JP4830645B2 - Method for detecting disconnection of connection line in communication system - Google Patents

Description

  The present invention relates to a plurality of ECUs (Electronic Control Units) that control in-vehicle devices, two communication lines that are connected to each other by terminal resistors, and a connection that connects the plurality of ECUs and the two communication lines. The present invention relates to a method for detecting disconnection of a connection line in a communication system (for example, CAN (Controller Area Network)) configured with a line.

Conventionally, it is composed of a plurality of ECUs for controlling in-vehicle devices, two communication lines that are connected to each other by terminal resistors, and a connection line that connects the plurality of ECUs and the two communication lines. There is a disconnection detection method in a communication system, for example, as described in Patent Document 1. In this prior art, each ECU has a resistor and a switch for connecting two communication lines, and when a communication abnormality occurs, the internal switches are turned on in order from the ECU closest to the terminating resistor. Detecting a disconnection point of a communication line is performed.
JP 2003-304265 A

  However, in such a conventional method, each ECU needs to be separately provided with a resistor and a switch, so that there is a problem that the number of parts of each ECU increases, resulting in an increase in cost and weight. In addition, even if the disconnection of the communication line can be detected, the disconnection of the connection line cannot be detected. In order to detect the disconnection of the connection line, the impedance is measured by removing the connection line from each communication line. Therefore, there is a problem that the working time is increased.

  In view of the above problems, the present invention provides a connection line of a communication system that can detect disconnection of a connection line without increasing the number of parts constituting the communication system and without increasing work time. An object of the present invention is to provide a disconnection detection method.

In order to solve the above problem, a disconnection detection method for a connection line of a communication system according to the present invention includes
It comprises a plurality of control means for controlling the in-vehicle device, two communication lines that are connected to each other by a terminating resistor, and a connection line that connects the plurality of control means and the two communication lines. And a plurality of control means pressurizing a predetermined signal voltage to the two communication lines to perform communication using a differential voltage between the two communication lines, and the two communication lines. A power saving mode in which a voltage including zero less than the predetermined signal voltage is applied to the line using two ground paths respectively corresponding to the two communication lines, and the two communications are performed in the power saving mode. A method for detecting disconnection of a connection line in a communication system that shifts to a normal control mode when a differential voltage between lines is generated,
After all of the plurality of control means are shifted from the normal control mode to the power saving mode, any one control means is shifted from the power saving mode to the normal control mode, and further, the normal control mode is shifted to the power saving mode. When one of the two ground paths passes through the termination resistor and a transient differential voltage based mainly on the stray capacitance of the two communication lines is generated, the control means and the two It is determined that the connection line connecting the communication line is disconnected.

  The communication system referred to here is, for example, a CAN (Controller Area Network).

  Here, the generation of the differential voltage may be detected by transition from a power saving mode to a normal control mode in a control unit other than the one arbitrary control unit.

  According to this, the occurrence of the differential voltage is detected by the operation of the control means constituting the communication system without using the external detection means, and the disconnection and the disconnection location of the connection line are detected. Can do.

  Alternatively, the generation of the differential voltage may be detected by an external detection means.

  According to this, the occurrence of the differential voltage can be detected by simple means, and the disconnection and the disconnection location of the connection line can be detected.

  According to the present invention, a disconnection detection method for a connection line of a communication system that enables detection of a disconnection of the connection line without increasing the number of parts constituting the communication system and without increasing work time. Can be provided.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing an embodiment of a CAN to which a connection line disconnection detecting method of a communication system according to the present invention can be applied, and FIG. 2 shows a driver circuit inside each ECU of the CAN according to the present invention. It is. FIG. 3 is a schematic diagram showing a ground path of a CAN communication line according to the present invention, and FIG. 4 is a schematic diagram showing a ground path when the CAN communication line according to the present invention is disconnected.

  The CAN according to the present invention includes a body ECU 1 (Electronic Control Unit), a window ECU 2, a wiper ECU 3, a seat ECU 4, a meter ECU 5, and two communication lines whose ends are connected to each other by terminal resistors R 1 and R 2. It comprises CANH, CANL, two communication lines CANH, CANL, and connection lines CH, CL for connecting the window ECU 2, the wiper ECU 3, the seat ECU 4, and the meter ECU 5.

  The body ECU 1 includes, for example, a CPU, a ROM, a RAM, and a data bus connecting them, and the CPU performs predetermined processing according to a program stored in the ROM. Based on opening / closing of a door switch (not shown), the courtesy lamp On / off control is performed, and on / off control of the light is performed based on the operation of a light control switch (not shown), and when any of IG on, ACC on, door open, or light control switch is operated, the status signal is sent to the meter ECU 5 And control which transmits to other ECU2-4 is performed.

  The window ECU 2 includes, for example, a CPU, a ROM, a RAM, and a data bus connecting them, and the CPU performs predetermined processing according to a program stored in the ROM. Based on an operation of a master switch (not shown), the power window The opening / closing control is performed, and when the master switch is operated, a state signal is transmitted to another ECU.

  The wiper ECU 3 is composed of, for example, a CPU, a ROM, a RAM, and a data bus connecting them, and the CPU performs predetermined processing in accordance with a program stored in the ROM. Based on the operation of a wiper control switch (not shown), the wiper ECU 3 The motor is driven to operate the wiper, and when the wiper control switch is operated, control for transmitting a status signal to other ECUs is performed.

  The seat ECU 4 is composed of, for example, a CPU, a ROM, a RAM, and a data bus connecting them, and the CPU performs predetermined processing according to a program stored in the ROM, and is set by a user by a seat position memory switch (not shown). In addition to moving the seat to the selected position, control is performed to transmit a status signal to other ECUs when the memory switch is operated.

  The meter ECU 5 includes, for example, a CPU, a ROM, a RAM, and a data bus connecting them, and the CPU performs predetermined processing in accordance with a program stored in the ROM, and vehicle information such as a vehicle speed and an engine speed is stored. In addition to displaying on a meter (not shown), control is performed to turn on the lamp of the meter based on a status signal from the body ECU 1.

  The body ECU 1, window ECU 2, wiper ECU 3, seat ECU 4, and meter ECU 5 described above all pressurize the H signal to the communication line CANH via the connection line CH based on the command from the CPU, and via the connection line CL. The communication line CANL is provided with a driver that pressurizes the L signal, and a receiver that detects a differential voltage generated between the communication lines CANH and CANL as a signal. Communicate by sending and receiving signals. In FIG. 1, only the CPU and driver are shown for convenience.

  The driver is represented by a circuit as shown in FIG. 2, and the circuit on the side of the connection line CH is a switch SW1, SW2, a voltage adjustment circuit 1, a CANH driver, and a transmission control circuit made of MOSFET as shown in FIG. The circuit on the connection line CL side is configured by connecting switches SW3 and SW4 made of MOSFETs, a voltage adjustment circuit 2, a CANL driver, and a transmission control circuit as shown in FIG.

  The CANH driver turns on the switch SW1 based on a command from the transmission control circuit based on a transmission signal from the CPU, presses the switch SW2 to pressurize the connection line CH, turns off the switch SW1, turns on the switch SW2, and turns on the connection line CH. Ground. The signal voltage applied to the connection line CH is adjusted to 3.5V or 2.5V by the voltage adjustment circuit 1.

  In the normal control mode, the CANL driver turns on the switch SW3 based on the command from the transmission control circuit based on the transmission signal from the CPU, turns off the switch SW4, pressurizes the connection line CL, turns off the switch SW3, and turns off the switch SW4. The connection line CL is grounded by turning it on. The signal voltage applied to the connection line CL is adjusted to 1.5V or 2.5V by the voltage adjustment circuit 2.

  That is, in the normal control in the normal control mode, the voltage of the connection line CH = 3.5V or 2.5V, the voltage of the connection line CL = 1.5V or 2.5V, and the sleep mode that appears when shifting to the power saving mode , The voltage of the connection line CH = the voltage of the connection line CL = 2.5V, and in the power saving mode, the voltage of the connection line CH = the voltage of the connection line CL = 0V.

  The body ECU 1, window ECU 2, wiper ECU 3, seat ECU 4, and meter ECU 5 all do not transmit or receive status signals for 1 minute or more, that is, the door and any switch are 1 minute or more when IG is off or ACC is off (time An example) is provided with a power saving function for shifting from the normal control mode to the power saving mode in order to reduce dark current when not operated.

  Furthermore, the body ECU 1, the window ECU 2, the wiper ECU 3, the seat ECU 4, and the meter ECU 5 all shift to the normal control mode when receiving a status signal in the power saving mode, and after the time T1 shifts from the normal control mode to the power saving mode. In order to prevent an unexpected state from occurring due to an unstable voltage, the transition from the power saving mode to the normal control mode is not performed.

  In addition, the body ECU 1, the window ECU 2, the wiper ECU 3, the seat ECU 4, and the meter ECU 5 of this embodiment all have disconnection detection software, and the ECU that has been activated by external input in the power saving mode is The system shifts to the normal control mode after time T2, and shifts to the power saving mode after time T3.

  The external input is, for example, turning on / off the switches connected to the body ECU 1, the window ECU 2, the wiper ECU 3, the seat ECU 4, and the meter ECU 5 20 times in 30 seconds. Further, if there is a body ECU1, window ECU2, wiper ECU3, seat ECU4, or meter ECU5 that is connected to a communication standard other than CAN, for example, serial communication or LIN (Local Interconnect Network), the external device is used. It is also possible to perform external input using a diagnostic tool.

  Thus, when shifting from the sleep mode of the normal control mode to the power saving mode, for example, paying attention to the meter ECU 5, both the switches SW2 and SW4 in the driver shown in FIG. When not disconnected, as shown in FIG. 3, the communication lines CANH and CANL are grounded via the connection lines CH and CL, respectively, and the potential VA at the point A of the communication line CANH and the potential at the point B of CANL. Both VB shift from 2.5V to 0V.

  However, when the connection line CH of the meter ECU 5 is disconnected as shown in FIG. 4, even if both the switches SW2 and SW4 inside the driver shown in FIG. Is grounded via the grounding resistors R1, B, the connection line CL, and the switch SW4, the potential VA at the point A of the communication line CANH has a long grounding path. The speed at which the potential VA drops becomes longer as shown in FIG. On the other hand, the ground path of the communication line CANL is not changed because the connection line CL is not disconnected, and the potential VB at the point B of the communication line CANL falls in a square wave shape as shown in FIG. Therefore, a potential difference between the communication line CANH and the communication line CANL, that is, a transient differential voltage VA-VB is generated as shown in FIG. 5C, and the body ECU1, window ECU2, and wiper ECU3 other than the meter ECU5. The seat ECU 4 assumes that the meter ECU 5 has transmitted the status signal, and the body ECU 1, the window ECU 2, the wiper ECU 3, and the seat ECU 4 shift from the power saving mode to the normal control mode. The first embodiment uses this phenomenon to detect disconnection of a connection line.

  Depending on the characteristics of the disconnected part and the entire electric wire, even when the connection line CH of the meter ECU 5 is disconnected as shown in FIG. 4, the potential VA at the point A of the communication line CANH and the potential at the point B of the communication line CANL In some cases, the differential voltage between VB is small and it cannot be considered that the status signal has been transmitted. In that case, since a differential voltage is generated between CH and CL of the meter ECU 5, the meter ECU 5 considers that a status signal is transmitted by a device other than its own ECU. As a result, the meter ECU 5 shifts to the normal control mode and starts transmission. The ECU other than the meter ECU 5 shifts to the normal control mode by the transmission voltage of the meter ECU 5.

  FIG. 6 shows how the body ECU 1, the window ECU 2, the wiper ECU 3, the seat ECU 4, and the meter ECU 5 mutually shift from the normal control mode to the power saving mode. For example, when the body ECU 1, the window ECU 2, the wiper ECU 3, the seat ECU 4, and the meter ECU 5 are all in the normal control mode (indicated by N in FIG. 6, the same applies hereinafter), the state signal is not transmitted or received for 1 minute or more. When the door and any switch are not operated for 1 minute or more with IG off and ACC off, the normal control mode (N) to the power saving mode (indicated by S in FIG. 6; the same applies hereinafter) to reduce dark current. Migrate to

  In this state, the body ECU 1, the window ECU 2, the wiper ECU 3, and the seat ECU 4 change from the normal power saving mode (S) to the normal power saving mode (S) until the time T 1 elapses after the normal control mode (N) shifts to the power saving mode (S). In order to prohibit the transition to the control mode (N), the body ECU 1, the window ECU 2, the wiper ECU 3, and the seat ECU 4 transition from the normal control mode (N) to the power saving mode (S), and after the time T1 has elapsed, The disconnection detection software of the meter ECU 5 is activated by an external input, and the meter ECU 5 shifts to the normal control mode (N) after time T2, and shifts to the power saving mode (S) after time T3. When the meter ECU 5 shifts from the normal control mode (N) to the power saving mode (S) after time T3, a differential voltage is generated between the communication lines CANH and CANL as described above, and a status signal is transmitted. Then, the other body ECU 1, window ECU 2, wiper ECU 3, and seat ECU 4 determine and shift from the power saving mode (S) to the normal control mode (N).

  The procedure of the connection line disconnection detection method of the communication system according to the present invention described above will be described with reference to the flowchart shown in FIG.

  In S1, if the CAN detects the CAN communication abnormality described above, for example, the meter lamp does not light even when the door is opened, and the user detects this, as shown in S2, the customer enters the dealer and the service person shows in S2. All ECUs of the CAN to which the connection line presumed to be disconnected belongs, that is, the body ECU 1, the window ECU 2, the wiper ECU 3, the seat ECU 4, and the meter ECU 5, IG off, ACC off, doors and any switches for 1 minute. By not performing the above operation, the normal control mode is shifted to the power saving mode.

  Subsequently, the meter ECU 5 is selected as an ECU in S3, and after the time T1 has elapsed since the body ECU 1, the window ECU 2, the wiper ECU 3, and the seat ECU 4 have shifted from the normal control mode to the power saving mode, the disconnection detection software for the meter ECU 5 is detected. Is activated by the external input described above. Thereby, only meter ECU5 shifts to normal control mode in S4, and meter ECU5 shifts to power saving mode in S5.

  In this case, if the connection line CH or CL of the meter ECU 5 is disconnected, a differential voltage is generated between the communication lines CANH and CANL in S6 as described above, and a state signal is transmitted from the meter ECU 5. The other body ECU 1, window ECU 2, wiper ECU 3, and seat ECU 4 determine and shift from the power saving mode to the normal control mode.

  In this case, the process proceeds to S7, where it is presumed that one of the connection lines CH and CL of the ECU ECU5 is disconnected here, and the service person replaces the connection lines CH and CL at that location.

  In S6, the connection lines CH and CL are not disconnected, no differential voltage is generated between the communication lines CANH and CANL, and the other body ECU1, window ECU2, wiper ECU3, and seat ECU4 are in the power saving mode. If the transition to the normal control mode is not performed, it is presumed that the connection lines CH and CL of the meter ECU 2 are not disconnected. Therefore, the process proceeds to S8 to determine whether or not the disconnection investigation of all the ECUs has been completed. If it is finished, the procedure is finished. If it is not finished, N is incremented, that is, any other body ECU1, window ECU2, wiper ECU3, or seat ECU4 is targeted for ECUN from S2. Repeat the procedure of S8.

  According to the first embodiment described above, between the communication lines CANH and CANL, which occurs when the ECU is shifted from the normal control mode to the power saving mode due to disconnection of the connection line CH or CL of a certain ECU. Detection of the occurrence of differential voltage by the transition operation from the power saving mode to the normal control mode of other ECUs constituting the CAN without using an external diagnostic tool, and detecting disconnection and disconnection location of the connection line Can do.

  Note that the combinations of the ECUs 1 to 5 in the CAN are merely examples, and are not limited to the combinations described above. Therefore, various CAN communication abnormalities are conceivable in addition to the fact that the meter lamp does not light even when the door is opened.

  In the first embodiment described above, if the connection line CH or CL of any ECU is disconnected, a differential voltage is generated between the communication lines CANH and CANL as described above, and a status signal is transmitted. When there is an external diagnostic tool that can monitor the differential voltage itself, although the other ECU 4 determines that the transition from the power saving mode to the normal control mode is detected and the disconnection of the tangential line CH or CL is detected. Alternatively, the disconnection and the disconnection location may be detected by detecting the differential voltage itself.

  The example about it is shown below. Note that the basic configuration of the CAN to which the disconnection detection method is applied is the same as that shown in the first embodiment, and thus the description thereof is omitted. Here, it is assumed that a diagnostic tool (not shown) capable of detecting a differential voltage is connected to the communication lines CANH and CANL.

  FIG. 8 is a flowchart showing one embodiment of a connection line disconnection detection method of a communication system according to the present invention. Hereinafter, the procedure of the disconnection detection method will be described with reference to FIG.

  In S11, when the CAN communication abnormality described above, for example, the meter lamp does not light even when the door is opened, and the user detects this, as shown in S12, the service person enters the dealer and the service person shows in S12. All ECUs of the CAN to which the connection line presumed to be disconnected belongs, that is, the body ECU 1, the window ECU 2, the wiper ECU 3, the seat ECU 4, and the meter ECU 5, IG off, ACC off, doors and any switches for 1 minute. By not performing the above operation, the normal control mode is shifted to the power saving mode.

  Subsequently, the meter ECU 5 is selected as the ECUN in S13, and the body ECU1, the window ECU2, the wiper ECU3, and the seat ECU4 are shifted from the normal control mode to the power saving mode, and after the time T1 has elapsed, the disconnection detection of the meter ECU5 is detected. Start the software by external input. Thereby, only meter ECU5 shifts to normal control mode in S14, and meter ECU5 shifts to power saving mode in S15.

  In this case, if the connection line CH or CL of the meter ECU 5 is disconnected, a serviceman confirms by the external diagnostic tool that a differential voltage is generated between the communication lines CANH and CANL in S16 as described above. it can.

  In this case, the process proceeds to S17, where it is estimated that one of the connection lines CH and CL of the ECU ECU5 is disconnected here, and the service person performs the replacement work of the connection lines CH and CL at the corresponding part.

  If the external diagnostic tool confirms that the connection lines CH and CL are not disconnected and no differential voltage is generated between the communication lines CANH and CANL in S16, the connection lines CH and CL of the meter ECU 2 are Since it is presumed that no disconnection has occurred, the process proceeds to S18, where it is determined whether the disconnection investigation of the connection lines of all ECUs has been completed. N is incremented, that is, the procedure from S12 to S18 is repeated for any other body ECU1, window ECU2, wiper ECU3, or seat ECU4 as an ECUN target.

  According to the second embodiment described above, the occurrence of the differential voltage of the communication lines CANH and CANL due to the disconnection of the connection line CH or CL is detected by simple means, and the disconnection and the disconnection location of the connection lines CH and CL are detected. Can be detected.

  In the second embodiment described above, the meter ECU 5 designated as ECUN is shifted from the power saving mode to the normal control mode, and then is shifted again to the power saving mode, so that the differential voltage is generated between the communication lines CANH and CANL. Was detected and detected to detect disconnection and disconnection location. However, when the meter ECU 5 shifts from the power saving mode to the normal control mode after shifting all the ECUs to the power saving mode, the connection of the connection lines CH and CL connecting the meter ECU 5 and the communication lines CANH and CANL is connected. When the line CH is disconnected, as shown in FIG. 9, the path through which the meter ECU 5 pressurizes the communication line CANH is the connection line CL, point B, termination resistor R1, and point A. When the line CH is not disconnected as shown in FIG. Longer, and the increase in stray capacitance and resistance takes longer pressurization time, which also generates a minute differential voltage.

  If the external diagnostic tool is capable of detecting minute differential voltages, it detects the differential voltage generated at the time of transition from the power saving mode to the normal control mode, and detects disconnection and disconnection location. It is also possible. The example about it is shown below. In this case as well, since the basic configuration of the CAN to which the disconnection detection method is applied is the same as that shown in the first embodiment, the description thereof will be omitted, and a diagnosis that can detect a differential voltage (not shown) on the communication lines CANH and CANL is possible. Assume that the tool is connected.

  FIG. 11 is a flowchart showing an embodiment of a method for detecting disconnection of a connection line in a communication system according to the present invention. Hereinafter, the procedure of the disconnection detection method for the connection line of the communication system according to the third embodiment will be described with reference to FIG.

  In S21, when the CAN communication abnormality described above, for example, the meter lamp does not turn on even when the door is opened, and the user detects this, as shown in S22, the customer enters the dealer or the like, All ECUs of the CAN to which the connection line presumed to be disconnected belongs, that is, the body ECU 1, the window ECU 2, the wiper ECU 3, the seat ECU 4, and the meter ECU 5, IG off, ACC off, doors and any switches for 1 minute. By not performing the above operation, the normal control mode is shifted to the power saving mode.

  Subsequently, the meter ECU 5 is selected as the ECUN in S23, and after the time T1 has elapsed after the body ECU1, the window ECU2, the wiper ECU3, and the seat ECU4 have shifted from the normal control mode to the power saving mode, the disconnection detection of the meter ECU5 is detected. Start the software by external input. As a result, only the meter ECU 5 is shifted to the normal control mode in S24.

  In this case, if the connection line CH or CL of the meter ECU 5 is disconnected, the service person can confirm that a differential voltage is generated between the communication lines CANH and CANL in S25 using an external diagnostic tool.

  In this case, the process proceeds to S26, where it is presumed that one of the connection lines CH and CL of the ECU ECU5 is disconnected here, and the service person replaces the connection lines CH and CL at that location.

  When the connection lines CH and CL are not disconnected in S25 and no differential voltage is generated between the communication lines CANH and CANL, it is estimated that the connection lines CH and CL of the meter ECU 2 are not disconnected. Therefore, it progresses to S27, it is determined whether the disconnection investigation of the connection line of all ECUs is complete | finished, and when complete | finished, a procedure is complete | finished, and when not complete | finished, N is incremented. The procedure from S21 to S27 is repeated for any one of the body ECU1, the window ECU2, the wiper ECU3, and the seat ECU4.

According to the third embodiment described above, the occurrence of the differential voltage of the communication lines CANH and CANL due to the disconnection of the connection line CH or CL is detected by simple means, and the disconnection and the disconnection location of the connection lines CH and CL are detected. Can be detected.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions are made to the above-described embodiments without departing from the scope of the present invention. be able to. Moreover, although CAN (Controller Area Network) has been shown as a communication system to which the present invention can be applied, a normal control mode in which a predetermined signal voltage is applied to two communication lines and communication is performed using a differential voltage between the communication lines; And a power saving mode in which a voltage lower than a predetermined signal voltage, typically zero voltage, is applied. When a differential voltage between two communication lines is generated in the power saving mode, the mode is shifted to the normal control mode. The present invention can be applied to any communication system that has a control means.

  Since the disconnection detection method of the connection line of the communication system according to the present invention can detect the disconnection of the connection line of the communication system without installing hardware, only by installing the disconnection detection software in each control means. It is useful when applied to various vehicles such as passenger cars, trucks, and buses.

It is a block diagram which shows CAN which can apply the disconnection detection method of the connection line of the communication system which concerns on this invention. It is a schematic diagram which shows the circuit inside the driver of CAN which can apply the disconnection detection method of the connection line of the communication system which concerns on this invention. It is a block diagram which shows the grounding path | route of CAN which can apply the disconnection detection method of the connecting line of the communication system which concerns on this invention. It is a block diagram which shows the grounding path | route of CAN which can apply the disconnection detection method of the connecting line of the communication system which concerns on this invention. It is a schematic diagram which shows the aspect of the voltage drop at the time of making it transfer to the power saving mode from the communication control mode of CAN which can apply the disconnection detection method of the connection line of the communication system which concerns on this invention. It is a schematic diagram which shows the transfer aspect of communication control mode and power saving mode of each ECU of CAN which can apply the disconnection detection method of the connection line of the communication system which concerns on this invention. It is a flowchart which shows the procedure of the disconnection detection method of the connection line of the communication system which concerns on this invention. It is a flowchart which shows the procedure of the disconnection detection method of the connection line of the communication system which concerns on this invention. It is a block diagram which shows the pressurization path | route of CAN which can apply the disconnection detection method of the connecting line of the communication system which concerns on this invention. It is a block diagram which shows the pressurization path | route of CAN which can apply the disconnection detection method of the connecting line of the communication system which concerns on this invention. It is a flowchart which shows the procedure of the disconnection detection method of the connection line of the communication system which concerns on this invention.

Explanation of symbols

ECU1 Body ECU
ECU2 Window ECU
ECU3 Wiper ECU
ECU4 Seat ECU
ECU5 Meter ECU
CANH communication line CANL communication line R1 Termination resistor R2 Termination resistor CH Connection line CL Connection line N Normal control mode S Power saving mode

Claims (3)

It comprises a plurality of control means for controlling the in-vehicle device, two communication lines that are connected to each other by a terminating resistor, and a connection line that connects the plurality of control means and the two communication lines. And a plurality of control means pressurizing a predetermined signal voltage to the two communication lines to perform communication using a differential voltage between the two communication lines, and the two communication lines. A power saving mode in which a voltage including zero less than the predetermined signal voltage is applied to the line using two ground paths respectively corresponding to the two communication lines, and the two communications are performed in the power saving mode. A method for detecting disconnection of a connection line in a communication system that shifts to a normal control mode when a differential voltage between lines is generated,
After all of the plurality of control means are shifted from the normal control mode to the power saving mode, any one control means is shifted from the power saving mode to the normal control mode, and further, the normal control mode is shifted to the power saving mode. When one of the two ground paths passes through the termination resistor and a transient differential voltage based mainly on the stray capacitance of the two communication lines is generated, the control means and the two A disconnection detection method for a connection line in a communication system, characterized in that it is determined that the connection line connecting the communication line is disconnected.   The disconnection of the connection line in the communication system according to claim 1, wherein the generation of the differential voltage is detected by a transition from a power saving mode to a normal control mode in a control means other than the one arbitrary control means. Detection method.   The disconnection detection method for a connection line in a communication system according to claim 1, wherein the generation of the differential voltage is detected by an external detection means.

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