METHOD AND APPARATUS FOR REVERSING THE RASTER SCAN OF A CRT

Abstract: The apparatus of the invention enables a CRT to be readily adapted to display either one type of language from left to right or a different type of language from right to left. The apparatus includes a first relay (30) for connecting a power supply (25) to a CRT driver (32), and a second relay (42) connecting the CRT to the CRT driver (32), actuation of the second relay (42) serving to reverse the signals applied to first and second leads connected to horizontal deflection coil means of the CRT. Logic means (36) control the operation of the first and second relays (30, 42) whereby, in response to the generation of a control signal indicative of raster scan reversal, the first relay (30) is actuated to disconnect the power supply (25) from the CRT driver (32) prior to actuation of the second relay (42), after which the first relay (30) is reset so as to reconnect the power supply (25) to the CRT driver (32).

Description: METHOD AND APPARATUS FOR REVERSING THE RASTER SCAN OF A CRT Technical Field The invention relates to cathode ray tubes which are utilized for providing a visual display of text material. Background Art It is generally known that some languages are displayed in one direction across the screen of a cathode ray tube and that other languages are displayed in the other direction. Specifically, in the case of- English and like European languages, the raster scan normally goes from left to right on the screen whereas in the case of Arabic and like languages, the raster scan normally goes from right to left on the screen. Summary of the Invention It is an object of the present invention to provide a method and apparatus which enables the raster scan across the screen of a cathode ray tube to be reversed in a positive and simple manner, so that the cathode ray tube can be readily adapted to display either one type of language from left to right or a different type of language from right to left. According to one aspect of the invention there is provided a method for reversing the raster scan across the screen of a cathode ray tube, characterized by the steps of generating a control signal indicative of a raster scan reversal, actuating first relay means in response to generation of said control signal so as to disconnect power supply means from driver means for the cathode ray tube, initiating operation of counter means in response to generation of said control signal, actuating second relay means in response to said counter means reaching a first count so as to reverse the signals applied to first and second leads connected to horizontal deflection coil means of the cathode ray tube, said first count being reached following disconnection of said power supply means from said driver means, and resetting said first relay means in response to said counter means reaching a second count so as to reconnect said power supply means to said driver means, said second count being reached following actuation of said second relay means. According to another aspect of the invention there is provided an apparatus for reversing the raster scan across the screen of a cathode ray tube including power supply means and driver means for supplying vertical drive and horizontal deflection signals to the cathode ray tube, characterized by first relay means for connecting said power supply means to said driver means, second relay means for connecting first and second leads connected to horizontal deflection coil means of the cathode ray tube to third and fourth leads connected to horizontal deflection signal supply means of said driver means, actuation of said second relay means serving to bring about a reversal of the connections between said first and SBcond leads and said third and fourth leads, generating means for generating a signal indicative of raster scan reversal, and control means connected .o said generating means and to said first and second relay means, said control means including timing means for controlling the operation of said first and second relay; means, whereby in response to generation of said control signal and first relay means is actuated so as to disconnect said power supply means from said driver means, whereafter said second relay means is actuated and then said first relay means is reset so as to reconnect said power supply means to said driver means. Brief Description of the Drawing One embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a block diagram of an apparatus in accordance with the invention; Fig. 2 illustrates the manner of orientation of Figs. 2A, 2B and 2C; Figs. 2A, 2B and 2C, taken together, constitute a logic circuit diagram of a CRT raster reversal board included in the apparatus of Fig. 1; Fig. 3 is a timing diagram used in explaining the operation of the apparatus; and Fig. 4 is a flow diagram of the essential steps in the operation of the apparatus. Best Mode for Carrying Out the Invention Referring now to the drawings, Fig. 1 is a block diagram of the essential components of the apparatus which include a main logic board 20 and a raster reversal board 22. A power supply 25 of 26.5 volts, or any other suitable power supply voltage, is connected by lead 24 to the raster reversal board 22. A cable 26 containing a five volt supply line and a ground return line is connected to the power supply 25 and to the main logic board 20. A 26.5 volt line 28 is coupled from a relay 30 on the raster reversal board 22 to a CRT driver board 32. The main logic board 20 is connected by a lead 34 to a control logic panel 36 on the board 22, and a cable 38 containing a five volt supply line and a ground return line couples the main logic board 20 to the raster reversal board 22. A lead 40 connects a relay 42 on the raster reversal board 22 to a CRT yoke 44. The control logic panel 36 is coupled by leads 46 and 48 to the relay 30 and the panel 36 is coupled by leads 50 and 52 to the relay 42. The CRT driver board 32 is connected to the relay 42 by cable 54 and the driver board 32 is connected to the control logic panel 36 by cable 56. Fig. 2A, 2B and 2C illustrate the raster reversal board 22 utilized in the present invention. The circuitry includes a dual D-type positive-edge- triggered flip-flop 60 with preset and clear features, which flip-flop is coupled to a quadruple 2-input exclusive OR gate 62 (Fig. 2A) , in turn connected with a dual D-type flip-flop 64 which is coupled to a hex inverter 66 (Fig. 2B) . A FONT signal on line 68 generated by the main logic board 20 of Fig. 1 provides an input for the exclusive OR gate 62, and the line 68 is connected to the flip-flop 60 and to a similar flip-flop 70 (Fig. 2A) . The output of exclusive OR gate 62 provides a DELTA FONT signal over line 72 to the flip- flop 64 (Fig. 2B). The output of inverter 66 is directed through a 51K resistor 74 and then to a pair of transistor drivers 102 and 104 which will be described later. A supply of five volts is provided through a 4.7K resistor 71 to the flip-flop 70 (Fig. 2A). A vertical drive signal for the CRT is provided over line 76 to the flip-flop 60 and to a dual 4-bit decode and binary counter 78 (Fig. 2A) , an output thereof being coupled over line 80 to a similar counter 82 and to a quadruple 2-input positive AND gate 84. The vertical drive signal is the clock signal for the reverse raster board 22. All timing values are dependent on the frequency of the vertical drive signal and the hardware is provided and set up under the assumption that the vertical drive signal is 80 Hz. The output of the AND gate 84 is coupled to a hex inverter 86, the output being connected as one input over line 88 to a 2-input positive AND gate 90. The output of AND gate 90 is coupled over lead 92 to the flip-flop 64 (Fig. 2B). A lead 94 couples the flip-flop 60 with the flip-flop 70 and provides the second input to the AND gate 90 (Fig. 2A) . A lead 96 couples the flip-flop 64 to the counters 78 and 82. The flip-flop 70 is coupled over line 98 through a 51K resistor 100 and then to a pair of transistor drivers 126 and 128 (Fig. 2B) which will be described later. The transistor drivers 102 and 104 (Fig. 2B), which are of Darlington type, are coupled together with a diode 106. A common lead 108 is coupled to the collectors of the transistors 102 and 104, to the diode 106, and to one side of a coil 110 of the relay 30 on the board 22 (Fig. 1). The lead 108 is also connected tO one side of a diode 114 (Fig. 2B), the other side of the diode being coupled by a common lead 116 to the other side of the coil 110, to a pair of capacitors 118 and 120 and to a supply of five volts. A lead 107 couples the grounding side of the diode 106 and the emitter of the transistor 104. The relay 30 includes a pair of contact type switches 122 and 124 connected to a supply voltage of 26.5 volts. The relay 30 which is driven by the transistors 102 and 104 operates to disconnect the 26.5 volt supply from the CRT driver board 32 and operates later to reconnect the supply voltage. In similar manner, the transistor drivers 126 and 128 (Fig. 2B) , which are also of Darlington type, are coupled together with a diode 130. A common lead 132 is coupled to the collectors of the transistors 126 and 128, to the diode 130, and to one side of a coil 134 of the relay 42 on the board 22 (Fig. 1). The lead 132 is also connected to one side of a diode 136 (Fig. 2B) , the other side of the diode being coupled by a common lead 138 to the other side of the coil 134, to a pair of capacitors 140 and 142 and to a supply of five volts. A lead 131 couples the grounding side of the diode 130 and the emitter of the transistor 128. The relay 42, which is of the double throw type, includes a pair of contact type switches 144 and 146 connected to individual leads 148, 150 of the cable 40 (Fig. 1) and to individual leads, 152 and 154 of the cable 54 (Fig. 1). The relay 42 which is driven by the transistors 126 and 128 operates to reverse the connections of the leads 148, 150 to the . leads 152, 154. With reference to Fig. 1, it should be noted that the cable 54 is connected to horizontal deflection signal means of the CRT driver board 32, the cable 40 is connected to horizontal deflection coil means of the CRT yoke 44, and the cable 56 is connected to the vertical drive signal supply means of the CRT driver board 32. Fig. 2C illustrates reset circuitry of a well-known type which is associated with the flip- flops 60 and 70 (Fig. 2A) and includes a lead 160 connected to lead 94 connected as an input to the flip-flops. The reset circuitry includes a timer 162 (Fig. 2C) coupled to a hex inverter 166 by lead 168, the inverter being connected to the lead 160. The reset circuitry also includes an R-C coupling network having a 47K resistor 170 and a capacitor 172 connected with a diode 174. Another R-C coupling network having a 1M resistor 176 and a capacitor 178 is connected with a diode 180. A 3.3K resistor 182 is coupled to one side of the diode 180 and to the timer 162, and a capacitor 184 is connected to the timer 162 and to ground. Fig. 3 illustrates the various timing operations of the reversing system wherein a change in • state of the FONT signal on line 68 generates a DELTA FONT signal on line 72. The DELTA FONT signal is latched through the flip-flop 64 (Fig. 2B) which in turn opens the relay 30 through the transistors 102 and 104, to disconnect the supply voltage of 26.5 volts from the CRT driver board 32 (Fig. 1). This operation enables a bleed-off of the voltage at the horizontal deflection coil means of the CRT which voltage bleed-off takes about 120 msec. At the same time that the DELTA FONT signal is generated, the counters 78, 82 (Fig. 2A) are enabled. After a count of 400 msec dependent upon the frequency of the vertical drive signal on line 76, a signal from the counters 78, 82 triggers the relay 42 (Fig. 2B) through the transistors 126 and 128 to reverse the signals applied by the leads 148, 150 to the horizontal deflection coil means. The counters 78, 82 generate another signal at the 500 msec time from the time that the DELTA FONT signal was generated. This signal resets the flip-flop 64 that is holding the relay 30 in a supply voltage disconnect position. The supply voltage of 26.5 volts is reconnected to the CRT driver board 32 and the raster scan is now oriented in a reverse direction. Fig. 4 is a flow diagram of the various steps in the practice of the invention. The start step 190 indicates a ready condition for the reversal of the raster scan. Step 192 inquires whether or not the FONT signal has changed state. The next step 193 is an indication of whether a DELTA FONT signal 72 has been generated to open the 26.5 volts supply, as at 194. The next step 196 questions whether or not the counter has effected the 400 msec count since the DELTA FONT signal 72 was generated. If true, the next step, as 198, is to reverse the polarity of the horizontal deflection coil at the CRT. The next step 200 questions whether or not the counter has effected the 500 msec count from the time that the DELTA FONT signal 72 was generated. If true, the last step 202, is to reconnect the 26.5 volts supply. The 400 msec and 500 msec times are effective and dependent upon the frequency of the vertical drive signal 76. When it is desired to return to the original scan direction, the relays 30 and 42 are operated to effect a reversal of the connections of the horizontal deflection coil means in the manner as described above. It is thus seen that herein shown and described is apparatus for reversing the raster scan across the screen of a CRT which apparatus utilizes hardware to effect the reversing operation.

Claims: CLAIMS : 1. A method for reversing the raster scan across the screen of a cathode ray tube, characterized by the steps of generating a control signal indicative of a raster scan reversal, actuating first relay means (30) in response to generation of said control signal so as to disconnect power supply means. (25) from driver means (32) for the cathode ray tube, initiating operation of counter means (78, 82) in response to generation of said control signal, actuating second relay means (42) in response to said counter means reaching a first count so as to reverse the signals applied to first and second leads (148, 150) connected to horizontal deflection coil means of the cathode ray tube, said first count being reached following disconnection of said power supply means (25) from said driver means (32), and resetting said first relay means (30) in response to said counter means (78, 82) reaching a second count so as to reconnect said power supply means to said driver means, said second count being reached following actuation of said second relay means (42) . 2. A method according to claim 1, characterized in that a vertical drive signal used in the operation of the cathode ray tube serves also as a clock signal for said counter means (78, 82). 3. A method according to either claim 1 or claim 2, characterized in that said first count occurs ' a sufficient period of time after the actuation of said first relay means (30) to enable bleed-off of the supply voltage to said driver means (32) to have taken place prior to the occurrence of said first count. 4. An apparatus for reversing the raster scan across the screen of a cathode ray tube including power supply means (25) and driver means (32) for • supplying vertical drive and horizontal deflection signals to the cathode ray tube, characterized by first relay means (30) for connecting said power supply means C25) to said driver means (32), second relay means (42) for connecting first and second leads (148, 150) connected to horizontal deflection coil means of the cathode ray tube to third and fourth leads (152, 154) connected to horizontal deflection signal supply means of said driver means (32), actuation of said second relay means serving to bring about a reversal of the connections between said first and second leads and said third and fourth leads, generating means (20) for generating a signal indicative of raster scan reversal, and control means (36) connected to said generating means and to said first and second relay means, said control means including timing means (78, 82) for controlling the operation of said first and second relay means (30, 42), whereby in response to generation of said control signal said first relay means (30) is actuated so as to disconnect said power supply means (25) from said driver means (32), whereafter said second relay means (42) is actuated and then said first relay means is reset so as to reconnect said power supply means to said driver means. 5. An apparatus according to claim 4, characterized in that said timing means includes counter means (78, 82), said driver means (32) being connected to said counter means whereby vertical drive signals supplied by said driver means serve as clock signals for said counter means.

Inventors: DUELAND KARL EDWARD, GIVENS MICHAEL DUANE, DUELAND, KARL, EDWARD, GIVENS, MICHAEL, DUANE
Applicants: NCR CO, NCR CORPORATION
Application year: 1988
Main classification: G09G1
IPC codes: G09G1, G09G5