Patent Publication Number: US-2009225067-A1

Title: Display Panel and Display Device

Description:
TECHNICAL FIELD 
     The present invention relates to a display panel having a function of detecting the wiring condition of signal lines and/or scanning lines. The present invention also relates to a display device having such a display panel. 
     BACKGROUND ART 
     One method of detecting defects in scanning lines and signal lines in a display device using a liquid crystal display panel or the like is to directly touch each wiring conductor with a test probe. As displays come to have increasingly high resolutions and increasingly large screens, however, that method becomes increasingly difficult to adopt. In view of this, various methods for inspecting scanning lines and/or signal lines for defects have been proposed. 
     For example, according to Patent Document 1 listed below, in an output portion of a horizontal scanning circuit, a group of transfer transistor switches is provided, and the terminal ends of signal lines in respective columns are connected to the gates of a group of inspection switches. When pulses for inspection are fed to the group of transfer transistor switches, the group of inspection switches yields outputs, based on the waveforms of which the signal lines are inspected. 
     For another example, according to Patent Document 2 listed below, one ends of scanning lines are connected via capacitive elements to the gates of inspection transistors. In an inspection mode, when scanning pulses are fed to one scanning line after another, the inspection transistors yield outputs, based on the waveforms of which the scanning lines are inspected. 
     For yet another example, according to Patent Document 3 listed below, inspection cells each composed of a switching transistor, a capacitive element, etc. are provided one for each scanning line to build an inspection circuit. When, for example, pulses for inspection are fed as an image signal, defective spots are located. 
     Patent Document 1: Japanese Patent No. 2618042   
     Patent Document 2: JP-A-H10-97203   
     Patent Document 3: JP-A-2004-199054   
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     Inconveniently, however, the method of Patent Document 1 mentioned above requires a group of transfer transistor switches; the method of Patent Document 2 mentioned above requires capacitive elements one for each of inspection transistors; the method of Patent Document 3 mentioned above requires capacitive elements; thus, these methods all require many elements for inspection. Moreover, the methods of Patent Documents 1 to 3 mentioned above all assume that scanning lines etc. are inspected in an inspection mode provided separately from actual operation, and are difficult to adopt for inspection in actual operation. 
     In view of the above, it is an object of the present invention to provide a display panel and a display device that allow detection of wiring condition of scanning lines and/or signal lines in actual operation. 
     Means for Solving the Problem 
     To achieve the above object, a display panel according to the present invention has a plurality of scanning lines and a plurality of signal lines that are formed to form a matrix, and has, respectively at the intersections between the scanning lines and the signal lines, drive switching elements that are turned on and off according to scanning voltages fed to the scanning lines and pixel circuits that are connected via the drive switching elements to the signal lines. Here, the display panel has detection switching elements of which the control electrodes are connected respectively to the scanning lines. The first conducting electrodes of the detection switching elements are connected together so that, from these first conducting electrodes thus connected together, a detection signal representing the logical sum of any on-state among the detection switching elements is outputted. 
     The scanning lines are individually fed with scanning voltages for turning on and off the drive switching elements. Having their control electrodes connected to the scanning lines, the detection switching elements are also turned on and off according to the corresponding scanning voltages. If, however, any scanning line is broken or otherwise defective, the scanning voltage applied to it is not accurately transmitted to the corresponding detection switching element, and thus the detection signal contain information on line breakage or the like. Thus, based on the detection signal, it is possible to detect the wiring condition of the individual scanning lines with an extremely small number of elements. Moreover, since the detection signal is derived by use of the scanning voltages for turning the drive switching elements on and off, it is possible to detect the wiring condition of the scanning lines in actual operation. 
     Specifically, for example, the detection switching elements each turn on when receiving at the control electrodes thereof a first-level scanning voltage that turns the drive switching elements on, and turn off when receiving at the control electrodes thereof a second-level scanning voltage that turns the drive switching elements off. 
     These detection switching elements have characteristics similar to those of the drive switching elements, and thus can be formed by a single process by which the drive switching elements are formed. 
     That is, the drive switching elements and the detection switching elements may be transistors formed on a single substrate by a single process. 
     This eliminates the need to provide a separate process for forming a circuit for detecting the wiring condition of the scanning lines. 
     A first display device according to the present invention is provided with: the display panel described above; a scanning line driver that feeds the first-level scanning voltage to one after another of the scanning lines; and a first wiring condition detector that detects, based on the detection signal, the wiring condition of the scanning lines one by one. 
     For example, in the first display device described above, the scanning voltage from the scanning line driver is fed to the scanning lines via first protection switching elements provided one for each of the scanning lines, and the first wiring condition detector identifies as an abnormal scanning line any scanning line across which the transmission of the first-level scanning voltage to the corresponding one of the detection transistors is abnormal, and turns off the corresponding one of the first protection switching elements which is inserted in the thus identified abnormal scanning line. 
     This makes it possible to prevent an abnormal current from continuing to flow when any scanning line becomes abnormal. 
     For example, the first display device described above is further provided with: a signal line driver that is connected to the first ends of the signal lines; and a second wiring condition detector that is connected to the second ends of the signal lines. Here, while the scanning line driver is feeding the second-level scanning voltage to all the scanning lines, the signal line driver feeds an inspection voltage having a predetermined level to the signal lines so that, based on how the inspection voltage is transmitted, the second wiring condition detector detects the wiring condition of the signal lines. 
     With this configuration, it is possible to detect the wiring condition of the signal lines in actual operation. 
     To achieve the above object, a second display device according to the present invention has: a display panel having a plurality of scanning lines and a plurality of signal lines that are formed to form a matrix, and having, respectively at the intersections between the scanning lines and the signal lines, drive switching elements that are turned on and off according to scanning voltages fed to the scanning lines and pixel circuits that are connected via the drive switching elements to the signal lines; a signal line driver that is connected to the first ends of the signal lines; and a scanning line driver that feeds one after another of the scanning lines with a first-level scanning voltage that turns the drive switching elements on. Here, the display device is further provided with: a second wiring condition detector connected to second ends of the signal lines. While the scanning line driver is feeding all the scanning lines with a second-level scanning voltage that turns the drive switching elements off, the signal line driver feeds an inspection voltage having a predetermined level to the signal lines so that, based on how the inspection voltage is transmitted, the second wiring condition detector detects the wiring condition of the signal lines. 
     In actual operation, the plurality of scanning lines are fed, one after another, with the first-level scanning voltage that turns the drive switching elements on. Here, there usually exist periods during which the second-level scanning voltage that holds the drive switching elements off is fed to all the scanning lines. By use of these periods, the inspection voltage having a predetermined level is fed to the signal lines so that, based on how the inspection voltage is transmitted, the wiring condition of the signal lines is detected. Thus, with the above configuration, it is possible to detect the wiring condition of the signal lines in actual operation. 
     For example, in the second display device described above, the signal line driver is connected to the signal lines via second protection switching elements provided one for each of the signal lines, and the second wiring condition detector identifies as an abnormal signal line any signal line across which the transmission of the inspection voltage to the second wiring condition detector is abnormal, and turns off the corresponding one of the second protection switching elements which is inserted in the thus identified abnormal signal line. 
     This makes it possible to prevent an abnormal current from continuing to flow when any signal line becomes abnormal. 
     Advantages of the Invention 
     As described above, with a display panel and a display device according to the present invention, it is possible to detect the wiring condition of scanning lines and/or signal lines in actual operation. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  A block diagram showing the configuration of a display unit included in a display device according to the first embodiment of the present invention. 
         FIG. 2  A waveform diagram showing the relationship between the scanning voltage and the detection signal in the display unit shown in  FIG. 1  over the display period of one screen (with all scanning lines normal). 
         FIG. 3  A waveform diagram showing the relationship between the scanning voltage and the detection signal in the display unit shown in  FIG. 1  over the display period of one screen (with some scanning lines abnormal). 
         FIG. 4  A block diagram showing the configuration of a modified example of the display unit shown in  FIG. 1 . 
         FIG. 5  A waveform diagram showing the relationship between the scanning voltage and the detection signal in the display unit shown in  FIG. 4  over the display period of one screen (with all scanning lines normal). 
         FIG. 6  A waveform diagram showing the relationship between the scanning voltage and the detection signal in the display unit shown in  FIG. 4  over the display period of one screen (with some scanning lines abnormal). 
         FIG. 7  A block diagram showing the configuration of a modified example of the display unit shown in  FIG. 1  ( FIG. 4 ). 
         FIG. 8  A waveform diagram showing the relationship between the scanning voltage and the detection signal in the display unit shown in  FIG. 7  over the display period of one screen (with all scanning lines normal). 
         FIG. 9  A block diagram showing the configuration of a display unit included in a display device according to the second embodiment of the present invention. 
         FIG. 10  A block diagram showing the configuration of a display unit included in a display device according to the third embodiment of the present invention. 
         FIG. 11  A waveform diagram showing the scanning voltage in the display unit shown in  FIG. 10  over the display period of one screen. 
         FIG. 12  A diagram showing an example of the configuration of the second wiring condition detector shown in  FIG. 10 . 
         FIG. 13  A block diagram showing the configuration of a modified example of the display unit shown in  FIG. 10 . 
         FIG. 14  A diagram showing the overall configuration of a vehicle-mounted system according to the fourth embodiment of the present invention. 
         FIG. 15  A diagram showing the contents of the event conversion table shown in  Fig. 14 . 
         FIG. 16  A diagram showing an example of the image displayed on the display panel shown in  FIG. 14 . 
         FIG. 17  A diagram showing another example of the image displayed on the display panel shown in  FIG. 14 . 
     
    
    
     LIST OF REFERENCE SYMBOLS 
     
         
           1 ,  1   a ,  1   b ,  1   c ,  1   d  Display Unit 
           2 ,  2   a  Display Panel 
           3  Gate Driver 
           4  Source Driver 
           5 ,  5   a,    5   b,    5   c  First Wiring Condition Detector 
           6  Group of Detection Transistors 
           7  Charge Feeder 
           8  Groups of Protection Switches 
           9  Second Wiring Condition Detector 
         S 0 -S 4  Signal Lines 
         G 0 -G 4  Scanning Lines 
         T 00 -T 44 , T 00   a -T 44   a  Drive Transistors 
         TG 0 -TG 4 , TG 0   a -TG 4   a  Detection Transistors 
         P 00 -P 44  Pixel Circuits 
         SW 0 -SW 4 , SW 0   a -SW 4   a  Protection Switching Elements 
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     First Embodiment  
     As a first embodiment of the present invention, how it is applied to a display device will be described specifically below with reference to the drawings.  FIG. 1  is a block diagram showing the configuration of a display unit  1  included in a display device according to the first embodiment. 
     The display unit  1  has, or is composed of, a display panel  2 , a gate driver  3 , a data driver  4 , and a first wiring condition detector  5 . The display panel  2  (and  2   a  described later) is, for example, a liquid crystal display panel, an organic EL (electroluminescence) display panel, an inorganic EL display panel, a plasma display panel, or the like. For the sake of concreteness, the following description assumes that the display panel  2  (and  2   a  described later) is a liquid crystal display panel. 
     In the display panel  2 , a plurality of scanning lines G 0 , G 1 , G 2 , G 3 , G 4 , . . . and a plurality of signal lines S 0 , S 1 , S 2 , S 3 , S 4 , . . . are arranged to cross each other, with an unillustrated insulating film interposed between the former and the latter; that is, they are arranged to form a matrix. 
     At each of the intersections between the scanning lines and the signal lines, there are provided a drive transistor and a pixel circuit. Specifically, at the intersection between the scanning line G 0  and the signal line S 0 , there are provided a drive transistor T 00  and a pixel circuit P 00 . Likewise, at the intersection between the scanning line G 0  and the signal line S 1 , there are provided a drive transistor T 01  and a pixel circuit P 01 , and, at the intersection between the scanning line G 1  and the signal line S 0 , there are provided a drive transistor TI 0  and a pixel circuit P 10 . In generalized terms, when m and n are arbitrary natural numbers, at the intersection between the scanning line Gm and the signal line Sn, there are provided a drive transistor Tmn and a pixel circuit Pmn. 
     For the sake of concreteness and simplicity, in the description of this and all the following embodiments, focus is placed, in principle, on the scanning lines G 0 , G 1 , G 2 , G 3 , and G 4  and the signal lines S 0 , S 1 , S 2 , S 3 , and S 4 ; with the other elements, focus is placed on their parts connected to the scanning lines G 0  to G 4  and the signal lines S 0  to S 4 . Accordingly, even where the scanning lines G 0 , G 1 , G 2 , G 3 , G 4 , . . . for instance, are referred to as the scanning lines G 0  to G 4  or the like, the relevant description applies, as well as to the scanning lines G 0  to G 4  or the like, to the other scanning lines (for example, the scanning line G 5 ) or the like. 
     The drive transistors (drive switching elements) T 00  to T 44  are thin-film transistors formed with amorphous silicon or the like on an insulating substrate (unillustrated) such as a glass substrate, and are formed as N-channel insulated-gate field-effect transistors. 
     Each of the pixel circuits P 00  to P 44  has a pixel electrode and a common electrode, with a liquid crystal layer interposed between the former and the latter (none of those electrodes are illustrated). In each of the pixel circuits P 00  to P 44 , capacitive coupling between a pixel electrode and a common electrode produces pixel capacitance. 
     The pixel electrodes of the pixel circuits P 00  to P 44  are connected to the drains of the corresponding drive transistors T 00  to T 44 . Specifically, the pixel electrode of the pixel circuit P 00  is connected to the drain of the drive transistor T 00 , and the pixel electrode of the pixel circuit P 01  is connected to the drain of the drive transistor T 01 . Put in generalized terms using m and n mentioned above, the pixel electrode of the pixel circuit Pmn is connected to the drain of the drive transistor Tmn. On the other hand, the common electrodes of the pixel circuits P 00  to P 44  are connected together so as to be collectively fed with a common potential. 
     The gate (control electrode) and the source of the drive transistor arranged at a given intersection are connected to the scanning line and the signal line, respectively, that form the intersection. Specifically, for example, the gate and the source of the drive transistor T 00  are connected to the scanning line G 0  and the signal line S 0 , respectively, and the gate and the source of the drive transistor T 01  are connected to the scanning line G 0  and the signal line S 1 , respectively. Put in generalized terms using m and n mentioned above, the gate and the source of the drive transistor Tmn are connected to the scanning line Gm and the signal line Sn, respectively. The display panel  2  is further provided with a group  6  of detection transistors. The group  6  of detection transistors consists of the same number of detection transistors (detection switching elements) TG 0 , TG 1 , TG 2 , TG 3 , and TG 4  as the total number of scanning lines. The gates (control electrodes) of the detection transistors TG 0 , TG 1 , TG 2 , TG 3 , and TG 4  are connected to the scanning lines G 0 , G 1 , G 2 , G 3 , and G 4 , respectively. The drains (first conducting electrodes) of the detection transistors TG 0  to TG 4  are connected together so as to be collectively fed with a supply voltage VDD (for example, 5V) via a resistor R 1 . Similarly, the sources of the detection transistors TG 0  to TG 4  are connected together so as to be collectively fed with a reference potential of 0 V (connected to a ground line). The detection transistors TG 0  to TG 4 , like the drive transistors T 00  to T 44 , are thin-film transistors formed with amorphous silicon or the like on an insulating substrate such as a glass substrate, and are formed as N-channel insulated-gate field-effect transistors. The detection transistors TG 0  to TG 4  and the drive transistors T 00  to T 44  may be formed on a single substrate by a single process for forming thin-film transistors. 
     The first wiring condition detector  5  receives, as a detection signal DG, the signal that appears at the drains, connected together, of the detection transistors TG 0  to TG 4 . Based on the detection signal DG, the first wiring condition detector  5  checks whether the wiring condition of the scanning lines G 0  to G 4  is normal or abnormal. Here, a “normal” wiring condition is one in which a given wiring conductor is not broken, short-circuited, or otherwise defective and thus can transmit a signal (voltage) as it is meant to; by contrast, an “abnormal” wiring condition is one in which a given wiring conductor is broken, short-circuited, or otherwise defective and thus cannot transmit a signal (voltage) as it is meant to. The first wiring condition detector  5  plus the group  6  of detection transistors may be regarded as a wiring condition detector. 
     The gate driver  3  is composed of shift registers or the like. In synchronism with a timing signal (clock signal) fed from a timing generator (unillustrated), the gate driver  3  feeds the scanning lines G 0  to G 4  sequentially with a high-level scanning voltage (first-level scanning voltage) for turning the corresponding drive transistors on. Specifically, here, a high-level scanning voltage is a comparatively high voltage of, for example, 10 to 20 V (volts); on receiving a high-level scanning voltage at its gate, any of the drive transistors T 00  to T 44  turns on; likewise, on receiving a high-level scanning voltage at its gate, any of the detection transistors TG 0  to TG 4  turns on. 
     The gate driver  3  feeds each of the scanning lines G 0  to G 4  with either a high-level scanning voltage as mentioned above or a low-level scanning voltage. Here, a low-level scanning voltage (second-level scanning voltage) is a comparatively low voltage of, for example, 0 V for turning a drive transistor off; on receiving a low-level scanning voltage at its gate, any of the drive transistors T 00  to T 44  turns off, likewise, on receiving a low-level scanning voltage at its gate, any of the detection transistors TG 0  to TG 4  turns off. 
     As shown in  FIG. 1 , one ends of the scanning lines G 0  to G 4  are connected to the gate driver  3 , and the other ends (terminal ends) of the scanning lines G 0  to G 4  are connected to the gates of the detection transistors TG 0  to TG 4 . Thus, between the node where the scanning line G 0  is connected to the gate driver  3  and the gate of the detection transistor TG 0 , there lie the nodes where the scanning line G 0  is connected to the gates of the drive transistors T 00  to T 04 ; likewise, between the node where the scanning line G 1  (G 2 , G 3 , or G 4 ) is connected to the gate driver  3  and the gate of the detection transistor TG 1  (TG 2 , TG 3 , or TG 4 ), there lie the nodes where the scanning line G 1  (G 2 , G 3 , or G 4 ) is connected to the gates of the drive transistors T 10  to T 14  (T 20  to T 24 , T 30  to T 34 , or T 40  to T 44 ). 
     The source driver  4  receives image data representing the image to be displayed on the display panel  2 , and feeds signal voltages according to the image data to the signal lines S 0  to S 4  with the timing according to the above-mentioned timing signal. These signal voltages have varying voltages between, for example, about 0 and 3 V depending on the contents of the image data. 
     The gate driver  3 , the source driver  4 , etc. are fed with supply voltages, for driving, from a unillustrated power supply circuit. 
     Next, a description will be given of the method by which the wiring condition of the scanning lines is detected in the display unit  1  configured as described above.  FIGS. 2 and 3  are waveform diagrams showing the relationship between the scanning voltage and the detection signal DG over the display period of one screen.  FIGS. 2 and 3  each show, from top, the voltage waveform appearing on the scanning line G 0 , the voltage waveform appearing on the scanning line G 1 , the voltage waveform appearing on the scanning line G 2 , the voltage waveform appearing on the scanning line G 3 , the voltage waveform appearing on the scanning line G 4 , and the voltage waveform of the detection signal DG. 
       FIG. 2  shows the waveforms observed when all the scanning lines are normal. First, with reference to  FIG. 2 , the method of detecting the wiring condition of the scanning lines will be described. 
     The display period of one screen (the one-frame period) on the display panel  2  is represented by T. In a case where the frame frequency is 60 Hz (hertz), T is about 16.7 msec (milliseconds). When T divided by the total number of scanning lines is represented by t, within the display period of one screen, the scanning lines G 0  to G 4  are fed, one after another, with a high-level scanning voltage, each for a period of t (or each for a period slightly shorter than a period of t). 
     The period starting at the start of the display period of one screen and ending at the end of the period of t thereafter is referred to as period t 0 ; after the end of period t 0 , every period of t that passes is referred to as period t 1 , t 2 , t 3 , t 4  . . . . When period t 0  starts, of the scanning lines G 0  to G 4 , which all have been receiving a low-level scanning voltage until then, the scanning line G 0  alone starts to be fed with a high-level scanning voltage. During period t 0 , the pixel circuits P 00  to P 04  corresponding to the scanning line G 0  are fed with signal voltages according to image data from the source driver  4  via the signal lines S 0  to S 4  and the drive transistors T 00  to T 04 . 
     When period t 0  ends, period t 1  starts, at which point the scanning voltage fed to the scanning line G 0  is turned low and instead the scanning line G 1  alone starts to be fed with a high-level scanning voltage. During period t 1 , the pixel circuits P 10  to P 14  corresponding to the scanning line G 1  are fed with signal voltages according to image data from the source driver  4  via the signal lines S 0  to S 4  and the drive transistors T 10  to T 14 . 
     When period t 1  ends, period t 2  starts, at which point the scanning voltage fed to the scanning line G 1  is turned low and instead the scanning line G 2  alone starts to be fed with a high-level scanning voltage; when period t 2  ends, period t 3  starts, at which point the scanning voltage fed to the scanning line G 2  is turned low and instead the scanning line G 3  alone starts to be fed with a high-level scanning voltage; when period t 3  ends, period t 4  starts, at which point the scanning voltage fed to the scanning line G 3  is turned low and instead the scanning line G 4  alone starts to be fed with a high-level scanning voltage. In this way, during the display period of one screen, signal voltages according to image data are written to all the pixel circuits. 
     The group  6  of detection transistors and the resistor RI together form a logical summation (OR) circuit. When any one or more of the detection transistors are on, the OR circuit outputs a low-level detection signal DG (of, for example, several hundred mV); when all the detection transistors are off, the OR circuit outputs a high-level detection signal DG having a voltage equal to the supply voltage VDD. When the on-state and off-state of a detection transistor are expressed as “true (1)” and “false (0)”, respectively, the detection signal DG represents the logical sum (OR) of the on-state of the detection transistors TG 0  to TG 4 . It should be noted that, in the circuit configuration shown in  FIG. 1 , a low level and a high level in the detection signal DG represent “true (1)” and “false (0)”, respectively. 
     Accordingly, when fed with a scanning voltage as described above, the detection transistors TG 0  to TG 4  turn on one after another; thus, during the display period of one screen, the detection signal DG remains at a low level (of, for example, several hundred mV). In response to this detection signal DG, the first wiring condition detector  5  judges that all the scanning lines are normal. 
     If, for example, cracks develop where the drive transistors T 30 , T 31 , T 40 , and T 41  are formed and make the scanning lines G 3  and G 4  abnormal (broken, short-circuited, or otherwise defective), the detection signal DG stays at a high level during periods t 3  and t 4  as shown in  FIG. 3 . This is because, even though the gate driver  3  feeds a high-level scanning voltage to the scanning lines G 3  and G 4  during periods t 3  and t 4 , this high-level scanning voltage is not transmitted to the gates of the detection transistors TG 3  and TG 4 , and thus the detection transistors TG 3  and TG 4  remain off. In response to this detection signal DG, the first wiring condition detector  5  judges that the scanning lines G 3  and G 4  are abnormal (broken, short-circuited, or otherwise defective). The first wiring condition detector  5  refers not only to the detection signal DG but also to, for example, the above-mentioned timing signal fed to the gate driver  3  so as to be capable of detecting whether the wiring condition of each scanning line is normal or abnormal. 
     As described above, by detecting, for each scanning line, whether or not a high-level scanning voltage (first-level scanning voltage) for turning on the drive transistors (the corresponding ones among T 00  to T 44 ) is transmitted to the gate of the corresponding detection transistor, the first wiring condition detector  5  detects whether each scanning line is normal or abnormal (detects whether or not the transmission across each scanning line is normal or abnormal). 
       FIG. 1  shows an example in which the drive transistors and the detection transistors are N-channel thin-film transistors. Needless to say, the display unit may be modified so that those transistors are P-channel thin-film transistors. Even in that case, the drive transistors and the detection transistors can be formed on a single substrate by a single process. 
       FIG. 4  is a diagram showing the configuration of a display unit  1   a  including a display panel  2   a  in which P-channel thin-film transistors (insulated-gate field-effect transistors) are used as drive transistor and detection transistors.  FIGS. 5 and 6  are waveform diagrams showing the relationship between the scanning voltage and the detection signal DG over the display period of one screen in the configuration shown in  FIG. 4 . In  FIG. 4 , such parts as are the same as in  FIG. 1  are identified by common reference signs. In  FIGS. 5 and 6 , such parts as find their counterparts in  FIGS. 2 and 3  are identified by common reference signs.  FIG. 5  shows the waveforms observed when all the scanning lines are normal, and  FIG. 6  shows the waveforms observed when the scanning lines G 3  and G 4  are abnormal (broken, short-circuited, or otherwise defective). 
     The drive transistors T 00  to T 44  in  FIG. 1  are here replaced with P-channel drive transistors (drive switching elements) T 00   a  to T 44   a.  Likewise, the detection transistors TG 0  to TG 4  in  FIG. 1  are here replaced with P-channel detection transistors (detection switching elements) TG 0   a  to TG 4   a,  which thus form a group  6   a  of detection transistors. 
     The gates (control electrodes) of the detection transistors TG 0   a , TG 1   a , TG 2   a , TG 3   a,  and TG 4   a  are connected to the scanning lines G 0 , G 1 , G 2 , G 3 , and G 4 , respectively. The sources of the detection transistors TG 0   a  to TG 4   a  are connected together so as to be collectively fed with a supply voltage VDD (for example, 5V). Similarly, the drains of the detection transistors TG 0   a  to TG 4   a  are connected together so as to be collectively fed with a reference potential of 0 V via a resistor R 2 . A detection signal DG appears at the drains (first conducting electrodes), connected together, of the detection transistors TG 0   a  to TG 4   a,  and is fed to a first wiring condition detector  5   a,  which functions similarly to the first wiring condition detector  5  in  FIG. 1 . 
     In the configuration shown in  FIG. 4 , as shown in  FIGS. 5 and 6 , the gate driver  3  feeds the scanning lines G 0  to G 4  sequentially with a low-level scanning voltage (first-level scanning voltage), having a comparatively low voltage, as a scanning voltage for turning the corresponding drive transistors on. In the configuration shown in  FIG. 4 , a high-level scanning voltage (second-level scanning voltage), having a comparatively high voltage, serves as a voltage for turning the drive transistors off. 
     In the configuration shown in  FIG. 4 , when all the scanning lines are normal, the detection transistors TG 0   a  to TG 4   a  turn on one after another, one by one. Thus, during the display period of one screen, the detection signal DG remains at a high level (approximately equal to VDD). In response to this detection signal DG, the first wiring condition detector  5   a  judges that all the scanning lines are normal. If for example, cracks develop where the drive transistors T 30   a , T 31   a , T 40   a , and T 41   a  are formed and make the scanning lines G 3  and G 4  abnormal (broken, short-circuited, or otherwise defective), the detection signal DG stays at a low level during periods t 3  and t 4  as shown in  FIG. 6 . This is because, even though the gate driver  3  feeds a low-level scanning voltage to the scanning lines G 3  and G 4  during periods t 3  and t 4 , this low-level scanning voltage is not transmitted to the gates of the detection transistors TG 3   a  and TG 4   a,  and thus the detection transistors TG 3   a  and TG 4   a  remain off. In response to this detection signal DG, the first wiring condition detector  5   a  judges that the scanning lines G 3  and G 4  are abnormal (broken, short-circuited, or otherwise defective). 
     The group  6   a  of detection transistors and the resistor R 2  together form a logical summation (OR) circuit. When any one or more of the detection transistors are on, the OR circuit outputs a high-level detection signal DG (approximately equal to VDD); when all the detection transistors are off, the OR circuit outputs a low-level detection signal DG (0 V). When the on-state and off-state of a detection transistor are expressed as “true (1)” and “false (0)”, respectively, the detection signal DG represents the logical sum (OR) of the on-state of the detection transistors TG 0   a  to TG 4   a.  It should be noted that, in the circuit configuration shown in  FIG. 4 , a high level and a low level in the detection signal DG represent “true (1)” and “false (0)”, respectively. 
     The display unit la shown in  FIG. 4  may further be modified to the display unit lb shown in  FIG. 7 .  FIG. 7  is a diagram showing the configuration of the display unit lb. In  FIG. 7 , such parts as are the same as in  FIG. 4  are identified by common reference signs. The display unit  1   b  of  FIG. 7  differs from the display unit  4   a  of  FIG. 4  in that a charge feeder  7  is connected to the sources, connected together, of the detection transistors TG 0   a  to TG 4   a,  and in that the first wiring condition detector  5   a  is replaced with a first wiring condition detector  5   b;  in other respects, the display unit  1   a  and the display unit  1   b  are the same. The charge feeder  7  feeds electric charge to the line D to which the sources of the detection transistors TG 0   a  to TG 4   a  are connected together. 
       FIG. 8  is a waveform diagram showing the relationship between the scanning voltage and the detection signal DG over the display period of one screen in the configuration shown in  FIG. 7 . In  FIG. 8 , such parts as find their counterparts in  FIGS. 2 ,  5 , etc. are identified by common reference signs. Although  FIG. 5  etc. show as if, for example, when the scanning voltage fed to the scanning line G 0  turns from a low level to a high level, simultaneously the scanning voltage fed to the scanning line G 1  turns from a high level to a low level, in reality there exists a short non-active subperiod t N  between the time points at which they so turn. Such a non-active subperiod t N  is set to occur in a last part of each of periods t 0  to t 4  and have a length equal to about several % to 10% of the length of period t 0  (or any one of t 1  to t 4 ). 
     In each non-active subperiod t N , the drive transistors are fed with a scanning voltage such that all of them are off. Specifically, in the configuration shown in  FIG. 7 , in each of periods t 0  to t 4 , during a first part of it (hereinafter referred to as an “active subperiod”), the gate driver  3  feeds a low-level scanning voltage to the corresponding scanning line to turn the corresponding drive transistors on; during a last part of the same period, that is, during a non-active subperiod t N , the gate driver  3  feeds a high-level scanning voltage to all the scanning lines to turn, or keep, the drive transistors off. 
     During the non-active subperiod t N  of each of periods t 0  to t 4 , the charge feeder  7  feeds electric charge to the line D; for example, it feeds electric charge such that the line D has a potential of about 5 V to 10V. On the other hand, during the active subperiod of each of periods t 0  to t 4 , the output portion of the charge feeder  7  connected to the line D is kept at a high impedance (for example, several tens to several hundred megohms). 
     Thus, in the active subperiod of each of periods t 0  to t 4 , when the corresponding detection transistor (one of the detection transistors TG 0   a  to TG 4   a ) turns on, the electric charge stored on the line D is discharged via that detection transistor and the resistor R 2 , and thus a pulse signal appears as the detection signal DG. If, however, the scanning line G 3  is abnormal, in period t 3 , no such discharge takes place, and thus no pulse signal appears as the detection signal DG. 
     By referring to the presence/absence of pulse signals in the detection signal DG and also to the above-mentioned timing signal fed to the gate driver  3 , the first wiring condition detector  5   b  detects whether the wiring condition of each scanning line is normal or abnormal. 
     The first wiring condition detector  5   b  may instead count the number of pulse signals appearing in the detection signal DG during the display period of one screen. This makes it possible to check whether or not any scanning line is abnormal. For example, in a case where the total number of scanning lines is  60 , if 60 pulses appear in the detection signal DG during the display period of one screen, it can be judged that all the scanning lines are normal; if 59 or less pulses appear in the detection signal DG during the same period, it can be judged that one or more of the scanning lines are abnormal. This does not allow location of defective spots, but allows judgment of whether the scanning lines are normal or abnormal with a simple configuration. With a configuration according to the first embodiment, it is possible to detect whether or not scanning lines are normal or abnormal on a real-time basis in actual operation, that is, in the middle of an image according to image data being displayed; it is also possible to achieve inspection of scanning lines with an extremely small number of elements. 
     Second Embodiment   
     Next, as a modified example of the first embodiment, a second embodiment of the present invention will be described.  FIG. 9  is a diagram showing the configuration of a display unit  1   c  included in a display device according to the second embodiment. 
     The display unit  1   c  of  FIG. 9  differs from the display unit  1  of  FIG. 1  in that a group  8  of protection switches is added, and in that, to cope with that addition, the first wiring condition detector  5  is replaced with a first wiring condition detector  5   c;  in other respects, the display unit  1  and the display unit  1   c  are the same. In  FIG. 9 , such parts as are the same as in  FIG. 1  are identified by common reference signs, and no overlapping description of those parts will be repeated. 
     The group  8  of protection switches consists of the same number of protection switching elements SW 0 , SW 1 , SW 2 , SW 3 , and SW 4  as the total number of scanning lines, with the protection switching elements inserted in the scanning lines G 0 , G 1 , G 2 , G 3 , and G 4 , respectively. 
     The protection switching element SW 0  is inserted between the node where the scanning line G 0  is connected to the gate driver  3  and the nodes where the scanning line G 0  is connected to the gates of the drive transistors T 00  to T 04 , so as to turn on and off the conduction between the former node to the latter nodes according to a control signal from the first wiring condition detector  5   c.  Likewise, the protection switching element SW 1  is inserted between the node where the scanning line G 1  is connected to the gate driver  3  and the nodes where the scanning line G 1  is connected to the gates of the drive transistors T 10  to T 14 , so as to turn on and off the conduction between the former node to the latter nodes according to a control signal from the first wiring condition detector  5   c.  A similar description applies to each of the other protection switching elements SW 2  to SW 4 . The protection switching elements SW 0  to SW 4  are all normally on. 
     The first wiring condition detector  5   c  is provided with, in addition to the functions of the first wiring condition detector  5  shown in  FIG. 1 , the function of outputting the above-mentioned control signal. Based on the detection signal DG, the first wiring condition detector  5   c  identifies, as an abnormal scanning line, any scanning line that is abnormal (broken, short-circuited, or otherwise defective), and turns off the protection switching element inserted in that abnormal scanning line to stop the drive transistors corresponding to that abnormal scanning line from receiving at their gates the scanning voltages from the gate driver  3 . 
     For example, when the detection signal DG is as shown in  FIG. 2 , and thus it is judged that all the scanning lines are normal, the first wiring condition detector  5   c  keeps all the protection switching elements SW 0  to SW 4  on. By contrast, when the detection signal DG is as shown in  FIG. 3 , and thus it is judged that the scanning lines G 3  and G 4  are abnormal (broken, short-circuited, or otherwise defective), the first wiring condition detector  5   c  identifies the scanning lines G 3  and G 4  as abnormal scanning lines, and turns the protection switching elements SW 3  and SW 4  off. This stops the drive transistors T 30  to T 34  and T 40  to T 44  corresponding to the scanning lines G 3  and G 4  from receiving at their gates the scanning voltage from the gate driver  3 . 
     When it is judged that any scanning line is abnormal, it may be short-circuited to a ground line; even in that case, with the protection switching elements provided as described above, it is possible to prevent an abnormal current from continuing to flow. The protection switching elements SW 0  to SW 4  may be formed, for example, as thin-film transistors (for example, N-channel insulated-gate field-effect transistors) like the drive transistors T 00  etc. The protection switching elements SW 0  to SW 4  may be provided outside the display panel  2  as shown in  FIG. 9 , or may be provided inside it. In a case where the protection switching elements SW 0  to SW 4  are provided inside the display panel  2 , the protection switching elements SW 0  to SW 4 , the detection transistors TG 0  to TG 4 , and the drive transistors T 00  to T 44  may be formed on a single substrate by a single process. 
     In the second embodiment, any feature described previously in connection with the first embodiment may be applied unless inconsistent. Accordingly, for example, in a manner similar to how the display unit  1  of  FIG. 1  is modified to the display unit  1   a  of  FIG. 4 , the N-channel drive transistors in  FIG. 9  may be replaced with P-channel drive transistors. In that case, the circuit configuration around them needs to be modified accordingly. The charge feeder  7  shown in  FIG. 7  may also be applied so that whether the scanning lines are normal or abnormal is checked based on pulse signals resulting from discharge of electric charge. 
     Third Embodiment   
     Next, a third embodiment of the present invention will be described.  FIG. 10  is a block diagram showing the configuration of a display unit  1   d  included in a display device according to the third embodiment. 
     The display unit  1   d  of  FIG. 10  differs from the display unit  1  of  FIG. 1  in that the display unit  1  of  FIG. 1  is here additionally provided with a second wiring condition detector  9 ; in other respects, the display unit  1  and the display unit id are the same. In  FIG. 10 , such parts as are the same as in  FIG. 1  are identified by common reference signs, and no overlapping description of those parts will be repeated. 
     One ends of the signal lines S 0  to S 4  are connected to the source driver  4 , and the other ends (terminal ends) of the signal lines S 0  to S 4  are connected to the second wiring condition detector  9 . Thus, between the node where the signal line S 0  is connected to the source driver  4  and the node where the signal line S 0  is connected to the second wiring condition detector  9 , there lie the nodes where the signal line S 0  is connected to the drive transistors T 00 , T 10 , T 20 , T 30 , and T 40 . A similar description applies to each of the other signal lines. 
     As shown in  FIG. 11 , in periods t 0  to t 4 , the gate driver  3  feeds the scanning lines G 0  to G 4  sequentially with a high-level scanning voltage. Here, as in the case described previously with reference to  FIG. 8 , during a last part of each of periods t 0  to t 4 , that is, during a non-active subperiod t N , the gate driver  3  feeds the scanning lines with a scanning voltage such that all the drive transistors stay off. Specifically, in the configuration shown in  FIG. 10 , in each of periods t 0  to t 4 , during a first part of it (an active subperiod), the gate driver  3  feeds a high-level scanning voltage to the corresponding scanning line to turn the corresponding drive transistors on; during a last part of the same period, that is, during a non-active subperiod t N , the gate driver  3  feeds a low-level scanning voltage to all the scanning lines to turn, or keep, the drive transistors off. 
     During the active subperiod of each of periods t 0  to t 4 , the source driver  4  feeds signal voltages according to image data to the signal lines S 0  to S 4 . For example, during the active subperiod of period to, the pixel circuits P 00  to P 04  corresponding to the scanning line G 0  are fed with signal voltages according to image data from the source driver  4  via the signal lines S 0  to S 4  and the drive transistors T 00  to T 04 . 
     During the non-active subperiods t N  of part or all of periods t 0  to t 4 , the source driver  4  feeds the signal lines, including the signal lines S 0  to S 4 , with an inspection voltage having a predetermined level different from those of the above-mentioned signal voltages according to image data. Based on how the inspection voltage is transmitted to it, the second wiring condition detector  9  detects whether the wiring condition of the signal lines is normal or abnormal. 
       FIG. 12  shows an example of the configuration of the second wiring condition detector  9 . The second wiring condition detector  9  shown in  FIG. 12  is provided with, or is composed of: a four-input NAND circuit A 0  to the different input terminals of which the signal lines S 0 , S 1 , S 2 , and S 3  are connected respectively; a four-input NAND circuit Al to the different input terminals of which the signal lines S 4 , S 5 , S 6 , and S 7  are connected respectively; a four-input NAND circuit A 2  to the different input terminals of which the signal lines S 8 , S 9 , S 10 , and S 11  are connected respectively; . . . ; and a judgment circuit  10  that judges whether the signal lines are normal or abnormal based on the outputs of the NAND circuits A 0 , A 1 , A 2 , . . . . The signal lines S 5  to S 11  are, like signal lines S 0  to S 4 , among the signal lines provided in the display panel  2 . 
     In this configuration, for example, during the non-active subperiod t N  of period to, which is the period in which to activate the scanning line G 0 , the source driver  4  feeds a high-level voltage (corresponding to the above-mentioned inspection voltage) only to the signal lines S 0  to S 3  and feeds a low-level voltage to the other signal lines. Here, if the signal lines S 0  to S 3  are all normal, the NAND circuit A 0  outputs a low level as its output signal; if at least one of the signal lines S 0  to S 3  is abnormal, the NAND circuit A 0  outputs a high level as its output signal. Meanwhile, the other NAND circuits A 1  etc. output a high level as their output signal. 
     Next, during the non-active subperiod t N  of period t 1 , which is the period in which to activate the scanning line G 1 , the source driver  4  feeds a high-level voltage (corresponding to the above-mentioned inspection voltage) only to the signal lines S 4  to S 7  and feeds a low-level voltage to the other signal lines. Here, if the signal lines S 4  to S 7  are all normal, the NAND circuit A 1  outputs a low level as its output signal; if at least one of the signal lines S 4  to S 7  is abnormal, the NAND circuit A 1  outputs a high level as its output signal. Meanwhile, the other NAND circuits A 0  etc. output a high level as their output signal. Similar processing is performed with the NAND circuit A 2 , . . . . 
     In this configuration, building the judgment circuit  10  with a NAND circuit that receives the output signals of the NAND circuits A 0 , A 1 , A 2 , . . . makes it possible to judge whether every four of the signal lines are normal or abnormal. For example, if the signal line S 0  is abnormal, during the non-active subperiod t N  of period t 0 , the NAND circuit A 0  outputs a high level, and thus the NAND circuit forming the judgment circuit  10  outputs a low level as its output signal. By referring not only to this low-level output signal but also to the above-mentioned timing signal, it is possible to judge that at least one of the signal lines S 0  to S 3  is abnormal. Alternatively, during the non-active subperiods t N  of part or all of periods t 0  to t 4 , the source driver  4  may feed a high-level voltage (corresponding to the above-mentioned inspection voltage) to all the signal lines simultaneously. With this configuration, based on each of the output signals of the NAND circuits A 0 , A 1 , A 2 , . . . outputted simultaneously during those non-active subperiods t N , the judgment circuit  10  can judge whether every four of the signal lines are normal or abnormal. As described above, the signal lines provided in the display panel  2  are divided into a plurality of signal line blocks, and the signal lines belonging to each signal line block (for example, in the above example, the signal lines A 0  to A 3  connected to the NAND circuit A 0 ) are connected to one NAND circuit, so that whether the signal lines are normal or abnormal is judged on a block-by-block basis. Although each signal line block consists of four signal lines in the above example, this number is merely given as an example and may be changed; for example, each signal line block may consist of 32 to 128 signal lines. 
     The second wiring condition detector  9  is, for example, fabricated as a circuit separate from the display panel  2  so as to be externally fitted to it. In a case where no detection of whether or not the scanning lines are normal or abnormal is necessary, the first wiring condition detector  5 , the group  6  of detection transistors, and the resistor R 1  in the display unit Id shown in  FIG. 10  may be omitted. 
     In a manner similar to how the display unit  1  of  FIG. 1  is modified to the display unit  1   a  of  FIG. 4 , the N-channel drive transistors in  FIG. 10  may be replaced with P-channel drive transistors. In that case, the circuit configuration around them needs to be modified accordingly. This embodiment may be combined with the second embodiment ( FIG. 9 ) so that the configuration of this embodiment is additionally provided with the group  8  of protection switches shown in  FIG. 9 . 
     In a manner similar to how the display unit  1  of  FIG. 1  is modified to display unit  1   c  of  FIG. 9 , as shown in  FIG. 13 , the same number of protection switching elements SW 0   a , SW 1   a , SW 2   a,  SW 3   a,  and SW 4   a  as the total number of signal lines may be additionally provided, with the protection switching elements inserted in the signal lines S 0 , S 1 , S 2 , S 3 , and S 4 , respectively. 
     The protection switching element SW 0   a  is inserted between the node where the signal line S 0  is connected to the source driver  4  and the nodes where the signal line S 0  is connected to the sources of the drive transistors T 00 , TI 0 , T 20 , T 30 , and T 40 , so as to turn on and off the conduction between the former node to the latter nodes according to a control signal from the second wiring condition detector  9 . Likewise, the protection switching element SW 1   a  is inserted between the node where the signal line S 1  is connected to the source driver  4  and the nodes where the signal line S 1  is connected to the sources of the drive transistors T 01 , T 11 , T 21 , T 31 , and T 41 , so as to turn on and off the conduction between the former node to the latter nodes according to a control signal from the second wiring condition detector  9 . A similar description applies to each of the other protection switching elements SW 2   a  to SW 4   a.  The protection switching elements SW 0   a  to SW 4   a  are all normally on. 
     In this configuration, based on how the above-mentioned inspection signal is transmitted to it, the second wiring condition detector  9  identifies, as an abnormal signal line, any signal line across which transmission is abnormal (one that does not transmit the above-mentioned inspection signal), and turns off the protection switching element inserted in that abnormal signal line to stop the drive transistors corresponding to that abnormal signal line from receiving at their sources the output voltages (signal voltages etc.) of the source driver  4 . 
     For example, in a case where the second wiring condition detector  9  is configured as shown in  FIG. 12 , if it is judged that at least one of the signal lines S 0  to S 3  is abnormal, the second wiring condition detector  9  identifies the signal lines S 0  to S 3  as abnormal scanning lines (an abnormal scanning line block), and turns the protection switching elements SW 0   a  to SW 3   a  off. This stops the drive transistors connected to the signal lines S 0  to S 3  from receiving at their sources the output voltages of the source driver  4 . Needless to say, when it is judged that all the signal lines are normal, all the protection switching elements SW 0   a  to SW 4   a  are turned, or kept, on. 
     When it is judged that any signal line is abnormal, it may be short-circuited to a ground line; even in that case, with the. protection switching elements provided as described above, it is possible to prevent an abnormal current from continuing to flow. 
     The protection switching elements SW 0   a  to SW 4   a  may be formed, for example, as thin-film transistors (for example, N-channel insulated-gate field-effect transistors) like the drive transistors T 00  etc. The protection switching elements SW 0   a  to SW 4   a  may be provided outside the display panel  2  as shown in  FIG. 13 , or may be provided inside it. In a case where the protection switching elements SW 0   a  to SW 4   a  are provided inside the display panel  2 , the protection switching elements SW 0   a  to SW 4   a,  the detection transistors TG 0  to TG 4 , and the drive transistors T 00  to T 44  may be formed on a single substrate by a single process. 
     With a configuration according to the second embodiment, it is possible to detect whether or not signal lines are normal or abnormal on a real-time basis in actual operation, that is, in the middle of an image according to image data being displayed 
     Fourth Embodiment  
     Next, a vehicle-mounted system incorporating a display unit according to one of the first to third embodiments described above will be described as a fourth embodiment of the present invention. The following description deals with, as an example, a vehicle-mounted system incorporating a display unit  1   d  ( FIG. 10 ) according to the third embodiment. 
     The vehicle-mounted system includes, or is built with, a vehicle instrument panel (display platform-electrical control unit, abbreviated to DPF-ECU).  FIG. 14  is a diagram showing the overall configuration of the vehicle-mounted system incorporating the display unit id ( FIG. 10 ). This vehicle-mounted system is installed on an unillustrated vehicle such as an automobile. 
     A DPF-ECU  31 , a main ECU (electrical control unit)  32 , a gear ECU  33 , a winker ECU  34 , and a water temperature thermometer ECU  35  are connected to a CAN (controller area network) bus  30  so as to be bidirectionally communicable with one another across the CAN bus  30 . 
     The gear ECU  33  monitors and controls the state of gears (unillustrated) provided in the vehicle. The winker ECU  34  monitors and controls the state of blinkers (unillustrated) provided in the vehicle. The water temperature thermometer ECU  35  monitors the temperature indicated by a water thermometer (unillustrated) provided in the vehicle; that is, it monitors the temperature of coolant fluid. The DPF-ECU  31  has, or is composed of: the display unit ld including a display panel  2 ; a CAN microcomputer  37 ; and an image output controller  38 . 
     The main ECU  32  determines a main event number (hereinafter abbreviated to “MEN”) that specifies the overall layout of the screen to be displayed on the display panel  2  provided in the display unit  1   d.  In addition, based on information on the state of the gears from the gear ECU  33 , information on the state of the blinkers from the winker ECU  34 , and information on the above-mentioned temperature from the water temperature thermometer ECU  35 , the main ECU  32  also determines a sub event number (hereinafter abbreviated to “SEN”) that specifies the layouts of parts of the screen to be displayed on the display panel  2  provided in the display unit  1   d.    
     Referring to an event conversion table  36  having contents, for example, as shown in  FIG. 15 , the main ECU  32  determines an SDN (scene design number) having a MEN and a SEN put together. The main ECU  32  determines the SDN periodically such that, every 10 ms, the determined SDN is transmitted to the CAN microcomputer  37  provided in the DPF-ECU  31 ; simultaneously, along with the SDN, information on the traveling speed of the vehicle, information on the rotation speed of a crank shaft (unillustrated) of an engine, etc. is also transmitted to the CAN microcomputer  37 . 
     The CAN microcomputer  37  then transmits the received SDN to the image output controller  38 . Here, the received SDN may first be subjected to predetermined processing before being transmitted to the image output controller  38 . Based on the SDN thus received, the image output controller  38  controls the display unit  1   d  and transmits image data to the source driver  4  so that an image with a screen layout according to the SDN is displayed on the display panel  2  provided in the display unit  1   d.    
     In this way, the main ECU  32  determines the screen layout according to the state of the gears etc., and the display panel  2  displays, in a periodically refreshed fashion, an image with a screen layout according to the state of the gears etc. 
     At a time point that no refreshing of the screen is specified in the event data file referred to by the main ECU  32 , the same SDN as previously transmitted is once again transmitted to the DPF-ECU  31 . Also, if, in response to the SDN transmitted from the main ECU  32 , no acknowledgment of completion of its reception is returned from the DPF-ECU  31 , or an error notification indicating an error in its reception is returned, even when transmission of a next SDN is requested in the above-mentioned event data file, the same SDN as previously transmitted is once again transmitted to the DPF-ECU  31 . 
       FIGS. 16 and 17  show examples of screen layouts determined by the main ECU  32  for display on the display panel  2 . In the screen layouts shown in  FIG. 16 and 17 , the display area of the display panel  2  is divided into subareas  51 ,  52 ,  53 ,  54 , and  55  and the remaining subarea  56  for separate use. Display of an image in a given area is always achieved with the same drive transistors and pixel circuits. Screen layouts like those shown in  FIGS. 16 and 17  are designed beforehand and stored in a memory or the like, and information that identifies those screen layouts is referred to by the main ECU  32  and the DPF-ECU  31 . 
     In the screen layouts shown in  FIGS. 16 and 17 , the area  53  is allotted to the display of the state of the blinkers, the area  54  is allotted to the display of a map around the vehicle, and the area  55  is allotted to the display of the state of the gears etc. In the screen layout shown in  FIG. 16 , the area  51  is allotted to the display of the traveling speed (for example, 0 to 180 km/hour) of the vehicle, and the area 52 is allotted to the display of a tachometer (for example, 0 to 9 000 rpm) indicating the above-mentioned rotation speed. In the screen layout shown in  FIG. 17 , reversely, the area  51  is allotted to the display of a tachometer, and the area  52  is allotted to the display of the traveling speed of the vehicle. 
     Suppose now that, while an image is being displayed on the display panel  2  with the screen layout shown in  FIG. 16 , some of the signal lines for feeding signal voltages to the pixel circuits for displaying the image in the area  51  have become abnormal. For example, assume that, in a case where the signal lines for feeding signal voltages to the pixel circuits for displaying the image in the area  51  consist of signal lines S 200  to S 263 , it is judged that the signal lines S 200  to S 231  have become abnormal while the signal lines other than the signal lines S 200  to S 231  are normal. This judgment is made by the second wiring condition detector  9  configured as shown in  FIG. 12 . Here, the signal lines S 200  to S 263  (unillustrated) are, like the signal lines S 0  to S 4 , among the signal lines provided in the display panel  2 . 
     The result of the judgment of whether the signal lines are normal or abnormal by the second wiring condition detector  9  is transmitted via the CAN microcomputer  37  and the CAN bus  30  to the main ECU  32 . The main ECU  32  distinguishes the different degrees of display precedence assigned to the different kinds of information displayed on the display panel  2 . In the screen layouts shown in  FIG. 16 and 17 , the information on the traveling speed of the vehicle is assigned a higher degree of display precedence than the information on the rotation speed. This is because loss of display of the traveling speed of the vehicle greatly diminishes the safety of travel of the vehicle. 
     In response to the result of the above-mentioned judgment of whether the signal lines are normal or abnormal, the main ECU  32  changes the SDN such that the screen layout is changed from the one shown in  FIG. 16  to the one shown in  FIG. 17 . That is, it instantaneously changes the screen layout such that the information (image) on the traveling speed, which has up to now been displayed in the area  51 , is from now on displayed in the area  52  and that the information (image) on the rotation speed, which has up to now been displayed in the area  52 , is from now on displayed in the area  51 . The changed SDN is transmitted via the CAN bus  30  etc, to the image output controller  38 , so that the screen layout on the display panel  2  is changed from the one shown in  FIG. 16  to the one shown in  FIG. 17 . 
     As described above, if, while information with a higher degree of display precedence (in the above example, the traveling speed of the vehicle) is being displayed in a first area (in the above example, the area  51 ), the first area has come to involve a pixel circuit corresponding to an abnormal signal line, then the information with the higher degree of display precedence is thereafter displayed on a second area different from the first area. The second area involves no pixel circuit corresponding to an abnormal signal line. This helps maintain accurate display of information with so high a degree of display precedence that impaired display of it may lead to a serious hazard (in the above example, the traveling speed of the vehicle). 
     Although the above description deals with an example in which a signal line has become abnormal, a scanning line that has become abnormal can be coped with similarly. Specifically, if, while information with a higher degree of display precedence is being displayed in a first area, the first area has come to involve a pixel circuit corresponding to an abnormal scanning line, then the information with the higher degree of display precedence is thereafter displayed on a second area different from the first area. The second area involves no pixel circuit corresponding to an abnormal scanning line. 
     Needless to say, even if a scanning line and a signal line have become abnormal simultaneously, they can be coped with similarly. Specifically, if, while information with a higher degree of display precedence is being displayed in a first area, the first area has come to involve a pixel circuit corresponding to an abnormal scanning and/or signal line, then the information with the higher degree of display precedence is thereafter displayed on a second area different from the first area. The second area involves no pixel circuit corresponding to an abnormal scanning and/or signal line. 
     Modifications and Variations  
     In the embodiments described above, the gate driver  3  functions as a scanning line driver, the source driver  4  functions as a signal line driver. In the fourth embodiment, the image output controller  38  functions as an image data outputter. The image data outputter may be regarded as being composed of the image output controller  38  and the main ECU  32 . 
     INDUSTRIAL APPLICABILITY 
     The present invention offers display panels such as liquid crystal display panels, organic EL (electroluminescence) display panels, inorganic EL display panels, and plasma display panels, and is suitable for display devices incorporating such display panels. The present invention is also suitable for vehicle-mounted systems incorporating such display devices.