cuts the output of the CI signal. Other embodiments using for example logic gates combined in they are usable; for this same purpose, it is also possible to modify the diagram of the digitizing member so that the appearance of the signal CE inhibits the action of the signal CI inside the digitizing member.

The modem 9 shown in FIG. 5 comprises a modulator-demodulator proper 91; and an input and output member 92.

The input and output device 92 essentially consists of a parallel / serial register, which receives, possibly via a buffer register, the messages ME sent or received in parallel from the transfer device and interpolation 7. This member receives from the modulator-demodulator 91 a clock specific to it via a connection 94. This clock makes it possible to transfer the content of the member 92 to the modulator-demodulator 91 in series. by means of an output connection 93, during transmission, and conversely of filling the member 92 from the modulator-demodulator 91 by an input connection 95.

The modulator-demodulator 91 receives from the transfer and interpolation member a transmission control signal TRON, and it then transmits its modulation on the line L.

When, in the absence of this TRON signal, it receives a modulation by the line, it transmits to the transfer and interpolation member 7 a RON signal.

In transmission, the content of the member 92 is continuously transmitted over the connection 93 and the transfer and interpolation member transmits the message ME at intervals such that there is no loss of information.

On reception, a decoder internal to organ 92 makes it possible to detect the moment when a complete word constituting a message ME has arrived in this organ 92. It then sends a signal MP to the transfer and interpolation member which allows the latter to take into account the message ME on the output of member 92.

The transfer and interpolation member 7, the diagram of which is shown in FIG. 6, is advantageously composed of a microprocessor 71, of the 6800 type for example, of a working memory 72 comprising for example 64 bytes, and a read-only memory 73 comprising for example 1000 program bytes.

This microprocessor is connected via a bus type link 74 to a set of peripheral couplers 75 of the PIA type for example.

These PIA couplers allow all links with the other organs of the remote writing device, with the exception of the interrupt command which is received directly on an IT input of the microprocessor.

• - avec l'organe de numérisation 8 :
  • . commande d'inscription CI 1 eb
  • . commande d'effacement CE 1 eb
  • . lecture des coordonnées LC 1 eb
  • . compteur du nombre de points CNP 10 eb
  • . compteur du nombre de lignes CNL 9 eb
  • . horloge H 1 eb
• - avec la mémoire d'image 6 :
  • . horloge H 1 eb
  • . temps utile TU 1 eb
  • . numéro de ligne NL 9 eb
  • . début de segments DS 10 eb
  • fin de segment PS 10 eb
  • . ordre d'inscription OI 1 eb
  • . ordre d'effacement OE 1 eb
• - avec le modem' 9 :
  • . signal de réception RON 1 eb
  • . ordre de transmission TRON 1 eb
  • . message prêt MP 1 eb
  • . message ME 24 eb

Summarizing all these links, and giving the number of binary elements, abbreviated eb, used in the embodiment, we find:

• - with digitization unit 8:
  • . registration order CI 1 eb
  • . erase command CE 1 eb
  • . reading of coordinates LC 1 eb
  • . counter for the number of CNP 10 eb points
  • . counter for the number of lines CNL 9 eb
  • . clock H 1 eb
• - with image memory 6:
  • . clock H 1 eb
  • . useful time TU 1 eb
  • . line number NL 9 eb
  • . beginning of segments DS 10 eb
  • end of segment PS 10 eb
  • . registration order OI 1 eb
  • . erase order OE 1 eb
• - with modem '9:
  • . reception signal RON 1 eb
  • . transmission order TRON 1 eb
  • . message ready MP 1 eb
  • . message ME 24 eb

This 24 eb message will be transmitted or received with each frame and since there are 50 frames per second, there is therefore an online speed of 1200 Bauds. This speed corresponds to a very common modem.

• - un préfixe de 3 eb servant essentiellement à la synchronisation ;
• - une syllabe de 2 eb indiquant l'inscription ou l'effacement ;
• - une syllabe de 10 eb indiquant l'abscisse du point à traiter sur la ligne ;
• - une syllabe de 9 eb indiquant le numéro de la ligne où se situe ce point.

Each 24 eb message will include, for example:

• - a prefix of 3 eb essentially used for synchronization;
• - a syllable of 2 eb indicating the inscription or the erasure;
• - a syllable of 10 eb indicating the abscissa of the point to be treated on the line;
• - a syllable of 9 eb indicating the number of the line where this point is located.

The general organization of the system software is represented in FIG. 7. It can be seen that this software essentially consists of two main programs.

An EMI program for entering the registrations memory introduces the information necessary for the drawing of each line and then prepares the information necessary for the next line. This program is triggered on an IT interrupt supplied at each start of useful line from the line synchronization signal SL.

When this EMI program is finished, we pass to a PP preparation program which takes place when the spot on the screen is outside the useful area and prepares the parameters which are necessary for the EMI program. It also prepares the route information which is necessary for the first useful line. In this PP program, there is a module which is common with EMI.

At the end of the PP program, we return to wait for the interrupt which will trigger EMI again.

The PP program in which you enter 1 and exit 2 is detailed in Figure 8.

Coming from EMI in 1, we first proceed in an acquisition phase to the acquisition of TU, CE, CI, and MP data.

This acquisition is followed by a test which makes it possible to know if one is in the useful area by checking whether TU is zero or equal to 1.

If TU is not zero, we enter a waiting phase which returns to the previous acquisition to return to a connection point until TU goes to O ..

When TU is equal to O, we pass on a second connection phase where we test the value of the RON signal to know if we are receiving.

If RON is equal to 1, then we go into a slave mode where the local device is under the control of the remote device.

This enslaved mode leads to a new test in which it is sought whether the received message is indeed available in the reception register. For this we test if the signal MP is equal to 1.

If MP = O, we wait for the message by going back through the acquisition phase.

If MP = 1, the local device becomes active and we arrive in a data acquisition module CNP _r , CNL, CI _r , and CE. These data are extracted from the message ME and the index r indicates that they correspond to the data of the same reference taken from the digitizer.

We then enter via point 3 in the CPR parameter calculation module which will be described later, then we come out of this module via point 4.

If RON = O, then we go into local mode.

In this local mode, you can be passive if there is no command from the photostyle or active otherwise. To determine this, a test is made on the presence of the CE or CI signals. If none of these signals is equal to 1, we are in passive mode and we then go into a phase where we confirm the position of the modem awaiting reception, that is to say that the the position of the TRON signal is confirmed on O and that an internal logic variable 1 to O is placed. This internal variable is intended to indicate that there is no tracing in progress; it will subsequently change to 1 during the execution of the CPR subroutine.

If one of the CE or CI signals is equal to 1, we then switch to active mode.

In this active mode, we start by performing a test of the variable 1. If this is equal to O, this means that there has not previously been a calculation of the coordinates of the point to be registered, and that the we cannot therefore transmit a message containing these coordinates. A roll loading subroutine, that is to say an agreed signal such as a succession of 1 and O, is then executed in the register of the message to be transmitted. This rolling message will thus be transmitted so as to synchronize the modem of the writing device located at the other end of the transmission. We then pass through an acquisition module for LC, CNP and CNL signals which are the coordinates of the point indicated by the photostyle on the screen, and the validation of these.

If 1 is equal to 1, we enter a module for loading the signal ME _n-1 which corresponds to the coordinates calculated during the previous iteration. After this loading, we enter the acquisition module of LC, CNP and CNL described above.

From this module for acquiring CL, CNP and CNL, we pass to a module for preparing the MEL message which will be loaded during the next iteration.

At the end of this ME preparation module, you enter the CPR sub-program via point 3 and you come out of this CPR sub-program via point 4.

At the end of the CPR subroutine, we pass through an IT interrupt unmasking module. This is indeed hidden during the execution of the PP program so as not to disturb the execution of the latter. At the end of this module, we go towards waiting for an interruption, passing through point 2.

• - une partie de préparation qui permet de déterminer le début et la fin du segment à tracer et se déroule entre les points 3 et 5 ;
• - une partie d'interpolation constituant une routine commune avec le programme EMI et qui se déroule entre les points 5 et 6 ;
• - une partie terminale qui se déroule entre les points 6 et 4.

The CPR sub-program, the flowchart of which is represented in FIG. 9, comprises 3 parts

• - a preparation part which makes it possible to determine the beginning and the end of the segment to be traced and takes place between points 3 and 5;
• - an interpolation part constituting a common routine with the EMI program and which takes place between points 5 and 6;
• - a terminal part which takes place between points 6 and 4.

Starting from a point M _{n + 1} provided by the digitizer and whose coordinates will be defined by u, t, the point previously entered, if there is one, will be M _n whose coordinates will be v, s.

In this case, we will name A and B the highest and lowest points of the line, and whose coordinates will be m, n and p, q respectively.

First, we examine whether M exists by testing the value of the logic variable 1 defined above.

If 1 = O we first give it the value 1 since at the next pass the point M _{n + 1} currently acquired will become M, then for the same reasons we do v = u and s = t. We then join the PP program via point 1.

If 1 = 1 we test the relative values of t and s and possibly of u and v to know if M _{n + 1} is above or below M _n , or possibly on the same line.

According to the result of this comparison, we then assign to the coordinates m, n, p, q of the points A and B, the coordinates u, t, v, s of the points M or M ', according to the respective positions of these two points.

We then do a test on the respective values of m and p in order to know if point A is to the left or to the right of point B.

Depending on whether the line from A to B goes from right to left, or from left to right, a logic variable α internal to the program is assigned a value O or 1.

The value of α being fixed, we finally give at point A the coordinates γ and β of a point C which will be the current point used in the interpolation calculation which will follow.

We are then at the end of the preparatory part of the program in point 5.

The interpolation routine which takes place between points 5 and 6 makes it possible to calculate the abscissas ∂ and φ of the start and end of a segment to be written or erased on a line of ordinate β.

.For this, after a test on the value of α, the slope of the segment CB is calculated. This slope is given by the value of a parameter e =

.

If α = 1, we give to ∂ the rounded value of γ, this value being rounded to the nearest digit corresponding to a point on the line. We give to γ the rounded value of (γ + e).

In the case where α = O we give to a the rounded value of (Y + e), and to φ the rounded value of Y.

In order for the iteration to continue in the next course of the CPR program, we then force Y on the value (γ + e) and β on the value (β + 1).

We thus arrive at exit 6 of the interpolation routine.

In the terminal part of the CPR program which runs from point 6, point M is replaced by point M _{n + 1} by doing v = u and s = t. We then leave this terminal part, and at the same time from the CPR program, by point 4.

When an interruption arrives during the useful time, one leaves the waiting-interruption block to enter - passing through point O in the EMI program, the flowchart of which is represented in FIG. 10.

This EMI program takes place for the duration of a line due to the speed of the microprocessor used, and begins with the acquisition of the line number NL.

We then carry out a test on the value of NL with respect to the ordinate n of point A obtained during the PP program. If NL is less than N, that is to say if the line is located above point A, and therefore does not include any inscription to be made or deleted, we go directly to the end of the program where we exit via point 2 which brings us back to the interrupt waiting block.

If on the other hand NL is greater than n, then we test its value with respect to the ordinate of B. If NL is greater than q, that is to say if the line is below the point ending the segment, we mask the interruption and exit the program via point 1 which leads directly to the PP program; the interruption being thus masked, the following lines of the useful zone will not stop the microprocessor to restart it on the EMI program.

If NL is less than q, it is necessary to mark a segment on the line which is between points A and B.

For that one transcodes the abscissas ∂ and φ, which are expressed in a code necessary for the calculations, to form the numbers of start of segment DS and end of segments FS which will be usable by the image memory.

The DS, FS, and CE or CI signals are then sent depending on whether you want to delete or write.

For the first line thus treated ∂ and φ are those calculated beforehand by the PP program.

To obtain the abscissa d and φ of the line following this first line, an interpolation is carried out using the interpolation subroutine represented in FIG. 9 between points 5 and 6. We then exit the interpolation program simultaneously and from the EMI program, to go to point 2 entry of the waiting for interruption.

On the next line, on the triggering of the following interrupt, the EMI program runs again with the new values of this of φ and so on until we pass below point D where then NL becomes greater than q and we go to the PP program.

It is possible to add other subroutines extracted from an existing library into this program, making it possible to obtain numerous drawing possibilities with the photostyle.

The device according to the invention can comprise several screens and photostyles located in the vicinity, the common operation of which is obtained by sending on all of the same video signal and by the parallel connection of the contacts and output signals of the photodiodes, thus allowing the realization of a conference with telewriting. Two identical groups located remotely comprising the device which can thus be connected by the telephone line as devices with a single screen and a single photostyle.

It is possible to use "locally" such a group of one or more screens or photostyles (without it being connected by a transmission line to another remote group) for applications of the board game type for example.

Similarly, such a group can be connected remotely to any device capable of interpreting the messages transmitted, or of emitting similar ones, for example a computer allowing the storage of graphic information.

Claims (10)

1. Writing device on television screen, characterized in that it comprises: - a television set comprising a screen scanned by a spot according to a standard scan, receiving a video signal, and delivering synchronization signals; - a photostyle making it possible to designate a determined point on the television screen, and to transmit a detection signal and a first recording or erasing control signal; _- a scanner for from the synchronization signals and signals transmitted by the light pen to draw a first digital signal representing the coordinates of the designated point by the light pen; a centralized control device making it possible to receive the photostyle control signal and the first digital signal, to transmit for each line of the scan a second recording or erasing control signal and a second digital signal representing a segment to write or delete on this scan line; and - an image memory making it possible to store the data representing the video signal received by the television set, to generate this video signal from this data, and to modify this data according to the second control signal and the second digital signal emitted by the centralized control device. 2. Device according to claim 1, characterized in that it further comprises a modem making it possible to transmit or receive on a transmission line a message designating the point determined on the screen and indicating the command to register or to erasure, and that the centralized control device makes it possible to deliver to the modem or to acquire from it the message sent or received on the transmission and function line operate under control of the photostyle signal and the first digital or message signal received by the modem. 3. Device according to any one of claims 1 and 2, characterized in that the photostyle comprises: - a photodiode making it possible to detect the passage of the spot on the screen and to emit the detection signal thereof; - a first contact making it possible to emit the first registration control signal when the photo-style is pressed on the television screen with a first determined force; and - a second contact making it possible to emit the first erase control signal when the photostyle is pressed on the television screen with a second determined force of value greater than the first. 4. Device according to claim 3, characterized in that the photostyle comprises means allowing between the operating positions of the first and second contact to increase the reaction force perceived by the operator handling the photostyle. 5. Device according to any one of claims 1 to 3, characterized in that the centralized control device also makes it possible to control the illumination of the entire television screen under the action of the first control signal d registration, and to control the highlighting of the image displayed under the action of the first erase control signal. 6. Device according to any one of claims 1 to 5, characterized in that the digitizer comprises: - a line counter and means allowing operating this counter at a first determined speed until the spot detection signal appears, operating it at half the speed of this first speed for the duration of this signal, then stopping it at the end of the signal; a point counter and means enabling it to count a clock signal at a second determined speed until the appearance of the spot detection signal, to operate it at a speed half of this second speed during the duration of this signal, then stop it at the end of the signal; - Means allowing when the two counters stop transmitting a validation signal of the content of these counters. 7. Device according to any one of claims 1 to 6, characterized in that the image memory comprises: - a circulating digital memory whose output is looped over the input and comprising a number of words limited to a value determined by the useful surface of the television screen; - Means for rotating this memory only during the exploration of the useful surface by the spot; means allowing the action of the second recording or erasing control signal and the second digital signal to modify the content of this memory by modifying the looping of the output on the input; and - a digital-analog converter connected to the output of the digital memory and delivering the video signal. 8. Device according to claim 7, characterized in that the image memory comprises: - means allowing under the action of the second registration control signal to decrease the contrast of the video signal while keeping constant the value of the maxima of this video signal; and - Means allowing under the action of the second erase control signal to increase the contrast of the video signal while keeping constant the value of the minima of this video signal. 9. Device according to any one of claims 1 to 8, characterized in that the centralized control device comprises: - a microprocessor; - a read only memory allowing to control the functioning of the microprocessor; - a random access memory allowing the storage of intermediate variables; and - peripheral couplers allowing the centralized control device to be connected to the digitizer, the image memory, and the modem. 10. Remote writing system, characterized in that it comprises at least two devices according to any one of claims 1 to 9, connected by a transmission line.

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