Method and apparatus for driving display panel

Abstract: An apparatus and method for driving the display panal, e.g., AC PDP, having a first substrate, at least one display line involving first electrodes and second electrodes disposed in parallel with each other on the first substrate, a second substrate facing the first substrate, and third electrodes disposed on the second substrate and extending orthogonally to the first and second electrodes, in which write operation of the display data by a light emission is executed by carrying out a selective write discharge utilizing a memory function, are adapted to execute a write discharge for all calls and to execute an erase discharge for all cells before the selective write discharge, to thereby accumulate wall charges over the third electrodes in advance.

Description: The present invention relates to a technique of driving a display panel composed of display elements having a memory function, and particularly, to a method of and an apparatus for driving an alternating current (AC) plasma display panel (PDP). Such driving methods/apparatus can provide multiple intensity levels and adjust the luminance of a full color image plane. In an AC PDP, voltage waveforms are alternately applied to two sustain discharge electrodes, to maintain discharge and display an image by emission. Each shot of discharge lasts several microseconds after the application of a pulse. Ions, i.e. positive charges produced by the discharge,are accumulated over an insulation layer on an electrode having a negative voltage. Electrons, i.e. negative charges produced by the discharge,accumulate over an insulation layer on an electrode having a positive voltage. At first, a pulse (a write- pulse) having a relatively high voltage (a write voltage) is applied to cause discharge and produce wall charges. Thereafter, a pulse (a sustain discharge pulse) having a relatively low voltage (a sustain discharge voltage) whose polarity is opposite to that of the high voltage and which is lower than the high voltage is applied to enhance the accumulated wall charges. As a result, the potential of the wall charges with respect to a discharge space exceeds a discharge threshold voltage at which discharging starts. In this way, once the wall charges are accumulated in a cell by such a write discharge, the cell can continuously discharge if sustain discharge pulses having opposite polarities are alternately applied to the cell. This phenomenon is called a memory effect or a memory drive. The AC PDP enables various image data to be displayed by utilizing such a memory effect. These kinds of AC PDPs are classified into a two-electrode type, employing two electrodes for carrying out selective discharge (addressing discharge) and sustain discharge, and a three-electrode type additionally employing a third electrode to carry out addressing discharge. A color PDP, capable of displaying color images (full color images) with multiple intensity levels, may have a phosphor located within each cell which is excited by ultraviolet rays generated due to a discharge between different kinds of electrodes. However, this phosphor is relatively fragile against a hitting of ions, i.e. positive charges, also generated due to the discharge. The former two-electrode type PDP has a construction such that the ions collide directly with the phosphor, and therefore the life of the phosphor is likely to become shortened. On the other hand, in the latter three-electrode PDP, a surface-discharge with high voltage is carried out between a first electrode and a second electrode that are located in the same plane. In such a construction, the phosphor at the side of the third electrode is protected from the direct and strong bombardment of ions, and consequently a life of the phosphors is likely to be longer. Namely, the three-electrode PDP is advantageous in displaying color (full color) images with multiple intensity levels. Accordingly, the three-electrode type is currently used to realise such a color PDP. The amount of emission (luminance) of the three-electrode PDP is determined by the number of pulses applied to the PDP. Fig. 1 is a plan view schematically showing a conventional three-electrode and surface-discharge PDP. In Fig. 1, numeral 1 is a panel, 2 is an X electrode, 3 1 , 3 2 , ---, 3 K , ---, 3 1000 are Y electrodes, and 4 1 , 4 2 , --- 4 K , --- 4 M are addressing electrodes. A cell 5 is formed at each intersection where a pair of the X and Y electrodes crosses one of the addressing electrodes, to provide M x 1000 cells 5 in total. Numeral 6 is a wall for partitioning the cells 5, and 7 1 to 7 1000 are display lines. Fig. 2 is a sectional view schematically showing the basic structure of the cell 5. Numeral 8 is a front glass substrate, 9 is a rear glass substrate, 10 is a dielectric layer for covering the X electrode 2 and Y electrode 3 k , 11 is a protective film of an MgO film or the like, 12 in a phosphor, and 13 is a discharge space. Fig. 3 shows the conventional PDP of Fig. 1 and its peripheral circuits. Numeral 14 is an X driver circuit for supplying a write pulse and a sustain discharge pulse to the X electrode 2, 15 1 to 15 4 are Y driver ICs for supplying addressing pulses to the Y electrodes 3 1 to 3 1000 , 16 is a Y driver circuit for supplying pulses other than the addressing pulses to the Y electrodes 3 1 to 3 1000 , 17 1 to 17 5 are addressing driver ICs for supplying addressing pulses to the addressing electrodes 4 1 to 4 M , and 18 is a control circuit for controlling the X driver circuit 14, Y driver ICs 15 1 to 15 4 , Y driver circuit 16, and addressing driver ICs 17 1 to 17 5 . Fig. 4 is a waveform diagram showing a first conventional method of driving the PDP of Fig. 1. More precisely, this figure shows a drive cycle of a conventional "sequential line driving and self-erase addressing" method. This method selects one of the display lines to write display data thereto during the drive cycle. The Y electrode of the selected line is set to a ground level (GND: 0V), and the Y electrodes of the other display lines (unselected lines) are set to a potential level of Vs. A write pulse 19 having a voltage of Vw is applied to the X electrode 2, to discharge all cells of the selected line. At this time, a voltage difference between the X and Y electrodes of the selected line is Vw, and a voltage difference between the X and Y electrodes of the unselected lines is Vw-Vs. By setting Vw>Vf>Vw-Vs (where Vf is a discharge start voltage), all cells of the selected line will discharge. As the discharge progresses, the protective film 11, e.g., an MgO film over the X electrode 2 of the selected line accumulates negative wall charges, and the MgO film over the Y electrode of the selected line accumulates positive wall charges. Since the polarities of these wall charges act to reduce an electric field in the discharge space, the discharge quickly dissipatesand ends within about a microsecond. Sustain discharge pulses 20 and 21 are alternately applied to the X and Y electrodes of the selected line, so that the accumulated wall charges are added to the voltages applied to the electrodes so as to bring about repeated discharge (sustain discharge) in certain cells (ON cells) of the selected line. As explained below, other cells (OFF cells) of the selected line are not turned ON (not caused to emit light) by such sustain discharge pulses. In the case of the cells (OFF cells) that are not to be turned ON, when the first sustain discharge pulse 20a is applied to the X electrode 2, positive wall charges accumulate in the MgO film over the X electrode 2 of the selected line, and negative wall charges in the MgO film over the Y electrode of the selected line. In synchronism with the first sustain discharge pulse 21a applied to the Y electrode of the selected line, an addressing pulse (an erase pulse) 22 having a positive voltage of Va is selectively applied to the addressing electrodes of the cells not to be turned ON, i.e. the OFF cells. At this time, sustain discharge occurs in every cell of the selected line, and in the cells (the OFF cells) that have received the positive addressing pulse 22 through the addressing electrodes a further discharge occurs between the addressing electrodes and the Y electrode, resulting in a large accumulation of positive wall charges in the MgO film over the Y electrode. If the voltage Va is set such that the voltage of the wall charges exceeds the discharge start voltage, the voltage of the wall charges induces discharge when the external voltages are removed, i.e. when the potential of the X and Y electrodes is returned to Vs and that of the addressing electrodes to GND. This causes self-erase discharge, which dissipates the wall charges, in the cells not to be turned ON. Accordingly, from this moment, the further sustain discharge pulses 20 and 21 will never cause sustain discharge in the OFF cells for the remainder of the drive cycle. In the case of the cells to be turned ON (ON cells), the erase pulse (addressing pulse) 22 is not applied to the corresponding addressing electrodes, so that no self-erase discharge is caused in these cells. Accordingly, the sustain discharge pulses 20 and 21 repeatedly cause discharge (sustain discharge) in the cells turned ON. Numeral 23 represent sustain discharge pulses applied to the Y electrodes of the unselected lines. In this way, display data are written to a selected line in each drive cycle. In the example mentioned above, the write operation is carried out on the display lines line by line. Fig. 5 is a time chart showing the write operation. In the figure, "W" is a write cycle, "S" is a sustain discharge cycle, and "s" is a sustain discharge cycle of a preceding frame (field). Fig. 6 is a waveform diagram showing a second conventional method of driving the PDP of Fig. 1. More precisely, the figure shows a frame of a conventional "separately addressing and sustain-discharging type self-erase addressing" method. This method divides the frame into a total write period, an addressing period, and a sustain discharge period. During the total write period, the potential of the Y electrodes 3 1 to 3 1000 is set to GND, and a write pulse 24 having a voltage of Vw is applied to the X electrode 2, to cause discharge in all cells of all of the display lines. The Y electrodes 3 1 to 3 1000 are then returned to Vs, and a sustain discharge pulse 25 is applied to the X electrode 2, to cause sustain discharge in every cell. During the addressing period, display data are sequentially written to the display lines starting from the display line 7 1 . At first, an addressing pulse 26 1 having a level of GND is applied to the Y electrode 3 1 , and an addressing pulse 27 having a voltage of Va is applied to selected ones of the addressing electrodes 4 1 to 4 M that correspond to cells (OFF cells) not to be turned ON of the display line 7 1 , to cause self-erase discharge in these cells. This completes the write operation of the display line 7 1 . The same operation is carried out for the display lines 7 2 to 7 1000 sequentially, to write new data to all of the display lines 7 1 to 7 1000 . Numerals 26 2 to 26 1000 are addressing pulses sequentially and separately applied to the Y electrodes 3 2 to 3 1000 . During the sustain discharge period, sustain discharge pulses 28 and 29 are alternately applied to the Y electrodes 3 1 to 3 1000 and X electrode 2, to carry out sustain discharge to display an image for the frame. According to the separately addressing and sustain-discharging type self-erase addressing method, the length of the sustain discharge period determines luminance. The separately addressing and sustain-discharging type self-erase addressing method, therefore, is used for displaying an image with multiple intensity levels. For example, this method is disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 4-195188. Fig. 7 shows a method of realizing 16 intensity levels as an example of the multiple intensity level displaying technique. In this example, a frame is divided into four subframes (subfields) SF1, SF2, SF3, and SF4. In the subframes SF1, SF2, SF3, and SF4, total write periods Tw1, Tw2, Tw3, and Tw4 are equal in duration to one another, and addressing periods Ta1, Ta2, Ta3, and Ta4 are also equal in duration to one another. Sustain discharge periods Td1, Td2, Td3, and Td4 have duration ratios of 1:2:4:8. The 16 intensity levels are achieved by selectively combining the subframes to turn cells ON. Fig. 8 is a waveform diagram showing a third conventional method of driving the PDP of Fig. 1. More precisely, the figure shows a drive cycle of a conventional "sequential line driving and selective-write addressing" method. This method can be employed to drive a display panel comprising a first substrate, at least one display line, the or each display line having respective first and second electrodes disposed in parallel with one another on the said first substrate, a second substrate facing the said first substrate, and a plurality of third electrodes disposed on the said second substrate and extending orthogonally to the said first and second electrodes, the or each display line having display cells at respective locations at which one of the third electrodes crosses over the said first and second electrodes of the display line concerned. In the method a selective write discharge operation is performed on a selected display line, in which operation discharges are brought about in those cells of the selected display line that are designated by display data as being ON cells, followed by a sustain discharge display operation in which discharges are sustained in the ON cells so that, utilising a memory function of the cells, light is emitted by the ON cells during the sustain discharge display operation; the method further including an erase discharge operation carried out on the selected display line, before the said selective write discharge operation, in which subsequent discharges are prevented in all cells of the selected display line using an erase pulse applied to the first and second electrodes. In this method, generally, a negative voltage (-V s ) is applied to X and Y electrodes. Therefore, in Fig. 8, the potentials of the X and Y electrodes are changed between GND level and (-V s ). This method applies a narrow erase pulse 30 to the Y electrode of a selected line in the erase discharge operation, to turn OFF cells that are ON. In the selective write discharge operation an addressing pulse (a write pulse) 31 of a voltage (-V s ) is applied to the Y electrode of the selected line, while the potential of the Y electrodes of the other unselected lines is kept at a ground (GND) level. An addressing pulse (a write pulse) 32 having a voltage of Va is applied to the addressing electrodes of cells to be turned ON, to cause discharge in these ON cells. In the sustain discharge display operation, sustain discharge pulses 33 and 34 are alternately applied to the X electrode and the Y electrode of the selected line, to repeatedly cause sustain discharge in the ON cells so that display data is displayed by the selected display line. Numeral 35 is a sustain discharge pulse applied to the Y electrodes of the unselected lines. However, the following problems have existed in the above-mentioned driving methods of PDP (prior arts). First problem According to the driving method of Fig. 4 (the sequential line driving and self-erase addressing method) and the driving method of Fig. 6 (the separately addressing and sustain-discharging type self-erase addressing method), display data are written (i.e. selected cells are turned OFF) by self-erase discharge. The self-erase discharge occurs in the vicinity of the X and Y electrodes of each target cell at first, and gradually expands outwardly. If the cell in question has a high discharge start voltage, the cell does not accumulate sufficient wall charges, and an insufficient self-erase discharge occurs. This causes an erase error, which leads to a write error of display data. Second problem According to the driving method of Fig. 8 (the sequential line driving and selective-write addressing method), wall charges remaining in a cell in which neutralizing erase discharge has been just completed with the narrow erase pulse 30 may differ from wall charges remaining in a cell which has been OFF during a preceding frame. Neutralizing wall charges produced in a cell by the application of the narrow erase pulse 30 does not always completely remove the wall charges. Namely, the erasing will be successful if a sum of the potential of the remaining wall charges and the potential of a sustain discharge pulse does not exceed the discharge start voltage. Namely, the erasing may be complete with some wall charges being left. This is the reason why wall charges remaining in a cell in which neutralizing erase discharge has been just completed by applying the narrow erase pulse 30 sometimes differ from wall charges remaining in a cell which has been OFF in a preceding frame. If a cell adjacent to a given cell whose wall charges have been erased continues to discharge, spatial charges produced by the discharge may move toward the given cell and couple with the remaining wall charges of the given cell, to nearly cancel the wall charges of the given cell. In this case, unlike a cell that has just received the narrow erase pulse 30 and holds residual wall charges, the given cell must receive a higher voltage (V w >V f , V x =V a +V s ) to start discharging. On the other hand, the cell that has just received the narrow erase pulse 30 and holds residual wall charges may start discharging at a lower voltage (Vw=Vf, Vw>Vf) than that of the given cell, if the voltage applied has a polarity that enhances the residual wall charges. This phenomenon causes the write voltages in cells to fluctuate, so that some cells may be correctly written but others may not at the same voltage, thereby causing a write error of display data. Third problem Since parallel display panelssuch as PDPs mostly employ digital control, it is preferable to adjust luminance by digital control. However, the above-mentioned luminance adjusting method (Fig. 7) causes problems when controlling intensity levels by the use of separate addressing and sustain emission periods mentioned above. When the frequency of sustain discharge operations is about 30 KHz at the maximum, the numbers of sustain discharge cycles in subframes achieving 256 intensity levels are 2, 4, 8, 16, 32, 64, 128, and 256, respectively, because each cycle always involves two discharge operations. Namely, the number of the sustain discharge cycles is 510 in total, and if the frequency of frames is 60 Hz, the maximum frequency of sustain discharge operations will be 30.6 KHz. With the respective subframes involving these numbers of sustain discharge cycles, the minimum (LSB) subframe involves only two sustain discharge cycles, so that luminance is adjustable only in two levels between a maximum level and a half level. This is quite inconvenient. To provide a display comparable to a CRT, the display must have a function of linearly adjusting luminance in multiple levels. This is a difficult function to achieve. Further, full color display data are usually provided as analog signals, so that a display unit such as a PDP employing digital control converts the analog signals into digital signals. In this case, the analog signals may be amplified by 0% to 100%, to adjust luminance. This sort of processing of analog signals is not preferable because it may cause deterioration of the quality of the original signals. Furthermore, according to the latter luminance adjusting method, the number of sustain discharge cycles is unchanged even when the luminance is adjusted. Therefore, a number of unnecessary sustain discharge pulses, each of which is not concerned with the discharge in practice, are periodically applied to electrodes. Thus, these sustain discharge pulses cause useless power consumption which is difficult to reduce. Furthermore, even if the number of sustain discharge pulses can be successfully decreased, the number of total write operations for all cells remains unchanged. Accordingly, the relative ratio of luminance in total write period is likely to be increased as a whole. Consequently, in the case where the display is operated under lower luminance as a whole, the contrast is likely to become lower. According to a first aspect of the present invention there is provided a method of driving a display panel comprising a first substrate, at least one display line, the or each display line having respective first and second electrodes disposed in parallel with one another on the said first substrate, a second substrate facing the said first substrate, and a plurality of third electrodes disposed on the said second substrate and extending orthogonally to the said first and second electrodes, the or each display line having display cells at respective locations at which one of the third electrodes crosses over the said first and second electrodes of the display line concerned, in which method a selective write discharge operation is performed on a selected display line, in which operation discharges are brought about in those cells of the selected display line that are designated by display data as being ON cells, followed by a sustain discharge display operation in which discharges are sustained in the ON cells so that, utilising a memory function of the cells, light is emitted by the ON cells during the sustain discharge display operation; the method further including an erase discharge operation carried out on the selected display line, before the said selective write discharge operation, in which subsequent discharges are prevented in all cells of the selected display line using an erase pulse applied to the first and second electrodes; characterised in that the method further includes a total write discharge operation, performed on the selected display line before the said erase discharge operation, in which all cells of the selected line are addressed using either one of the first and second electrodes and using the said third electrodes and discharges are brought about in all cells of the line using a write pulse applied to the first and second electrodes, so that the total write discharge and erase discharge operations serve to facilitate accumulation of wall charges over the third electrodes of the cells of the selected display line in advance of the selective write discharge operation, which wall charges promote effective discharge in the designated ON cells during that selective write discharge operation. According to a second aspect of the present invention there is provided display apparatus including: a display panel comprising a first substrate, at least one display line, the or each display line having respective first and second electrodes disposed in parallel with one another on the said first substrate, a second substrate facing the said first substrate, and a plurality of third electrodes disposed on the said second substrate and extending orthogonally to the said first and second electrodes, the or each display line having display cells at respective locations at which one of the first electrodes crosses over the said first and second electrodes of the display line concerned; driving means connected to the said first, second and third electrodes of the display panel and operable to apply thereto a plurality of driving voltage pulses; and control means connected to the said driving means for controlling such application of the driving voltage pulses to the display panel such that in use of the display apparatus a selective write discharge operation is performed on a selected display line, in which operation discharges are brought about in those cells of the selected display line that are designated by display data as being ON cells, followed by a sustain discharge display operation in which discharges are sustained in the ON cells so that, utilising a memory function of the cells, light is emitted by the ON cells during the sustain discharge operation, and such that an erase discharge operation is performed on the selected display line, before the said selective write discharge operation, in which an erase pulse is applied to the said first and second electrodes of the selected display line so as to prevent subsequent discharges in all cells of the selected line; characterised in that the said control means are also operative to cause a total write discharge operation to be performed on the selected display line before the said erase discharge operation, in which total write discharge operation the control means cause address signals to be applied to either one of the said first and second electrodes and to the said third electrodes to address all cells of the said selected display line and also cause a write pulse to be applied to the first and second electrodes to bring about discharges in all cells of the selected display line, so that the total write discharge and erase operations serve to facilitate accumulation of wall charges over the third electrodes of the cells of the selected display line in advance of the said selective write discharge operation, which wall charges promote effective discharge in the designated ON cells during that selective write discharge operation. In such a method of driving a display panel such as a PDP, and in such display apparatus, write errors of display data which can occur due to an insufficiency of a self-erase discharge, etc., can be prevented and an image of improved quality can be displayed. Embodiments of the invention can provide the above advantages when the display panel is of a novel AC PDP of three-electrode and surface-discharge type, i.e. write errors occurring due to an insufficiency of a self-erase discharge etc., can be prevented and an image of improved quality can be displayed. Preferably, the said display panel is an alternating current plasma display panel in which the said memory function is realised by wall charges accumulated by means of the said selective write discharge operation. Preferably, the said display panel has a plurality of such display lines, the respective first electrodes of which are all connected together and the respective second electrodes of which display lines are independent of one another. In one preferred embodiment the method comprises: sequentially selecting said display lines one by one, carrying out such a total write discharge operation on the selected display line using the first and second electrodes, carrying out such an erase discharge operation on the selected display line by applying such an erase pulse to said second or said first electrode of that line so as to prevent discharges in all cells of that selected display line, and carrying out such a selective write discharge operation on the selected display line to turn on the designated ON cells of that line using the said second and third electrodes, thereby to write said display data to said selected display line. In another preferred embodiment the method comprises: sequentially selecting a plurality of the display lines, carrying out such a total write discharge operation on the selected display lines to bring about discharges in all cells of those selected lines using the said first and second electrodes, carrying out such an erase discharge operation by applying such an erase pulse to said second or said first electrode of each said selected display line so as to prevent discharges in all cells of the select display lines, and carrying out such a selective write discharge operation on the said selected display lines to turn on the designated ON cells of each said selected display line using the said second and third electrodes, thereby to write said display data to said selected display lines. In another preferred embodiment the method comprises: carrying out such a total write discharge operation on all of the display lines of the panel to bring about discharges in all cells of all display lines using the said first and second electrodes, carrying out such an erase discharge operation on every display line by applying such an erase pulse to said second or to said first electrode of every display line so as to prevent discharges in all cells of all the display lines, sequentially selecting the display lines one by one, carrying out such a selective write discharge operation on the selected display line to turn on the designated ON cells of that line using the said second and third electrodes, thereby to write said display data to said selected display line, and after the display data are so written to all of the display lines, carrying out such a sustain discharge display operation on all of said display lines, to sustain discharges in the designated ON cells of all said display lines, using said first and second electrodes. Preferably, in the latter embodiment, after the said selective write discharge operation is performed on each selected display line in turn, a sustain discharge pulse is applied immediately to said first electrode so as to perform a sustain discharge stabilising operation for stabilising wall charges in the cells of the selected line concerned. The said display panel may alternatively have a plurality of such display lines, which display lines are grouped into a plurality of blocks, the respective first electrodes of the lines of each block all being connected together and the respective second electrodes of the lines of each block being independent of one another. In this case the method preferably comprises: carrying out such a total write discharge operation on all of the said display lines to bring about discharges in all display lines using said first and second electrodes, carrying out such an erase discharge operation on every display line by applying such an erase pulse to said second or said first electrode of every display line so as to prevent discharges in all cells of all of the display lines, sequentially selecting the display lines one by one, carrying out such a selective write discharge operation on the said selected display line to turn on the designated ON cells of that display line using the said second and third electrodes, thereby to write said display data to the said selected display line, immediately applying a sustain discharge pulse to the said first electrode of the block that includes the selected display line so as to carry out a sustain discharge stabilising operation for stabilising wall charges in the cells of the selected display line, and after the display data are so written to all of the display lines, carrying out such a sustain discharge display operation on all of the said display lines, to sustain discharges in the designated ON cells of all said display lines, using said first and said second electrodes. A further sustain discharge operation may be carried out between the total write discharge and erase discharge operations. In another preferred embodiment the display panel has a plurality of such display lines, the respective second electrodes of which are sequentially selected and driven line by line, and the respective first electrodes of which are driven by a single driver circuit, the first and second electrodes being arranged so that the respective second electrodes of two successive display lines lie between the respective first electrodes of those two lines, and the method comprises: applying to the said second electrodes of unselected display lines a voltage that is lower than the potential of a sustain discharge pulse applied to the said second electrodes when the said sustain discharge display operation is being performed, or that is equal to an addressing voltage applied to the said third electrodes when the said selective write discharge operation is being performed. A further erase discharge operation may be carried out using the said first and second electrodes, just before the said total write discharge operation is executed. The above-mentioned further sustain discharge operation may be carried out by applying a narrow pulse, such that subsequent discharges are not prevented, immediately after the said total write discharge operation is executed. In another preferred embodiment, a frame used to write the display data of an entire image is made up of a succession of individual subframes, each of which subframes provides a different luminance and includes an addressing period, in which such selective write discharge operations are performed to rewrite such display data, and also includes a sustain emission operation in which such sustain discharge display operations are performed to display the rewritten display data, there being a plurality of sustain emission cycles in the sustain emission period of each subframe and the addressing and sustain emission periods of one subframe being temporarally separated from those of the next subframe, and the total number of sustain discharge cycles performed on each display cell in each frame being adjustable to provide the cells with a set of different possible intensity levels and to enable adjustment of luminance of said image, wherein the numbers of sustain emission cycles in the respective subframes are increased or decreased to control the luminance of the image, the ratios of the numbers of sustain discharge cycles in the different subframes being kept unchanged. This embodiment is applicable in the case in which luminance control with multiple levels is carried out by driving an AC PDP of three-electrode and surface-discharge type (this type of PDP being advantageous in applications requiring a full color display with multiple intensity levels), and can enable the electric power consumption to be reduced and can prevent an undesirable lowering of contrast in the image plane. The subframes are preferably ranked according to the amount of luminance they provide and the number of sustain emission cycles of a given subframe is determined in dependence upon the number of sustain emission cycles of the subframe of rank one higher than that of the said given subframe, the number of sustain emission cycles of the highest-ranking subframe being determined at first, and the number of sustain emission cycles of the second-highest-ranking subframe being then determined in dependence upon the determined number of cycles in the said highest-ranking subframe, and so on for all the lower-ranking subframes. The number of sustain emission cycles of the said given subframe is preferably set to be half that of the said subframe of rank one higher than that of the said given subframe. Fractions, if any, are preferably rounded up or discarded when halving the number of sustain emission cycles of the said subframe of rank one higher than that of the said given subframe. In one preferred embodiment of display apparatus embodying the invention the said control means are operative to control the said driving means to sequentially select the display lines one by one, to apply such a write pulse to the said first and second electrodes so that such a total write discharge operation is carried out on the selected display line to bring about discharges in all cells of that line, to apply such an erase pulse to the said second or the said first electrode of the said selected display line so that such an erase discharge operation is carried out on that line to prevent discharges in all cells of the selected display line, and to apply further write pulses selectively to the second and third electrodes of the selected display line to carry out such a write discharge operation on the said selected display line so that the designated ON cells of the line are turned on, thereby to write said display data to the said selected display line. In another preferred embodiment the said control means are operative to control the driving means to sequentially select a plurality of the display lines, to apply such a write pulse to the said first and second electrodes so that such a total write discharge operation is carried out on the selected display lines to bring about discharges in all cells of those lines, to apply such an erase pulse to the said second or the said first electrode of each said selected display line so that such an erase discharge operation is carried out on those lines to prevent discharges in all cells of the selected display lines, and to apply further write pulses selectively to the second and third electrodes of the selected display lines to carry out such a selective write discharge operation on those lines so that the designated ON cells thereof are turned on, thereby to write said display data to said selected display lines. The said control means are preferably operative to control the driving means such that a sustain pulse is applied between the said total write discharge and erase discharge operations. The said display panel preferably comprises an insulation layer, which in each display cell separates the third electrode from a discharge space formed between the third electrode and the said first and second electrodes, so that said wall charges can be accumulated on the said insulation layer. In one preferred embodiment a frame used to write the display data of an entire image is made up of a succession of individual subframes, each of which subframes provides a different luminance and includes an addressing period, in which such selective write discharge operations are performed to rewrite such display data, and a sustain emission period, in which such sustain discharge display operations are performed to display the rewritten display data, there being a plurality of sustain emission cycles in the sustain emission period of each subframe and the addressing and sustain emission periods of one subframe being temporally separated from those of the next subframe, and the total number of sustain emission cycles performed on each display cell in each frame being adjustable to provide the cells with a set of different possible intensity levels and to enable adjustment of luminance of said image, the numbers of sustain emission cycles in the respective subframes being increased or decreased to control the luminance of said image whilst the ratios of the numbers of sustain discharge cycles in the different sub frames are kept unchanged. The subframes are ranked according to the amount of luminance they provide, and the apparatus further comprises: first means for determining the number of sustain emission cycles of the highest-ranking subframe; and second means for determining, in dependence upon the said number determined by the first means, the number of sustain emission cycles of the next-highest ranking subframe. Means are preferably provided for preventing operations from being carried out in a subframe, if the result of the determinations by the first and second means is that the number of sustain emission cycles of the subframe concerned is zero. The apparatus preferably further comprises means for holding data according to which the number of sustain emission cycles of the next subframe is determined; means for counting the number of sustain emission cycles carried out in the present subframe; means for comparing the count value of the counting means with the data held by the holding means; and means for providing an instruction to start the next subframe if the comparison means indicates agreement between the said count value and the held data. The said first means preferably has means for optionally setting the number of sustain emission cycles of the highest-ranking subframe. In one embodiment the display lines are grouped into a plurality of blocks, the respective first electrodes of the lines of each block all being connected together and the respective second electrodes of the lines of each block being independent of one another. BRIEF DESCRIPTION OF THE DRAWINGS Reference will now be made, by way of example, to the accompanying drawings, wherein: Fig. 1 is a plan view schematically showing an example of a conventional PDP; Fig. 2 is a sectional end view schematically showing the basic structure of a cell in the Fig. 1 PDP; Fig. 3 is a view showing the conventional PDP of Fig. 1 and peripheral circuits thereof; Fig. 4 is a waveform diagram showing a first conventional method for driving the PDP of Fig. 1; Fig. 5 is a timing diagram showing a method of selecting display lines; Fig. 6 is a waveform diagram showing a second conventional method of driving the PDP of Fig. 1; Fig. 7 is a view explaining a method of displaying 16 intensity levels; Fig. 8 is a waveform diagram showing a third conventional method of driving the PDP of Fig. 1; Fig. 9 is a schematic view for explaining a method of driving a display panel embodying the present invention; Fig. 10 is a schematic view showing an operational model and drive waveforms relating to driving a conventional two-electrode type PDP; Fig. 11 is a schematic view showing an operational model and drive waveforms relating to driving a conventional PDP of three-electrode and self-erase addressing type; Fig. 12 is a schematic view showing an operational model and drive waveforms relating to driving a conventional PDP of three-electrode and selective-write addressing type; Fig. 13 is a schematic view showing an X-Y-Y-X arrangement of electrodes in a PDP; Figs. 14(a) and 14(b) show first models for explaining abnormal discharge in the Fig. 13 PDP; Figs. 15(a) and 15(b) show second models for explaining abnormal discharge in the Fig. 13 PDP; Figs. 16(a) and 16(b) shown third models for explaining abnormal discharge in the Fig. 13 PDP; Figs. 17(a) and 17(b) show fourth models for explaining abnormal discharge in the Fig. 13 PDP; Fig. 18 is a waveform diagram relating to a first embodiment of the present invention; Fig. 19 is a waveform diagram relating to a second embodiment of the present invention; Fig. 20 is a waveform diagram relating to a third embodiment of the present invention; Fig. 21 is a waveform diagram relating to a fourth embodiment of the present invention; Fig. 22 is a time chart showing an example of a method of selecting display lines according to the fourth embodiment of the present invention; Fig. 23 is a waveform diagram relating to a fifth embodiment of the present invention; Fig. 24 is a waveform diagram relating to a sixth embodiment of the present invention; Fig. 25 is a view showing capacitance present between X and Y electrodes in the Fig. 24 embodiment; Fig. 26 is a plan view schematically showing parts of a seventh embodiment of the present invention; Fig. 27 is a block circuit diagram relating to the Fig. 26 embodiment; Figs. 28 and 29 together form a waveform diagram showing a method of driving the Fig. 26 embodiment; Fig. 30 is a waveform diagram relating to an eighth embodiment of the present invention; Figs. 31(a) to 31(c) show models relating to respective operations in the Fig. 30 embodiment; Fig. 32 is another waveform diagram relating to the Fig. 30 embodiment; Figs. 33(a) to 33(c) show further models relating to respective operations in the Fig. 30 embodiment; Fig. 34 is a block diagram showing a PDP employing a driving method according to the Fig. 30 embodiment; Fig. 35 is a circuit diagram of one example of circuitry, including a Y scan driver and a Y driver, shown in Fig. 34; Fig. 36 is a waveform diagram showing an operation of the Fig. 35 circuitry; Fig. 37 is a simplified view of the Fig. 35 circuitry; Fig. 38 is a detailed circuit diagram of an X driver shown in Fig. 34; Fig. 39 is a detailed circuit diagram of an addressing driver shown in Fig. 34; Fig. 40 is a circuit diagram of another example of the above-mentioned circuitry, including a Y scan driver and a Y driver, of Fig. 34; Fig. 41 is a waveform diagram showing an operation of the Fig. 40 circuitry; Fig. 42 is a simplified view of the Fig. 40 circuitry; Fig. 43 is a circuit diagram of still another example of the above-mentioned circuitry, including a Y scan driver and a Y driver, of Fig 34; Fig. 44 is a sectional view showing a preferable PDP cell; Fig. 45 is a waveform diagram relating to a ninth embodiment of the present invention; Fig. 46 is a waveform diagram relating to a tenth embodiment of the present invention; Fig. 47 is a waveform diagram relating to an eleventh embodiment of the present invention; Fig. 48 is an operational model relating to driving the Fig. 47 embodiment; Fig. 49 is a waveform diagram relating to a twelfth embodiment of the present invention; Fig. 50 is an operational model relating to driving a thirteenth embodiment of the present invention; Fig. 51 is a waveform diagram relating to the Fig. 50 embodiment; Fig. 52 is a timing chart for explaining an example of how a driving method embodying the present invention can be adapted to adjust luminance of a PDP; Fig. 53 is a block diagram showing a circuit for realising the driving method of Fig. 52; Fig. 54 is a timing chart for explaining a conventional method of driving a PDP which does not adjust luminance; Fig. 55 is a timing chart for explaining a conventional method of driving a PDP in which luminance is adjusted by utilising erase discharge; Fig. 56 is a view showing drive waveforms of the method of Fig. 55; Fig. 57 is a timing chart for explaining a conventional method of driving a PDP in which luminance is adjusted by removing sustain discharge cycles; Fig. 58 is a view showing drive waveforms of the method of Fig. 57; Fig. 59 is a timing chart for explaining a conventional method of driving a PDP to provide multiple intensity levels and luminance adjustment; Fig. 60 is a timing chart for explaining a conventional method of driving a PDP which realise multiple intensity levels by using separate addressing and sustain discharge periods; and Fig. 61 is a view showing drive waveforms of the method of Fig. 60. DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the embodiments of the present invention, an operational model of a display panel embodying the present invention will be described with reference to the accompanying drawings, compared with conventional operational models according to prior arts. Fig. 9 is a schematic view showing an operational model relating to driving a display panel in an embodiment of the present invention. In this case, the display panel of AC PDP is illustrated schematically. Further, to clarify the characteristics of the present invention, an operational model and drive waveforms for a conventional two-electrode type PDP are illustrated in Fig. 10. Further, an operational model and drive waveform for a conventional PDP of three-electrode and self-erase addressing type are illustrated in Fig. 11. Further, an operational model and drive waveform for a conventional PDP of three-electrode and selective-write addressing type are illustrated in Fig. 12. In Fig. 9, AC PDP has a first substrate (not shown in Fig. 9), display lines each having a first electrode (X electrode 2 in Fig. 9) and a second electrode (Y electrode 3 k in Fig. 9) disposed in parallel with each other on the first substrate, a second substrate (not shown in Fig. 9) facing the first substrate, and third electrodes (addressing electrode 4 k in Fig. 9) disposed on the second substrate and extending orthogonally to the first and second electrodes. Each cell has a discharqe space formed between the first and second electrodes and the third electrode. Further, an insulation layer (a phosphor 12 or an insulation layer), which separates the addressing electrode 4 k from the discharge space, is provided. Also, another insulation layer (a protective film 11 or an insulation layer), which separates the X electrode 2 and Y electrode 3 k from the discharge space, is provided. Here, a total write discharge operation is executed by selecting the cell by the Y electrode 3 k and addressing electrode 4 k , at the first stage (1 ○), and applying a write pulse of a voltage V w to the X electrode, so that a write discharge is performed between the X electrode 2 and the Y electrode 3 k which is at ground GND (0V). Namely, in such a total write discharge operation, write discharge for all the cells of the selected display line is performed, and positive charges (ions) are accumulated over the addressing electrode 4 k . Next, at the second stage (2 ○), a sustain discharge pulse of a voltage V s (V s < V w ) is applied to the electrode 3 k , and then a sustain discharge for all the cells of the selected display line is performed. Further, at the third stage (erase discharge operation) (3 ○), an erase pulse of a voltage V s (or lower than V s ) is applied to the X electrode 2, so as to cause an erase discharge for all cells of the selected display line. Namely, wall charges at the sustain discharge electrode (over Y and X electrode) are forced to be decreased, so that the write discharge does not occur even if the sustain discharge pulse is applied to the Y electrode 3 k . At this stage, if negative wall charges (electrons) are accumulated over the Y electrode, these wall charges can work effectively on a selective write discharge of the next (fourth) stage. At the fourth stage (4 ○) (selective write discharge operation), the addressing pulse of a voltage V a is applied to the addressing electrode 4 k and the selective write discharge (addressing discharge) of the selected cell is performed utilising the wall charges that have been accumulated over the addressing electrode 4 k . Namely, it is a main characteristic of a method for driving a PDP embodying the present invention that the wall charges, which work effectively on the selective write discharge, are accumulated over the addressing electrode (phosphor 12 or dielectric layer), before the selective write discharge is executed. Further, if the charges having the opposite polarity to the charges at the addressing electrodes are accumulated over the sustain discharge electrode (Y electrode or X electrode), such wall charges further work on the selective write discharge. As a measure for realizing such a process of wall charge accumulation, it is necessary for the write discharge for all the cells and erase discharge for all the cells to be carried out. On the other hand, in a conventional two-electrode type PDP as shown in Fig. 10 (e.g., a monochrome PDP of neon orange lamp), a write discharge for all the cells is executed at the first stage (1 ○), and then a sustain discharge for all the cells is executed at the second stage (2 ○). Further, at the third stage (3 ○), a narrow erase pulse is applied to the selected cell and a selective erase discharge (erase address discharge) is performed. The unselected cell (the cell that is turned ON) is prevented from being turned OFF due to the erase discharge, by applying a cancel pulse of a voltage V s to the X electrode. In this case, by utilizing electrons and ions generated in an ON state of the first stage remain for relatively long time as the residual space charges, the selective erase discharge is performed. However, in this method, a process of accumulating wall charges over the addressing electrode is not carried out at all, before the selective erase discharge (selective write discharge) is executed, different from the method of the present invention. Further, in a conventional PDP of three electrode and self-erase addressing type shown in Fig. 11, a write discharge for all the cells is executed at the first stage (1 ○), and then a sustain discharge for all the cells is executed at the second stage (2 ○). Further, at the third stage (3 ○), the sustain discharge is executed between X and Y electrodes and simultaneously a selective write discharge is executed between addressing electrode and Y electrode. Due to this selective write discharge, large amounts of wall charges are generated. Further, at the fourth stage (4 ○), when a voltage difference between X and Y electrodes is set to zero (0), the discharge is started by virtue of the voltage generated only from the wall charges. In this case, there is no voltage difference between X and Y electrodes, and the space charges that were generated due to the discharge are neutralized and dissipated. At this time, a process of selective erase discharge (self-erase discharge) is completed. Also, in this case, a process of accumulating wall charges over the addressing electrode is not carried out at all, before the selective erase discharge is executed. Further, in a conventional PDP of three-electrode and selective-write addressing type shown in Fig. 12, an erase discharge for all the cells of the selected display line is executed at the first stage (1 ○), so that all the wall charges can be dissipated assuredly. Next, at the second stage (2 ○), an addressing pulse is applied to the addressing electrode, and then the selective write discharge (addressing discharge) is executed. Also, in this case, a process of accumulating the wall charges over the addressing electrode is not carried out. As described before, none of the above prior art methods makes effective use of wall charges that are accumulated, in advance of the selective write discharge, by carrying out the write discharge for all cells and the erase discharge for all cells, as in a method embodying the present invention. Hereinafter, an abnormal discharge which is likely to occur in an AC PDP will be explained in detail. The applicant has proposed, in Japanese Patent Application No. 4-3234 filed on January 10, 1992, a display unit that employs a novel arrangement of Y and X electrodes, to suppress reactive power caused by parasitic capacitance between the electrodes. This arrangement is an X-Y-Y-X arrangement shown in Fig. 13. In the figure, two Y electrodes (for example, Y 1 and Y 2 , Y 3 and Y 4 , ..., Y N-1 and Y N ) are disposed between X electrodes that are orthogonal to addressing electrodes A 1 to A M . Compared with a usual arrangement (an X-Y-X-Y arrangement) of X and Y electrodes, the proposed arrangement can halve a distance between opposing X and Y electrodes, to thereby suppress parasitic capacitance and reactive power. This arrangement, however, causes inconvenience depending on driving methods. In Figs. 14(a) and 14(b), an area surrounded by a dotted line shows a sectional model of two discharge cells included in the X-Y-Y-X arrangement. In Fig. 14(a), a ground (GND) voltage is applied to an addressing electrode, and a voltage of Vs is applied to the X-Y-Y-X electrodes. In Fig. 14(b), a voltage of Va is applied to the addressing electrode, and a potential of GND (a selection pulse) is applied to a selected Y electrode (Y 1 ). The cell of the electrode Y 1 then discharges to produce positive wall charges. Under this state, if the GND (a selection pulse) is applied to the adjacent electrode (Y 2 ) as shown in Fig. 15(a), abnormal discharge occurs between the cell of the electrode Y 1 that has already carried out write discharge and produced the wall charges and the cell of the electrode Y 2 , as shown in Fig. 15(b). As a result, the cell of the electrode Y 1 excessively accumulates negative wall charges, which hinders sustain discharge thereafter. Although this explanation is related to a write addressing method, the same is applicable for an erase addressing method. In Fig. 16(a), the voltage GND is applied to the addressing and X electrodes, and the voltage Vs is applied to the Y electrodes. Thereafter, the voltage Va is applied to the addressing electrode, and the GND (a selection pulse) is applied to a selected Y electrode (Y 1 ), as shown in Fig. 16(b). The cell of the electrode Y 1 discharges to produce positive wall charges. At this time, the GND (a selection pulse) is applied to the adjacent electrode Y 2 as shown in Fig. 17(a). Then, as shown in Fig. 17(b), abnormal discharge occurs between the cell of the electrode Y 1 that has already carried out write discharge and produced the wall charges and the cell of the electrode Y 2 . As a result, the cell of the electrode Y 1 enables sustain discharge, while the cell of the electrode Y 2 in extinguished to disable sustain discharge. Such an abnormal discharge in the X-Y-Y-X arrangement is avoidable by lowering the voltage applied to the Y electrodes of unselected lines less than the potential of a sustain discharge pulse, or by equalizing the same with an addressing voltage, to thereby suppress an effective voltage applied to a discharge cavity between adjacent Y electrodes below a discharge start voltage. First to eighth embodiments of the present invention will be explained with reference to Figs. 18 to 51. Fig. 18 is a waveform diagram showing the first embodiment of the present invention. The figure shows one drive cycle. This embodiment drives the PDP of Fig. 1 according to the sequential line driving method. According to this embodiment, the potential of the Y electrode of a selected line is set to GND, the potential of the Y electrodes of unselected lines is set to Vs, and a write pulse 36 having a voltage of Vw is applied to the X electrode 2, to discharge all cells of the selected line. Thereafter, the potential of the Y electrode of the selected line is returned to Vs, and a sustain discharge pulse 37 is applied to the X electrode 2, to carry out sustain discharge. A narrow erase pulse 38 is applied to the Y electrode of the selected line, to carry out erase discharge in all cells of the selected line. An addressing pulse (a write pulse) 39 having a potential level of GND is applied to the Y electrode of the selected line. The Y electrodes of the unselected lines are kept at Vs. An addressing pulse (a write pulse) 40 having a voltage of Va is applied to the addressing electrodes that correspond to cells to be turned ON of the selected line, to discharge these cells. Sustain discharge pulses 41 and 42 are alternately applied to the X electrode 2 and the Y electrode of the selected line, to repeatedly carry out sustain discharge. Consequently, display data is written to the selected line. Numeral 43 is a sustain discharge pulse applied to the Y electrodes of the unselected lines. In this way, the first embodiment carries out write discharge and then erase discharge in all cells of a selected display line, to equalize these cells before writing display data thereto. The sequential line driving method according to the first embodiment, therefore, prevents a write error of display data and displays a quality image. Fig. 19 is a waveform diagram showing a second embodiment of the present invention. The figure shows one drive cycle. Similar to the first embodiment, the second embodiment drives the PDP of Fig. 1 according to the sequential line driving method. The second embodiment applies a wide erase pulse 44 to the Y electrode of a selected line. The rest of this embodiment is the same as the first embodiment. The second embodiment equalizes all cells of a selected line before writing display data thereto. Similar to the first embodiment, the sequential line driving method according to the second embodiment prevents a write error and displays a quality image. Fig. 20 is a waveform diagram showing a third embodiment of the present invention. The figure shows one drive cycle. Similar to the first embodiment, the third embodiment drives the PDP of Fig. 1 according to the sequential line driving method. Instead of the narrow erase pulse 38 of Fig. 18, the third embodiment applies a narrow erase pulse 45 to the X electrode 2. Before the narrow erase pulse 45 to the X electrode 2, a sustain discharge pulse 46 is applied to the Y electrode of a selected line, to accumulate negative wall charges in the MgO film over the X electrode of the selected line as well as positive wall charges in the MgO film over the Y electrode of the selected line, so that the narrow erase pulse 45 may trigger erase discharge. The rest of this embodiment is the same as the first embodiment. The third embodiment equalizes all cells of a selected line before writing display data thereto. Similar to the first embodiment, the sequential line driving method according to the third embodiment prevents a write error and displays a quality image. Fig. 21 is a waveform diagram showing a fourth embodiment of the present invention. The figure shows one drive cycle. The fourth embodiment drives the PDP of Fig. 1 according to, unlike the first embodiment, the sequential multiple line driving method. According to the fourth embodiment, two display lines 7m and 7n are selected, the Y electrodes of the selected lines 7m and 7n are set to GND, the Y electrodes of unselected lines are kept at Vs, and a write pulse 47 having a voltage of Vw is applied to the X electrode 2, to discharge all cells of the selected lines 7m and 7n. Thereafter, the potential of the Y electrodes of the selected lines 7m and 7n is returned to Vs. A sustain discharge pulse 48 is applied to the X electrode 2, to carry out sustain discharge. Narrow erase pulses 49 and 50 are applied to the Y electrodes of the selected lines 7m and 7n, to carry out erase discharge in all cells of the selected lines 7m and 7n. An addressing pulse (a write pulse) 51 having a potential level of GND is applied to the Y electrode of one selected line 7m. The Y electrode of the other selected line 7n and the Y electrodes of unselected lines are kept at Vs. An addressing pulse (a write pulse) 52 having a voltage of Va is applied to addressing electrodes that correspond to cells to be turned ON of the selected line 7m, to discharge these cells. An addressing pulse (a write pulse) 53 having a potential level of GND is applied to the Y electrode of the other selected line 7n. The Y electrode of the selected line 7m and the Y electrodes of the unselected lines are kept at Vs. An addressing pulse (a write pulse) 54 having a voltage of Va is applied to addressing electrodes that correspond to cells to be turned ON of the selected line 7n, to discharge these cells. Sustain discharge pulses 55 and 56 are alternately applied to the X electrode 2 and the Y electrodes of the selected lines 7m and 7n, to repeatedly carry out sustain discharge. Consequently, display data are written to the selected lines 7m and 7n. Numeral 57 is a sustain discharge pulse applied to the Y electrodes of the unselected lines. Fig. 22 is a time chart showing the display lines sequentially selected. In the figure, "W" is a write cycle of a present frame, "S" is a sustain discharge cycle of the present frame, "w" is a write cycle of a preceding frame, and "s" is a sustain discharge cycle of the preceding frame. In this way, the sequential multiple line driving method according to the fourth embodiment equalizes all cells of selected lines before writing display data thereto, to thereby prevent a write error and display a quality image. According to the fourth embodiment, the narrow erase pulses 49 and 50 are applied to the Y electrodes of the selected lines 7m and 7n. Instead, wide erase pulses may be applied to the Y electrodes of the selected lines and a narrow erase pulse to the X electrode. Fig. 23 is a waveform diagram showing a fifth embodiment of the present invention. The figure shows one drive cycle. The fifth embodiment drives the PDP of Fig. 1 according to, unlike the first embodiment, the separately addressing and sustain-discharging method. According to the fifth embodiment, a frame is divided into a total write and erase period, an addressing period, and a sustain discharge period. The total write and erase period deals with discharge cells that have been ON in a preceding frame as well as discharge cells that have been OFF in the preceding frame, to equalize all discharge cells, i.e., to eliminate wall charges from all discharge cells. During the total write and erase period, the Y electrodes 3 1 to 3 1000 are set to GND, and a write pulse 58 having a voltage of Vw is applied to the X electrode 2, to discharge all cells. The potential of the Y electrodes 3 1 to 3 1000 is then returned to Vs, and a sustain discharge pulse 59 is applied to the X electrode 2, to carry out sustain discharge. A narrow erase pulse 60 is applied to the Y electrodes 3 1 to 3 1000 , to carry out erase discharge. This completes the total write and erase operation. During the addressing period, display data are sequentially written to the display lines from the display line 7 1 . At first, an addressing pulse 61 1 having a potential level of GND is applied to the Y electrode 3 1 . An addressing pulse 62 having a voltage of Va is applied to selected ones of the addressing electrodes 4 1 to 4 M that correspond to cells to be turned ON of the display line 7 1 , to discharge these cells. This completes the writing operation of display data to the display line 7 1 . The above operation is repeated on the display lines 7 2 to 7 1000 sequentially, to write display data to all of the display lines 7 1 to 7 1000 . Numerals 61 2 to 61 1000 are addressing pulses applied to the Y electrodes 3 2 to 3 1000 , respectively. During the sustain discharge period, sustain discharge pulses 63 and 64 are alternately applied to the Y electrodes 3 1 to 3 1000 and X electrode 2, to carry out sustain discharge and display an image for one frame. In this way, the fifth embodiment carries out write discharge and then erase discharge in all cells of all display lines, to equalize these cells before writing display data thereto. The separately addressing and sustain-discharging method according to the fifth embodiment thus prevents a write error and displays a quality image. Fig. 24 is a waveform diagram showing a sixth embodiment of the present invention. The figure shows one drive cycle. The sixth embodiment drives the PDP of Fig. 1 according to, unlike the first embodiment, the separately addressing and sustain-discharging method. The fifth embodiment (Fig. 23) applies the addressing pulses 61 1 to 61 1000 to the Y electrodes 3 1 to 3 1000 , respectively, and the addressing pulse 62 to the addressing electrodes, to discharge and write display data to the display lines. Such discharge may excessively accumulate wall charges, which will be destabilized by the application of the addressing pulse 61 1 to cause discharge just after the application of the addressing pulse 61 1 only with the voltage of the wall charges. If this happens, the wall charges will be neutralized. The sixth embodiment is intended to solve this problem. Just after the application of each of the addressing pulses 61 1 , to 61 1000 , the sixth embodiment applies a corresponding one of the sustain discharge pulses 65 1 to 65 1000 to the X electrode 2, to stabilize wall charges up to the sustain discharge period. Similar to the fifth embodiment, the separately addressing and sustain-discharging method according to the sixth embodiment prevents a write error, displays a quality image, and stabilizes wall charges after the writing of display data up to the sustain discharge period. The sixth embodiment, however, sequentially applies the sustain discharge pulses 65 1 to 65 1000 to the X electrodes 2 after the respective write addressing operations during the addressing period, even to cells of display lines where no display data are written. For example, when display data is written to the display line 7 1 , the sustain discharge pulse 65 1 is applied even to the display lines 7 2 to 7 1000 to which no display data are written. Similarly, when display data is written to the display line 7 2 , the sustain discharge pulse 65 2 is applied even to the display lines 7 1 and 7 3 to 7 1000 to which no display data are written. As shown in Fig. 25, a gap between the X electrode 2 and the Y electrode 3 K involves capacitance 66 due to the dielectric layer between the X electrode 2 and the discharge space, capacitance 67 due to the discharge cavity between the surface of the dielectric layer over the X electrode 2 and the surface of the dielectric layer over the Y electrode 3 K , and capacitance 68 due to the dielectric layer between the Y electrode 3 K and the discharge cavity. Also, capacitance Cx that does not involve the discharge cavity is present between the X electrode 2 and the Y electrode 3 K because these electrodes are formed on the same substrate. When a sustain discharge pulse is applied to discharge cells of display lines to which no display data are written during an addressing period, a charging or discharging current flows to the capacitance (the capacitance Cx that does not involve the discharge space) of the cells of the display lines where no display data are written, to thereby increase power consumption. The seventh embodiment explained below is to reduce such power consumption. Fig. 26 is a plan view schematically showing a seventh embodiment of the present invention. In the figure, numeral 69 is a panel, 70 1 to 70 4 are X electrodes, 71 1 to 71 1000 are Y electrodes, 72 1 to 72 M are addressing electrodes, and 73 is a cell. There are M x 1000 cells 73 each located at an intersection of a pair of the X and Y electrodes and one addressing electrode. Numeral 74 is a wall partitioning the cells 73, and 75 1 to 75 1000 are display lines. According to the seventh embodiment, the display lines 75 1 to 75 1000 are grouped into four blocks 76 1 to 76 4 containing consecutive 250 display lines 75 1 to 75 250 , 75 251 to 75 500 , 75 501 to 75 750 , and 75 751 to 75 1000 , respectively. These blocks 76 1 to 76 4 have X electrodes 70 1 to 70 4 , respectively. Fig. 27 shows the PDP according to the seventh embodiment and peripheral circuits thereof. In the figure, numerals 77 1 to 77 4 are X driver circuits for supplying write pulses and sustain discharge pulses to the X electrodes 70 1 to 70 4 , 78 1 is a Y driver IC for supplying addressing pulses to the Y electrodes 71 1 to 71 250 , 78 2 is a Y driver IC for supplying addressing pulses to the Y electrodes 71 251 to 71 500 , 78 3 is a Y driver IC for supplying addressing pulses to the Y electrodes 71 501 to 71 750 , 78 4 is a Y driver IC for supplying addressing pulses to the Y electrodes 71 751 to 71 1000 , 79 in a Y driver circuit for supplying pulses other than the addressing pulses to the Y electrodes 71 1 to 71 1000 , 80 1 to 80 5 are addressing driver ICs for supplying addressing pulses to the addressing electrodes 72 1 to 72 M , and 81 is a control circuit for controlling the X driver circuits 77 1 to 77 4 , Y driver ICs 78 1 to 78 4 , Y driver circuit 79, and addressing driver ICs 80 1 to 80 5 . Figs. 28 and 29 are waveform diagrams each showing a method of driving the PDP of the seventh embodiment. According to this embodiment, a frame is divided into a total write and erase period, an addressing period, and a sustain discharge period. The addressing period is further divided into first to fourth addressing periods. During the total write and erase period, the potential of the Y electrodes 71 1 to 71 1000 is set to GND, and a write pulse 82 having a voltage of Vw is applied to the X electrodes 70 1 to 70 4 , to discharge all cells of all of the display lines 75 1 to 75 1000 . The potential of the Y electrodes 71 1 to 71 1000 is then returned to Vs, and a sustain discharge pulse 83 is applied to the X electrodes 70 1 to 70 4 , to carry out sustain discharge. A narrow erase pulse 84 is applied to the Y electrodes 71 1 to 71 1000 , to carry out erase discharge. This completes the total write and erase operation. During the addressing period, display data are written to the display lines sequentially from the display line 75 1 . During the first addressing period, an addressing pulse 85 1 having a potential level of GND is applied to the Y electrode 71 1 . At the same time, an addressing pulse 86 having a voltage of Va is applied to selected ones of the addressing electrodes 72 1 to 72 M that correspond to cells to be turned ON, to discharge these cells. Immediately after that, a sustain discharge pulse 87 1 is applied to the X electrode 70 1 , to carry out sustain discharge for stabilizing wall charges up to the sustain discharge period. This completes the writing of display data to the display line 75 1 . The same operations are repeated for the display lines 75 2 to 75 250 sequentially, so that display data are written to all of the display lines 75 1 to 75 250 in the block 76 1 . Numerals 85 2 to 85 250 are addressing pulses sequentially applied to the Y electrodes 71 2 to 71 250 , respectively, and 87 2 to 87 250 are sustain discharge pulses sequentially applied to the X electrodes 70 1 after the respective addressing pulses 85 2 to 85 250 . During the second addressing period, an addressing pulse 85 251 having a potential level of GND is applied to the Y electrode 71 251 . At the same time, an addressing pulse 86 having a voltage of Va is applied to selected ones of the addressing electrodes 72 1 to 72 M that correspond to cells to be turned ON, to discharge these cells. Immediately after that, a sustain discharge pulse 87 251 is applied to the X electrode 70 2 , to carry out sustain discharge for stabilizing wall charges up to the sustain discharge period. This completes the writing of display data to the display line 75 251 . The same operations are repeated for the display lines 75 252 to 75 500 sequentially, so that display data are written to all of the display lines 75 252 to 75 500 in the block 76 2 . Numerals 85 252 to 85 500 are addressing pulses sequentially applied to the Y electrodes 71 252 to 71 500 , respectively, and 87 252 to 87 500 are sustain discharge pulses sequentially applied to the X electrodes 70 2 after the respective addressing pulses 85 252 to 85 500 . During the third addressing period (Fig. 29), an addressing pulse 85 501 having a potential level of GND is applied to the Y electrode 71 501 . At the same time, an addressing pulse 86 having a voltage of Va is applied to selected ones of the addressing electrodes 72 1 to 72 M that correspond to cells to be turned ON, to discharge these cells. Immediately after that, a sustain discharge pulse 87 501 is applied to the X electrode 70 3 , to carry out sustain discharge for stabilizing wall charges up to the sustain discharge period. This completes the writing of display data to the display line 75 501 . The same operations are repeated for the display lines 75 502 to 75 750 sequentially, so that display data are written to all of the display lines 75 502 to 75 750 in the block 76 3 . Numerals 85 502 to 85 750 are addressing pulses sequentially applied to the Y electrodes 71 502 to 71 750 , respectively, and 87 502 to 87 750 are sustain discharge pulses sequentially applied to the X electrodes 70 3 after the respective addressing pulses 85 502 to 85 750 . During the fourth addressing period, an addressing pulse 85 751 having a potential level of GND is applied to the Y electrode 71 751 . At the same time, an addressing pulse 86 having a voltage of Va is applied to selected ones of the addressing electrodes 72 1 to 72 M that correspond to cells to be turned ON, to discharge these cells. Immediately after that, a sustain discharge pulse 87 751 is applied to the X electrode 70 4 , to carry out sustain discharge for stabilizing wall charges up to the sustain discharge period. This completes the writing of display data to the display line 75 751 . The same operations are repeated for the display lines 75 752 to 75 1000 sequentially, so that display data are written to all of the display lines 75 752 to 75 1000 in the block 76 4 . Numerals 85 752 to 85 1000 are addressing pulses sequentially applied to the Y electrodes 71 752 to 71 1000 , respectively, and 87 752 to 87 1000 are sustain discharge pulses sequentially applied to the X electrodes 70 4 after the respective addressing pulses 85 752 to 85 1000 . Next, during the sustain discharge period, sustain discharge pulses 88 and 89 having a potential level of GND are alternately applied to the Y electrodes 71 1 to 71 1000 and X electrodes 70 1 to 70 4 , to carry out sustain discharge to display an image for one frame. In this way, the seventh embodiment carries out write discharge and then erase discharge in all cells of all display lines, to equalize these cells before writing display data thereto. The separately addressing and sustain-discharging method according to the seventh embodiment thus prevents a write error, displays a quality image, and maintains a stabilized state of wall charges up to a sustain discharge period after writing display data to the display lines. As mentioned above, the seventh embodiment groups the display lines 75 1 to 75 1000 into the four blocks 76 1 to 76 4 containing the consecutive 250 display lines 75 1 to 75 250 , 75 251 to 75 500 , 75 501 to 75 750 , and 75 751 to 75 1000 , respectively. These blocks 76 1 to 76 4 have the X electrodes 70 1 to 70 4 , respectively. During the addressing period, a sustain discharge pulse for stabilizing wall charges is applied only to the X electrode of the block that contains a display line to which display data is written. Accordingly, during the first addressing period, the sustain discharge pulses 87 1 to 87 250 to the X electrode 70 1 are applied only to the cells of the display lines 75 1 to 75 250 in the block 76 1 but not to the cells of the display lines 75 251 to 75 1000 of the other blocks 76 2 , 76 3 , and 76 4 . During the second addressing period, the sustain discharge pulses 87 251 to 87 500 to the X electrode 70 2 are applied only to the cells of the display lines 75 251 to 75 500 in the block 76 2 but not to the cells of the display lines 75 1 to 75 250 , and 75 501 to 75 1000 of the other blocks 76 1 , 76 3 , and 76 4 . During the third addressing period, the sustain discharge pulses 87 501 to 87 750 to the X electrode 70 3 are applied only to the cells of the display lines 75 501 to 75 750 in the block 76 3 but not to the cells of the display lines 75 1 to 75 500 , and 75 751 to 75 1000 of the other blocks 76 1 , 76 2 , and 76 4 . During the fourth addressing period, the sustain discharge pulses 87 751 to 87 1000 to the X electrode 70 4 are applied only to the cells of the display lines 75 751 to 75 1000 in the block 76 4 but not to the cells of the display lines 75 1 to 75 750 of the other blocks 76 1 , 76 2 , and 76 3 . In this way, according to the seventh embodiment, the sustain discharge pulses 87 1 to 87 1000 to the X electrodes 70 1 to 70 4 are applied only to the cells of corresponding 250 display lines during the addressing period, so that, compared with the sixth embodiment that applies sustain discharge pulses to all cells of all 1000 display lines, the seventh embodiment reduces the power consumption of sustain discharge pulses applied to the X electrodes to one fourth. The seventh embodiment groups display lines into four blocks and provides each block with X electrodes connected together. In other embodiments of the present invention, display lines may be grouped into "n" blocks ("n" being an optional number) each being provided with X electrodes connected together. In this case, the power consumption of sustain discharge pulses applied to the X electrodes during the addressing period can be reduced to l/n of that of the sixth embodiment. To provide multiple intensity levels, for example, 16 intensity levels, a frame is divided into four subframes SF1, SF2, SF3, and SF4 as shown in Fig. 7, and the operations explained above are carried out in each of the subframes. The number of sustain discharge pulses applied to the X electrode during an addressing period is larger than that of a single intensity level, so that the effect of reducing the power consumption is more pronounced with multiple intensity levels than with a single intensity level. Figs. 30 to 43 show an eighth embodiment of the present invention. This embodiment relates to a three-electrode surface-discharge AC PDP having sustain discharge electrodes of X-Y-Y-X arrangement (the arrangement of Fig. 13). To drive this PDP, the eighth embodiment turns ON all cells, erases all the cells, and addresses the cells to write display data thereto. This embodiment employs an addressing period and a sustain discharge period that are independent of each other. Fig. 30 is a waveform diagram showing the embodiment. The figure shows one drive cycle of a write addressing method according to the embodiment. Each frame comprises a total write and erase period, an addressing period, and a sustain discharge period. The total write and erase period deals with cells that have been ON in a preceding frame as well as cells that have been OFF in the preceding frame, to equalize all cells, i.e., to eliminate wall charges from all cells. Alternatively, the total write and erase period equalizes all cells with these cells keeping residual wall charges. During the total write and erase period, the Y electrodes Y 1 to Y N are set to GND, and a write pulse 90 having a voltage of Vw is applied to the X electrode, to discharge all cells. The potential of the Y electrodes Y 1 to Y N is then returned to Vs, and a discharge pulse 91 is applied to the X electrode, to carry out sustain discharge. A narrow erase pulse 92 is applied to the Y electrodes Y 1 to Y N , to carry out erase discharge. This completes the total write and erase operation. During the addressing period, display data are written to the display lines sequentially. At first, addressing pulses 93 1 to 93 N having a potential level of GND are sequentially applied to the Y electrodes Y 1 to Y N , respectively. In each of the addressing operations, an addressing pulse 94 having a voltage of Va is applied to selected ones of the addressing electrodes A 1 to A M that correspond to cells to be turned ON of the addressed display line, to discharge these cells. Consequently, display data are written to the display lines. During the sustain discharge period, sustain discharge pulses 95 and 96 are alternately applied to the Y electrodes Y 1 to Y N and X electrodes, to carry out sustain discharge and display an image for one frame. During the addressing period, this embodiment changes the voltage applied to the Y electrodes Y 1 to Y N between the potential GND of the addressing pulses 93 1 to 93 N and an intermediate potential Vy (preferably Vy=Va) that in intermediate between GND and Vs. Namely, this embodiment applies the addressing pulse of GND to the Y electrode of a selected line and the voltage Vy to the Y electrodes of the other unselected lines. Figs. 31(a) to 31(c) are models of the driving method (the write addressing method) of Fig. 30. Fig. 31(a) shows a state after the total write and erase operation. All cells are equalized. Under this state, the addressing electrode is at GND, and two Y electrodes (Y 1 , Y 2 ) adjacent to the X electrodes are at Vs. In Fig. 31(b), the addressing pulse 93 1 (GND) is applied to the Y electrode Y 1 , to carry out addressing discharge. The addressing electrode is at Va, and the electrode Y 1 is at GND. Under this state, positive wall charges (whose level is expressed as V WY1 for the sake of convenience) are produced over the electrode Y 1 by the addressing discharge. In Fig. 31(c), the addressing pulse 93 2 (GND) is applied to the adjacent Y electrode (Y 2 ). Under this state, the voltage Vy (=Va) is applied to the electrode Y 1 . Since the positive wall charges V WY1 are accumulated over the electrode Y 1 , an effective voltage applied to the discharge cavity between the electrodes Y 1 and Y 2 is given as Va+V WY1 , if no write discharge occurs between the electrode Y 2 and the addressing electrode. (In this case, wall charges above the electrode Y 2 are negligible.) Generally, Va+V WY1 <Vf (Vf being a discharge start voltage), so that abnormal discharge in the discharge space between the adjacent two Y electrodes (Y 1 , Y 2 ) is avoidable and the wall charges V WY1 over the electrode Y 1 are kept as they are. Fig. 32 is another waveform diagram according to the embodiment. The figure shows one drive cycle of an erase addressing method. Similar to Fig. 30, each frame is divided into a total write period, an addressing period, and a sustain discharge period. During the total write period, the Y electrodes Y 1 to Y N are set to GND, and a write pulse 97 having a voltage of Vw is applied to the X electrode, to discharge all cells. The potential of the Y electrodes Y 1 to Y N is then returned to Vs, and the same potential level (GND) as that of a sustain discharge pulse 98 is applied to the X electrode, to carry out sustain discharge. During the addressing period, display data are written to the display lines sequentially. At first, addressing pulses 99 1 to 99 N having a potential level of GND are sequentially applied to the Y electrodes Y 1 to Y N , respectively. In each of the addressing operations, an addressing pulse 100 having a voltage of Va is applied to selected ones of the addressing electrodes A 1 to A M that correspond to cells in which no sustain discharge is to be carried out, i.e., cells which are not turned ON of the addressed display line, to carry out erase discharge in these cells. Consequently, display data are written to the display lines. During the sustain discharge period, sustain discharge pulses 98 and 101 are alternately applied to the Y electrodes Y 1 to Y N and X electrodes, to carry out sustain discharge and display an image for one frame. Figs. 33(a) to 33(c) show models of the driving method (the erase addressing method) of Fig. 32. Fig. 33(a) shows a condition that wall charges have been produced in every cell by total writing and thereafter a sustain discharge has been already executed. The addressing electrode is at GND, and two Y electrodes (Y 1 , Y 2 ) adjacent to the X electrodes are at Vs. Fig. 33(b) shows that the addressing pulse 99 1 (GND) is applied to the electrode Y 1 to carry out erase discharge (addressing discharge). The addressing electrode is at Va, and the electrode Y 2 is at Va. The discharge produces positive wall charges over the dielectric layer in the vicinity of the electrode Y 1 . Since the positive wall charges are present over the X electrodes, the addressing discharge causes the X and Y 1 electrodes to have positive wall charges, so that no sustain discharge will occur thereafter even if sustain discharge pulses are applied. Fig. 33(c) shows that the addressing pulse 99 2 (GND) has been applied to the adjacent Y electrode (Y 2 ). Under this state, the electrode Y 1 receives a voltage of Vy (=Va), and the electrode Y 2 receives GND. Although the electrode Y 1 has the positive wall charges (whose level is expressed as V WY1 for the sake of convenience), an effective voltage (Va+V WY1 ) applied to the discharge cavity between the adjacent two Y electrodes (Y 1 , Y 2 ) does not exceed the discharge start voltage Vf, if no write discharge occurs between the electrode Y 2 and the addressing electrode, so that, similar to the write addressing method, abnormal discharge is avoidable and the wall charges over the electrode Y 1 are kept as they are. Fig. 34 is a block diagram showing a PDP driven by the method of the eighth embodiment. In the figure, numeral 102 is a controller including a display data controller 102a and a panel drive controller 102d. The display data controller 102a includes a frame memory F. The panel drive controller 102d includes a scan driver controller 102b and a common driver controller 102c. Numeral 103 is an addressing driver, 104 is a Y scan driver, 105 is a Y driver, 106 is an X driver, and 107 is a display panel. The addressing driver 103 sequentially selects addressing electrodes A 1 to A M and applies a voltage of Va thereto, according to display data A-DATA, transfer clock A-CLOCK, and latch clock A-LATCH provided by the control circuit 102. The Y scan driver 104, Y driver 105, and X driver 106 drive Y electrodes Y 1 to Y N and X electrode at predetermined voltages (Vs, Va, Vw) according to scan data Y-DATA, Y clock Y-CLOCK, first Y strobe YSTB1, second Y strobe YSTB2, Y up drive signal Y-UD, Y down drive signal Y-DD, X up drive signal X-UD, and X down drive signal X-DD provided by the control circuit 102. Fig. 35 is a schematic view showing the Y scan driver 104 and Y driver 105. The Y scan driver 104 has electrode selection circuits M 1 to M n provided for the Y electrodes, respectively, and a shift register R for generating signals Q 1 to Q n for sequentially specifying the electrode selection circuits M 1 to M n . Each (M 1 is shown as an example) of the electrode selection circuits complementarily turns ON and OFF two MOS transistors T 1 and T 2 (when one is ON, the other is OFF) during an addressing period according to an output of a logical circuit, which comprises three AND gates G 1 to G 3 and an inverter gate G 4 . When the transistor T 1 is ON, a predetermined voltage Vy (which is Va given through the blocking diode D 3 ) appears as an output O 1 . When the transistor T 2 is ON, the ground potential GND appears as the output O 1 . Namely, the Y scan driver 104 turns ON and OFF (ON=GND, OFF=Vy) a pulse (an addressing pulse) for selecting one of the Y electrodes during an addressing period. The output O 1 is connected to two MOS transistors T 3 and T 4 of the Y driver 105 through the diodes D 1 and D 2 . The transistors T 3 and T 4 turn ON and OFF (ON=GND, OFF=Vs) a pulse (a sustain discharge pulse) applied to all of the Y electrodes, according to the signals Y-UD and Y-DD. Fig. 36 is a waveform diagram showing an operation of Fig. 35. When the signal Y-UD is at high level, the transistor T 3 of the Y driver 105 is turned ON to supply the voltage Vs to all Y electrodes. When the signal Y-DD is at high level, the transistor T 4 of the Y driver 105 is turned ON to supply the voltage GND to all Y electrodes. During an addressing period, the two transistors T 3 and T 4 of the Y driver 105 are both turned OFF, and the two transistors T 1 and T 2 disposed in each of the electrode selection circuits M 1 to M n of the Y scan driver 104 are turned ON and OFF at predetermined timing. The electrode selection circuit M 1 corresponding to the electrode Y 1 will be explained. The transistor T 2 of the selection circuit M 1 is turned ON if a logical product of Y-STB1, Y-STB2, and the signal Q 1 prepared by the shift register R in synchronism with Y-CLOCK is "1." The output O 1 is then changed to GND, which is supplied to the electrode Y 1 . The transistor T 1 of the selection circuit M 1 is turned ON if a logical product of the signal Q 1 and Y-STB1 is "0" and Y-STB2 is at high level. Then, a voltage of Vy is supplied to the electrode Y 1 . Fig. 37 is a simplified view of Fig. 35. In the figure, the two transistors T 3 and T 4 of the Y driver 105 are kept OFF, and the two transistors T 1 and T 2 of the selection circuit M i (i being one of 1 to n) are turned ON and OFF to secure a current path (indicated with white arrow marks) for providing addressing discharge pulses. Alternatively, the two transistors T 1 and T 2 of the selection circuit M i are kept OFF, and the two transistors T 3 and t 4 of the Y driver 105 are turned ON and OFF to secure a current path (indicated with black arrow marks) for providing sustain discharge pulses. As explained above, the embodiment sequentially applies addressing pulses 106 1 to 106 N having a potential level of GND to the Y electrodes Y 1 to Y N , respectively, during an addressing period. While a given Y electrode is not receiving the addressing pulse, i.e., during an unselected period of the given Y electrode, this Y electrode receives a voltage of Vy (=Va), which is substantially intermediate between GND and Vs. As a result, an effective voltage including the potential of positive wall charges accumulated due to write discharge can be reduced (compared with applying a voltage of Vs), to avoid abnormal discharge between adjacent two Y electrodes when one of them is selected (at GND). Accordingly, the wall charges are kept stabilized up to a sustain discharge period. According to the eighth embodiment, the range of voltages handled by the Y scan driver 104 is from GND to Vy, which is about half the range of voltages (GND to Vs) handled by the Y driver 105. This helps reducing the withstand voltage of the Y scan driver 104 whose scale is increased in proportion to the number of Y electrodes, and thus contributing to high integration (LSI). Further, the detailed circuit diagram of the X driver 106 of Fig. 34 is illustrated in Fig. 38. This X driver 106 includes a pair of complementary MOS transistors T 5 , T 6 in which switching operation under high electric power can be performed, so that a write pulse of a voltage V w and a sustain discharge pulse of a voltage V s can be supplied to the given X electrode. Typically, the transistor T s at the upper side is composed of P-channel MOS, to which up drive signal X-UD is input, so that the voltage level of X electrode becomes V w or V s . On the other hand, the transistor T 6 is composed of n-channel MOS, to which down drive signal X-DD is input, so that the voltage level of X electrode becomes GND (0V). For example, in the case where the write pulse of a voltage V w is applied to the given X electrode, the power supply voltage of the transistor T 5 , to which up drive signal X-UD is supplied, is transferred to V w in accordance with the timing of level change of up drive signal X-UD. Further, the detailed circuit block diagram of the addressing driver 103 of Fig. 34 is illustrated in Fig. 39. In Fig. 39, the addressing driver 103 comprises an N bit·shift register 407 which serially transfers display data of N bit, in accordance with display data A-DATA and transfer clock A-CLOCK issued from a control circuit 402. The above-mentioned addressing driver 103 further comprises an N bit·latch 408 which selects a plurality of address electrodes A 1 to A M sequentially in accordance with latch clock A-LATCH; and a plurality of high voltage supply units 409 which supplies relatively high voltage V a to the addressing electrode selected in accordance with output signals issued from the N bit·latch 408. Further, the high voltage supply units 409 of N are provided corresponding to the N bit data. Each of these units includes at least one logical circuit 409a composed of AND gate, etc., and a pair of complementary transistor T 7 , T 8 . In this case, only when the given data which is output from the latch 408 is "1" and the corresponding addressing strobe A-STB becomes enable, the corresponding addressing pulse (outputs 1 to N) of a voltage V a is output from the corresponding high voltage supply unit 409. Fig. 40 shows other arrangements of the Y scan driver and Y driver. What is different from Fig. 35 is that the Y scan driver is of floating type. Namely, two transistors T 1 ' and T 2 ' of the Y scan driver 104' are connected between a voltage of Vy (=Va) given through the blocking diode D3 and a voltage (Vs or GND) supplied from two transistors T 3 ' and T 4 ' of the Y driver 105'. The transistors T 1 ', T 2 ', T 3 ', and T 4 ' are selectively turned ON and OFF to set an output O i of a selection circuit M i ' to one of GND, Vs and Vy. Numeral 108 is an isolation photocoupler, G 11 and G 12 are AND gates, G 13 and G 14 are inverter gates, and G 15 is an OR gate. Fig. 41 is a waveform diagram showing an operation of Fig. 40. When the signal Y-UD is at high level, the transistor T 3 ' of the Y driver 105' is turned ON to provide all of the Y electrodes with a voltage of Vs. When the signal Y-DD is at high level, the transistor T 4 ' of the Y driver 105' is turned ON to provide all of the Y electrodes with a potential of GND. During an addressing period, the transistor T 4 ' of the Y driver 105' is kept ON to fix the floating potential of the Y scan driver 104' at GND. When the transistor T 2 ' of the selection circuit M 1 ' is turned ON under this state, the output O 1 is set to GND, which is provided to the electrode Y 1 . When the transistor T 1 ' is turned ON, a voltage of Vy is supplied to the electrode Y 1 through the transistor T 1 '. Fig. 42 is a simplified view of Fig. 40. When the transistor T 4 ' of the Y driver 105' is ON, the two transistors T 1 ' and T 2 ' of each selection circuit M i ' are turned ON and OFF, to secure a current path (indicated with white arrow marks) for providing addressing discharge pulses. When the transistor T 2 ' of the selection circuit M i ' is ON, the two transistors T 3 ' and T 4 ' of the Y driver 105' are turned ON and OFF, to secure a current path (indicated with black arrow marks) for providing sustain discharge pulses. Fig. 43 shows a modification of Fig. 35. A switch 109 switches two voltages Va and Vs from one to another. During an addressing period, the voltage Va is selected, and during other periods, the voltage Vs is selected. Fig. 44 is a sectional view showing a cell of a preferable PDP applicable for the above embodiments. This PDP cell has a novel structure around an addressing electrode, to positively accumulate wall charges on a dielectric layer over the addressing electrode, thereby increasing a margin in an applied voltage between the addressing electrode and a Y electrode during write discharge, and reducing an applied voltage between the addressing electrode and the Y electrode during selective discharge. In Fig. 44, the addressing electrode 310 is separated from a discharge space 311 by completely filling a gap between walls 312a and 312b with a dielectric layer 313 and phosphors 314a and 314b. The phosphors 314a and 314b may be made of ceramics such as: (Green) Zn 2 SiO 4 :Mn (Red) Y 2 O 3 :Eu (Blue) BaMgAl 14 4O 23 :Eu 2+ The thickness of the phosphors is set to be sufficient to isolate the addressing electrode from the discharge space and accumulate charges. If these conditions are satisfied, a phosphor may be disposed in place of the dielectric layer 313, to accumulate charges. To sequentially drive display lines of the PDP having such arrangement, write discharge is firstly carried out between the X electrode and a selected Y electrode, to promote discharge between each addressing electrode and the X electrode and form spatial charges. The polarities of the spatial charges are negative on the X electrode and positive on the addressing electrode and on the Y electrode. Electrons (negative charges) are accumulated over the X electrode, and ions (positive charges) are accumulated over the addressing electrode and over the Y electrode. When a sustain discharge pulse causes sustain discharge in every cell, wall charges having an inverted polarity are accumulated, so that an erase pulse applied to the Y electrodes causes erase discharge in every cell. The erase discharge reduces the wall charges, so that no sustain discharge will occur even with the application of sustain discharge pulses, because an effective voltage in insufficient. The effective discharge voltage for causing write discharge between a selected Y electrode and an addressing electrode is a sum of the potential of wall charges accumulated over the addressing electrode and a voltage (an addressing voltage) applied to the addressing electrode, so that even a low addressing voltage can surely cause write discharge. Fig. 45 is a waveform diagram showing a ninth embodiment of the present invention. According to the first to eighth embodiments as described before, the method for driving a display panel such as a PDP carries out write discharge in all cells at the first stage to accumulate wall charges on an insulation layer covering addressing electrodes. These wall charges effectively work and enhance a voltage applied to the addressing electrodes to carry out addressing write discharge for selecting cells. This results in decreasing the addressing voltage. This method, however, is likely to cause some troubles if the wall charges are excessively formed on the insulation layer on the addressing electrodes. These excessive wall charges may cause excessive addressing write discharge to write even unselected cells, The excessive addressing write discharge also produces a large amount of wall charges, which may cause self-erase (self-extinguish) discharge just after the application of the write addressing pulse. There are several reasons why such excessive wall charges are formed on the insulation layer on the addressing electrodes by the write discharge carried out in each cell. When a cell has been ON in the preceding frame, wall charges remaining in the cell from the preceding frame is added to a total write pulse applied to the cell through the X electrode. Namely, the effective voltage in the discharge space of the cell will be a sum of the applied voltage and the voltage of the remaining wall charges, to cause very strong discharge. In this case, positive charges, i.e., ions hit the insulation layer, which may be made of phosphor, on the addressing electrodes. The phosphor is vulnerable to the ions so that its composition will be changed by the hitting ions, to deteriorate its light emitting performance. To address these troubles, as shown in Fig. 45, it is preferable that an erase discharge is carried out in cells which have been ON in the preceding frame, to erase or reduce wall charges in these cells, and total write discharge for all these cells is carried out. In such a method, irrespective of ON and OFF states of cells in the preceding frame, it is possible for uniform total write discharge to be carried out in every cell, to thereby prevent extremely strong discharge, which may otherwise cause addressing errors, the erroneous writing of adjacent cells, unwanted self-erase discharge, and damage to phosphor. The ninth embodiment thus stabilizes images displayed on a display panel and extends the service life of the panel. To be more specific, the ninth embodiment shown in Fig. 45 applies an erase discharge pulse to the Y electrode of the selected display line just before a write pulse to the X electrode. This erase discharge pulse erases or reduces wall charges in cells of the selected display line that have been ON in the preceding frame. As a result, excessively strong total write discharge will never occur in any cell. Fig. 46 shows drive waveforms of a tenth embodiment. This embodiment applies an erase pulse to the Y electrode of every display line just before total write discharge. Similar to the ninth embodiment, the total write discharge will never be too strong in any cell. According to the above-mentioned ninth and tenth embodiments, an erase pulse is inserted just before a total write operation, to prevent excessively strong total write discharge and addressing errors, and extend the service life of phosphor of a display panel. Fig. 47 is a waveform diagram showing an eleventh embodiment of the present invention. In this embodiment, in the case where a write discharge for all cells is carried out, the method is adapted to accumulate charges on an insulating layer made of, for example, phosphor covering addressing electrodes. The accumulated charges advantageously work in the next addressing write discharge. This results in further reducing the addressing voltage Va. The novel means utilized in the eleventh embodiment additionally accumulates charges by a sustain discharge to be carried out after the total write discharge. The charges thus accumulated more advantageously work in the addressing write discharge, to thereby help further decrease the addressing voltage. Such a lowered addressing voltage enables the addressing drivers to be integrated, images to be displayed with full colors and multiple intensity levels, and power consumption to be reduced. In Fig. 47, it should be noted that a sustain discharge pulse applied to an X electrode just after a write pulse is narrow. Fig. 48 is a model of an operation of the eleventh embodiment involving the narrow sustain discharge pulse. At the first stage (1 ○), write discharge carried out in all cells accumulates positive charges on an insulation layer covering addressing electrodes in the vicinity of the X electrode. Since addressing write discharge is going to be carried out between the addressing electrodes and a Y electrode, it is preferable if the charges on the insulation layer are located in the vicinity of the Y electrode. At the second stage (2 ○), when the narrow sustain discharge pulse is applied, the X electrode is set to GND (0V) to carry out sustain discharge. Immediately after this, i.e., before space charges produced by the discharge entirely accumulate as wall charges on the X and Y electrodes to extinguish the space charges, the narrow sustain discharge pulse disappears. As a result, the X and Y electrodes are set to a potential level of Vs, and only the addressing electrodes are at GND. Positive charges among the remaining space charges accumulate on the insulation layer covering the addressing electrodes at a position having the lowest potential, in particular, in the vicinity of the Y electrode. Thereafter, at the third stage (3 ○), an erase discharge is carried out between the X and Y electrodes. Lastly, addressing write discharge is carried out. At this time, the positive wall charges on the addressing electrodes in the vicinity of the Y electrode advantageously work. This results in remarkably reducing the externally applied addressing voltage. Fig. 49 shows drive waveforms of a twelfth embodiment. This embodiment also applies a narrow sustain discharge pulse after a total write operation, to provide the same effect as in the eleventh embodiment. The twelfth embodiment employs a narrow sustain discharge pulse to accumulate wall charges that advantageously work in addressing the write discharge. Figs. 50 and 51 show an operational model and drive waveforms of a thirteenth embodiment, respectively. In all the embodiments described before, a display panel is constructed such that the write pulse of a voltage Vw is applied to X electrodes. However, in an alternative driving method the write pulse can be applied to Y electrodes, instead of X electrodes, as shown in Figs. 50 and 51, and in this case also it is expected to accumulate wall charges over the addressing electrode, as in the other embodiments. Hereinafter, a concrete example, in which a method and apparatus according to the present invention are applied to the adjusting of luminance of an AC PDP will be described with reference to the accompanying drawings. Fig. 52 is a timing chart showing an AC PDP driving method for adjusting luminance of a PDP. This method handles 256 intensity levels and, when the frame frequency is 60Hz, has a maximum frequency of sustain discharge of 30.6KHz. In the figure, a frame that forms an image plane is composed of subframes SF1 to SF8. The weight of luminance of the subframe SF1 is maximum, and the number of sustain discharge cycles thereof is N SF1 , which is 256. When an image is displayed with maximum luminance, the number of sustain discharge cycles in the subframe SF1 is 256, and the number of sustain discharge cycles (N SF2 ) in the next subframe (whose weight of luminance is the second largest)is half of N SF1 , i.e., 128. In this way, the numbers N SF1 to N SF8 of sustain discharge cycles in the subframes SF1 to SF8 are determined as follows: N SF1 :N SF2 :N SF3 :N SF4 :N SF5 :N SF6 :N SF7 :N SF8 =256: 128: 64: 32: 16: 8: 4: 2 If it is required to reduce the luminance by, for example, 10%, the number N SF1 of sustain discharge cycles in the subframes SF1 is reduced to 230 (256 x 0.9). The numbers N SF1 to N SF8 of sustain discharge cycles of the subframes SF1 to SF8 are determined by successively halving the preceding (higher) number of cycles as follows: N SF1 :N SF2 :N SF3 :N SF4 :N SF5 :N SF6 :N SF7 :N SF8 =230: 115: 57: 28: 14: 7: 3: 1 In this way, the numbers of sustain discharge cycles (the numbers of sustain emission operations) in the subframes SF1 to SF8 are increased or decreased (in the above example, decreased to 0.9 of the full values) to adjust the luminance. When displaying an image on a PDP with multiple intensity levels, the embodiment shown in Fig. 52 adjusts luminance in multiple levels by digital control, to thereby make the display unit comparable to a CRT. Fig. 53 shows a circuit for determining the numbers of sustain discharge cycles in the respective subframes. In the figure, adjusting means (a volume unit) 111 enables a user to freely set a luminance value from the outside. An A/D converter 112 converts an analog voltage signal set through the volume unit 111 into an 8-bit digital signal. A selector 113 selects an input A (an output of the A/D converter 112) or an input B (an output Y of a divider 115) in response to a selection signal SEL (an output Y of a decoder 119). A latch 114 latches an output Y of the selector 113 in response to a clock input CK (an output Y of a comparator 117). The latch 114 comprises a D flip-flop for holding a value that determines the number of sustain discharge cycles of the next subframe. The divider 115 halves an input A (an output Q of teh latch 114). The divider 115 comprises, for example, a shift register whose output Y (= A/2) is connected to the input B of the selector 113. If the halved input A provides fractions, the divider 115 discards the fractions. An 8-bit 256-base counter 116 is reset in response to a clear input CLR (the output Y of the comparator 117). The counter 116 counts the number of sustain discharge cycles in response to a clock input CK (a clock signal CKS provided by a drive waveform generator). The comparator 117 compares an input A (the output Q of the latch 114) with an input B (an output Q of the counter 116). A 3-bit octal counter 118 is reset in response to a clear input CLR (a vertical synchronous signal VSYN) and is activated in response to an enable signal ENA (the output Y of the decoder 119), to count a clock input CK (the output Y of the comparator 117) for specifying a subframe. The NAND logic decoder 119 responds to three output bits QA, QB, and QC of the counter 118. An OR logic decoder 120 responds to the 8-bit output of the selector 113. A latch 121 holds an output Y of the decoder 120 in response to a clock input CK (the output Y of the comparator 117). An output Q of the latch 121 provides a high-voltage circuit with a disable signal D-ENA for disabling a high-voltage drive waveform. Operations of the circuit of Fig. 53 will be explained. The volume unit 111 determines the potential of an analog signal provided to the A/D converter 112. The A/D converter 112 provides an 8-bit output. If the input signal is at the maximum level, the A/D converter 112 will provide a digital value of 255. This "255" determines the number of sustain discharge cycles of the subframe SF1 having the maximum luminance. The counter 116 counts 256 counts ranging from 0 to 255, each of which corresponds to the number of sustain discharge cycles. When the subframe SF1 is started, the subframe specifying counter 118 must have been just cleared in response to the vertical synchronous signal VSYN, and therefore, the counter 118 provides 0 (QA to QC). Namely, signals MSF0 to MSF2 are each 0, and therefore, the output Y of the decoder 119 will be 1 due to NAND logic. Accordingly, the selector 113 selects the input B in response to "1" of the output Y (the selection signal SEL) of the decoder 119. Before this, the decoder 119 has provided the selector 113 with "0" for the subframe SF8 (the last subframe) in a preceding frame. Due to this "0", the selector 113 has selected the input A (the output of the A/D converter 112), which has been temporarily stored in the latch 114. The output Q (255 at present) of the latch 114 and the output Q (the number of sustain discharge cycles) of the counter 116 are simultaneously provided to the inputs A and B of the comparator 117, respectively, and compared with each other. Once sustain discharge is repeated 256 times, the counter 116 provides "255" so that A=B in the comparator 117, which then activates the output Y. In response to the activated output Y of the comparator 117, the counter 118 is incremented by one. As a result, the subframe SF1 is complete, and the next subframe SF2 in started. The latch 114 holds a new value. When the subframe SF1 is started, the output Y of the decoder 119 is changed to "1", and the selector 113 selects the input B, i.e., the output Q f the latch 114 halved by the divider 115. Accordingly, the latch 114 holds "127" obtained by halving "255". When sustain discharge is repeated 128 times in the subframe SF2, the next subframe SF3 is started. After all subframes SF1 to SF8 are complete, the operations are stopped until the next frame is started in response to the vertical synchronous signal VSYN. To adjust luminance, the volume unit 111 is controlled to change an analog voltage value provided to the A/D converter 112. In the luminance adjusting method of Figure 52, as the luminance is decreased, there will come a point at which one or a plurality of subframes should have no sustain discharge cycles. In this case, the number of sustain discharge cycles is zeroed sequentially starting from the first subframe which should have no sustain discharge cycles. If the number of sustain discharge cycles is zeroed in a subframe, the addressing period of the subframe will be entirely useless because no sustain discharge nor emission display operation are carried out even if cells are selected by addressing discharge in the subframe. In spite of this, the conventional driving method employing the addressing method explained above (Figure 7) turns ON all cells and then carries out erase discharge to extinguish cells to be turned OFF. Accordingly, even the cells to be turned OFF will slightly emit light (so-called "background emission") during the addressing period, resulting in deterioration of contrast. When display luminance is increased, the background emission will not cause a big problem in the contrast because there is a large difference between the display luminance and the background luminance. When the display luminance is decreased the background luminance may cause deterioration in the contrast because the background luminance is unchanged even though the display luminance is decreased. This results in deterioration in the quality of an image displayed. To solve this problem, a preferred embodiment of the present invention does not carry out any operations (the display data rewriting operation) during the addressing period in a subframe that carries out no sustain discharge. The number of sustain discharge cycles of the next subframe is obtainable during the present subframe. Namely, if the output Y of the selector 3 is zero in a subframe "N", the number of sustain discharge cycles in a subframe "N+1" will be one. Accordingly, the numbers of sustain discharge cycles of subframes following the subframe "N+1" are each zero, so that these subframes do not require the addressing operation. To realize this sort of control, the embodiment of Figs. 52 and 53 employs the decoder 120, which computes an OR logic of an 8-bit input (bits A0 to A7), i.e., the value (the output Y of the selector 113) that determines the number of sustain discharge cycles of the next subframe. If this value becomes zero, the latch 121 holds the value when the next subframe is started, and the output Q of the latch 121 provides the disable signal D-ENA for disabling a high-voltage drive waveform. In the following subframes, the output Q of the latch 114, the output Y of the divider 115, the output Y of the selector 113, and the output Y of the decoder 120 are zeroed, so that the high-voltage drive waveform is continuously disabled. In the subframe SF1 of the next frame, the disabled state is canceled. Stopping high-voltage pulses in subframes which do not carry out sustain discharge eliminates useless power consumption, to thereby drive the PDP with less power. Since the total write operation is not carried out in these subframes, contrast is not deteriorated, and a quality image is displayed with high contrast even under low luminance. As explained above, the Figure 52 embodiment drives a display panel with use of separate addressing and sustain emission (discharge) periods to display a full color image with multiple intensity levels and adjust luminance in multiple levels. The embodiment of Figs. 52 and 53 decreases the luminance of the display panel without increasing reactive power and drives the display panel with low Dower depending on the luminance. If the present embodiment is applied for an AC PDP involving a total write operation, it improves contrast under low luminance. Further, to clarify the characteristics of a method of adjusting the luminance of an AC PDP embodying the present invention, some conventional methods (prior arts) of adjusting the luminance of AC PDP will be briefly described with reference to Figs. 54 to 61 mentioned below. Fig. 54 is a timing chart showing an example of a conventional method of driving a monochrome PDP that does not adjust luminance. In the figure, "W" is a write cycle in which write discharge may be carried out, "S" is a sustain discharge cycle for turning ON cells that have been written during the write cycle W, and "S" is a sustain discharge cycle for turning ON cells that have been written during a write cycle in a preceding frame. Each frame involves a write discharge, a sustain discharge, and an erase discharge. When achieving the maximum luminance, the erase discharge is not carried out, and only a rewriting operation is carried out according to new data in a write cycle of the next frame. There are two methods to reduce the maximum luminance. One achieves a predetermined number of sustain discharge cycles and then an erase discharge cycle by inserting an erase pulse, to stop the sustain discharge. The other periodically removes sustain discharge cycles. Fig. 55 is a timing chart showing an example of the former method (the erase pulse inserting method), and Fig. 56 shows drive waveforms of Fig. 55. In Fig. 55, the rewrite cycles W and sustain discharge cycles S are the same as those of Fig. 54. "E" is an erase discharge cycle for applying an erase pulse, and "e" is a sustain discharge cycle. In the cycle e, a cell is not turned ON (kept OFF) because it has been extinguished in a preceding erase cycle E. In Fig. 56, a write pulse (1) is applied to a Y-electrode to carry out write discharge in all cells of a corresponding line. Selective erase pulses (2) and (3) are applied to the Y-electrode and A-electrodes. Cells selected by the pulse (3) are extinguished. The pulses (1) to (3) are applied during the cycle W. An erase pulse (4) is applied during the cycle E. According to this method, an emission period is equal to a sustain discharge period that starts with a write pulse and ends with an erase pulse. Namely, luminance is controllable depending on a position where the erase pulse is inserted after the write cycle. Fig. 57 is a timing chart showing an example of the latter method (the sustain discharge thinning method), and Fig. 58 shows drive waveforms of Fig. 57. In Fig. 57, cycles W and S are the same as those of Figs. 54 and 55. If a cycle for applying no sustain discharge pulses coincides with a cycle W, only a rewriting operation is carried out therein. In Fig. 58, pulses (1) to (3) are the same as those of Fig. 56. Sustain discharge pulses (4) are not applied in the "sustain discharge pulse removed" cycles shown in Fig. 57. If the intervals between such "removed" cycles according to this method are eight cylces, the luminance is adjustable in eight levels. The above two known methods are widely used for adjusting luminance in AC PDPs. Luminance adjustment and intensity levels will be explained. Fig. 59 is a timing chart showing a method of driving a PDP, which adjusts luminance and displays a plurality (4 to 16) of intensity levels. In the figure, cycles W and S are the same as those of Fig. 55. This method selects (addresses) two lines per drive cycle, so that it must apply two selective erase pulses per drive cycle. This means that there is no temporal margin for inserting an erase pulse, and therefore, sustain discharge pulses are removed to adjust luminance. luminance. To maintain a ratio of intensity levels, intervals of removing sustain discharge pulses must be a divisor of the number of drive cycles in a subframe whose weight of luminance is minimum (LSB). For example, if 16 intensity levels are employed and if a frame comprises 480 drive cvcles (the frequency of a horizontal synchronous signal), a ratio of drive cycles of the subframes will be 1:2:4:8. Namely, the subframes involve 32, 64, 128, and 256 drive cycles, respectively. In this case, luminance is adjustable in 32 levels because the minimum (LSB) subfield involves 32 cycles. For displaying an image with full colors, each color must involve 64 to 256 intensity levels. This is not achievable by the conventional multiple addressing method of Fig. 59. Accordingly, the present applicant has proposed a panel driving method, which controls intensity levels with use of separate addressing and sustain emission (discharge) periods (Japanese Unexamined Patent Publication (KOKAI) No. 4-195188). Fig. 60 is a timing chart showing this proposal, and Fig. 61 shows driving waveforms of the proposal. In Fig. 60, subframes SF1 to SF4 are temporally separated from one another over a full image plane. Each of the subframes involves an addressing period for rewriting display data and a sustain emission (discharge) period for carrying out an emission display operation according to the rewritten display data. Reference marks N SF1 to N SF4 are the numbers of sustain discharge cycles carried out in the subframes SF1 to SF4, respectively. In this example, N SF1 :N SF2 :N SF3 :N SF4 = 1:2:4:8. In Fig. 61, a total write operation is carried out at first. Therefore, lines are sequentially selected one by one, and erase discharge is selectively carried out in cells not to be turned ON of the selected line according to display data. After the selective erase discharge is carried out in every line, sustain discharge is carried out. The numbers of sustain discharge cycles of the subframes differ from one another. If there are 256 intensity levels, a ratio of the sustain discharge cycles of the subframes will be 1:2:4:8:16:64:128. The number of sustain discharge cycles per frame is usually about 500. If the frequency of frames is 60 Hz, the frequency of sustain discharge cycles is 30 KHz. Instead of changing the numbers of sustain discharge cycles in the subframes to adjust luminance, there is a method of changing the level of an input signal (display data). Parallel display panels such as PDPs mostly employ digital control. Accordingly, an analog input signal (display data) is converted into a digital signal, which is supplied to a control circuit. In this case, luminance is adjustable by controlling the amplitude of the analog data just before the AD conversion. Alternatively, the digital data after the AD conversion may be multiplied by 0 to 100%, to control the level of the signal. In any case of the conventional methods for adjusting luminance as shown in Figs. 54 to 61, a function that luminance of each subframe can be controlled substantially linearly is not provided, utilizing the wall charges accumulated over addressing electrodes. Therefore, in the conventional method not utilizing a process of accumulating wall charges in advance of selective write discharge, it is difficult for luminance to be accurately adjusted. In the case where the adjusting of luminance with multiple intensity levels is carried out, if each color involves 256 intensity levels, 16.76 million colors will be displayable. It is said that human eyes discriminate 10 million colors in the best environment. This is why a high-definition television needs 256 intensity levels. 128 intensity levels are insufficient because they provide only 2 million colors. When luminance is lowered, it is not necessary to provide 16.76 million colors (= 256 intensity levels), because the discrimination capacity of human eyes is far less than 10 million colors under the low luminance. Taking this into account, 128 intensity levels will be sufficient under 50% luminance with respect to the 256 intensity levels for the maximum luminance. If the luminance is far lower, for example 10% of the maximum luminance, 16 intensity levels (= 4096 colors) will do. These facts provide an idea of controlling luminance in multiple levels. As explained above, in an embodiment of the present invention, it is possible for the wall charges that work effectively on a selective write discharqe to be accumulated over the address electrode before the selective write discharge is executed in a display panel such as an AC PDP. Therefore, the voltage of addressing pulse can be reduced and a write error in displaying data due to an erase error can be prevented. As a means for realizing process of accumulating wall charges, a write discharge for all cells and a erase discharge for all cells are executed. Further, an embodiment of the present invention carries out a write discharge and then an erase discharge in all cells of a selected display line, to equalize these cells before writing display data thereto. A sequential line driving method embodying the present invention can therefore prevent a write error in displaying data and can display a quality image. Further, one embodiment of the present invention carries out the write discharge and then the erase discharge in all cells of selected plural display lines, to equalize these cells before writing display data thereto. A sequential multiple line driving method embodying to the present invention can therefore prevent a write error and can display a quality image. Further, another embodiment of the present invention carries out the write discharge and then the erase discharge in all cells of all display lines, to equalize these cells before writing display data thereto. A separately addressing and sustain discharging methoa embodying the present invention can therefore prevent a write error and can display a quality image. Further, another embodiment of the present invention carries out the write discharge and then the erase discharge in all cells of all display lines, to equalize these cells before writing display data thereto. A separately addressing and sustain-discharging method embodying the invention can therefore prevent a write error and can display a qaulity image. This embodiment sequentially selects the display lines one by one, carries out write discharge in cells to be turned ON of the selected display line with use of the Y and addressing electrodes, to thereby write display data to the selected display line, and immediately applies a sustain discharge pulse to the X electrode, to carry out the sustain discharge for stabilizing wall charges and maintaining the stabilized wall charges up to a sustain discharge period. Further, another embodiment of the present invention groups the display lines into a plurality of blocks and connects X electrodes together in each of the blocks. This PDP is driven by, for example, a driving method embodying the present invention, to avoid a write error, display a quality image, and stabilize wall charges up to a sustain discharge period. Such an arrangement into blocks helps in reducing the power consumption of sustain discharge pulses for stabilizing wall charge during an addressing period. In particular, in such a block arrangement, during an addressing period in which display data are written, sustain discharge pulses for stabilizing wall charges are applied only to the X electrode of the block that includes a display line to which the display data is written but not to the X electrodes of blocks that do not include the display line to which the data is written. Further, another embodiment of the present invention sets a voltage applied to the second electrodes of unselected lines to be lower than the potential of a sustain discharge pulse, or equal to an addressing voltage, to thereby decrease an effective voltage applied to a discharge space between adjacent Y electrodes lower than a discharge start voltage and avoid abnormal discharge between the adjacent Y electrodes. Further, in an embodiment intended to permit adjustment of luminance, the present invention can drive a display panel with use of separate addressing and sustain discharge periods to display a full color image with multiple intensity levels and to adjust luminance in multiple levels with high accuracy. The above arrangement increases or decreases the numbers of sustain emission operations in the respective subframes at the same ratio, to digitally control in multiple levels, the luminance of a display plane involving, for example, 64 to 256 intensity levels, to thereby realize a display comparable to a CRT. Further, the latter embodiment may additionally employ means for stopping original operations (for example, high-voltage pulse applying operations) in subframes that do not require sustain discharge, to eliminate wasteful power consumption. Therefore, it becomes possible to drive the display unit with desirably low power, by means of the effect of accumulating the wall charges. Further, in a subframe in which no sustain discharge is executed, a write discharge for all cells and an erase discharge for all cells are also not executed. Therefore, background emission caused by such write and erase discharges can be reduced. Consequently, the deterioration of the contrast in a display panel can be prevented, and it is also possible for a display panel with high contrast to be realised even when low luminance is desired.

Claims: A method of driving a display panel comprising a first substrate (9), at least one display line (7 1-1000 ; 75 1-1000 ), the or each display line having respective first and second electrodes (2, 3k) disposed in parallel with one another on the said first substrate (9), a second substrate (8) facing the said first substrate, and a plurality of third electrodes (4k) disposed on the said second substrate (8) and extending orthogonally to the said first and second electrodes (2, 3k), the or each display line having display cells at respective locations at which one of the third electrodes (4k) crosses over the said first and second electrodes (2, 3k) of the display line concerned, in which method a selective write discharge operation is performed on a selected display line, in which operation discharges are brought about in those cells of the selected display line that are designated by display data as being ON cells, followed by a sustain discharge display operation in which discharges are sustained in the ON cells so that, utilising a memory function of the cells, light is emitted by the ON cells during the sustain discharge display operation; the method further including an erase discharge operation carried out on the selected display line, before the said selective write discharge operation, in which subsequent discharges are prevented in all cells of the selected display line using an erase pulse (38; 44; 46; 49, 50; 60; 84; 92) applied to the first and second electrodes; characterised in that the method further includes a total write discharge operation, performed on the selected display line before the said erase discharge operation, in which all cells of the selected line are addressed using either one of the first and second electrodes and using the said third electrodes and discharges are brought about in all cells of the line using a write pulse (36; 47; 58; 82; 90; 97) applied to the first and second electrodes, so that the total write discharge and erase discharge operations serve to facilitate accumulation of wall charges over the third electrodes of the cells of the selected display line in advance of the selective write discharge operation, which wall charges promote effective discharge in the designated ON cells during that selective write discharge operation. A method as claimed in claim 1, wherein the said display panel is an alternating current plasma display panel in which the said memory function is realised by wall charges accumulated by means of the said selective write discharge operation. A method as claimed in claim 2, wherein the said display panel has a plurality of such display lines (7 1 to 7 1000 ), the respective first electrodes (2) of which are all connected together and the respective second electrodes (3 1 to 3 1000 ) of which display lines are independent of one another; the method comprising: sequentially selecting said display lines 17 1 to 7 1000 ) one by one, carrying out such a total write discharge operation on the selected display line using the first and second electrodes (2, 3), carrying out such an erase discharge operation on the selected display line by applying such an erase pulse (38; 44; 46) to said second or said first electrode of that line so as to prevent discharges in all cells of that selected display line, and carrying out such a selective write discharge operation on the selected display line to turn on the designated ON cells of that line using the said second and third electrodes (3, 4), thereby to write said display data to said selected display line. A method as claimed in claim 2, wherein the said display panel has a plurality of such display lines (7 1 to 7 1000 ), the respective first electrodes (2) of which are all connected together and the respective second electrodes (3) of which display lines are independent of one another, the method comprising: sequentially selecting a plurality (7M, 7N) of the display lines, carrying out such a total write discharge operation on the selected display lines to bring about discharges in all cells of those selected lines using the said first and second electrodes (2, 3), carrying out such an erase discharge operation by applying such an erase pulse (49, 50) to said second or said first electrode of each said selected display line so as to prevent discharges in all cells of the select display lines, and carrying out such a selective write discharge operation on the said selected display lines to turn on the designated ON cells of each said selected display line using the said second and third electrodes (3, 4), thereby to write said display data to said selected display lines. A method as claimed in claim 2, wherein the said display panel has a plurality of such display lines (7 1 to 7 1000 ), the respective first electrodes (2) of which are all connected together and the respective second electrodes (3) of which display lines are independent of one another, the method comprising: carrying out such a total write discharge operation on all of the display lines of the panel to bring about discharges in all cells of all display lines using the said first and second electrodes (2, 3), carrying out such an erase discharge operation on every display line by applying such an erase pulse (60; 84; 92) to said second or to said first electrode (2, 3) of every display line so as to prevent discharges in all cells of all the display lines, sequentially selecting the display lines one by one, carrying out such a selective write discharge operation on the selected display line to turn on the designated ON cells of that line using the said second and third electrodes (3, 4), thereby to write said display data to said selected display line, and after the display data are so written to all of the display lines, carrying out such a sustain discharge display operation on all of said display lines, to sustain discharges in the designated ON cells of all said display lines, using said first and second electrodes (2, 3). A method as claimed in claim 5, wherein, after the said selective write discharge operation is performed on each selected display line in turn, a sustain discharge pulse (65; 87) is applied immediately to said first electrode (2) so as to perform a sustain discharge stabilising operation for stabilising wall charges in the cells of the selected line concerned. A method as claimed in claim 2, wherein the said display panel has a plurality of such display lines (75 1 to 75 1000 ), which display lines are grouped into a plurality of blocks (76 1 to 76 4 ), the respective first electrodes (70 1 to 70 4 ) of the lines of each block all being connected together and the respective second electrodes (71 1 to 71 1000 ) of the lines of each block being independent of one another, the method comprising: carrying out such a total write discharge operation on all of the said display lines to bring about discharges in all display lines using said first and second electrodes, carrying out such an erase discharge operation on every display line by applying such an erase pulse (84) to said second or said first electrode (71) of every display line so as to prevent discharges in all cells of all of the display lines, sequentially selecting the display lines one by one, carrying out such a selective write discharge operation on the said selected display line to turn on the designated ON cells of that display line using the said second and third electrodes (71, 72), thereby to write said display data to the said selected display line, immediately applying a sustain discharge pulse (87) to the said first electrode (70) of the block that includes the selected display line so as to carry out a sustain discharge stabilising operation for stabilising wall charges in the cells of the selected display line, and after the display data are so written to all of the display lines, carrying out such a sustain discharge display operation on all of the said display lines, to sustain discharges in the designated ON cells of all said display lines, using said first and said second electrodes (70, 71). A method as claimed in any one of claims 3 to 7, wherein a further sustain discharge operation is carried out between the total write discharge and erase discharge operations. A method as claimed in claim 2, wherein the display panel has a plurality of such display lines, the respective second electrodes (Y 1 to Y N ) of which are sequentially selected and driven line by line, and the respective first electrodes (X) of which are driven by a single driver circuit, the first and second electrodes being arranged so that the respective second electrodes (Y 1 , Y 2 ; Y 3 , Y 4 ,...) of two successive display lines lie between the respective first electrodes (X) of those two lines, the method comprising: applying to the said second electrodes of unselected display lines a voltage (V y ) that is lower than the potential of a sustain discharge pulse (V s ) applied to the said second electrodes when the said sustain discharge display operation is being performed, or that is equal to an addressing voltage (V a ) applied to the said third electrodes (A 1 to A M ) when the said selective write discharge operation is being performed. A method as claimed in any one of claims 3 to 8, wherein a further erase discharge operation is carried out using the said first and second electrodes, just before the said total write discharge operation is executed. A method as claimed in claim 8, wherein the said further sustain discharge operation is carried out by applying a narrow pulse (37; 48; 59; 83; 91), such that subsequent discharges are not prevented, immediately after the said total write discharge operation is executed. A method as claimed in claim 1 or 2, wherein a frame used to write the display data of an entire image is made up of a succession of individual subframes (SF1 to SF8), each of which subframes provides a different luminance and includes an addressing period (Ta), in which such selective write discharge operations are performed to rewrite such display data, and also includes a sustain emission period (Td) in which such sustain discharge display operations are performed to display the rewritten display data, there being a plurality of sustain emission cycles in the sustain emission period of each subframe and the addressing and sustain emission periods of one subframe being temporarally separated from those of the next subframe, and the total number of sustain discharge cycles performed on each display cell in each frame being adjustable to provide the cells with a set of different possible intensity levels and to enable adjustment of luminance of said image, wherein the numbers (N SF1 to N SF8 ) of sustain emission cycles in the respective subframes are increased or decreased to control the luminance of the image, the ratios (N SF1 : N SF2 : N SF3 : N SF4 : N SF5 : N SF6 : N SF7 : N SF8 ) of the numbers of sustain discharge cycles in the different subframes being kept unchanged. A method as claimed in claim 12, wherein the subframes (SF1 to SF8) are ranked according to the amount of luminance they provide and the number of sustain emission cycles of a given subframe is determined in dependence upon the number of sustain emission cycles of the subframe of rank one higher than that of the said given subframe, the number (N SF1 ) of sustain emission cycles of the highest-ranking subframe (SF1) being determined at first, and the number of (N SF2 ) sustain emission cycles of the second-highest-ranking subframe (SF2) is then determined in dependence upon the determined number (N SF1 ) of cycles in the said highest-ranking subframe, and so on for all the lower-ranking subframes (SF3-SF8). A method as claimed in claim 13, wherein the number of sustain emission cycles of the said given subframe is set to be half that of the said subframe of rank one higher than that of the said given subframe. A method as claimed in claim 14, wherein fractions, if any, are rounded up or discarded when halving the number of sustain emission cycles of the said subframe of rank one higher than that of the said given subframe. Display apparatus including: a display panel comprising a first substrate (9), at least one display line (7 1 to 7 1000 ; 75 1 to 75 1000 ), the or each display line having respective first and second electrodes (2, 3k) disposed in parallel with one another on the said first substrate (9), a second substrate (8) facing the said first substrate, and a plurality of third electrodes (4k) disposed on the said second substrate (8) and extending orthogonally to the said first and second electrodes (2, 3k), the or each display line having display cells at respective locations at which one of the first electrodes (4k) crosses over the said first and second electrodes (2, 3k) of the display line concerned; driving means (14 to 17) connected to the said first, second and third electrodes (2, 3k, 4k) of the display panel and operable to apply thereto a plurality of driving voltage pulses; and control means (18) connected to the said driving means (14 to 17) for controlling such application of the driving voltage pulses to the display panel such that in use of the display apparatus a selective write discharge operation is performed on a selected display line, in which operation discharges are brought about in those cells of the selected display line that are designated by display data as being ON cells, followed by a sustain discharge display operation in which discharges are sustained in the ON cells so that, utilising a memory function of the cells, light is emitted by the ON cells during the sustain discharge operation, and such that an erase discharge operation is performed on the selected display line, before the said selective write discharge operation, in which an erase pulse is applied to the said first and second electrodes of the selected display line so as to prevent subsequent discharges in all cells of the selected line; characterised in that the said control means (18) are also operative to cause a total write discharge operation to be performed on the selected display line before the said erase discharge operation, in which total write discharge operation the control means cause address signals to be applied to either one of the said first and second electrodes and to the said third electrodes to address all cells of the said selected display line and also cause a write pulse to be applied to the first and second electrodes to bring about discharges in all cells of the selected display line, so that the total write discharge and erase operations serve to facilitate accumulation of wall charges over the third electrodes of the cells of the selected display line in advance of the said selective write discharge operation, which wall charges promote effective discharge in the designated ON cells during that selective write discharge operation. Apparatus as claimed in claim 16, wherein the said display panel is an alternating current plasma display panel in which the said memory function is realised by wall charges accumulated by means of the said selective write discharge operation. Apparatus as claimed in claim 17, wherein the said control means (18) are operative to control the said driving means (14-17) to sequentially select the display lines one by one, to apply such a write pulse (36) to the said first and second electrodes so that such a total write discharge operation is carried out on the selected display line to bring about discharges in all cells of that line, to apply such an erase pulse (38; 44; 46) to the said second or the said first electrode of the said selected display line so that such an erase discharge operation is carried out on that line to prevent discharges in all cells of the selected display line, and to apply further write pulses (39, 40) selectively to the second and third electrodes of the selected display line to carry out such a write discharge operation on the said selected display line so that the designated ON cells of the line are turned on, thereby to write said display data to the said selected display line. Apparatus as claimed in claim 17, wherein the said control means (18) are operative to control the driving means (14-17) to sequentially select a plurality of the display lines (7M, 7N), to apply such a write pulse (47) to the said first and second electrodes so that such a total write discharge operation is carried out on the selected display lines (7M, 7N) to bring about discharges in all cells of those lines, to apply such an erase pulse (49, 50) to the said second or the said first electrode of each said selected display line so that such an erase discharge operation is carried out on those lines to prevent discharges in all cells of the selected display lines, and to apply further write pulses (51-54) selectively to the second and third electrodes of the selected display lines to carry out such a selective write discharge operation on those lines so that the designated ON cells thereof are turned on, thereby to write said display data to said selected display lines. Apparatus as claimed in claim 18 or 19, wherein the said control means (18) are operative to control the driving means (14 to 17) such that a sustain pulse (37; 48) is applied between the said total write discharge and erase discharge operations. Apparatus as claimed in claim 17, wherein the said display panel comprises an insulation layer (12; 313), which in each display cell separates the third electrode (4 k ; 310) from a discharge space (311) formed between the third electrode (4 k ; 310) and the said first and second electrodes (2, 3k; X,Y), so that said wall charges can be accumulated on the said insulation layer (12; 313). Apparatus as claimed in claim 16 or 17, wherein a frame used to write the display data of an entire image is made up of a succession of individual subframes (SF1 to SF8), each of which subframes provides a different luminance and includes an addressing period (Ta), in which such selective write discharge operations are performed to rewrite such display data, and a sustain emission period (Td), in which such sustain discharge display operations are performed to display the rewritten display data, there being a plurality of sustain emission cycles in the sustain emission period (Td) of each subframe and the addressing and sustain emission periods (Ta, Td) of one subframe being temporally separated from those of the next subframe, and the total number of sustain emission cycles performed on each display cell in each frame being adjustable to provide the cells with a set of different possible intensity levels and to enable adjustment of luminance of said image, the numbers (N SF1 to N SF8 ) of sustain emission cycles in the respective subframes being increased or decreased to control the luminance of said image whilst the ratios (N SF1 : N SF2 : N SF3 : N SF4 : N SF5 : N SF6 : N SF7 : N SF8 ) of the numbers of sustain emission cycles in the different subframes are kept unchanged, and the subframes being ranked according to the amount of luminance they provide; the apparatus further comprising: first means (111 to 113) for determining the number (N SF1 ) of sustain emission cycles of the highest-ranking subframe (SF1); and second means (115) for determining, in dependence upon the said number (N SF1 ) determined by the first means, the number (N SF2 ) of sustain emission cycles of the next-highest-ranking subframe (SF2). Apparatus as claimed in claim 22, further comprising means (120, 121) for preventing operations from being carried out in a subframe, if the result of the determinations by the first and second means (111 to 113, 115) is that the number of sustain emission cycles of the subframe concerned is zero. Apparatus as claimed in claim 23, further comprising: means (114) for holding data according to which the number of sustain emission cycles of the next subframe is determined; means (116) for counting the number of sustain emission cycles carried out in the present subframe; means (117) for comparing the count value of the counting means (116) with the data held by the holding means (114); and means (118, 119) for providing an instruction to start the next subframe if the comparison means (117) indicates agreement between the said count value and the held data. Apparatus as claimed in claim 22, 23 or 24, wherein the said first means (111 to 113) has means (111) for optionally setting the number (N SF1 ) of sustain emission cycles of the highest-ranking subframes. Apparatus as claimed in claim 17, wherein the display lines (75 1 to 75 1000 ) are grouped into a plurality of blocks (76 1 to 76 4 ), the respective first electrodes (70 1 to 70 4 ) of the lines of each block all being connected together and the respective second electrodes (71 1 to 71 1000 ) of the lines of each block being independent of one another.

Inventors: KANAZAWA YOSHIKAZU, KANAZAWA, YOSHIKAZU, KANAZAWA, YOSHIKAZU, C/O FUJITSU LIMITED
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1992
Main classification: G09G3
IPC codes: G09G3