Communication system

Abstract

To allow a communication system to perform fault diagnosis of a communication line without using a measurement line.SOLUTION: A communication system 1 includes a master ECU 10 and an ECUa 20. The master ECU 10 is connected to a communication line 5 and is configured to diagnose the presence or absence of a failure in the communication line 5 by transmitting a pulse wave to the communication line 5 and measuring its reflected wave. The ECUa 20 is connected to a branch line 5B branching off from the communication line 5 and is configured to connect a termination circuit 52 to the communication line 5 during diagnosis and disconnect the termination circuit 52 from the communication line 5 during other than diagnosis, in steps S110 to S130.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to a communication system configured to diagnose the presence or absence of a fault on a communication line. [Background technology]

[0002] For example, Patent Document 1 listed below discloses a technique for identifying the location of a fault using a radar pulse method, using both a communication line to be diagnosed and a measurement line running parallel to the communication line. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-189739 Summary of the Invention [Problem to be solved by the invention]

[0004] However, as a result of detailed investigation by the inventors, it was found that the technique of Patent Document 1 has a problem in that it is necessary to lay a measurement line running parallel to the communication line to be diagnosed. One aspect of the present disclosure is to enable fault diagnosis of a communication line in a communication system without using a measurement line. [Means for solving the problem]

[0005] One aspect of the present disclosure is a communication system (1) configured to diagnose the presence or absence of a fault in a communication line (5). The communication system includes a diagnostic device (10) and a communication device (20). The diagnostic device is configured to be connected to the communication line and to diagnose the presence or absence of a fault in the communication line by transmitting a pulse wave to the communication line and measuring the reflected wave. The communication device is connected to a branch line (5B) branching off from the communication line and has a termination circuit (52) that can be connected to the communication line. The diagnostic device or the communication device includes a connection / disconnection unit (51, S110 to S130) configured to connect the termination circuit to the communication line during diagnosis and to disconnect the termination circuit from the communication line during other than diagnosis.

[0006] According to this configuration, a termination circuit is provided in a communication device connected to a branch of a communication line that does not require a termination circuit, so that reflection of a pulse wave at the end of the branch can be suppressed, and therefore fault diagnosis of the communication line can be performed without using a measurement line. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram showing a configuration of a communication system. [Diagram 2] FIG. 2 is a block diagram showing a configuration of a master ECU. [Diagram 3] 2 is a block diagram showing a configuration of an ECUa according to the embodiment. FIG. [Figure 4] FIG. 4A is a graph showing an example of a waveform of a reflected wave in a normal state, and FIG. 4B is a graph showing an example of a waveform of a reflected wave in the event of a disconnection. [Diagram 5] 13 is a flowchart of a connection / disconnection process. [Figure 6] 13 is a flowchart of a diagnosis process. [Figure 7] FIG. 13 is a block diagram showing a configuration of an ECUa in a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. [1. Embodiment] [1-1. Relationship between the configuration of the embodiment and the configuration of the present disclosure] The master ECU 10 in the embodiment corresponds to the diagnosis device in the present disclosure, and the ECU a 20 in the embodiment corresponds to the communication device in the present disclosure. The functions of the switching element 51 and S110 to S130 in the embodiment correspond to the connection / separation unit in the present disclosure. The functions of S110 and S210 in the embodiment correspond to the diagnosis / determination unit in the present disclosure.

[0009] [1-2. Configuration] 1 is a system configured to diagnose the presence or absence of a fault in a communication line 5. The communication line 5 is configured as a differential communication line for implementing communication in, for example, CAN (Registered Trademark, Controller Area Network). The communication system 1 can detect a break or short circuit as a fault in the communication line 5. However, the short circuit is limited to a short circuit with a small contact area where the reflection of a pulse wave can be detected.

[0010] The communication system 1 includes a communication line 5, a master ECU 10, an ECUa 20, and an ECUn 30. The communication system 1 may include other ECUs. Note that ECU stands for electronic control unit.

[0011] The master ECU 10 has a function as a diagnostic device. The master ECU 10 is connected to an end of the communication line 5, and has a function of diagnosing the presence or absence of a failure in the communication line 5 by transmitting a pulse wave to the communication line 5 and measuring the reflected wave. This diagnostic method is called a radar pulse method or a pulse radar method. An external device (not shown) may be connected to the master ECU 10. The external device is configured to be able to read data in the memory 12 of the master ECU 10 during inspection, etc., at a dealer or the like that inspects and repairs vehicles.

[0012] The ECUa 20 is connected to an intermediate portion of the communication line 5 that is not the end, that is, a branch line 5B branched off from the communication line 5. The ECUn 30 is connected to the end of the communication line 5 opposite the master ECU 10.

[0013] Each of the ECUs 10, 20, 30 includes a microcomputer having a microprocessor unit (hereinafter, MPU) 11, 21, 31 and a semiconductor memory (hereinafter, memory) 12, 22, 32 such as a RAM or a ROM. Each function of the ECUs 10, 20, 30 is realized by the MPU executing a program stored in a non-transient real recording medium. In this example, the memory corresponds to the non-transient real recording medium storing the program. Furthermore, the program is executed to execute a method corresponding to the program. Each of the ECUs 10, 20, 30 may include one microcomputer or multiple microcomputers.

[0014] The method of realizing the functions of each of the ECUs 10, 20, and 30 is not limited to software, and some or all of the functions may be realized by one or more pieces of hardware. For example, when the functions are realized by electronic circuits that are hardware, the electronic circuits may be realized by digital circuits, analog circuits, or a combination of these.

[0015] A common power supply 7 is connected to each of the ECUs 10, 20, 30, and each of the ECUs 10, 20, 30 operates on power supplied from the power supply 7. A common power supply 8 for termination processing is also connected to the master ECU 10 and ECUa 20, and the master ECU 10 and ECUa 20 use power supplied from the power supply 8 for termination processing to perform connection / disconnection processing and diagnostic processing, which will be described later.

[0016] The termination processing power supply 8 is configured to be able to temporarily supply power after the supply of power from the common power supply 7 is cut off. Thus, the master ECU 10 and the ECUa 20 can receive power from the termination processing power supply 8 and perform necessary processing such as diagnostic processing and sleep processing.

[0017] As shown in Fig. 1, each of the ECUs 10, 20, and 30 includes a communication circuit 13, 23, or 33. As shown in Fig. 2 and Fig. 3, the communication circuit 13, 23 includes a protection circuit 17, 27, a coil 18, or 28, and a transceiver IC 19, or 29. The communication circuit 33 has the same configuration as the communication circuit 13.

[0018] The protection circuits 17 and 27 are circuits for suppressing an overcurrent that may be input to the transceiver ICs 19 and 29 via the communication line 5, and for protecting the transceiver ICs 19 and 29. The protection circuits 17 and 27 are configured to include, for example, a plurality of grounded Zener diodes.

[0019] The coils 18 and 28 function as common mode choke coils and are configured to effectively suppress noise. The transceiver ICs 19 and 29 have a configuration as a well-known transceiver for transmitting and receiving signals via the communication line 5.

[0020] 1 and 2, the master ECU 10 is provided with a termination circuit 40. The ECUn 30 is also provided with a similar termination circuit 40. The termination circuit 40 has a function of suppressing reflection of a signal transmitted through the communication line 5 at the termination of the communication line 5. The termination circuit 40 is configured to include a resistor and a capacitor.

[0021] 1 and 3, the ECUa 20 is provided with a termination adjustment circuit 50. The termination adjustment circuit 50 includes a switching element 51 and a termination circuit 52. The termination circuit 52 has the same configuration as the termination circuit 40 described above. The switching element 51 is two FETs arranged between the communication line 5 and the termination circuit 52. The FET stands for Field Effect Transistor. The switching element 51 may be another transistor such as a bipolar transistor, a relay, or the like.

[0022] 3, the two switching elements 51 are configured to be turned on and off approximately simultaneously in response to a drive signal transmitted from the MPU 21. When the switching element 51 transitions to the on state, the termination circuit 52 is connected to the communication line 5. When the switching element 51 transitions to the off state, the termination circuit 52 is disconnected from the communication line 5.

[0023] In this embodiment, the ECUa 20 operates the switching element 51 to connect the termination circuit 52 to the communication line 5 when diagnosing a fault in the communication line 5, and to disconnect the termination circuit 52 from the communication line 5 at other times.

[0024] Here, if the ECUa 20 is not provided with the termination circuit 52, the pulse wave is reflected at the termination of the branch line 5B, making it difficult to distinguish this from the reflected wave of the pulse wave caused by a fault in the communication line 5 in this vicinity. For example, if the branch line 5B of the communication line 5 is disconnected at a fault location 90, a waveform as shown in FIG. 4B is obtained. In this waveform, the reflected wave at the fault location 90 is detected as a voltage peak as shown in waveform "B". However, even when the termination circuit 52 is not connected to the communication line 5 and the communication line 5 is not faulty, a voltage peak roughly like waveform "B" is detected, making it difficult to distinguish between them.

[0025] Therefore, in this embodiment, the ECUa 20 is provided with the termination circuit 52, so that the reflection of the pulse wave at the termination of the branch line 5B is suppressed. Therefore, when the communication line 5 is not broken, for example, a waveform as shown in FIG. 4A is obtained. That is, in the waveform shown in FIG. 4A, the reflected wave at the branch point 5A of the communication line 5 and the branch line 5B is detected as a voltage peak shown by waveform "A", but the peak shown by waveform "B" in FIG. 4B, which indicates a break or the termination point of the branch line 5B, is not detected. Therefore, the reflection of the pulse wave shown by waveform "B" can be detected only when the communication line 5 is broken. Therefore, the failure diagnosis can be performed satisfactorily.

[0026] On the other hand, when the termination circuit 52 is connected to the communication line 5 during normal communication or other times other than during diagnosis, the signal is more likely to be attenuated, which may adversely affect communication. In addition, the communication may not meet the standards required for communication. However, in this configuration, the termination circuit 52 is separated from the communication line 5 during times other than during diagnosis, so that signal attenuation can be suppressed.

[0027] Each of the ECUs 10, 20, 30 is connected to the communication line 5 or the branch line 5B via a connector 14, 24. The connectors 14, 24 are locations where disconnections and connection failures are likely to occur, and in a configuration having the connectors 14, 24, the fault diagnosis in this embodiment can be effectively utilized.

[0028] [1-3. Processing] Next, the connection / disconnection process executed by the ECUa 20 will be described with reference to the flowchart of FIG.

[0029] The connection / disconnection process is started, for example, when the power supply of the ECUa20 is turned on, and is then repeatedly performed. In the connection / disconnection process, first, in S110, the ECUa20 determines whether or not the conditions for diagnosis are satisfied. Here, when the communication system 1 transitions to sleep, that is, when it detects that the power supply from the power source 7 has been cut off, it is determined that the conditions for diagnosis are satisfied. Note that the following process can be performed using power from the termination process power source 8.

[0030] If it is determined that diagnosis is required, the ECUa 20 connects the termination circuit 52 of the termination adjustment circuit 50 to the communication line 5 in S120. That is, the ECUa 20 switches on the switching element 51 to energize the communication line 5 and the termination circuit 52. When this process ends, the process ends.

[0031] If it is determined that it is not time for diagnosis, the ECUa 20, in S130, separates the termination circuit 52 of the termination adjustment circuit 50 from the communication line 5. That is, the ECUa 20 switches the switching element 51 to the off state, so that no current flows between the communication line 5 and the termination circuit 52. When this process ends, the process ends.

[0032] Next, the diagnostic process executed by the master ECU 10 will be described with reference to the flowchart of FIG. The diagnostic process is started, for example, when the power supply of the master ECU 10 is turned on, and is then repeatedly performed. In the diagnostic process, first, in S210, the master ECU 10 determines whether or not the diagnostic conditions are satisfied. Here, when the master ECU 10 detects that the power supply from the power source 7 is cut off, it determines that the diagnostic conditions are satisfied.

[0033] If it is determined that the diagnosis is not currently being performed, the master ECU 10 repeats the process of S210. If it is determined that the diagnosis is currently being performed, the master ECU 10 outputs a pulse wave to the communication line 5 and measures the reflected wave in S220. Measuring the reflected wave means recording what kind of reflected wave was detected and at what timing after the pulse wave was output. The reflected wave is detected as a change in voltage.

[0034] For example, as shown in Fig. 4B, when the master ECU 10 detects a reflected wave, it determines that a reflected wave has been detected if the voltage of the monitored communication line 5 changes beyond a threshold value Th (e.g., ±0.1 V). Specifically, in the example shown in Fig. 4A, a pulse wave of 3.0 V is input at time 0, and a voltage change of approximately -1.0 V is detected as a waveform approximately 100 ns later.

[0035] Next, in S230, the master ECU 10 determines whether or not a past waveform representing a waveform measured in the past is stored in the memory 12. If a past waveform is stored, the master ECU 10 compares the past waveform with the current waveform in S240, calculates the distance to the fault location using the timing at which the waveform change was detected and the transmission speed already calculated, and records the distance in the memory 12. Note that the current waveform refers to the waveform of the reflected wave newly obtained after the past waveform. The transmission speed is the speed at which the voltage change progresses in the communication line 5. The transmission speed depends on the metal material constituting the communication line 5, the material of the coating of the communication line 5, etc.

[0036] Specifically, for example, when waveform "B" shown in Fig. 4B is detected in the current waveform as a change in the reflected wave from the past waveform, the already calculated transmission speed is multiplied by the time it takes for waveform "B" to be obtained to obtain the distance to the fault location 90. For example, if the transmission speed is 0.1 m / ns and the timing when change "B" was obtained is 120 nm, the distance to the fault location 90 is estimated to be 12 m by multiplying these together. When this process ends, the master ECU 10 ends this process.

[0037] On the other hand, if no past waveform has been stored in S230, the master ECU 10 stores the measured reflected wave in the memory 12 in S250. At this time, the transmission speed of the pulse wave on the communication line 5 is calculated from the distance to the first branch point 5A on the communication line 5 as seen from the master ECU 10 and the timing at which the first reflected wave was detected. It is assumed that the distance to the first branch point 5A is known.

[0038] For example, if the distance from the master ECU 10 to the branching point 5A is 10 m, and the time it takes to obtain the waveform "A" is ΔT (=100 ns) as shown in Fig. 4A, a transmission speed of 0.1 m / ns is obtained by dividing the distance by the time ΔT. The master ECU 10 stores this transmission speed in the memory 12. When this process ends, the master ECU 10 ends this process.

[0039] [1-4. Effects] According to the embodiment described above in detail, the following effects are achieved. (1a) One aspect of the present disclosure is a communication system 1 configured to diagnose the presence or absence of a fault in a communication line 5. The communication system 1 includes a master ECU 10 and an ECUa 20. The master ECU 10 is connected to the communication line 5 and configured to diagnose the presence or absence of a fault in the communication line 5 by transmitting a pulse wave to the communication line 5 and measuring the reflected wave. The ECUa 20 is connected to a branch line 5B branched from the communication line 5. The ECUa 20 has a termination circuit 52 that can be connected to the communication line 5. The ECUa 20 is configured to connect the termination circuit 52 to the communication line 5 during diagnosis in steps S110 to S130 and to separate the termination circuit 52 from the communication line 5 during non-diagnosis, that is, to function as a connection / disconnection unit. The ECUa 20 includes a switching element 51 for realizing the function as a connection / disconnection unit.

[0040] According to this configuration, the reflection of the pulse wave can be suppressed by arranging the termination circuit 52 for the ECUa 20 connected to the branch line 5B of the communication line 5, which does not originally require the termination circuit 52, and by operating the termination circuit 52. Therefore, it is possible to perform a fault diagnosis of the communication line 5 without using a dedicated measurement line.

[0041] (1b) In one aspect of the present disclosure, the master ECU 10 stores a past waveform representing the waveform of a reflected wave measured in the past, and estimates the location of the failure based on the timing at which a difference occurred between the past waveform and a current waveform representing the waveform of a newly obtained reflected wave. According to such a configuration, it is possible to estimate the occurrence of a fault in the communication line 5 as well as the location of the fault, based on the timing at which the difference in waveforms occurs.

[0042] (1c) In one aspect of the present disclosure, the master ECU 10 calculates the transmission speed of the pulse wave in the communication line 5 by using the distance to a known branch point 5A of the communication line 5 and a waveform that indicates the branch point 5A in a past waveform. Then, the master ECU 10 calculates the distance from the master ECU 10 to the location of the failure by using the transmission speed and the timing at which the difference occurs. With this configuration, the distance to the fault location can be estimated using the transmission speed of the pulse wave.

[0043] (1d) In one aspect of the present disclosure, the master ECU 10 and the ECU a 20 are configured to determine whether or not it is time for diagnosis when the ECU a 20 transitions to sleep, and are configured to recognize whether or not it is time for diagnosis based on the result of this determination.

[0044] According to such a configuration, it is possible to determine whether or not it is time for diagnosis by a specific configuration. In particular, when the timing when the communication system 1 does not need to communicate is set as the time for diagnosis, the diagnosis can be performed without impeding necessary communication.

[0045] (1e) In one aspect of the present disclosure, the switching element 51 is used to realize the function of a connection / separation unit. According to this configuration, the switching element 51 can be used to connect and disconnect the termination circuit 52 to and from the communication line 5 with a relatively simple configuration.

[0046] 2. Other embodiments Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments and can be implemented in various modified forms.

[0047] (2a) In the above embodiment, the communication line 5 is configured as a differential communication line, but is not limited to this. For example, the communication line 5 may be configured as a single-wire communication line.

[0048] (2b) In the above embodiment, the transmission speed of the pulse wave is calculated by calculation, but this is not limiting. For example, the transmission speed of the pulse wave may be stored in advance as a design value. The transmission speed of the pulse wave may be written in the memory 12, for example, at the time of shipment from a factory. In this configuration, the master ECU 10 may calculate the distance from the master ECU 10 to the location of the failure by using the prepared transmission speed of the pulse wave and the timing at which a difference in waveform occurs. According to this configuration, since a prepared transmission rate is used, there is no need to calculate the transmission rate, and therefore the process for identifying the location of a fault can be simplified.

[0049] (2c) In the above embodiment, the ECU a20 is configured to control the operation of the switching element 51 arranged in the ECU a20, but this is not limited to the above. For example, a device that controls the operation of the switching element 51 and the switching element 51 may be mounted on separate devices. Specifically, for example, the master ECU 10 may control the operation of the switching element 51 arranged in the ECU a20.

[0050] In this configuration, the connection / disconnection process and the diagnosis process can be executed by the master ECU 10. Therefore, it is not necessary for both the master ECU 10 and the other ECUs to recognize that diagnosis is being performed, and it is not necessary to configure multiple devices to synchronize for diagnosis.

[0051] (2d) In the above embodiment, the common power supply 7 and the termination processing power supply 8 are used as a configuration for synchronizing diagnosis among a plurality of devices, but this is not limiting. For example, a configuration can be adopted in which a signal line separate from the power supply line is connected to both the master ECU 10 and the ECUa 20, and the same transition signal (e.g., a common external signal) indicating a transition during diagnosis is input via this signal line. Also, when this signal line is provided, a configuration can be adopted in which one device detects the state and outputs a transition signal to the other device.

[0052] (2e) In the above embodiment, the ECU a20 is configured to recognize that it is time for diagnosis when it transitions to sleep, but this is not limiting. The ECU a20 may be configured to recognize that it is time for diagnosis based on, for example, the power supply state of the vehicle, an input signal from another device indicating the time for diagnosis, or the ECU a20 being woken up.

[0053] (2f) In the above embodiment, the MPU 21 of the ECU a 20 drives and controls the switching element 51, but this is not limited thereto. For example, as shown in FIG. 7, the ECU a 20 may include an MPU 21A instead of the MPU 21, and a transceiver IC 29A instead of the transceiver IC 29. In this configuration, the MPU 21A is not connected to the termination adjustment circuit 50, and the transceiver IC 29A is connected to the termination adjustment circuit 50. That is, the transceiver IC 29A may be configured to control the switching element 51. Furthermore, power from the power source 7 may be supplied to the MPU 21A via the transceiver IC 29A. Furthermore, the transceiver IC 29A may be connected to an external input signal line indicating whether or not it is time for diagnosis, and this signal line may be input to the MPU 21A.

[0054] (2g) The ECU 10, 20 and the method described in the present disclosure may be realized by a dedicated computer provided by configuring a processor and a memory programmed to execute one or more functions embodied in a computer program. Alternatively, the ECU 10, 20 and the method described in the present disclosure may be realized by a dedicated computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the ECU 10, 20 and the method described in the present disclosure may be realized by one or more dedicated computers configured by a combination of a processor and a memory programmed to execute one or more functions and a processor configured with one or more hardware logic circuits. In addition, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions to be executed by a computer. The method for realizing the functions of each unit included in the ECU 10, 20 does not necessarily need to include software, and all of the functions may be realized using one or more hardware.

[0055] (2h) Multiple functions possessed by one component in the above embodiments may be realized by multiple components, or one function possessed by one component may be realized by multiple components. Also, multiple functions possessed by multiple components may be realized by one component, or one function realized by multiple components may be realized by one component. Also, part of the configuration of the above embodiments may be omitted. Also, at least part of the configuration of the above embodiments may be added to or substituted for the configuration of another of the above embodiments.

[0056] (2i) In addition to the communication system 1 described above, the present disclosure can also be realized in various forms, such as devices such as ECUs 10, 20, 30 that are components of the communication system 1, programs for causing a computer to function as these devices, non-transient physical recording media such as semiconductor memories on which these programs are recorded, and diagnostic methods.

[0057] [Technical idea disclosed in this specification] [Item 1] A communication system (1) configured to diagnose the presence or absence of a fault in a communication line (5), a diagnostic device (10) connected to the communication line and configured to diagnose whether or not there is a fault in the communication line by transmitting a pulse wave to the communication line and measuring the reflected wave; a communication device (20) connected to a branch line (5B) branched off from the communication line, the communication device (20) having a termination circuit (52) that can be connected to the communication line; The diagnostic device or the communication device includes a connection / disconnection unit (51, S110 to S130) configured to connect the termination circuit to the communication line during diagnosis and to disconnect the termination circuit from the communication line at times other than diagnosis. [Item 2] Item 1 is a communication system according to the present invention, The diagnostic device stores a past waveform representing a waveform of a reflected wave measured in the past, and estimates a location of a fault based on a timing at which a difference occurs between the past waveform and a current waveform representing a waveform of a newly obtained reflected wave. A communication system configured as follows. [Item 3] Item 2. A communication system according to the present invention, The diagnostic device calculates a transmission speed of the pulse wave in the communication line using a distance to a known branch point of the communication line and a waveform indicating the branch point in the past waveform, and calculates a distance from the diagnostic device to a fault point using the transmission speed and a timing at which the difference occurs. A communication system configured as follows. [Item 4] Item 2. A communication system according to the present invention, The diagnostic device calculates the distance from the diagnostic device to the location of the failure using the transmission speed of a pulse wave prepared in advance and the timing at which the difference occurs. A communication system configured as follows. [Item 5] A communication system according to any one of items 1 to 4, The diagnostic device or the communication device further includes a diagnosis determination unit (S110, S210) configured to determine whether or not it is time for diagnosis based on any one of a power supply state of the vehicle, an input signal from another device indicating the time for diagnosis, a wake-up state of the communication device, and a sleep state of the communication device; The connection / disconnection unit recognizes whether or not it is time for diagnosis based on a determination result of the diagnosis / determination unit. A communication system configured as follows. [Item 6] A communication system according to any one of items 1 to 5, the connection / separation unit further includes a switching element (51) disposed between the communication line and the termination circuit, The connection / separation unit turns on the switching element during the diagnosis and turns off the switching element at other times than the diagnosis. A communication system configured as follows. [Explanation of symbols]

[0058] 1...communication system, 5...communication line, 5A...branch, 5B...branch line, 7...power supply, 8...power supply for termination processing, 10...master ECU, 11,21,21A,31...MPU, 12,22,32...memory, 13,23,33...communication circuit, 14,24...connector, 17,27...protection circuit, 18,28...coil, 19,29,29A...transceiver IC, 20...ECUa, 40,52...termination circuit, 50...termination adjustment circuit, 51...switching element.

Claims

1. A communication system (1) configured to diagnose the presence or absence of a fault in a communication line (5), comprising: a diagnostic device (10) connected to the communication line and configured to diagnose whether or not there is a fault in the communication line by transmitting a pulse wave to the communication line and measuring the reflected wave; a communication device (20) connected to a branch line (5B) branched off from the communication line, the communication device having a termination circuit (52) that can be connected to the communication line; The diagnostic device or the communication device is provided with a connection / disconnection unit (51, S110 to S130) configured to connect the termination circuit to the communication line during diagnosis and to disconnect the termination circuit from the communication line at times other than diagnosis.

2. 2. The communication system according to claim 1, The diagnostic device stores a past waveform representing a waveform of a reflected wave measured in the past, and estimates a location of a fault based on a timing at which a difference occurs between the past waveform and a current waveform representing a waveform of a newly obtained reflected wave. A communication system configured as follows.

3. 3. The communication system according to claim 2, The diagnostic device calculates a transmission speed of the pulse wave in the communication line using a distance to a known branch point of the communication line and a waveform indicating the branch point in the past waveform, and calculates a distance from the diagnostic device to a fault point using the transmission speed and a timing at which the difference occurs. A communication system configured as follows.

4. 3. The communication system according to claim 2, The diagnostic device calculates the distance from the diagnostic device to the location of the failure using the transmission speed of a pulse wave prepared in advance and the timing at which the difference occurs. A communication system configured as follows.

5. A communication system according to any one of claims 1 to 4, The diagnostic device or the communication device further includes a diagnosis determination unit (S110, S210) configured to determine whether or not it is time for diagnosis based on any one of a power supply state of the vehicle, an input signal from another device indicating the time for diagnosis, a wake-up state of the communication device, and a sleep state of the communication device, The connection / disconnection unit recognizes whether or not it is time for diagnosis based on a determination result of the diagnosis / determination unit. A communication system configured as follows.

6. The communication system according to claim 1 or 2, The connection / separation unit further includes a switching element (51) disposed between the communication line and the termination circuit, The connection / separation unit turns on the switching element during the diagnosis and turns off the switching element at other times than the diagnosis. A communication system configured as follows.

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