Patent Publication Number: US-2015081041-A1

Title: Output apparatus and diagnosis method therefor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from prior Japanese Patent Applications No. 2013-193473, filed Sep. 18, 2013, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an output apparatus and a diagnosis method therefor. 
     BACKGROUND 
     In recent years, for the manufacturers and suppliers of apparatuses, an international functional safety standard has been established as the IEC61508 standard “Functional Safety of Electrical/Electronic/Programmable Electronic Safety-related Systems” of the IEC (International Electrotechnical Commission). Furthermore, in a functional safety system for a specific industry, a derivative standard for a specific application purpose has been stipulated. For example, with respect to a safety instrumentation system, IEC61511 has been stipulated for designers, integrators, and users of the system as the international process application standard. 
     In these standards, safety in the lifecycle of design, maintenance, and disposition of a system is assessed, and the SIL (Safety Integrity Level), which is the required level of risk reduction, is defined as a quantitative assessment scale. 
     The safety instrumentation system required to achieve a high SIL needs to detect a failure of a digital output circuit. It is necessary to diagnose a target digital output circuit not only at the time of start of the system but also during the operation of the system. If a failure is detected, it is necessary to cause the output of the system to transit to a safe state. 
     In connection from a digital output circuit including an output interruption circuit to an input circuit serving as a control apparatus (load), a failure of an output element in the output interruption circuit is diagnosed within the non-response time of the control apparatus. 
     Since, however, the non-response times of control apparatuses are different from each other, it is necessary to perform failure diagnosis by changing the diagnosis timing for each digital output circuit according to the response characteristic of a control apparatus connected to the digital output circuit. 
     To perform failure diagnosis of an interruption element and output element, therefore, it is necessary to control each of the interruption element and the output element. As the number of control apparatuses increases, the device cost and the part implementation area respectively increase. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram showing an example of the arrangement of the digital output circuits of an output apparatus according to the first embodiment; 
         FIG. 2  is a view for explaining an example of the overall operation at timings of element diagnosis by the output apparatus according to the first embodiment. 
         FIG. 3  is a view for explaining an example of an output element OFF diagnosis operation by the output apparatus according to the first embodiment; 
         FIG. 4  is a flowchart illustrating an example of a procedure for OFF diagnosis of the first output element  41  and second output element  43  by the output apparatus according to the first embodiment; 
         FIG. 5  is a view for explaining an example of an interruption element OFF diagnosis operation by the output apparatus according to the first embodiment; 
         FIG. 6  is a flowchart illustrating an example of a procedure for OFF diagnosis of the first interruption element and second interruption element by the output apparatus according to the first embodiment; 
         FIG. 7  is a view for explaining an example of an interruption element diagnosis operation by the output apparatus according to the first embodiment when the various output signals are ON; 
         FIG. 8  is a circuit diagram showing an example of the arrangement of the digital output circuits of the output apparatus according to the second embodiment; 
         FIG. 9  is a view for explaining an example of an output element diagnosis operation by the output apparatus according to the second embodiment; 
         FIG. 10  is a flowchart illustrating an example of a procedure for OFF diagnosis of the first output element and second output element by the output apparatus according to the second embodiment; 
         FIG. 11  is a view for explaining an example of an interruption element diagnosis operation by the output apparatus according to the second embodiment; 
         FIG. 12  is a flowchart illustrating an example of a procedure for OFF diagnosis of the first interruption element and second interruption element by the output apparatus according to the second embodiment; and 
         FIG. 13  is a circuit diagram showing an example of the arrangement of a conventional interruption/output element diagnosis circuit. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, there is provided an output apparatus connected to a first load and a second load whose response time to a signal is longer than that of the first load. The output apparatus includes a first digital output circuit including a first output element configured to output a signal to the first load, and a first interruption element connected to the first output element. The output apparatus includes a second digital output circuit including a second output element configured to output a signal to the second load, and a second interruption element connected to the second output element. The output apparatus includes a single driving circuit for an interruption element, configured to drive the first interruption element and the second interruption element collectively. The output apparatus includes a signal control unit configured to set a signal from the second output element in an OFF state at a timing earlier than a predetermined timing by the response time of the second load, and set signals from the first output element and the second output element in an ON state, and signals from the first interruption element and the second interruption element in an OFF state at a timing earlier than the predetermined timing by the response time of the first load The output apparatus includes a diagnosis unit configured to diagnose, at the predetermined timing, whether the first interruption element is in a normal state or a failure state, based on a signal from the first digital output circuit, and diagnose, at the predetermined timing, whether the second interruption element is in a normal state or a failure state, based on a signal from the second digital output circuit. 
     Embodiments will be described below with reference to the accompanying drawings. 
     For easy understanding of the embodiments, the arrangement of the digital output circuits of a conventional output apparatus will be explained first. 
       FIG. 13  is a circuit diagram showing an example of the arrangement of a conventional interruption/output element diagnosis circuit. 
     An output apparatus  10  includes a first digital output circuit  30  and a second digital output circuit  31 . The output apparatus  10  has a function of diagnosing the first digital output circuit  30  and the second digital output circuit  31 . 
     The first digital output circuit  30  will be described. 
     The first digital output circuit  30  includes a MOSFET (field effect transistor) of a first output element  41 . The MOSFET of the first output element  41  operates as a switching element for driving a first control apparatus  50  serving as a first load. The source of the first output element  41  is connected to an MPU  20  and the input terminal of the first control apparatus  50 . The MPU  20  monitors the output state of the first digital output circuit  30 . 
     The first digital output circuit  30  includes a MOSFET of a first interruption element  40 . The MOSFET of the first interruption element  40  operates as a switching element for interrupting the first digital output circuit  30 . The source of the first interruption element  40  is connected to the drain of the first output element  41  via a first interruption element-first output element connection line  123 . The gate of the first output element  41  is connected to a driving circuit  21   b  for the first output element  41 . 
     The drain of the first interruption element  40  is connected to the positive side of an external power supply apparatus  52  via a positive line  120  of the external power supply apparatus  52 . The gate of the first interruption element  40  is connected to a driving circuit  21   d  for the first interruption element  40 . As will be described later, the driving circuit  21   d  also serves as a driving circuit for a second interruption element  42 . 
     The driving circuit  21   b  for the first output element  41  and the driving circuit  21   d  for the first interruption element  40  are connected to the MPU  20  for driving the first output element  41  and the first interruption element  40 . 
     The second digital output circuit  31  will be described next. 
     The second digital output circuit  31  includes a MOSFET of a second output element  43 . The MOSFET of the second output element  43  operates as a switching element for driving a second control apparatus  51  serving as a second load. The source of the second output element  43  is connected to the MPU  20  and the input terminal of the second control apparatus  51 . The MPU  20  monitors the output state of the second digital output circuit  31 . 
     As the first control apparatus  50  connected to the first output element  41  of the first digital output circuit  30 , a control apparatus having a quick response characteristic, for example, a small time constant (tcr1&lt;tcr2) is used. 
     As the second control apparatus  51  connected to the second output element  43  of the second digital output circuit  31 , a control apparatus having a response characteristic slower than that of the first control apparatus  50 , for example, a large time constant (tcr2&gt;tcr1) is used. 
     The second digital output circuit  31  includes a MOSFET of the second interruption element  42 . The MOSFET of the second interruption element  42  operates as a switching element for interrupting the second digital output circuit  31 . The source of the second interruption element  42  is connected to the drain of the second output element  43  via a second interruption element-second output element connection line  124 . The gate of the second output element  43  is connected to a driving circuit  21   c  for the second output element  43 . The gate of the second interruption element  42  is connected to a driving circuit  21   e  for the second interruption element  42 . 
     The driving circuit  21   c  for the second output element  43  and the driving circuit  21   e  for the second interruption element  42  are connected to the MPU  20  for driving the second output element  43  and the second interruption element  42 . 
     Furthermore, the output terminals of the first control apparatus  50  and second control apparatus  51  are connected to the negative side of the external power supply apparatus  52  via a negative line  121  of the external power supply apparatus  52 . The positive side of the external power supply apparatus  52  is connected to the drain of the second interruption element  42 . 
     As described above, in the conventional arrangement shown in  FIG. 13 , the MPU  20  drives the first interruption element  40  and the second interruption element  42  via the different driving circuits  21   d  and  21   e , respectively. 
     The MPU  20  outputs a first interruption element control signal  110  for controlling the first interruption element  40  to the driving circuit  21   d  for the first interruption element  40 . The driving circuit  21   d  outputs a first interruption signal (first interruption element driving signal)  111  to the first interruption element  40 . 
     If the first interruption element  40  is normal, when the first interruption signal  111  is set in the ON state, the first interruption element  40  is set in the ON state. Furthermore, if the first interruption element  40  is normal, when the first interruption signal  111  is set in the OFF state, the first interruption element  40  is set in the OFF state. 
     The MPU  20  outputs a first output element control signal  102  for controlling the first output element  41  to the driving circuit  21   b  for the first output element  41 . The driving circuit  21   b  outputs a first output signal (first output element driving signal)  103  to the first output element  41 . 
     If the first output element  41  is normal, when the first output signal  103  is set in the ON state, the first output element  41  is set in the ON state. Furthermore, if the first output element  41  is normal, when the first output signal  103  is set in the OFF state, the first output element  41  is set in the OFF state. 
     The MPU  20  outputs a second interruption element control signal  112  for controlling the second interruption element  42  to the driving circuit  21   e  for the second interruption element  42 . The driving circuit  21   e  outputs a second interruption signal (second interruption element driving signal)  113  to the second interruption element  42 . 
     If the second interruption element  42  is normal, when the second interruption signal  113  is set in the ON state, the second interruption element  42  is set in the ON state. Furthermore, if the second interruption element  42  is normal, when the second interruption signal  113  is set in the OFF state, the second interruption element  42  is set in the OFF state. 
     The MPU  20  outputs a second output element control signal  104  for controlling the second output element  43  to the driving circuit  21   c  for the second output element  43 . The driving circuit  21   c  outputs a second output signal (second output element driving signal)  105  to the second output element  43 . 
     If the second output element  43  is normal, when the second output signal  105  is set in the ON state, the second output element  43  is set in the ON state. Furthermore, if the second output element  43  is normal, when the second output signal  105  is set in the OFF state, the second output element  43  is set in the OFF state. 
     Based on a first output diagnosis signal  106  and a second output diagnosis signal  107  according to the signal control of the various elements, the MPU  20  diagnoses whether each of various elements is in a normal state (an ON/OFF signal can be output) or a failure state (no OFF signal can be output). Diagnosis of whether each of various elements can output an ON signal may be referred to as ON diagnosis. Diagnosis of whether each of various elements can output an OFF signal may be referred to as OFF diagnosis. 
     That is, with the conventional arrangement, it is necessary to diagnose the first interruption element  40  and the second interruption element  42  individually in accordance with the response characteristic of each control apparatus. Therefore, both the driving circuit  21   d  for the first interruption element  40  and the driving circuit  21   e  for the second interruption element  42  are required. 
     When the output is ON during control output, the MPU  20  performs ON diagnosis for the first output element  41 , second output element  43 , first interruption element  40 , and second interruption element  42  collectively. 
     That is, the MPU  20  performs OFF diagnosis of the first output element  41  and second output element  43 , OFF diagnosis of the first interruption element  40  and second interruption element  42 , and ON diagnosis of the first output element  41 , second output element  43 , first interruption element  40 , and the second interruption element  42 . With this processing, the MPU  20  performs ON/OFF failure diagnosis of each element. 
     First Embodiment 
     The first embodiment will now be described. 
       FIG. 1  is a circuit diagram showing an example of the arrangement of the digital output circuits of an output apparatus according to the first embodiment. 
     Of components shown in  FIG. 1 , components different from those shown in  FIG. 13  will be mainly explained. 
     In the arrangement shown in  FIG. 1 , instead of respectively providing the driving circuits  21   d  and  21   e  for the first interruption element  40  and the second interruption element  42  as shown in  FIG. 13 , one driving circuit  21   a  common to a first interruption element  40  and a second interruption element  42  is provided. The driving circuit  21   a  is connected to the gate of the first interruption element  40  and that of the second interruption element  42 . This common driving circuit will be referred to as the driving circuit  21   a  for each interruption element, as needed. 
     An MPU  20  includes a signal control unit  20   a  for controlling signals to various elements, and a diagnosis unit  20   b  for diagnosing, based on a first output diagnosis signal  106  and second output diagnosis signal  107  according to the signal control, whether each of the various elements is in the normal or failure state. 
     The driving circuit  21   a  for each interruption element is configured to output a first/second interruption signal (interruption element driving signal)  101  as a signal common to the first interruption element  40  and the second interruption element  42  in accordance with an interruption element control signal  100  from the signal control unit  20   a  of the MPU  20 . 
     If the first interruption element  40  and the second interruption element  42  are normal, when the first/second interruption signal  101  is set in the ON state, the first interruption element  40  and the second interruption element  42  are set in the ON state. Furthermore, if the first interruption element  40  and the second interruption element  42  are normal, when the first/second interruption signal  101  is set in the OFF state, the first interruption element  40  and the second interruption element  42  are set in the OFF state. 
     As described above, in this embodiment, the first interruption element  40  and second interruption element  42  are connected to the one driving circuit  21   a  for the interruption elements; however, it is possible to reduce the number of driving circuits, as compared with the arrangement shown in  FIG. 13 . 
       FIG. 2  is a view for explaining an example of the overall operation at timings of element diagnosis by the output apparatus according to the first embodiment. Referring to  FIG. 2 , reference symbol A 1  denotes an output element diagnosis period; A 2 , an interruption element diagnosis period; and B, a control output period. 
       FIG. 2  shows timings at which OFF diagnosis is performed for a first output element  41 , a second output element  43 , the first interruption element  40 , and the second interruption element  42 , respectively. 
     Control of various signals for performing OFF diagnosis of the first output element  41  and second output element  43  will be described. 
     Before a predetermined timing at which OFF diagnosis is performed for the first output element  41  and the second output element  43 , the signal control unit  20   a  of the MPU  20  sets the first/second interruption signal  101  in the ON state. 
     To set the first/second interruption signal  101  in the ON state, the signal control unit  20   a  of the MPU  20  outputs the interruption element control signal  100  for setting the first/second interruption signal  101  in the ON state to the driving circuit  21   a  for each interruption element. Then, the driving circuit  21   a  outputs the first/second interruption signal  101  set in the ON state to the first interruption element  40  and the second interruption element  42 . The same applies to the processing of outputting a signal for setting the first/second interruption signal  101  in the OFF state, except that the ON/OFF state is different. 
     When the predetermined timing at which OFF diagnosis is performed for the first output element  41  and the second output element  43  comes, the signal control unit  20   a  of the MPU  20  outputs signals for setting a first output signal  103  and a second output signal  105  in the OFF state to the driving circuits  21   b  and  21   c  within the response times of a first control apparatus  50  and second control apparatus  51 , respectively, while the first/second interruption signal  101  is in the ON state. 
     To set the first output signal  103  in the OFF state, the signal control unit  20   a  of the MPU  20  outputs a first output element control signal  102  for setting the first output signal  103  in the OFF state to a driving circuit  21   b  for the first output element  41 . Then, the driving circuit  21   b  outputs the first output signal  103  set in the OFF state to the first output element  41 . The same applies to processing of outputting a signal for setting the first output signal  103  in the ON state, except that the ON/OFF state is different. 
     To set the second output signal  105  in the OFF state, the signal control unit  20   a  of the MPU  20  outputs a second output element control signal  104  for setting the second output signal  105  in the OFF state to a driving circuit  21   c  for the second output element  43 . Then, the driving circuit  21   c  outputs the second output signal  105  set in the OFF state to the second output element  43 . The same applies to the processing of outputting a signal for setting the second output signal  105  in the ON state, except that the ON/OFF state is different. 
     The diagnosis unit  20   b  of the MPU  20  performs OFF diagnosis of the first output element  41  by determining the voltage level of the first output diagnosis signal  106  when the driving circuit  21   b  is caused to set the first output signal  103  in the OFF state. 
     The diagnosis unit  20   b  of the MPU  20  performs OFF diagnosis of the second output element  43  by determining the voltage level of the second output diagnosis signal  107  when the driving circuit  21   c  is caused to set the second output signal  105  in the OFF state. 
     Control of various signals for performing OFF diagnosis of the first interruption element  40  and second interruption element  42  will be described next. 
     Before a predetermined timing at which OFF diagnosis is performed for the first interruption element  40  and the second interruption element  42 , the signal control unit  20   a  of the MPU  20  causes the driving circuits  21   b  and  21   c  to respectively output the first output signal  103  and the second output signal  105  while maintaining the ON or OFF state set at the time immediately preceding control output. 
     When the predetermined timing at which OFF diagnosis is performed for the first interruption element  40  and the second interruption element  42  comes, the signal control unit  20   a  of the MPU  20  outputs signals for setting the first output signal  103  and the second output signal  105  in the ON state to the driving circuits  21   b  and  21   c , respectively. At this timing, the signal control unit  20   a  of the MPU  20  outputs, to the driving circuit  21   a , a signal for setting the first/second interruption signal  101  in the OFF state within the response times of the first control apparatus  50  and second control apparatus  51 . 
     The diagnosis unit  20   b  of the MPU  20  performs OFF diagnosis of the first interruption element  40  by determining the voltage level of the first output diagnosis signal  106  when the first/second interruption signal  101  is set in the OFF state. The diagnosis unit  20   b  of the MPU  20  performs OFF diagnosis of the second interruption element  42  by determining the voltage level of the second output diagnosis signal  107  when the first/second interruption signal  101  is set in the OFF state. 
       FIG. 3  is a view for explaining an example of an output element OFF diagnosis operation by the output apparatus according to the first embodiment. 
       FIG. 3  shows OFF diagnosis of the first output element  41  and second output element  43  along with an elapsed time. 
     OFF diagnosis is performed for the first output element  41  and the second output element  43  while the first output element  41  is connected to the first control apparatus  50  and the second output element  43  is connected to the second control apparatus  51 . A diagnosis time is set according to the response characteristics of the first control apparatus  50  and second control apparatus  51 . The diagnosis unit  20   b  of the MPU  20  performs OFF diagnosis of the first output element  41  and second output element  43  during the diagnosis time. 
       FIG. 4  is a flowchart illustrating an example of a procedure for OFF diagnosis of the first output element  41  and second output element  43  by the output apparatus according to the first embodiment. 
     In the initial state, before a time t2 a time tcr2 earlier than a diagnosis determination point (detection point) t0 at which OFF diagnosis is performed for the first output element  41  and the second output element  43 , the signal control unit  20   a  of the MPU  20  outputs the first/second interruption signal  101  in the ON state, and causes the driving circuits  21   b  and  21   c  to respectively output the first output signal  103  and the second output signal  105  while maintaining the ON or OFF state set at the time immediately preceding control output (step S 1 ). 
     When the above-described time t2 is measured (step S 2 ), the signal control unit  20   a  of the MPU  20  outputs a signal for setting the second output signal  105  in the OFF state to the driving circuit  21   c  for the second output element  43  for OFF diagnosis of the second output element  43  (step S 3 ). This second output signal serves as a driving signal for the second output element  43  on the side of the second control apparatus  51  having a slow response characteristic. 
     Before a time t1 a time tcr1 earlier than the diagnosis determination point to, the signal control unit  20   a  of the MPU  20  causes the driving circuit  21   b  to output the first output signal  103  while maintaining the ON or OFF state set at the time immediately preceding control output. 
     When the above-described time t1 is measured (step S 4 ), the signal control unit  20   a  of the MPU  20  outputs a signal for setting the first output signal  103  in the OFF state to the driving circuit  21   b  for OFF diagnosis of the first output element  41  (step S 5 ). The first output signal  103  serves as a driving signal for the first output element  41  on the side of the first control apparatus  50  having a quick response characteristic. 
     When the time of the diagnosis determination point t0 is measured (step S 6 ), the diagnosis unit  20   b  of the MPU  20  inputs the first output diagnosis signal  106  from the first output element  41  and the second output diagnosis signal  107  from the second output element  43  (step S 7 ). After the diagnosis determination point t0, the diagnosis unit  20   b  of the MPU  20  causes the driving circuit  21   a  to output the first/second interruption signal  101  while maintaining the ON state, and causes the driving circuits  21   b  and  21   c  to respectively output the first output signal  103  and the second output signal  105  while maintaining the ON or OFF state set at the time immediately preceding control output. 
     If the voltage level of the first output diagnosis signal  106  is low (YES in step S 8 ), the diagnosis unit  20   b  of the MPU  20  determines that the first output element  41  is in the normal state (step S 9 ). If the voltage level is high (HI) (NO in step S 8 ), the diagnosis unit  20   b  of the MPU  20  determines that the first output element  41  is in the failure (abnormal) state (step S 10 ). In this way, it is possible to perform OFF diagnosis of the first output element  41 . Referring to  FIG. 3 , a square represents that the detection result indicates the failure state, a circle represents that the detection result indicates the normal state, and a dotted line represents a waveform when the output element is in the failure state. 
     Similarly, if the voltage level of the second output diagnosis signal  107  is low, the diagnosis unit  20   b  of the MPU  20  determines that the second output element  43  is in the normal state. If the voltage level is high, the diagnosis unit  20   b  of the MPU  20  determines that the second output element  43  is in the failure (abnormal) state. In this way, it is possible to perform OFF diagnosis of the second output element  43 . 
       FIG. 5  is a view for explaining an example of an interruption element OFF diagnosis operation by the output apparatus according to the first embodiment.  FIG. 6  is a flowchart illustrating an example of a procedure for OFF diagnosis of the first interruption element and second interruption element by the output apparatus according to the first embodiment.  FIG. 7  is a view for explaining an example of an interruption element diagnosis operation by the output apparatus according to the first embodiment when the various output signals are ON. 
       FIGS. 5 and 7  show OFF diagnosis of the first interruption element  40  and second interruption element  42  along with an elapsed time. 
     In this embodiment, the first interruption element  40  and the second interruption element  42  are collectively controlled. An example of control of the first/second interruption signal  101 , first output signal  103 , and second output signal  105  will be described with reference to  FIG. 7 . Before the time t1 the time tcr1 earlier than the diagnosis determination point t0, the signal control unit  20   a  of the MPU  20  causes the driving circuits  21   b  and  21   c  to respectively output the first output signal  103  and the second output signal  105  while maintaining the ON or OFF state set at the time immediately preceding control, as shown in  FIG. 7 . In this state, by synchronizing the OFF diagnosis timing of each interruption element with the first control apparatus  50  having a quick response characteristic, the signal control unit  20   a  of the MPU  20  causes the driving circuit  21   a  to set the first/second interruption signal  101  in the OFF state while causing the driving circuits  21   b  and  21   c  to respectively set the first output signal  103  and the second output signal  105  in the ON state at the time t1 the time tcr1 earlier than the diagnosis determination point t0, as shown in  FIG. 7 . In this case, the first interruption element  40  and the second interruption element  42  perform the same operation. 
     When, therefore, the second output element  43  is connected to the second control apparatus  51  having a slow response characteristic, if the driving circuit  21   c  is caused to set the second output signal  105  in the ON state and the driving circuit  21   a  is caused to set the first/second interruption signal  101  in the OFF state at the time t1 after the time t2 in synchronism with the first control apparatus  50  having a quick response characteristic as described above, the voltage level of the second output diagnosis signal  107  at the diagnosis determination point t0 indicates an intermediate level (uncertain) between low and high levels, as indicated by a triangle in  FIG. 7 . In this case, the diagnosis unit  20   b  cannot perform failure diagnosis of the first interruption element  40  and second interruption element  42 . 
     Another example of control of the first/second interruption signal  101  will be described next. Before the time t2 the time tcr2 earlier than the diagnosis determination point t0, the signal control unit  20   a  of the MPU  20  causes the driving circuits  21   b  and  21   c  to respectively output the first output signal  103  and the second output signal  105  while maintaining the ON or OFF state set at the time immediately preceding control. In this state, by synchronizing the OFF diagnosis timing of each interruption element with the second control apparatus  51  having a slow response characteristic, the signal control unit  20   a  of the MPU  20  causes the driving circuit  21   a  to set the first/second interruption signal  101  in the OFF state while causing the driving circuits  21   b  and  21   c  to respectively set the first output signal  103  and the second output signal  105  in the ON state at the time t2 the time tcr2 earlier than the diagnosis determination point t0. Under such control, however, the time during which the first/second interruption signal  101  is in the OFF state becomes long, and thus the first control apparatus  50  having a quick response characteristic may detect the OFF state of the first output element  41  to cause a malfunction. 
     To solve this problem, in this embodiment, to change the first or second output signal from the OFF state to the ON state, OFF diagnosis of each interruption element is performed using the characteristic that the response time of the first or second control apparatus as an output destination is short. Furthermore, in this embodiment, to change the first or second output signal from the ON state to the OFF state, OFF diagnosis of each interruption element is performed using the characteristic that the response time of the first or second control apparatus as an output destination is long. 
     As shown in  FIG. 5 , in this embodiment, the second output signal  105  is set in the OFF state at the time t2 the time tcr2 earlier than the diagnosis determination point t0. The time t2 is earlier than the time t1, at which the first/second interruption signal  101  is set in the OFF state, by the response time of the second control apparatus  51 . 
     Control will be explained again from a point before the time t2. Before the time t2, the signal control unit  20   a  of the MPU  20  sets the first/second interruption signal  101  in the ON state via the driving circuit  21   a , and causes the driving circuits  21   b  and  21   c  to respectively output the first output signal  103  and the second output signal  105  while maintaining the ON or OFF state set at the time immediately preceding control output (step S 21 ). 
     When the time t2 is measured (step S 22 ), the signal control unit  20   a  of the MPU  20  outputs a signal for setting the second output signal  105  in the OFF state to the driving circuit  21   c  (step S 23 ). 
     Before the time t1, the signal control unit  20   a  of the MPU  20  causes the driving circuit  21   b  to output the first output signal  103  while maintaining the ON or OFF state set at the time immediately preceding control output, similarly to the processing before the time t2. 
     When the time t1 is measured (step S 24 ), the signal control unit  20   a  of the MPU  20  outputs a signal for setting the first/second interruption signal  101  in the OFF state to the driving circuit  21   a  (step S 25 ), and also outputs a signal for setting the first output signal  103  and the second output signal  105  in the ON state to the driving circuits  21   b  and  21   c  (step S 26 ). 
     When the diagnosis determination point t0 is measured (step S 27 ), the diagnosis unit  20   b  of the MPU  20  inputs the first output diagnosis signal  106  and the second output diagnosis signal  107  (step S 28 ). After the diagnosis determination point t0, the diagnosis unit  20   b  of the MPU  20  outputs a signal for setting the first/second interruption signal  101  in the ON state to the driving circuit  21   a , and also causes the driving circuits  21   b  and  21   c  to respectively output the first output signal  103  and the second output signal  105  while maintaining the ON or OFF state set at the time immediately preceding control output. 
     If the voltage level of the first output diagnosis signal  106  is low (YES in step S 29 ), the diagnosis unit  20   b  of the MPU  20  determines that the first interruption element  40  is in the normal state (step S 30 ). If the voltage level is high (NO in step S 29 ), the diagnosis unit  20   b  of the MPU  20  determines that the first interruption element  40  is in the failure (abnormal) state (step S 31 ). Referring to  FIG. 5 , a square represents that the detection result indicates the failure state, a circle represents that the detection result indicates the normal state, and a dotted line represents a waveform when the output element is in the failure state. 
     If the voltage level of the second output diagnosis signal  107  is low, the diagnosis unit  20   b  of the MPU  20  determines that the second interruption element  42  is in the normal state. If the voltage level is high, the diagnosis unit  20   b  of the MPU  20  determines that the second interruption element  42  is in the failure (abnormal) state. 
     As described above, the first output signal  103  and the second output signal  105  are conventionally set in the ON state at the same predetermined timing for OFF diagnosis of the first interruption element  40  and second interruption element  42 . To the contrary, in this embodiment, the MPU  20  outputs signals for setting the first output signal  103  and second output signal  105  in the OFF state at different timings, according to the response characteristic of each control apparatus. 
     More specifically, at a timing earlier than the diagnosis determination point t0 by the response time of the second control apparatus  51 , the MPU  20  sets, in the OFF state, the second output signal  105 , of the various output signals, which concerns the second control apparatus  51  having a slow response characteristic. After that, the MPU  20  sets the second output signal  105  in the ON state at an early timing according to the response time of the first control apparatus  50  having a quick response characteristic. This can prevent the voltage level of the output signal concerning the second control apparatus  51  having a slow response characteristic from becoming an intermediate level at the diagnosis determination point to. 
     At a timing earlier by the response time of the control apparatus having a quick response characteristic, the MPU  20  sets, in the ON state, the output signal, of the various output signals, which concerns the control apparatus. This eliminates the need to set the first/second interruption signal  101  in the OFF state at an unnecessarily early timing. It is, therefore, possible to prevent the first control apparatus  50  having a quick response characteristic from detecting the OFF state of the first output element  41  to cause a malfunction when the time during which the first/second interruption signal  101  is in the OFF state becomes long. 
     Even if one common driving circuit is used as driving circuits as the driving circuit for various interruption elements, it is possible to correctly perform OFF diagnosis of the first interruption element  40  and second interruption element  42  based on the voltage levels of the first output diagnosis signal  106  and second output diagnosis signal  107  at the diagnosis determination point t0 of the first interruption element  40  and second interruption element  42 . 
     That is, it is possible to ensure the time for diagnosing the respective interruption elements collectively according to the response characteristic of each control apparatus, and diagnose the respective interruption elements collectively according to the response characteristic of the load of each digital output circuit. 
     Second Embodiment 
     The second embodiment of the present invention will be described next. Note that, of the functions of an output apparatus according to this embodiment, the same functions as those shown in  FIG. 1  are denoted by the same reference numerals, and a description thereof will be omitted. Different functions will be mainly explained. 
       FIG. 8  is a circuit diagram showing an example of the arrangement of the digital output circuits of the output apparatus according to the second embodiment. 
     The connection configuration between various driving circuits  21   a ,  21   b , and  21   c  and the first digital output circuit  30  and second digital output circuit  31  of an output apparatus  10  is the same as that shown in  FIG. 1 . 
     The arrangement shown in  FIG. 8  is an arrangement in which a so-called sink-driving control apparatus serves as a load. A difference from the arrangement shown in  FIG. 1  is that the sources of a first interruption element  40  and second interruption element  42  are connected to the negative side of an external power supply apparatus  52  via a negative line  121  of the external power supply apparatus. 
     The positive side of the external power supply apparatus  52  is connected to the input terminals of a first control apparatus  50  and second control apparatus  51  via a positive line  120  of the external power supply apparatus. 
     The output terminal of the first control apparatus  50  is connected to an MPU  20  and the drain of a first output element  41 . That is, a first output diagnosis signal  106  is output from the first control apparatus  50 . 
     The output terminal of the second control apparatus  51  is connected to the MPU  20  and the drain of a second output element  43 . That is, a second output diagnosis signal  107  is output from the second control apparatus  51 . 
     The source of the first output element  41  is connected to the drain of the first interruption element  40  via a first interruption element-first output element connection line  123 . That is, the connection relationship between the first output element  41  and the first interruption element  40  is reversed with respect to the arrangement shown in  FIG. 1 . 
     The source of the second output element  43  is connected to the drain of the second interruption element  42  via a second interruption element-second output element connection line  124 . That is, the connection relationship between the second output element  43  and the second interruption element  42  is reversed with respect to the arrangement shown in  FIG. 1 . 
       FIG. 9  is a view for explaining an example of an output element diagnosis operation by the output apparatus according to the second embodiment. 
       FIG. 9  shows OFF diagnosis of the first output element  41  and second output element  43  along with an elapsed time. 
     Similarly to the first embodiment, a control apparatus having a quick response characteristic, for example, a small time constant (tcr1&lt;tcr2) is used as the first control apparatus  50  connected to the first output element  41  of the first digital output circuit  30 . A control apparatus having a slow response characteristic, for example, a large time constant (tcr2&gt;tcr1) is used as the second control apparatus  51  connected to the second output element  43  of the second digital output circuit  31 . 
       FIG. 10  is a flowchart illustrating an example of a procedure for OFF diagnosis of the first output element and second output element by the output apparatus according to the second embodiment. 
     The control processes of various signals in steps S 1  to S 5  described in the first embodiment when a time t2 the time tcr2 earlier than a diagnosis determination point t0 is measured and when a time t1 the time tcr1 earlier than the diagnosis determination point t1 is measured are performed (step S 41  to S 45 ). 
     When the time of the diagnosis determination point t0 is measured (step S 46 ), a signal control unit  20   a  of the MPU  20  inputs the voltage level of the first output diagnosis signal  106  from the first control apparatus  50 , and the second output diagnosis signal  107  from the second control apparatus  51  (step S 47 ). 
     If the voltage level of the first output diagnosis signal  106  is high (YES in step S 48 ), a diagnosis unit  20   b  of the MPU  20  determines that the first output element  41  is in the normal state (step S 49 ). If the voltage level is low (NO in step S 48 ), the diagnosis unit  20   b  of the MPU  20  determines that the first output element  41  is in the failure (abnormal) state (step S 50 ). 
     Similarly, if the voltage level of the second output diagnosis signal  107  is high, the diagnosis unit  20   b  of the MPU  20  determines that the second output element  43  is in the normal state. If the voltage level is low, the diagnosis unit  20   b  of the MPU  20  determines that the second output element  43  is in the failure (abnormal) state. Referring to  FIG. 9 , a square represents that the detection result indicates the failure state, a circle represents that the detection result indicates the normal state, and a dotted line represents a waveform when the output element is in the failure state. 
       FIG. 11  is a view for explaining an example of an interruption element diagnosis operation by the output apparatus according to the second embodiment. 
       FIG. 11  shows OFF diagnosis of the first interruption element  40  and second interruption element  42  along with an elapsed time. 
       FIG. 12  is a flowchart illustrating an example of a procedure for OFF diagnosis of the first interruption element and second interruption element by the output apparatus according to the second embodiment. 
     The control processes of the various signals in steps S 21  to S 26  described in the first embodiment when the time t2 the time tcr2 earlier than the diagnosis determination point t0 is measured and when the time t1 the time tcr1 earlier than the diagnosis determination point t0 is measured are performed (step S 61  to S 66 ). 
     When the diagnosis determination point t0 is measured (step S 67 ), the diagnosis unit  20   b  of the MPU  20  inputs the first output diagnosis signal  106  and the second output diagnosis signal  107  (step S 68 ). 
     If the voltage level of the first output diagnosis signal  106  is high (YES in step S 69 ), the diagnosis unit  20   b  of the MPU  20  determines that the first interruption element  40  is in the normal state (step S 70 ). If the voltage level is low (NO in step S 69 ), the diagnosis unit  20   b  of the MPU  20  determines that the first interruption element  40  is in the failure (abnormal) state (step S 71 ). 
     Similarly, if the voltage level of the second output diagnosis signal  107  is high, the diagnosis unit  20   b  of the MPU  20  determines that the second interruption element  42  is in the normal state. If the voltage level is low, the diagnosis unit  20   b  of the MPU  20  determines that the second interruption element  42  is in the failure (abnormal) state (step S 71 ). Referring to  FIG. 11 , a square represents that the detection result indicates the failure state, a circle represents that the detection result indicates the normal state, and a dotted line represents a waveform when the output element is in the failure state. 
     As described above, according to the second embodiment, even the arrangement using sink driving makes it possible to obtain the same effects as those in the first embodiment. 
     Note that the method described in each of the aforementioned embodiments can be stored in a storage medium such as a magnetic disk (a Floppy® disk, a hard disk, or the like), an optical disk (a CD-ROM, a DVD, or the like), a magnetooptical disk (MO), or a semiconductor memory as a program executable by a computer, and can be distributed. 
     Any storage format may be adopted as long as the storage medium can store a program, and is readable by the computer. 
     An OS (Operating System) operating on the computer, MW (middleware) such as database management software or network software, or the like may execute part of each process for implementing the aforementioned embodiments based on the instruction of the program installed from the storage medium to the computer. 
     The storage medium according to each of the embodiments is not limited to a medium independent of the computer, and also includes a storage medium that stores or temporarily stores the program transmitted by a LAN, the Internet, or the like by downloading it. 
     The number of storage media is not limited to one. The storage medium according to the present invention also incorporates a case in which the processing of each of the aforementioned embodiments is executed from a plurality of media, and the media can have any arrangement. Note that the computer according to each of the embodiments is configured to execute each process of each of the aforementioned embodiments based on the program stored in the storage medium, and may be, for example, a single device formed from a personal computer or a system including a plurality of devices connected via a network. 
     The computer according to each of the embodiments is not limited to a personal computer, and also includes an arithmetic processing device or microcomputer included in an information processing apparatus. The term “computer” collectively indicates apparatuses and devices capable of implementing the functions of the present invention by the program. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.