JP2009111911A - Communication apparatus, communication system, and communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To disconnect a failed communication apparatus from a network by enabling the failed communication apparatus to be specified and further reducing an adverse effect exerted on other communication apparatuses by an abnormal waveform transmitted by such a communication apparatus. <P>SOLUTION: A communication apparatus in a communication system where communication is mutually performed via a two-wire type communication line in which termination resistors are connected in both ends, comprises: a termination circuit which is constituted of first and second resistors when each termination resistor is constituted of the first resistor and the second resistor connected in series to the first resistor, and a capacitor which is connected between the first resistor and the second resistor and of which the other end is grounded; and a communication error measuring means for measuring a communication error in the communication system. When the communication error measured by the communication error measuring means is equal to or greater than a predetermined threshold required for satisfying functions of the communication system, the termination circuit changes capacity of the capacitor. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a CAN communication method and system for performing communication between a plurality of communication devices connected to each other via a CAN (Controller Area Network) bus. In particular, the present invention specifies a fault location and isolates the fault location. The present invention relates to a communication device, a communication system, and a communication method.

  A CAN communication system is known that performs data communication between a plurality of communication devices that are connected to each other via a CAN bus and each have a CAN controller unit. CAN communication is a protocol for performing bidirectional serial communication via a differential serial bus.

In a CAN communication system, each communication device sends data with an identification ID code of its own communication device toward the CAN bus. If the CAN bus is not exclusively used by other communication devices when data is transmitted, the data sent from the communication device flows through the CAN bus and is received by the other communication device. On the other hand, when the CAN bus is exclusively used for data from other communication devices, the data to be sent out from the communication device is waited by the CAN controller unit. If there is a single communication device waiting for data, the data flows through the CAN bus when the CAN bus is free. On the other hand, when there are a plurality of communication devices waiting for data, the data of the communication device having the highest priority based on the ID code among these communication devices flows through the CAN bus before other standby data.
JP 2006-135375 A

  However, the background art described above has the following problems.

  The CAN communication system includes a plurality of communication devices (nodes), and the plurality of communication devices are respectively connected by a CAN bus having a twisted pair configuration, and transmit and receive data between the communication devices. One of the CAN bus twisted pair lines is a bus line called CAN High (hereinafter referred to as CANH) and the other as CAN Low (hereinafter referred to as CANL). Each communication device may be configured by, for example, a plurality of electronic control units (hereinafter referred to as ECUs) that control each part of the automobile.

  For example, as shown in FIG. 1, CAN buses connected to a plurality of ECUs are connected to a CAN hub and communicate with each other via the CAN hub. Specifically, the CAN bus connected to the plurality of ECUs A-ECU D is connected to the CAN hub 1, while the CAN bus connected to the plurality of ECUs E-ECU H is connected to the CAN hub 2. The The CAN hub 1 and the CAN hub 2 are connected by a CAN communication line. In the example shown in FIG. 1, a data link connector (DLC) is further connected to the CAN hub, and a service tool is connected to the data link connector. This service tool can check CAN communication.

  In the CAN communication system shown in FIG. 1, for example, consider a case where ECU C fails. For example, when one side of the branch line of the ECU C, for example, the CANL line is disconnected, the ECU C transmits a signal having an abnormal waveform as shown in FIG.

  In such a state, the ECU G that is in a normal state starts transmission. For example, the ECU G transmits a signal to the ECU D, for example, in order to exchange information with other ECUs. For example, the ECU G transmits a signal having a normal waveform as shown in FIG. However, since the signal transmitted from the ECU G is affected by the signal transmitted from the ECU C, the waveform of the signal received by the ECU D becomes a waveform as shown in FIG. May not be received normally. Similarly, since signals transmitted from other ECUs are also affected by signals transmitted from ECU C, the ECUs to which other ECUs are transmitted may not receive normal signals from other ECUs. . Therefore, communication between ECUs is destroyed, and communication between some ECUs becomes impossible. In such a situation, when the communication state is inspected by the service tool, a plurality of ECUs are determined to be faulty, so that the fault location cannot be specified.

  Until now, in the bus-type communication in which a plurality of communication devices are connected, the failure location is identified and the failure location can be separated by controlling a transistor or a relay connected to a computer or a communication line from the master circuit. The method of physically disconnecting a broken computer or electric wire was common. Here, the communication device includes a computer. In such a method, it is necessary to add a circuit and a control power supply. Since it is necessary to add an additional circuit on the communication line, the physical performance of communication may be affected. Further, when applied to a large-scale network, the cost of this additional circuit increases. Therefore, when an ECU connected to a CAN communication network or a CAN communication line breaks down, it is difficult to realize a circuit for separating a place for identifying the failed part at a low cost without affecting the communication performance. is there.

  Further, in a method for identifying a fault location and disconnecting a fault location in a one-side disconnection between bus-connected ECUs, a method is disclosed in which a fault node that detects its own abnormality stops CAN communication (for example, a patent) Reference 1).

  However, this method cannot reduce the influence of an abnormal waveform from a failed ECU on a normal ECU.

  The present invention has been made in view of the above points, and can identify a failed communication device, further reduce the influence of an abnormal waveform transmitted by the communication device on other communication devices, and perform the failed communication. It is an object of the present invention to provide a communication device, a communication system, and a communication method that can disconnect a device from a network.

In order to solve the above problems, the communication device of the present invention provides:
A communication device in a communication system that communicates with each other via a two-wire communication line having terminal resistors connected to both ends,
The termination resistor includes a first resistor and a second resistor connected in series to the first resistor,
A termination circuit constituted by the first and second resistors, and a capacitor connected between the first resistor and the second resistor and having the other end grounded;
Communication error measuring means for measuring a communication error in the communication system,
The termination circuit changes the capacitance of the capacitor when the communication error measured by the communication error measuring unit is equal to or greater than a predetermined threshold required to satisfy the function of the communication system. I will.

  With this configuration, the capacitance of the capacitor included in the termination circuit can be changed, and the abnormal waveform of the signal transmitted from the failed ECU can be adjusted. The influence on communication between ECUs can be reduced. In addition, normal communication between the ECUs can be restored.

In yet another configuration example,
The termination circuit is configured to change the capacitance of the capacitor so that a differential voltage is not generated before the sampling point.

  With this configuration, the differential waveform can be returned to a normal waveform before the sampling point. Therefore, communication between normal ECUs becomes possible.

In yet another configuration example,
The communication error measuring means measures a communication error at a predetermined cycle,
The termination circuit changes the capacitance of the capacitor to the capacitance before the change when the communication error measured by the communication error measuring means is less than the predetermined threshold when the capacitance of the capacitor is changed. Configured as follows.

  With this configuration, when it is considered that the failed ECU is not communicating via the CAN communication network, the communication device malfunctions by returning the changed capacitor capacity to the capacity before the change. Communication can be continued in the situation before the occurrence of.

In yet another configuration example,
Each communication device transmits a frame including information indicating the transmission source,
It is configured to include a communication device detecting unit that detects a frame error and detects a communication device that has transmitted the erroneous frame based on information indicating a transmission source included in the frame.

  With this configuration, it is possible to identify a communication device that transmits a frame received in error based on information indicating a transmission source included in a frame transmitted by each communication device. Here, the frame received in error includes a frame transmitted by the communication apparatus when the communication apparatus is out of order.

In yet another configuration example,
It is comprised so that it may have a notification means which notifies the communication apparatus detected by the said communication apparatus detection means.

  By configuring in this way, it is possible to notify the communication device in failure.

The communication system of the present invention includes:
A communication system having a communication device that communicates with each other via a two-wire communication line having terminal resistors connected to both ends,
The communication device includes a first communication device configured to include the termination resistor, and a second communication device other than the first communication device,
The termination resistor includes a first resistor and a second resistor connected in series to the first resistor,
The first communication device is:
First communication error measuring means for measuring a communication error in the communication system;
The first and second resistors and a capacitor connected between the first resistor and the second resistor and having the other end grounded are measured by the first communication error measuring means. A termination circuit that changes the capacitance of the capacitor when the communication error is greater than or equal to a predetermined threshold required to satisfy the function of the communication system, and
The second communication device is:
Second communication error measuring means for measuring a communication error in the communication system;
Control means for stopping communication when the communication error measured by the second communication error measuring means is greater than or equal to a predetermined threshold required for satisfying the function of the communication system. One.

  With this configuration, the capacitance of the capacitor included in the termination circuit can be changed, and the abnormal waveform of the signal transmitted from the failed ECU can be adjusted. The influence on communication between ECUs can be reduced. In addition, normal communication between the ECUs can be restored. Further, it is possible to determine whether or not the own ECU is in failure, and if it is in failure, communication can be stopped.

Another communication system of the present invention includes:
A communication system having a communication device that communicates with each other via a two-wire communication line having terminal resistors connected to both ends,
The termination resistor includes a first resistor and a second resistor connected in series to the first resistor,
A termination circuit constituted by the first and second resistors, and a capacitor connected between the first resistor and the second resistor and having the other end grounded;
A communication error measuring means for measuring a communication error in the communication system;
Capacity changing means for changing the capacity of the capacitor in the termination circuit when the communication error measured by the communication error measuring means is greater than or equal to a predetermined threshold required to satisfy the function of the communication system. It has one of the characteristics.

  With this configuration, the capacitance of the capacitor included in the termination circuit can be changed, and the abnormal waveform of the signal transmitted from the failed ECU can be adjusted. The influence on communication between ECUs can be reduced.

The communication method of the present invention includes:
A communication method in a communication system having a communication device that communicates with each other via a two-wire communication line having terminal resistors connected to both ends,
The communication device includes a first communication device configured to include the termination resistor, and a second communication device other than the first communication device,
The termination resistor includes a first resistor and a second resistor connected in series to the first resistor,
A first communication error measuring step in which the first communication device measures a communication error in the communication system;
When the communication error measured by the first communication error measurement step is equal to or greater than a predetermined threshold required for satisfying the function of the communication system, the first communication device A capacitance changing step configured to change the capacitance of the capacitor in the termination circuit, the capacitor being connected between the first resistor and the second resistor and having the other end grounded;
A second communication error measuring step in which the second communication device measures a communication error in the communication system;
Communication in which the second communication device stops communication when the communication error measured in the second communication error measurement step is equal to or greater than a predetermined threshold required to satisfy the function of the communication system. One of the features is that it has a stop step.

  By doing so, the capacitance of the capacitor included in the termination circuit can be changed, and the abnormal waveform of the signal transmitted from the failed ECU can be adjusted. The influence on communication between ECUs can be reduced. In addition, normal communication between the ECUs can be restored. Further, it is possible to determine whether or not the own ECU is in failure, and if it is in failure, communication can be stopped.

  According to the embodiment of the present invention, it is possible to identify a failed communication device, further reduce the influence of an abnormal waveform transmitted by the communication device on other communication devices, and disconnect the failed communication device from the network. A communication device, a communication system, and a communication method can be realized.

  Next, the best mode for carrying out the present invention will be described based on the following embodiments with reference to the drawings.

  In all the drawings for explaining the embodiments, the same reference numerals are used for those having the same function, and repeated explanation is omitted.

(First embodiment)
A CAN communication system according to an embodiment of the present invention will be described with reference to FIG.

  The CAN communication system 1000 according to the present embodiment includes, for example, a plurality of communication devices that perform communication according to a communication protocol of an in-vehicle LAN. For example, CAN (Controller Area Network) may be applied as a communication protocol for in-vehicle LAN. Each communication device includes, for example, a plurality of electronic control units (hereinafter referred to as ECUs) that control each part of the automobile.

In the CAN, as described above, the two-wire CAN communication line 400 including the CANH 200 and the CANL 300 is used as a communication line (communication bus), and a terminating resistor is connected to both ends of the two-wire CAN communication line 400. Is done. Further, in the example shown in FIG. 5, the terminating resistor is provided respectively inside the two arranged on the end of the CAN communication line 400 of the two-wire ECU 100 ₄ and ECU 100 _5. In CAN, a communication device that transmits data sends an inversion signal to CANH 200 and CANL 300, and a communication device that receives data causes the data on CAN communication line 400 to be “1” due to the voltage difference between CANH 200 and CANL 300. Or “0”.

Each of the ECUs 100 _{1 to} 100 ₅ includes a CPU 102 as a communication error measuring unit that executes a control process for controlling each part of the vehicle and a process for communicating with other ECUs, and the above-described two-wire CAN communication line. And a communication driver 104 that outputs transmission data given from the CPU 102 to the two-wire CAN communication line 400 and inputs data on the two-wire CAN communication line 400 to the CPU 102. The communication driver 104 includes two output buffers and a binarization circuit. For example, the first output buffer sets the voltage of the CANH 200 to a high level (for example, 5 V) when the transmission data is “0”, and sets the voltage of the CANH 200 to a low level (for example, 2.5 V) when the transmission data is “1”. Set. The second output buffer sets the voltage of the CANL 300 to a low level (for example, 0 V) when the transmission data is “0”, and sets the voltage of the CANL 300 to a high level (for example, 2.5 V) when the transmission data is “1”. . The binarization circuit generates a binary signal “1” or “0” representing data on the CAN communication line 400 from the difference between the input voltage of the CANH 200 and the voltage of the CANL 300.

Further, the ECUs 100 ₄ and 100 ₅ having termination resistors include a termination circuit 106. Termination circuit 106 includes a termination resistor and a capacitor (termination capacitor). For example, the termination resistor includes a first resistor 1061 and a second resistor 1062 connected in series to the first resistor 1061. The termination circuit 106 includes a first resistor 1061 and a second resistor 1062, and a capacitor 1063 connected between the first resistor 1061 and the second resistor 1062 and having the other end grounded. For example, the capacitor 1063 is composed of a variable capacitor, and its capacitance (constant) can be changed linearly.

Each ECU 100 ₁ -100 _5, in CPU 102, monitors the CAN communication. There ECU, for example, the case where ECU 100 ₁ fails. For example, when one side of the branch line of the ECU 100 ₁ , for example, CANL is disconnected, the ECU 100 ₁ transmits a signal having an abnormal waveform. In this embodiment, the case where CANL is disconnected will be described as an example of the cause of the failure of the ECU. However, the present invention can be similarly applied to the case where CANH is disconnected.

Each of the ECUs 100 _{1 to} 100 ₅ detects a CAN communication error in the CPU 102 based on the signal transmitted by the ECU 100 ₁ and recognizes “CAN communication failure”. For example, each ECU 100 ₁ -ECU 100 ₅ measures a CAN communication error, and based on whether or not the CAN communication error is equal to or greater than a predetermined threshold required to satisfy the function of the communication system, You may make it recognize as "CAN communication failure" when an error is more than the predetermined threshold value required in order to satisfy the function of a communication system.

When the ECU 100 ₄ and the ECU 100 ₅ having the termination circuit 106 recognize a failure in CAN communication, the CPU 102 instructs the termination circuit 106 to change the termination capacitance constant in the capacitor 1063 via the communication driver 104. To do. The termination circuit 106 changes the constant of the termination capacitance in the capacitor 1063 according to a command from the CPU 102. As a result, the signal transmitted by the ECU 100 ₁ is changed as shown in FIG. 6, ECU 100 ₁ of the destination ECU, as shown in FIG. 7, previously differential voltage sampling point no longer occurs Receive a signal. In this way, by changing the constant of the termination capacitance in the capacitor 1063, the generation of the differential voltage can be reduced before the sample point, so the influence on communication between other normal ECUs can be reduced.

Thereafter, the CPU 102 of each ECU 100 ₁ -ECU 100 ₅ continuously monitors the CAN communication error and determines whether or not the CAN communication error has been reduced. If it is determined that the CAN communication error is reduced, it is determined whether the CAN communication error is less than a predetermined threshold required to satisfy the function of the CAN communication system. When the CAN communication error becomes less than the threshold, the constant of the termination capacitance in the capacitor 1063 is returned to the value before the change after a predetermined time has elapsed. On the other hand, if the CAN communication error is equal to or greater than the predetermined threshold, the CPU 102 instructs the termination circuit 106 to further change the termination capacitance constant in the capacitor 1063 via the communication driver 104.

The ECU 100 ₄ and ECU 100 ₅ having a termination circuit 106, after being changed constants termination capacity in capacitors _1063, the ECU100 1 -ECU100 _5, in CPU 102, detects a CAN communication error of its own ECU, is the CAN communication error If it has decreased, communication is continued. If the CAN communication error does not decrease, it is determined that the ECU has failed, and communication is stopped. For example, each ECU 100 ₁ -ECU 100 ₅ measures a CAN communication error, and based on whether or not the CAN communication error is equal to or greater than a predetermined threshold required to satisfy the function of the communication system, If the error is equal to or greater than a predetermined threshold required for satisfying the function of the communication system, it may be determined that the ECU has failed and communication may be stopped.

  In this way, by changing the capacitance (constant) in the capacitor 1063 of the ECU having the termination circuit 106, the generation of the differential voltage can be reduced before the sampling point. Therefore, when a CAN communication error occurs due to a failure of a certain ECU, it is possible to reduce the influence of a signal transmitted by the failed ECU on communication between other normal ECUs. Further, for ECUs other than the EUC having the termination circuit 106, it is possible to determine whether or not the own ECU has failed by continuously monitoring CAN communication errors. Can do.

  Next, the operation of each ECU 100 will be described.

The operation of the ECUs 100 ₄ and 100 ₅ having the termination circuit 106 will be described with reference to FIG.

The ECUs 100 ₄ and 100 ₅ start communication (step S802).

  The CPU 102 determines whether or not a communication error has occurred (step S804).

  If it is determined that no communication error has occurred (step S804: NO), the process returns to step S804 and communication is continued. For example, the CPU 102 measures a CAN communication error, and the CAN communication error is determined based on whether the CAN communication error is equal to or higher than a predetermined threshold required to satisfy the function of the communication system. If it is less than a predetermined threshold required to satisfy the function, it is determined that no communication error has occurred.

  On the other hand, if it is determined that a communication error has occurred (step S804: YES), the CPU 102 instructs the termination circuit 106 to change the termination capacitance constant in the capacitor 1063. Termination circuit 106 changes the constant of the termination capacitance in capacitor 1063 according to the command from CPU 102 (step S806). For example, the CPU 102 measures a CAN communication error, and the CAN communication error is determined based on whether the CAN communication error is equal to or higher than a predetermined threshold required to satisfy the function of the communication system. It is determined that a communication error has occurred when the threshold value is equal to or greater than a predetermined threshold required to satisfy the above function.

  The CPU 102 continuously monitors the communication error and determines whether or not the communication error has disappeared (step S808). Here, it may be determined whether the communication error has become less than a predetermined threshold required to satisfy the function of the CAN communication system.

  If it is determined that the communication error does not disappear (step S808: NO), in other words, if the communication error does not become less than the predetermined threshold required to satisfy the function of the CAN communication system, the process returns to step S806. That is, the CPU 102 further instructs the termination circuit 106 to change the termination capacitance constant in the capacitor 1063. On the other hand, when it is determined that the communication error has disappeared (step S808: YES), in other words, when the communication error becomes less than a predetermined threshold required to satisfy the function of the CAN communication system, the CPU 102 After a certain time, the termination circuit 106 is commanded to return the termination capacitance constant in the capacitor 1063 to the constant before the change (step S810). In this case, it is determined that the failed ECU is disconnected from the CAN communication system and is not communicating.

The operation of the ECUs other than the ECUs 100 ₄ and 100 ₅ having the termination circuit 106, that is, the operations of the ECUs 100 ₁ , 100 ₂ and 100 ₃ will be described with reference to FIG.

The ECUs 100 ₁ , 100 ₂ and 100 ₃ start communication (step S902).

The CPU 102 determines whether or not a certain number of communication errors have occurred (step S904). For example, each of the ECUs 100 ₁ , 100 _2, and 100 ₃ measures a CAN communication error, and determines whether or not the CAN communication error is greater than or equal to a predetermined threshold required to satisfy the function of the communication system. .

When it is determined that no more than a certain number of communication errors have occurred (step S904: NO),
In other words, if the CAN communication error is less than the predetermined threshold required to satisfy the function of the communication system, the process returns to step S904 and communication is continued. On the other hand, if it is determined that a certain number or more of communication errors have occurred (step S904: YES), in other words, if the CAN communication error is greater than or equal to a predetermined threshold required to satisfy the function of the communication system, The CPU 102 instructs the communication driver 104 to stop communication (step S906).

  According to the present embodiment, by providing means for changing the constant of the termination capacitance of the capacitor 1063 in the termination circuit, the abnormal waveform output from the failed ECU can be adjusted (shaped), so that the failed ECU The influence which it has on the communication between other ECUs by the signal transmitted by can be reduced. For this reason, communication between normal ECUs can be restored. Also, by providing the ECU with a means for monitoring a communication error and stopping communication when a state where the communication error is a certain number or more continues, the failure location can be identified, in other words, the identified failure location, in other words The CANH can disconnect the ECU having the failure location from the disconnection communication network.

(Second embodiment)
A CAN communication system according to another embodiment of the present invention will be described. The CAN communication system according to the present embodiment has the same configuration as that described with reference to FIG.

In the CAN communication system according to the present embodiment, the termination circuit 106 provided in the ECUs 100 ₄ and 100 ₅ having the termination resistance is configured by the termination resistance and a plurality of capacitors. For example, the termination resistor includes a first resistor 1061 and a second resistor 1062 connected in series to the first resistor 1061. The termination circuit 106 is connected in series with a first resistor 1061 and a second resistor 1062, and a plurality of capacitors connected between the first resistor 1061 and the second resistor 1062 and having the other end grounded. And a variable capacitor 1063. With this configuration, the capacitance (constant) of the capacitor can be changed in multiple stages.

(Third embodiment)
A CAN communication system according to another embodiment of the present invention will be described with reference to FIG. In the CAN communication system according to the present embodiment, the termination resistor is configured by a first resistor 1061 and a second resistor 1062 connected in series to the first resistor 1061. The termination circuit 106 includes a first resistor 1061 and a second resistor 1062, and a capacitor 1063 connected between the first resistor 1061 and the second resistor 1062 and having the other end grounded. For example, the capacitor 1063 is composed of a variable capacitor, and its capacitance (constant) can be changed linearly.

One of the ECUs 100 (100 ₁ , 100 ₂ and 100 ₃ ) according to the present embodiment is a master ECU. The master ECU has the same function as the ECU having the termination circuit 106 in the above-described embodiment.

Each of the ECUs 100 _{1 to} 100 ₃ monitors the CAN communication state in the CPU 102. There ECU, for example, the case where ECU 100 ₁ fails. For example, when the branch line of the ECU 100 ₁ is disconnected, the ECU 100 ₁ transmits a signal having an abnormal waveform. For example, when one side of the branch line of the ECU 100 ₁ , for example, CANL is disconnected, the ECU 100 ₁ transmits a signal having an abnormal waveform. In the present embodiment, a case where CANL is disconnected will be described as an example of the cause of the failure of the ECU. However, the present invention can be similarly applied to a case where CANH is disconnected.

Each of the ECUs 100 _{1 to} 100 ₃ detects a CAN communication error in the CPU 102 based on the signal transmitted by the ECU 100 ₁ and recognizes “CAN communication failure”. For example, each of the ECUs 100 _{1 to} 100 ₃ measures the CAN communication error, and based on whether or not the CAN communication error is equal to or greater than a predetermined threshold required to satisfy the function of the communication system, You may make it recognize as "CAN communication failure" when an error is more than the predetermined threshold value required in order to satisfy the function of a communication system.

  When the master ECU recognizes a failure in CAN communication, the CPU 102 instructs the termination circuit 106 to change the constant of the termination capacitance in the capacitor 1063 via the communication driver 104. In this case, the master ECU controls the termination circuit 106 by transmitting control information through a dedicated communication line provided between the master ECU and the termination circuit 106, for example. The termination circuit 106 changes the constant of the termination capacitance in the capacitor 1063 according to a command from the CPU 102. Thus, by changing the constant of the termination capacitance in the capacitor 1063, the generation of a differential voltage is reduced before the sample point, and the influence on communication between other normal ECUs is reduced.

Thereafter, the CPU 102 of each ECU 100 ₁ -ECU 100 ₃ continuously monitors the CAN communication error and determines whether or not the CAN communication error has been reduced. If it is determined that the CAN communication error is reduced, it is determined whether the CAN communication error is less than a predetermined threshold required to satisfy the function of the CAN communication system. When the CAN communication error is less than the threshold value, the master ECU issues a command to return the terminal capacitance constant in the capacitor 1063 to the value before the change after a predetermined time has elapsed. On the other hand, if the CAN communication error is equal to or greater than the predetermined threshold, the CPU 102 instructs the termination circuit 106 to further change the termination capacitance constant in the capacitor 1063 via the communication driver 104.

After the termination capacity constant is changed by the termination circuit 106, the ECU 100 ₁ -ECU 100 ₃ detects a CAN communication error of its own ECU in the CPU 102, and continues communication when the CAN communication error decreases. If the CAN communication error does not decrease, it is determined that the ECU is out of order and communication is stopped. For example, each of the ECUs 100 _{1 to} 100 ₃ measures the CAN communication error, and based on whether or not the CAN communication error is equal to or greater than a predetermined threshold required to satisfy the function of the communication system, If the error is equal to or greater than a predetermined threshold required for satisfying the function of the communication system, it may be determined that the ECU has failed and communication may be stopped.

  Thus, by changing the capacitance (constant) of the capacitor of the termination circuit, the generation of differential voltage can be reduced before the sampling point. Therefore, when a CAN communication error occurs due to a failure of a certain ECU, it is possible to reduce the influence of a signal transmitted by the failed ECU on communication between other normal ECUs. Furthermore, since it is possible to determine whether or not the own ECU has failed by continuously monitoring CAN communication errors, communication can be stopped for the failed ECU.

  Next, the operation of the ECU 100 will be described with reference to FIG.

  In this embodiment, the operation of the master ECU will be described. The operations of the ECUs other than the master ECU are the same as those described with reference to FIG.

  The master ECU 100 starts communication (step S1102).

  The CPU 102 determines whether or not a communication error has occurred (step S1104).

  If it is determined that no communication error has occurred (step S1104: NO), the process returns to step S1104 and communication is continued. For example, the CPU 102 measures a CAN communication error, and the CAN communication error is determined based on whether the CAN communication error is equal to or higher than a predetermined threshold required to satisfy the function of the communication system. If it is less than a predetermined threshold required to satisfy the function, it is determined that no communication error has occurred.

  On the other hand, when it is determined that a communication error has occurred (step S1104: YES), the CPU 102 instructs the termination circuit 106 to change the termination capacitance constant in the capacitor 1063. For example, when recognizing a failure in CAN communication, the CPU 102 instructs the termination circuit 106 to change the constant of the termination capacitance in the capacitor 1063 via the communication driver 104. In this case, the master ECU controls the termination circuit 106 by transmitting control information through a dedicated communication line provided between the master ECU and the termination circuit 106. Termination circuit 106 changes the constant of the termination capacitance in capacitor 1063 in accordance with a command from CPU 102 (step S1106). For example, the CPU 102 measures a CAN communication error, and the CAN communication error is determined based on whether the CAN communication error is equal to or higher than a predetermined threshold required to satisfy the function of the communication system. It is determined that a communication error has occurred when the threshold is equal to or greater than a predetermined threshold required to satisfy the function.

  The CPU 102 continuously monitors the communication error and determines whether or not the communication error has disappeared (step S1108). Here, it may be determined whether the communication error has become less than a predetermined threshold required to satisfy the function of the CAN communication system.

  When it is determined that the communication error does not disappear (step S1108: NO), in other words, when the communication error does not become less than the predetermined threshold required to satisfy the function of the CAN communication system, the process returns to step S1106. That is, the CPU 102 further instructs the termination circuit 106 to change the termination capacitance constant in the capacitor 1063. On the other hand, when it is determined that the communication error has disappeared (step S1108: YES), in other words, when the communication error becomes less than a predetermined threshold required to satisfy the function of the CAN communication system, the CPU 102 After a certain time, the termination circuit 106 is commanded to return the termination capacitance constant in the capacitor 1063 to the constant before the change (step S1110).

  With this configuration, it is possible to consolidate additional functions for changing the capacitance of the capacitor 1063 of the termination circuit into one ECU. For this reason, cost reduction is possible.

(Fourth embodiment)
A CAN communication system according to another embodiment of the present invention will be described. The configuration of the CAN communication system according to the present embodiment is the same as the configuration described with reference to FIGS.

In the CAN communication system according to the present embodiment, the ECUs 100 ₄ and 100 ₅ or the master ECU having the termination circuit 106 check the frame transmitted by each ECU and identify the failed ECU. Each ECU transmits a unique frame that can identify the transmission source ECU. For example, the CPU 102 serving as the communication device detection unit and the notification unit detects an error in the frame, and when there is an error, the CPU 102 that has transmitted the frame based on information that can identify the transmission source ECU included in the frame. Identify. Then, based on whether or not the error rate of the frame in each ECU is equal to or higher than a predetermined threshold required to satisfy the function of the communication system, The transmission source ECU identified in this way is determined to be faulty. When a faulty ECU is detected, the CPU 102 may notify the user or a person in charge of the repair of the ECU.

  By configuring in this way, it is possible to check the frame transmitted from each ECU, and therefore, it is possible to identify the ECU that is not communicating, in other words, that is malfunctioning.

  For convenience of explanation, specific numerical examples will be described to facilitate understanding of the invention. However, unless otherwise specified, these numerical values are merely examples, and any appropriate value may be used.

  Although the present invention has been described above with reference to specific embodiments, each embodiment is merely an example, and those skilled in the art will understand various variations, modifications, alternatives, substitutions, and the like. I will. For convenience of explanation, an apparatus according to an embodiment of the present invention has been described using a functional block diagram, but such an apparatus may be realized by hardware, software, or a combination thereof. The present invention is not limited to the above-described embodiments, and various modifications, corrections, alternatives, substitutions, etc. are included without departing from the spirit of the present invention.

It is explanatory drawing which shows an example of a CAN connection form. It is explanatory drawing which shows an example of the waveform of the signal transmitted from failure ECU. It is explanatory drawing which shows an example of the waveform of the signal transmitted from normal ECU. It is explanatory drawing which shows an example of the received waveform of the signal transmitted from normal ECU in the condition where failure ECU exists. It is explanatory drawing which shows the communication system which concerns on one Example of this invention. It is explanatory drawing which shows an example of the waveform of the signal transmitted from ECU which concerns on one Example of this invention. It is explanatory drawing which shows an example of the received waveform of the signal transmitted from normal ECU in the condition where fault ECU which concerns on one Example of this invention exists. It is a flowchart which shows operation | movement of the communication apparatus which concerns on one Example of this invention. It is a flowchart which shows operation | movement of the communication apparatus which concerns on one Example of this invention. It is explanatory drawing which shows the communication system which concerns on one Example of this invention. It is a flowchart which shows operation | movement of the communication apparatus which concerns on one Example of this invention.

Explanation of symbols

100 (100 ₁ , 100 ₂ , 100 ₃ , 100 ₄ and 100 ₅ ) Electronic Control Unit
102 CPU
104 Communication Driver 106 Termination Circuit 1061 First Resistor 1062 Second Resistor 1063 Capacitor 200 CAN High (CANH)
300 CAN Low (CANL)
400 CAN communication line 1000 CAN communication system

Claims (8)

A communication device in a communication system that communicates with each other via a two-wire communication line having terminal resistors connected to both ends,
The termination resistor includes a first resistor and a second resistor connected in series to the first resistor,
A termination circuit constituted by the first and second resistors, and a capacitor connected between the first resistor and the second resistor and having the other end grounded;
Communication error measuring means for measuring a communication error in the communication system,
The termination circuit changes the capacitance of the capacitor when the communication error measured by the communication error measuring unit is equal to or greater than a predetermined threshold required to satisfy the function of the communication system. Communication device. The communication device according to claim 1,
The communication device according to claim 1, wherein the termination circuit changes a capacitance of the capacitor so that a differential voltage is not generated before a sampling point. The communication device according to claim 1 or 2,
The communication error measuring means measures a communication error at a predetermined cycle,
The termination circuit changes the capacitance of the capacitor to the capacitance before the change when the communication error measured by the communication error measuring means is less than the predetermined threshold when the capacitance of the capacitor is changed. A communication device. The communication device according to any one of claims 1 to 3,
Each communication device transmits a frame including information indicating the transmission source,
A communication apparatus comprising: a communication apparatus detecting unit that detects a frame error and detects a communication apparatus that has transmitted an erroneous frame based on information indicating a transmission source included in the frame. The communication device according to claim 4, wherein
A communication device comprising notification means for notifying the communication device detected by the communication device detection means. A communication system having a communication device that communicates with each other via a two-wire communication line having terminal resistors connected to both ends,
The communication device includes a first communication device configured to include the termination resistor, and a second communication device other than the first communication device,
The termination resistor includes a first resistor and a second resistor connected in series to the first resistor,
The first communication device is:
First communication error measuring means for measuring a communication error in the communication system;
The first and second resistors, and a capacitor connected between the first resistor and the second resistor and having the other end grounded, are measured by the first communication error measuring means. A termination circuit that changes the capacitance of the capacitor when the communication error is greater than or equal to a predetermined threshold required to satisfy the function of the communication system, and
The second communication device is:
Second communication error measuring means for measuring a communication error in the communication system;
Control means for stopping communication when the communication error measured by the second communication error measuring means is equal to or greater than a predetermined threshold required for satisfying the function of the communication system. Communication system. A communication system having a communication device that communicates with each other via a two-wire communication line having terminal resistors connected to both ends,
The termination resistor includes a first resistor and a second resistor connected in series to the first resistor,
A termination circuit constituted by the first and second resistors, and a capacitor connected between the first resistor and the second resistor and having the other end grounded;
A communication error measuring means for measuring a communication error in the communication system;
Capacity changing means for changing the capacity of the capacitor in the termination circuit when the communication error measured by the communication error measuring means is greater than or equal to a predetermined threshold required to satisfy the function of the communication system. A communication system comprising: A communication method in a communication system having a communication device that communicates with each other via a two-wire communication line having terminal resistors connected to both ends,
The communication device includes a first communication device configured to include the termination resistor, and a second communication device other than the first communication device,
The termination resistor includes a first resistor and a second resistor connected in series to the first resistor,
A first communication error measuring step in which the first communication device measures a communication error in the communication system;
When the communication error measured by the first communication error measurement step is equal to or greater than a predetermined threshold required for satisfying the function of the communication system, the first communication device A capacitance changing step configured to change the capacitance of the capacitor in the termination circuit, the capacitor being connected between the first resistor and the second resistor and having the other end grounded;
A second communication error measuring step in which the second communication device measures a communication error in the communication system;
Communication in which the second communication device stops communication when the communication error measured in the second communication error measurement step is equal to or greater than a predetermined threshold required to satisfy the function of the communication system. A communication method comprising: a stop step.

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