METHOD OF DISPLAYING ALPHANUMERICAL AND GRAPHIC CHARACTERS AND TERMINAL FOR USE OF THE SAID METHOD

Abstract: In order to increase the light intensity and legibility of the characters displayed on the screen of a cathode-ray tube, all dots of the same vertical line of the character or even all dots of this character are simultaneously excited by means of a multiple cathode while the line is scanned so that said excitation is repeated a predetermined number of times with short time intervals. When all the dots of the character are simultaneously excited, a shift of the picture transmitted by the multiple cathode is carried out at the same time in synchronism with and in opposite direction to the line scan, to compensate for the formation of stripes in the displayed picture which would otherwise be produced by said scan.

Description: "Method, of displaying alphanumerical and graphic charac¬ ters and terminal for use of t e said method." The present invention relates to a method of displaying alphanumerical and graphic characters and to a terminal for use of this method. Cathode-ray tubes which are -driven in a suitable 5 manner are usually used for the display or "visualisation" of alphanumerical and graphit output information of digital processing systems. When the cathode-ray tube is connected to suitable logic circuits it is possible to control the number of ■0 characters per written line as well as the number of hori¬ zontal lines forming each character, the number of written lines, the generation of characters vhich correspond to the character code, the memory storage of the character posi¬ tions on the written page, the movement and positioning 15 of a cursor, writing-in by means of a keyboard etc. so that terminals of different types are obtained ("active", "passive", "intelligent"). The system which is at present predominantly used for displaying characters on a screen is based on a scanning 20 method which corresponds to the scanning method used in television. On the luminescent material (the so—called "phosphor") of the cathode-ray tube a number of defined dots are excited and light up, a train of pulses being sequentially applied to the input of the tube, which pulses 25 correspond to the pulses which are obtained by successively reading the individual cots of each horizontal line of the characteris which form part of a written line. In the operating conditions which are at present usually required for high-resolution monitors (2000 - 6000 •>5 characters) it must be taken into account that the indi¬ vidual dot on the screen is excited every 20 milliseconds for 20-30 nanoseconds , with a duty cycle of approximately The light emission caused thereby depends on the properties a_s regards decay of the luminescent materials used. ■ To improve the legibility of characters, a great 5 number of parameters must be processed, such as dimensions and shape of the character, contrast, colour, electro- opcical aberrations, brightness, etc. When it is desired co increase τhe brightness of the character, the current of the impinging electron beam must be increased; however, 10 this increase causes a larger diameter of the spot, as a result of which the resolution becomes poorer, and also the contrast due to an increase of the halo across the thickness of the luminescent material. In view thereof the present invention has for '5 its object to increase the light emission of the individual dots of the luminescent material on which the electron beam impinges, so that the legibility of the displayed characters is correspondingly improved, however without the above-mentioned drawbacks. 20 According to the invention, this object; is accomplished by means of a novel display method which is . characterized in that several dots of the luminescent material arranged on τhe same vertical line of the charac¬ ter to be displayed are simultaneously excited and in that 2-a- such a line scan is ef ected that said excitation " is re¬ peated a predetermined number of times with short time in¬ tervals before it is moved in the vertical direction for the excitation of the dots of the subjacent line, .. This simultaneous and repeated excitation provided in -•J the method in accordance with the invention results in an improved duty cycle, vhich results in a higher light emission and consequently an improved legibility of the displayed character. Always in accordance with the method according - }= to the present invention, this advantageous effect can be still further increased by simultaneously exciting the corresponding dots on several vertical lines of the charac¬ ter to be displayed, or even all dors of this character, and by having the line scan effected such that this simul¬ taneous- excitation is repeated a predetermined, number of. . ti έs with short time intervals, a .synchronous shift of the transmitted picture being effected in a direction opposite to th.2 direction of line scan. An important consequence of this shift is that the occurrence of .stripes produced in the character by the scan is prevented. Normally, the horizontal scan has actually such a speed that a stripe is formed in the pic— fcure when the duration of the excitation corresponds to the period of time for analysing a complete character in¬ stead of one single dot. ¥hen the transmitted picture is caused to shift in the opposite direction with such a speed that the speed of the horizontal scan is compensated for, the formation of stripes in the picture will, however, be prevented from .occurring, so that the character appears on the screen in a fixed position without stripes and with an optimum light intensity and legibility. The- characteristics of the present invention will be better understood with reference to the accompanying drawings , in which Fig. 1 shows the variation of the excitation times of the several dots of a character on display with simultaneous and repeated excitation of a whole vertical line , Fig. 2 shows the variation of the excitation times of the several dots of the character on display with simultaneous and repeated excitation of the whole charac¬ ter, Fig. 3 is the simplified circuit diagram of an alphanumerical terminal which operates in accordance with this method and vhich serves for the simultaneous and repeated excitation of the whole character, Fig. h shows a more detailed circuit diagram of a system for emission of the electron beam, vhich system is preferably used in the terminal of Fig. 3 > Fig. 3 shows the time diagram of the current for τhe vertical deflection in the terminal shown in Fig. 3« Fig. 1 shows an example of the method for dis¬ playing an alphanumerical .character, in this case an E, with simultaneous and repeated excitation of the dots of a whole vertical line .of this character. Fig. la shows in greater detail a multiple cathode CT having seven independent emitters CT.,- CT~, arranged on a vertical line, each having a contact pin to vhich pulses are applied for activation, while Fig. 1b shows the for¬ mation of the character CR to be displayed, which is as- . - ≤embled from a large number of contiguous , vertical Tines I . - __,_ corresponding to those of the emitter cathode, - and Figs. 1c - 1g show the state of the above-mentioned cathode at consecutive operating instants t . - t - during a line scan. As shown in Figs. 1c - 1g, at instant t. all the emitters of the multiple cathode CT are energised to obtain a simultaneous excitation of all the dots of a vertical line of the luminescent material of the cathode ray tube, while the first vertical line L. of character CR is dis- played. In contrast therewith, at instant t, when the second vertical Tine I * of character CR is projected and displayed only the first, fourth and seventh emitters (CT- , CTL, CT„) of the multiple cathode will be energised and the same is effected at instants t~ and t for the lines L,.,' and Lj,. Finally, . at instant t~, which corresponds to - only the emitters CT 1 and CT~ are energized. At each of the five consecutive instants all dots of the character which form part of the same vertical line are projected and displayed, that is to say that the charac- ter is displayed by consecutive vertical lines. The same occurs, of course, also for the conse¬ cutive characters of the same written line, whose dots are projected on the luminescent material with a time interval corresponding to the spacing desired on the screen of the cathode-ray tube. Thereafter the line scanning operation is repeated some times (seven to be accurate) with short time intervals so that the simultaneous excitation of the points of several OMH lines is repeated at a high rate, which corresponds to the horizontal scanning frequency and thus -a high light intensity and. good legibility of the displayed character i≤ obtained. • As soon as this repeated scan has been ended, the scan of the next line starts. This is achieved by driving the vertiαal scan of the cathode-ray tube by a step-shaped signal which remains constant during the entire scan of a written line and is increased only at the end of the scan of the line with a fixed quantity (equal to the height of a written line plus a line space). For the practical usage of the method of Fig. 1 a terminal can be. employed vhich only differs from the conventional terminals by the use of a multiple cathode, which cathode is known per se, and by the presence of means for vertical scanning, which are suitable for effecting a step-vise scanning as described above. In contrast therewith, Fig. 2 shows an example of the display method which for ' the same alphanumerical character E effects a simultaneous and repeated excitation of all the dots of the said character. Fig. 2a shows in greater detail a multiple cathode CT with 35 independent emitters CT.. - CT_- arranged in a matrix having 7 lines and 5 columns, while Figs. 2b - 2f show the state of the above-mentioned cathode at conse¬ cutive operating instants t - t_ uring a line scan. As is shown in Figs. 2b - 2f, the operating states of the various emitters CT_. — CT,,.. are changed from one instant to the other to effect a gradual shift of the trans- mitted picture. This gradual shift is in synchronism with the line scan and in a direction opposite to the direction thereof. Thus, the formation of a stripe in the displayed picture which would otherwise be produced during the scanning motion is compensated for by the shift in the opposite direction of the transmitted picture, causing the displayed character to appear in a fixed position and with¬ out stripes on the screen. If this line scan is repeated seven times with short rime intervals, the excitation of these dots of the luminescent material of the cathode-ray tube will also be. repeated, which results in' an .increase in the duty cycle and,' consequently, the light intensity and the legibility of the character are. improved. Fig. 3 shows the simplified circuit diagram of a terminal with cathode-ray tube, which enables the dis¬ play of alphanumerical and graphic characters in accor¬ dance with the method of Fig. 2. This circuit diagram shows a cathode-ray tube TRC having a screen S, multiple—emitter cathode CT, so-called "optical electronics" OE and yokes for the horizontal and vertical deflection GO and GV. Associated with these yokes are respective circuits for horizontal and vertical deflec- tion CO and CT, the first circuit generating a normal ≤avtooτh-shaped drive signal, while the second generates a step-shaped signal of the type indicated in Fig. 5 > where¬ in T represents the total line scanning period and * £ * the period of time required for the transition "from one line ' to the other. The multiple cathode CT is driven via shift registers RS of a character generator GC which is formed by a memory of the type RA_M (random access memory) having a parallel output for columns and a controlled input for a chax-acter code signal SCC. Finally, the shift registers • R5 are coupled to a clock signal generator GS in view of the periodic shift of the data produced by character ge¬ nerator GC. The operation of the multiple cathodό CT and the shift registers RS for use of the method shown in Fig. 2 can be derived from the enlarged drawing of Fig. in which CT- j - CT 5 represent the several independent emitters of the multiple cathode, (preferably cold semiconductor- cathodes with field effect emission), RS.. - RS- represent the several shift registers, vhich are preferably included in the multiple cathode CT, CC represents the several sig¬ nals (pulses) produced by character generator GC and SC represents the clock signal produced by clock signal genera- tor C.S. It will be clear that registers RS respond to each clock pulse by moving the several data columns (ex- " citation signals for the emitter-cathodes) which we.re produced at an earlier instant by the character generator GC, one step from left to right (looking at Fig. 4) and by inserting a new data column in the column of emitters vhich is located further to the left (always in accor¬ dance with Fig. k ) . This results in the shift of the transmitted picture as shown in Figs. 2b - 2f. By means of the vertical deflection circuits CV it is further possible to repeat the line scan seven times so that the excitation of the relevant dots of the lumines¬ cent material LM of the cathode-ray tube is repeated, whereafter the scan of the next line is proceeded to. The terminal of figs. 3 and , which is only shown by way_..of example, may of course be modified exten¬ sively, which modifications are all within the scope of the invention. So it is, for example, possible to integrate the shift registers in the semiconductor material of the cathodes themselves or to provide them around or near the cathode, or even outside the cathode-ray tube. In addition, the step-vise vertical scan can be effected such tha the change from one line to the other is effected in the fly- back period of the line or in the scanning period of the line plus the flyback period. As regards the display method a middle course for the methods of Figs. 1 and 2 can be created by apply¬ ing the simultaneous excitation of corresponding dots to a character portion comprising, two or more vertical lines. It is furthermore possible to extend the simultaneous ex¬ citation of the corresponding dots to two or more charac¬ ters at a time. Further modifications will be obvious to persons skilled in the art. OMPI

Claims: CLAIMS 1. A method of displaying alphanumerical and graphic characters on the l luminescent material of a cathode-ray tube, characterized in that several dots of the lumines¬ cent material arranged on the same vertical line of the character to be displayed are simultaneously excited and that such a line scan is effected that said excitation is repeated a predetermined number of times with short time before it is moved in the vertical direction for the excitation of the dots of the subjacent line. 2. A method as claimed in Claim 1, characterized in that the corresponding dots on several vertical lines of the character to be displayed are. simultaneously ex- cited, that such a line scan is effected that said ex- - citation is repeated a predetermined number of times with short time intervals and a synchronous shift of the trans¬ mitted picture is effected in a direction opposite to the direction of line scan. 3. A method as claimed in Claim 1, characterized in that all dots of the character to be displayed- are 0 simultaneously excited, that such a line scan is effected that said excitation is repeated a predetermined number of times with short time intervals and a synchronous- shi t of τhe transmitted picture is effected in a direction op¬ posite to the direction of line scan. 5 k . A terminal for use in the method as claimed in Claim 1, characterized in that the terminal comprises a multiple cathode formed by a plurality of individual emitters , arranged on a vertical line which corresponds to a vertical line of the cathode to be displayed, while ° means are provided for simultaneously exciting the said emitters in an independent and variable way and from one instant to a subsequent instant in view of the emission of a sequence of pictures corresponding to the several lines of the above-mentioned character. 3. A terminal as claimed in Claim •-+, comprising means for horizontal and vertical deflection, arranged be¬ tween the said multiple cathode and the luminescent material of the cathode-ray tube, characterized in that said means for the vertical deflection are controlled such that a step-wise vertical scan is effected. ό. A terminal for use in the method as claimed in Claim 3, characterized in that it comprises a multiple cathode formed by a plurality of individual emitters ar¬ ranged, in a matrix of line and columns which include all dots of the character to be displayed, while means are provided for simultaneously exciting the said emitters in an independent and variable way and from one instant to a subsequent instant in view of the emission of a sequence of pictures corresponding to that of the said character but v-ith a relative synchronous shift in a direction oppo¬ site to the direction of line scan. 7. A terminal as claimed in Claim 6, characterized i that it comprises a plurality of shift registers which are controlled by a clock signal for effecting the said picture shift via the said multiple cathode. 8. A terminal as claimed in Claim 7 > characterized in that the said shift registers are integrated in the material of which the said cathode is made. 9. A terminal as claimed in Claim 6 comprising means for horizontal and vertical deflection arranged between the said multiple cathode and the luminescent material of the ' cathode-ray tube, characterized in that said means for the vertical deflection are controlled such that a step- wise vertical scan is effected.

Inventors: TISCHER ALESSANDRO, TISCHER, ALESSANDRO
Applicants: PHILIPS NV, N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1982
Main classification: G09G1
IPC codes: G09G1