JP2014232997A - Communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication system capable of preventing inhibition of communication due to transmission of an error frame by a lower node, in a communication system capable of communicating with a plurality of communication systems including at least one communication system conforming to ISO 11898-1 standard.SOLUTION: A communication system includes a CAN bus 10, and a plurality of ECUs mutually connected via the CAN bus. Each of the ECUs includes a microprocessor and a transceiver. An upper node ECU supports a first communication system and a second communication system. A lower node ECU 13 supports the first communication system, however, it does not support the second communication system. The ECU 13 includes a hold circuit 80, providing a function so that a transceiver 70 outputs a recessive level signal to a control part instead of outputting reception data to the control part.

Description

  The present invention relates to a communication system including a CAN bus and three communication nodes connected to each other via the CAN bus.

  Conventionally, as shown in Patent Document 1, for example, a communication system including a CAN bus and at least two communication nodes connected to each other via the CAN bus has been proposed. Of the two communication nodes, at least one communication node can operate in the first drive mode and the second drive mode. In the first drive mode, the communication node transmits a CAN data frame as a communication frame via the CAN bus using the first physical protocol. In the second drive mode, an ASC data frame is transmitted as a communication frame via the CAN bus by the second physical protocol. Furthermore, the communication node has first switching means suitable for switching between the first drive mode and the second drive mode according to at least one agreement valid between itself and at least one other communication node. Have.

Special table 2011-514772 gazette

  As described above, the communication system disclosed in Patent Document 1 has an upper node corresponding to the first physical protocol and the second physical protocol as communication protocols. That is, this higher order node can communicate via the CAN bus by the first physical protocol and the second physical protocol.

  By the way, although it is not a prior art, it is also conceivable to connect a lower node corresponding to only one of the first physical protocol and the second physical protocol to the CAN bus of this communication system. In this case, if the communication via the CAN bus is performed using the communication protocol supported by the lower node, no problem occurs in the lower node. However, there is a possibility that a problem may occur in the lower node if the communication is performed by a communication protocol that is not supported by the lower node.

  Specifically, when a communication frame of a non-compliant communication protocol is transmitted to the CAN bus, the lower node that has received the communication frame cannot recognize the communication frame correctly and recognizes that an error has occurred. An error frame indicating an active error is transmitted to the CAN bus. As a result, communication between communication nodes connected to the CAN bus is hindered.

  In order to prevent the communication from being hindered by the transmission of the error frame by the lower node, the lower node transmits an error frame indicating a passive error, which is an error frame that does not depend on the error counter value and does not inhibit the communication. It is conceivable to provide it. However, in ISO11898-1 which is the international standard of CAN, the communication node transmits an error frame indicating an active error until the count value of the error counter reaches a predetermined switching threshold value. The specified error frame is transmitted. Therefore, it is out of the ISO 11898-1 standard to provide a lower node so as to transmit an error frame indicating a passive error without depending on the value of the error counter.

  Therefore, in view of the above problems, an object of the present invention is to provide a communication system capable of suppressing communication from being hindered by transmission of an error frame by a lower node while complying with the standard of ISO11898-1.

  In order to achieve the above-mentioned object, the present invention is a communication system including a CAN bus (10) and at least three communication nodes (11, 12, 13) connected to each other via the CAN bus. Then, each communication node generates transmission data, and receives a control unit (20, 40, 60) for processing the reception data and transmission data generated by the control unit, and uses the transmission data as a communication frame. A transmitter (32, 52, 72) for sending to the CAN bus and a receiver (31, 52) for receiving data sent as a communication frame from another communication node and outputting the received data as received data to the control unit 51, 71) and a transceiver (30, 50, 70), and the control unit has received data input from the transceiver as an error. In some cases, it has an error frame generation unit (65) that generates an error frame indicating an active error as transmission data, and the three communication nodes include two upper nodes (11, 12) and one lower node (13 The upper node corresponds to the first communication method and the second communication method as the communication method used for communication via the CAN bus, and communication by the first communication method and the second communication method is possible. The lower node corresponds to the first communication method, but does not correspond to the second communication method, and communication by the first communication method is possible. Of the two upper nodes, At least one upper node (11) is an upper switching node, and the control unit of the upper switching node is configured to change the communication method from the first communication method to the second communication node with respect to other communication nodes connected to the CAN bus. There is provided switching instruction means (22) for generating a switching frame for instructing switching to a transmission method as transmission data, and there is no reception data in the lower node, instead of the transceiver outputting the reception data to the control unit. As an alternative signal, a substitute output means (80) is provided for executing a substitute output for outputting a recessive level signal to the control section and for stopping the execution. If the control unit of the lower-level node receives the switching frame, the alternative output is executed.

  As described above, according to the present invention, when the reception data is an error, the error frame generation unit generates an error frame indicating an active error as transmission data. Therefore, at least the lower node conforms to, for example, the standard of ISO11898-1, and is not an original special method. As a result, there are joys such as improvement in the degree of freedom of selection of communication nodes as communication partners and cost reduction by adopting mass-produced general-purpose microcomputers.

  Furthermore, in the present invention, when the upper switching node switches the communication method from the first communication method to the second communication method, the switching frame is generated as transmission data by the switching instruction means included in the upper switching node. The switching frame is sent to the CAN bus by the transceiver, and the lower-level node transceiver receives the switching frame and outputs the switching frame to its own control unit. When the control unit of the lower node receives the switching frame, the alternative output means executes the alternative output to the control unit of the lower node. As a result, a recessive level signal is input to the control unit of the lower node as a signal indicating that there is no reception data, instead of the reception data output from the transceiver to the control unit.

  As a result, when the communication method is switched from the first communication method to the second communication method as in the conventional configuration, the control unit of the lower node receives the received data according to the second communication method, and the received data is It will not be recognized correctly, and it will not be detected that there is an error in the received data. Therefore, the error frame generator does not generate an error frame as transmission data. Accordingly, it is possible to suppress communication from being hindered by transmission of an error frame by a lower node.

  Note that the reference numerals in the parentheses merely show an example of a correspondence relationship with a specific configuration in an embodiment described later in order to facilitate understanding of the present invention, and limit the scope of the present invention. It is not intended.

  Further, the features of the present invention other than the features described above will be apparent from the description of embodiments and the accompanying drawings described later.

1 is an overall configuration diagram of a communication system according to a first embodiment. It is a block diagram of 1st ECU shown in FIG. It is a block diagram of 2nd ECU shown in FIG. It is a block diagram of 3rd ECU shown in FIG. 3 is a flowchart showing a series of processes executed by a first ECU shown in FIG. 4 is a flowchart showing a series of processes executed by a third ECU shown in FIG. 1. 3 is a time chart showing the operation of each component in the third ECU shown in FIG. 1. It is a block diagram of 3rd ECU which concerns on 2nd Embodiment. It is the flowchart which showed a series of processes performed by 1st ECU which concerns on 2nd Embodiment. It is the flowchart which showed a series of processes performed by 3rd ECU which concerns on 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
First, the configuration of the communication system 100 according to the present embodiment will be described.

  As shown in FIG. 1, the communication system 100 includes a CAN bus 10, and a first ECU 11, a second ECU 12, and a third ECU 13 that are electrically connected to the CAN bus 10. The first ECU 11, the second ECU 12, and the third ECU 13 communicate with each other via the CAN bus 10 according to the CAN protocol. That is, the first ECU 11, the second ECU 12, and the third ECU 13 each operate as a communication node. Note that CAN is an abbreviation for Controller Area Network. ECU is an abbreviation for Electronic Control Unit.

  Among the plurality of ECUs 11 to 13, the first ECU 11 and the second ECU 12 correspond to two communication protocols that comply with the CAN protocol. The two communication protocols have different communication speeds, and include a high-speed protocol and a low-speed protocol having a communication speed slower than that of the high-speed protocol. The third ECU 13 supports the low speed protocol but does not support the high speed protocol. Note that the high-speed protocol may not be a CAN protocol compliant with ISO11898-1.

  Each of the first ECU 11 and the second ECU 12 corresponds to an upper node described in the claims. The third ECU 13 corresponds to a lower node described in the claims. The low-speed protocol corresponds to the first communication method described in the claims, and the high-speed protocol corresponds to the second communication method.

In this embodiment, as an example, two communication protocols have different communication speeds, but the present invention is not limited to this. The present invention can be applied if the two communication protocols are different. For example, the present invention is also applicable when the effective data bit length in one frame is different. Specifically, in the first communication protocol, the effective data bit length is set to be the same as or shorter than the longest bit length specified in ISO11898-1, while the second communication protocol is set to the effective data bit length. The bit length may be set longer than the longest bit length. In this case, it is possible to contribute to improvement in communication efficiency by transmitting and receiving data using the second communication protocol.

  Therefore, when the first ECU 11 and the second ECU 12 communicate with each other, communication is possible using both communication protocols. However, when communicating with the first ECU 11 and the second ECU 12 with the third ECU 13, communication is possible only with the low-speed protocol.

  The first ECU 11 has a function of instructing the other ECUs 12 and 13 of a communication protocol used for communication via the CAN bus 10. The first ECU 11 corresponds to an upper switching node described in the claims.

  Specifically, the first ECU 11 issues a switching instruction for switching the communication protocol used for communication via the CAN bus 10 from the low speed protocol to the high speed protocol, and a return instruction for switching from the high speed protocol to the low speed protocol.

  Regarding the switching instruction, the first ECU 11 transmits a switching frame for instructing the switching to the second ECU 12 and the third ECU 13 according to the switching timing. Accordingly, the second ECU 12 and the third ECU 13 that have received the switching frame grasp the switching instruction. And 1st ECU11 and 2ECU12 communicate by a high-speed protocol. At this time, the third ECU 13 does not perform communication.

  Further, the first ECU 11 issues a return instruction by transmitting a return timing frame indicating the return timing to the second ECU 12 and the third ECU 13 when transmitting the switching frame. Thereby, 2nd ECU12 and 3ECU13 grasp | ascertain return timing. Thereafter, the first ECU 11, the second ECU 12, and the third ECU 13 detect that the return timing has been reached, thereby determining that the return condition is satisfied, and perform communication using the low-speed protocol.

  ECU11-13 can be mounted in a vehicle, for example. In this case, the ECUs 11 to 13 communicate via the CAN bus 10 to exchange necessary data or perform control in cooperation.

  The vehicle is provided with various ECUs such as a motor ECU, an engine ECU, and a power supply ECU. Motor ECUs and engine ECUs are required to be controlled at high speed. Therefore, it is preferable to apply the first ECU 11 or the second ECU 12 that can communicate with the high-speed protocol.

  On the other hand, the power supply ECU or the like is not required to be controlled as fast as the motor ECU or the engine ECU. Therefore, it is preferable to apply 3rd ECU13 which can communicate by a low-speed protocol.

  As the CAN bus 10, a two-wire communication line is used. The plurality of ECUs 11 to 13 transmit a signal of “1” or “0” on the CAN bus 10 by generating two kinds of large and small potential differences in the two-wire communication line when transmitting data. In the CAN protocol, logic 0 is defined as a dominant level that causes a large potential difference in the two-wire communication line. On the other hand, logic 1 is defined as a recessive level that causes a small potential difference in the two-wire communication line. In addition, when a dominant level and a recessive level are simultaneously transmitted from a plurality of communication nodes, the dominant level has priority.

  Next, the first ECU 11, the second ECU 12, and the third ECU 13 will be described in detail.

  As shown in FIG. 2, the first ECU 11 includes a microcomputer 20 and a transceiver 30. The microcomputer 20 generates transmission data and processes received data. The microcomputer 20 corresponds to a control unit described in the claims. The transceiver 30 includes a receiver 31 and a transmitter 32. The receiver 31 transmits data transmitted on the CAN bus 10 to the microcomputer 20 as received data. The transmitter 32 transmits the transmission data of the microcomputer 20 onto the CAN bus 10 as a communication frame.

  The microcomputer 20 is a normal microcomputer having a processing unit that executes a program and a storage unit that stores a program and stores an execution result of the processing unit. Further, the microcomputer 20 includes a CAN controller 21 that performs processing of received data received from the transceiver 30 and processing of transmitting transmission data to the transceiver 30. Although not shown, the CAN controller 21 has a message buffer including a transmission buffer that stores transmission data and a reception buffer that stores reception data.

  Furthermore, the microcomputer 20 includes, as a functional block, a switching instruction unit 22 that instructs the transceiver 30 and the other ECUs 12 and 13 to switch the communication protocol used for communication via the CAN bus 10 to the low speed protocol or the high speed protocol. Have. This switching instruction | indication part 22 is corresponded to the switching instruction | indication means as described in a claim.

  The CAN controller 21 is electrically connected to the receiver 31 and data on the CAN bus 10 is input from the receiver 31 as received data. Specifically, the CAN controller 21 includes a reception unit 21a that stores input reception data in a reception buffer of a message buffer as a functional block. The receiving unit 21a is electrically connected to the receiver 31, and data on the CAN bus 10 is input from the receiver 31 as received data.

  Further, the CAN controller 21 includes a transmission unit 21 b that transmits transmission data stored in the transmission buffer of the message buffer to the transceiver 30 as a functional block. Generation of transmission data and storage of the data are performed by the processing unit of the microcomputer 20. Specifically, the CAN controller 21 is electrically connected to the transmitter 32 of the transceiver 30, and the transmission unit 21 b transmits the transmission data stored in the transmission buffer to the transmitter 32.

  The CAN controller 21 supports both a high-speed protocol and a low-speed protocol as communication protocols.

  The switching instruction unit 22 has a function of scheduling a switching timing for switching a communication protocol used for communication via the CAN bus 10 from a low-speed protocol to a high-speed protocol and a return timing for switching from the high-speed protocol to the low-speed protocol.

  The switching instruction unit 22 issues a switching instruction based on the scheduled switching timing. Specifically, the switching instruction unit 22 stores the switching frame in the transmission buffer as transmission data when performing the switching instruction. At this time, the switching instruction unit 22 also stores the return timing frame in the transmission buffer as transmission data.

  Further, the switching instruction unit 22 is electrically connected to the receiver 31 and the transmitter 32. The switching instruction unit 22 issues a switching instruction to the receiver 31 and the transmitter 32 when performing the switching instruction.

  The switching instruction unit 22 has a function of detecting that the scheduled return timing has been reached. When detecting the return timing, the switching instruction unit 22 determines that the return condition is satisfied, and issues a return instruction to the receiver 31 and the transmitter 32 of the transceiver 30.

  The transceiver 30 is electrically connected to the CAN bus 10. The receiver 31 of the transceiver 30 transmits the data on the CAN bus 10 to the CAN controller 21 of the microcomputer 20 as received data. The transmitter 32 sends the transmission data transmitted from the CAN controller 21 to the CAN bus 10 as a communication frame.

  The receiver 31 and the transmitter 32 support both a high-speed protocol and a low-speed protocol as communication protocols. The receiver 31 and the transmitter 32 switch the communication protocol based on a switching instruction from the switching instruction unit 22.

  Next, the second ECU 12 will be described. As shown in FIG. 3, the second ECU 12 includes a microcomputer 40 and a transceiver 50. Similar to the transceiver 30 described above, the transceiver 50 includes a receiver 51 and a transmitter 52.

  Similar to the microcomputer 20 described above, the microcomputer 40 is a normal microcomputer having a processing unit and a storage unit. The microcomputer 40 includes a CAN controller 41 as with the microcomputer 20 described above. Similar to the CAN controller 21 described above, the CAN controller 41 includes a reception unit 41a, a transmission unit 41b, and a message buffer (not shown). The message buffer has a reception buffer and a transmission buffer.

  The microcomputer 40 further includes a switching determination unit 42 that determines switching of the communication protocol based on the switching frame and the return timing frame sent to the CAN bus 10 by the first ECU 11.

  Specifically, the switching frame and the return timing frame sent out on the CAN bus 10 are transmitted to the CAN controller 41 via the transceiver 50. The receiving unit 41a of the CAN controller 41 stores the switching frame and return timing frame transmitted to the CAN controller 41 in the reception buffer. When the switching determination unit 42 detects that the switching frame is stored in the reception buffer, the switching determination unit 42 instructs a later-described receiver 51 and transmitter 52 of the transceiver 50 to switch the communication protocol from the low-speed protocol to the high-speed protocol. In addition, when the switching determination unit 42 detects that the return timing indicated by the return timing frame stored in the reception buffer is reached, the switch determination unit 42 determines that the return condition has been satisfied, and determines the receiver 51 and the transmitter 52 of the transceiver 50. And a return instruction for switching the communication protocol from the high-speed protocol to the low-speed protocol.

  Similar to the transceiver 30 described above, the transceiver 50 is electrically connected to the CAN bus 10 and includes a receiver 51 and a transmitter 52. The receiver 51 and the transmitter 52 correspond to both a high-speed protocol and a low-speed protocol as communication protocols. The receiver 51 and the transmitter 52 perform switching of the communication protocol based on a switching instruction from the switching determination unit 42.

  Next, the third ECU 13 that is a feature of the present invention will be described with reference to FIG. Similar to the first ECU 11 and the second ECU 12, the third ECU 13 includes a microcomputer 60 and a transceiver 70.

  The microcomputer 60 is electrically connected to the CAN bus 10 via the transceiver 70. The transceiver 70 transmits data on the CAN bus 10 to the microcomputer 60 as received data. At this time, the reception data is transmitted via a reception line 91 that electrically connects the microcomputer 60 and the transceiver 70.

  In addition, the transceiver 70 sends the transmission data transmitted from the microcomputer 60 onto the CAN bus 10 as a communication frame. Transmission of transmission data from the microcomputer 60 to the transceiver 70 is performed via a transmission line 92 that electrically connects the microcomputer 60 and the transceiver 70.

  Further, the third ECU 13 includes a holding circuit 80 in the receiving line 91 for holding the signal of the receiving line 91 as a recessive level signal. The holding circuit 80 corresponds to alternative output means described in the claims.

  Similar to the microcomputers 20 and 40, the microcomputer 60 is a normal microcomputer having a processing unit and a storage unit. Similar to the microcomputers 20 and 40, the microcomputer 60 includes a CAN controller 61. Similar to the CAN controllers 21 and 41, the CAN controller 61 includes a reception unit 62, a transmission unit 63, and a message buffer (not shown). The message buffer has a reception buffer and a transmission buffer.

  The CAN controller 61 further includes an error counter 64 that counts errors in received data. The CAN controller 61 includes, as functional blocks, an error frame generation unit 65 that generates an error frame, and a transmission stop unit 66 that instructs to stop transmission processing of transmission data stored in the transmission buffer.

  The reception unit 62 stores the reception data input from the transceiver 70 via the reception line 91 in the reception buffer. The receiving unit 62 has a function of detecting an error in received data. When an error is detected, the receiving unit 62 instructs the error counter 64 to add a count value.

  The error counter 64 adds the count value based on the instruction from the receiving unit 62. At this time, if the count value does not reach the predetermined threshold, the error counter 64 instructs the error frame generation unit 65 to generate an active error frame indicating an active error. On the other hand, when the count value reaches a predetermined threshold, the error frame generation unit 65 is instructed to generate a passive error frame indicating a passive error.

  The error frame generation unit 65 generates an active error frame or a passive error frame based on an instruction from the error counter 64, and stores it in the transmission buffer as transmission data.

  The transmission unit 63 has a function of transmitting the transmission data stored in the transmission buffer to the transceiver 30 via the transmission line 92. Transmission data is generated and stored in the transmission buffer by the error frame generation unit 65 and the processing unit of the microcomputer 60.

  The transmission stop unit 66 is a functional block that instructs the transmission unit 63 to stop and release the transmission processing of the transmission data stored in the transmission buffer. The transmission stop unit 66 gives an instruction to stop transmission processing when the switching frame is received, that is, when the communication protocol of the CAN bus 10 is switched from the low-speed protocol to the high-speed protocol not supported by the third ECU 13. The determination of switching frame reception is performed based on a switching frame reception instruction from the switching frame reception detection unit 67. Thereby, after the communication protocol of the CAN bus 10 is switched to the high-speed protocol, it is possible to prevent the third ECU 13 from transmitting a communication frame based on the low-speed protocol and hindering communication.

  Further, the transmission stop unit 66 issues a stop cancellation instruction for transmission processing when the communication protocol of the CAN bus 10 is switched from the high-speed protocol to the low-speed protocol. The transmission stop unit 66 recognizes the switching of the communication protocol based on a return instruction from the detection unit 69 described later. The transmission stop unit 66 corresponds to a stop unit described in the claims.

  In addition to the CAN controller 61, the microcomputer 60 further includes, as functional blocks, a switching frame reception detection unit 67, a holding instruction unit 68 that instructs the holding circuit 80, and a detection unit that detects that a return condition has been established. 69. The switching frame reception detection unit 67 has a function of detecting whether a switching frame is stored in the reception buffer of the CAN controller 61.

  When the switching frame reception detection unit 67 detects that the switching frame is stored in the reception buffer, the switching frame reception detection unit 67 generates a switching frame reception instruction indicating that the switching frame has been received, a transmission stop unit 66, a holding instruction unit 68, and a detection. To the unit 69.

  The holding instruction unit 68 gives the holding circuit 80 a holding instruction that is an instruction to hold the signal of the reception line 91 as a recessive level signal, and a holding release instruction that is a release instruction thereof. When the holding instruction unit 68 receives a switching frame reception instruction from the switching frame reception detection unit 67, the holding instruction unit 68 outputs a holding instruction. On the other hand, when a return instruction is received from the detection unit 69, a holding release instruction is output.

  The detection unit 69 has a timer 69a that measures an elapsed time from the switching frame reception time, and based on this elapsed time, a condition for switching the communication protocol used for the CAN bus 10 from the high-speed protocol to the low-speed protocol, That is, it is detected that the return condition is satisfied.

  Specifically, the detection unit 69 sets a return threshold based on the timing indicated by the return timing frame. When the detection unit 69 receives a switching frame reception instruction from the switching frame reception detection unit 67, the timer 69a starts counting to measure time. When detecting that the count value of the timer 69a has reached the return threshold, the detection unit 69 determines that the return timing indicated by the return timing frame has passed, that is, the return condition is satisfied. Then, the detection unit 69 outputs a return instruction indicating that the return condition is satisfied to the holding instruction unit 68 and the transmission stop unit 66. The detection unit 69 corresponds to the detection means described in the claims.

  In the present embodiment, the return threshold is set based on the return timing frame, but the present invention is not limited to this. For example, when it is not necessary to dynamically change the return timing, such as when the return timing is determined in advance between the ECUs 11 to 13, the return threshold may be set to a fixed value set in advance. By doing so, it is not necessary to transmit the return timing frame, and the bus load factor can be reduced.

  Next, the transceiver 70 includes a receiver 71 and a transmitter 72 as with the transceivers 30 and 50 described above, and supports a low-speed protocol as a communication protocol, but does not support a high-speed protocol. The transceiver 70 is electrically connected to the CAN bus 10.

  The receiver 71 of the transceiver 70 transmits data on the CAN bus 10 as reception data to the CAN controller 61 of the microcomputer 60 via the reception line 91. The transmitter 72 sends the transmission data transmitted from the CAN controller 61 via the transmission line 92 to the CAN bus 10 as a communication frame.

  Next, the holding circuit 80 is provided on a reception line 91 that transmits reception data from the transceiver 70 to the microcomputer 60. The holding circuit 80 is provided so that reception data is input from the transceiver 70. The holding circuit 80 is provided to receive a holding instruction and a holding release instruction from the holding instruction unit 68. The holding circuit 80 transitions between two states, a holding state and a holding release state. The holding circuit 80 outputs a recessive level signal to the microcomputer 60 regardless of the data received from the transceiver 70 in the holding state. On the other hand, the holding circuit 80 outputs the received data from the transceiver 70 to the microcomputer 60 as it is in the holding release state. The holding circuit 80 enters a holding state when receiving a holding instruction, and enters a holding releasing state when receiving a holding release instruction. The holding circuit 80 is normally in a holding release state. As the holding circuit 80, for example, a logic circuit such as an OR circuit is applied.

  As a result, even if reception data according to the high-speed protocol is input to the receiver 71, the reception data is first output to the holding circuit 80. At this time, prior to performing communication according to the high-speed protocol, the switching frame reception detection unit 67 has already detected reception of the switching frame and has output a switching frame reception instruction to the holding instruction unit 68. Receiving the switching frame reception instruction, the holding instruction unit 68 outputs a holding instruction to the holding circuit 80.

  Therefore, the holding circuit 80 outputs a recessive level signal to the microcomputer 60 regardless of the received data according to the high-speed protocol input from the receiver 71. Therefore, since the reception data according to the high-speed protocol is not input to the microcomputer 60, when the microcomputer 60 receives the reception data according to the high-speed protocol, it is not detected that there is an error in the reception data.

  Next, the operation of the communication system 100 will be described.

  First, an outline of communication performed in the communication system 100 will be described.

  The ECUs 11 to 13 communicate with each other via the CAN bus 10 according to a high-speed protocol or a low-speed protocol.

  A protocol used for communication via the CAN bus 10 is specified by an instruction from the first ECU 11. Specifically, the first ECU 11 transmits a switching frame for instructing to switch the communication protocol from the low-speed protocol to the high-speed protocol to the second ECU 12 and the third ECU 13. At this time, the first ECU 11 also transmits a return timing frame indicating the return timing to the second ECU 12 and the third ECU 13. As a result, a communication protocol to be used for communication via the CAN bus 10 is specified.

  Next, operations of the first ECU 11 and the third ECU 13 when the communication protocol used on the CAN bus 10 is switched will be described with reference to FIGS.

  The first ECU 11 and the third ECU 13 communicate using a low-speed protocol as a communication protocol (S101, S201). At this time, the second ECU 12 also performs communication using a low-speed protocol as a communication protocol. Therefore, a communication frame according to the low speed protocol is transmitted on the CAN bus 10.

  At this time, the transceiver 70 of the third ECU 13 receives the communication frame. The receiver 71 of the transceiver 70 outputs a signal indicating a dominant level or a recessive level to the holding circuit 80 via the reception line 91 according to the communication frame.

  At this time, the first ECU 11 has not yet transmitted a switching frame. For this reason, the switching frame reception detection unit 67 does not detect reception of the switching frame. Therefore, the switching frame reception detection unit 67 does not output a switching frame reception instruction to the holding instruction unit 68. Therefore, the holding instruction unit 68 outputs a holding release instruction to the holding circuit 80. Therefore, the holding circuit 80 is in the holding release state, and outputs the input signal indicating the dominant level or recessive level to the receiving unit 62 of the microcomputer 60 via the receiving line 91 as it is. As a result, the receiving unit 62 of the microcomputer 60 acquires data indicated by the communication frame transmitted on the CAN bus 10.

  Through these processes, the receiver 71 receives the communication frame transmitted on the CAN bus 10 as shown at time t0 in FIG. The receiver 71 outputs the received data corresponding to the received communication frame to the receiving unit 62 of the microcomputer 60 via the holding circuit 80 that is in the holding release state.

  Next, the first ECU 11 sends out a switching frame for instructing switching on the CAN bus 10 (S102). The third ECU 13 receives the switching frame via the CAN bus 10 (S202). At this time, the second ECU 12 also receives the switching frame via the CAN bus 10.

  The third ECU 13 detects that the switching frame has been received by the switching frame reception detection unit 67 of the microcomputer 60. Then, the switching frame reception detection unit 67 outputs a switching frame reception instruction indicating that the switching frame has been received, to the transmission stop unit 66, the holding instruction unit 68, and the detection unit 69. .

  The detection unit 69 to which the switching frame reception instruction is input starts time measurement by the timer 69a (S203). At this time, the detection unit 69 sets a return threshold based on the return timing frame transmitted from the first ECU 11 to the third ECU 13. Thereby, the return timing can be detected by detecting that the count value of the timer 69a has reached the return threshold.

  In addition, the holding instruction unit 68 to which the switching frame reception instruction is input outputs the holding instruction to the holding circuit 80 (S204).

  In addition, the transmission stop unit 66 to which the switching frame reception instruction is input instructs the transmission unit 63 to stop the transmission process of the transmission data stored in the transmission buffer (S205).

  By the above step 203, the timer 69a starts counting as shown at time t1 in FIG.

  In step 204, the holding circuit 80 enters the holding state and continues to output a signal indicating the recessive level to the receiving unit 62 of the microcomputer 60 as shown at time t1 in FIG. Therefore, even if a communication frame according to the high-speed protocol is transmitted on the CAN bus 10 after the third ECU 13 receives the switching frame, a signal corresponding to the communication frame is not input to the microcomputer 60. Therefore, when the signal corresponding to the communication frame according to the high-speed protocol is input to the microcomputer 60, the microcomputer 60 is prevented from recognizing that an error has occurred in the received data.

  Further, the step 205 prevents the third ECU 13 from performing communication using the low-speed protocol after receiving the switching frame. In other words, after the third ECU 13 receives the switching frame, when communication according to the high-speed protocol is performed on the CAN bus 10, the communication frame according to the low-speed protocol is transmitted, thereby hindering communication. Can be prevented. In the first embodiment, the process of step 205 is performed, but the present invention is not limited to this, and this process may not be performed. However, in order to prevent communication obstruction, it is preferable to perform the process of step 205.

  Further, when the process of step 205 is not performed, the third ECU 13 surely completes transmission of all transmission data remaining in its own transmission buffer before the first ECU 11 or the second ECU 12 starts communication using the high-speed protocol. Must be. In order to complete transmission of all the remaining transmission data, a waiting time including a certain margin is required. That is, the first ECU 11 and the second ECU 12 need to wait for this waiting time before starting communication using the high-speed protocol. However, according to the present embodiment, by performing the process of step 205, it is possible to prevent the occurrence of an error even if the waiting time is reduced, and it is possible to save the bus load factor.

  On the other hand, after sending the switching frame (S102), the first ECU 11 switches the communication protocol used for communication to the high-speed protocol (S103), and starts communication according to the high-speed protocol (S104). Further, after receiving the switching frame, the second ECU 12 switches the communication protocol used for communication to the high speed protocol and starts communication according to the high speed protocol.

  As a result, a communication frame according to the high-speed protocol is transmitted to the CAN bus 10. The receiver 71 of the third ECU 13 receives this communication frame, but since this communication frame conforms to a high-speed protocol that does not correspond to itself, the receiver 71 cannot output a correct signal corresponding to the communication frame to the holding circuit 80. . That is, the receiver 71 outputs a non-corresponding signal that does not correspond to the communication frame. However, since the holding circuit 80 is in the holding state at this time, the signal indicating the recessive level is output to the receiving unit 62 regardless of the input non-corresponding signal. Therefore, the non-corresponding signal is not input to the receiving unit 62. Therefore, the non-corresponding signal is input to the receiving unit 62, thereby preventing the receiving unit 62 from detecting the occurrence of an error.

  By these processes, the output signal of the receiver 71 becomes a non-corresponding signal as after the time t1 shown in FIG. Since the holding circuit 80 is in the holding state, the holding circuit 80 outputs a signal indicating a recessive level to the receiving unit 62 regardless of the input non-corresponding signal.

  Next, it is the return timing when the communication protocol used for communication via the CAN bus 10 is switched from the high-speed protocol to the low-speed protocol, and the first ECU 11 and the second ECU 12 have reached the return timing, that is, the return condition is satisfied. Is detected (S105). Accordingly, the first ECU 11 and the second ECU 12 switch the communication protocol from the high speed protocol to the low speed protocol (S106). Thereby, 1st ECU11 will be in the state which communicates by a low-speed protocol. And it changes to step S101.

  At this time, the third ECU 13 detects that the return condition for changing the communication protocol from the high-speed protocol to the low-speed protocol is established based on the fact that the count value of the timer 69a has reached the return threshold value (S206).

  When detecting that the condition is satisfied, the detection unit 69 outputs a return instruction to that effect to the holding instruction unit 68 and the transmission stop unit 66. Receiving the return instruction, the holding instruction unit 68 outputs a holding release instruction to the holding circuit 80 (S207). Receiving this, the holding circuit 80 enters a holding release state, and outputs the received data input from the receiver 71 to the receiving unit 62 of the microcomputer 60 as it is. Therefore, the receiving unit 62 can receive data transmitted as a communication frame on the CAN bus 10 as received data.

  Also, the transmission stop unit 66 that has received the return instruction instructs the transmission unit 63 to cancel the stop of the transmission process (S208). As a result, the transmission unit 63 resumes the transmission process.

  Through the above steps S207 and S208, the third ECU 13 can resume communication using the low-speed protocol. And it changes to step S201.

  Through these processes, the detection unit 69 of the third ECU 13 detects that the return condition is satisfied based on the count value of the timer 69a reaching the return threshold, as shown at time t2 in FIG. Is output to the holding instruction unit 68. Receiving this, the holding instruction unit 68 outputs a holding release instruction to the holding circuit 80. Accordingly, the holding circuit 80 that has received this enters a holding release state, and outputs the received data input from the receiver 71 to the receiving unit 62 of the microcomputer 60 as it is. Therefore, the reception data output from the receiver 71 is input to the reception unit 62 of the microcomputer 60.

  Then, after the time point t2, the first ECU 11, the second ECU 12, and the third ECU 13 communicate with each other by a low-speed protocol, similarly to the time point t0.

  In the above, steps S101 to S106 and steps S201 to S208, which are a series of processes executed by the first ECU 11 and the third ECU 13 respectively, have been described. The first ECU 11 and the third ECU 13 repeatedly execute steps S101 to S106 and steps S201 to S208, respectively.

  Next, effects of the communication system 100 according to the present embodiment will be described.

  According to this communication system 100, the error frame generation unit 65 is an active error indicating an active error when the reception unit 62 detects an error in received data and the count value of the error counter does not reach a predetermined threshold value. A frame is generated as transmission data. This active error frame is transmitted by the transmission unit 63. On the other hand, when the count value of the error counter reaches a predetermined threshold, a passive error frame indicating a passive error is generated as transmission data. The active error frame and the passive error frame generated as transmission data are transmitted by the transmission unit 63. Therefore, when the receiving unit 62 detects an error in the received data, if the count value of the error counter has not reached the predetermined threshold, an active error frame is transmitted. On the other hand, when the count value of the error counter reaches a predetermined threshold value, a passive error frame is transmitted. Therefore, the present invention complies with the standard of ISO11898-1.

  Furthermore, in the present invention, when the first ECU 11 switches the communication protocol used for communication via the CAN bus 10 from the low-speed protocol to the high-speed protocol, the switching instruction unit 22 included in the first ECU 11 generates a switching frame as transmission data. . This switching frame is sent to the CAN bus 10 by the transmitter 32 of the transceiver 30.

  The receiver 71 of the transceiver 70 of the third ECU 13 receives this switching frame and outputs it to the receiving unit 21 a of the third ECU 13. When the reception unit 21a of the lower node receives the switching frame, the switching frame reception detection unit 67 detects reception of the switching frame. The switching frame reception detection unit 67 that has detected the reception of the switching frame outputs a signal indicating that the reception of the switching frame has been detected to the holding instruction unit 68. Receiving this signal, the holding instruction unit 68 outputs a holding instruction to the holding circuit 80. Receiving the holding instruction, the holding circuit 80 enters the holding state, and outputs a recessive level signal to the receiving unit 62 as a signal indicating that there is no received data, instead of an output signal of the receiver 71 input to itself. Keep doing. That is, the output signal of the receiver 71 is not input to the receiving unit 62.

  As a result, as in the conventional configuration, when the communication protocol is switched from the low-speed protocol to the high-speed protocol, the reception unit 62 receives the reception data according to the high-speed protocol, and the reception data cannot be correctly recognized. It will not be detected if there is an error. Therefore, the error frame generation unit 65 does not generate an error frame as transmission data. Therefore, it is suppressed that communication is inhibited by transmission of the error frame by the third ECU 13.

  As another method for suppressing the error frame generation by the error frame generation unit 65 when the communication protocol is switched from the low-speed protocol to the high-speed protocol, a method of stopping the transmission / reception function of the CAN controller is also conceivable. However, when the transmission / reception function of the CAN controller is stopped, the processing unit of the microcomputer 60 is restricted from accessing the message buffer, and the processing load increases due to the addition of the countermeasure processing.

  For example, when access to the message buffer is stopped, the processing unit cannot store data to be transmitted in the transmission buffer of the message buffer. In this case, the processing unit must grasp the timing at which access to the message buffer is resumed, and store the transmission data in the transmission buffer at the timing at which it is resumed. Therefore, the processing load of the microcomputer 60 increases.

  However, according to the communication system 100, since the transmission / reception function of the CAN controller is not stopped, the processing load does not increase as in the prior art.

  Further, the third ECU 13 can detect the return timing at which the communication protocol used for communication via the CAN bus 10 is switched from the high-speed protocol to the low-speed protocol by the detection unit 69. Therefore, the third ECU 13 can resume communication with the low-speed protocol immediately after the return timing.

  The detecting unit 69 detects the return timing by the timer 69a. Therefore, the return timing detection can be implemented simply.

  In the communication system 100, communication of different communication protocols is performed by using the same communication line in a time-sharing manner. Therefore, there is no need to provide a communication line for each communication of a different communication protocol. Thereby, it is possible to reduce the cost by reducing the number of vehicle harnesses and the number of terminals of the ECU connector.

(Second Embodiment)
Next, a communication system 200 according to the second embodiment of the present invention will be described. Since the communication system 200 according to the second embodiment is often in common with that according to the first embodiment, a detailed description of the common parts will be omitted below, and different parts will be mainly described. In addition, the same code | symbol is provided to the element same as the element shown in 1st Embodiment.

  A configuration of the communication system 200 according to the second embodiment will be described.

  In the communication system 200, the configurations of the first ECU 11 and the second ECU 12 are the same as those in the first embodiment. The configuration of the third ECU 213 is different from the third ECU 13 of the first embodiment.

  The third ECU 213 has the configuration shown in FIG. Unlike the third ECU 13 of the first embodiment, the third ECU 213 does not include a detection unit 69 that outputs a return instruction. Instead, the third ECU 213 includes a return frame reception detection unit 73 in the transceiver 70 as a functional block. The return frame reception detection unit 73 outputs a return instruction.

  In the communication system 200 according to the second embodiment, when the first ECU 11 switches the communication protocol used for communication via the CAN bus 10 from the high-speed protocol to the low-speed protocol, the first ECU 11 places a return frame for instructing the return on the CAN bus 10. Transmit according to low-speed protocol. The return frame is received by the receiver 71 of the third ECU 213. The return frame reception detection unit 73 detects reception of the return frame by the receiver 71.

  Specifically, the return frame reception detection unit 73 is connected to the reception line 91 through which the output signal of the receiver 71 is transmitted, and receives the output signal of the receiver 71. The return frame reception detection unit 73 detects that the receiver 71 has received the return frame based on the output signal of the receiver 71. When the return frame reception detection unit 73 detects reception of the return frame, the return frame reception detection unit 73 outputs a return instruction to the transmission stop unit 66 and the holding instruction unit 68, assuming that the return condition is satisfied. The third ECU 213 is provided with a serial communication path for outputting a return instruction, and the microcomputer 60 and the transceiver 70 are connected by a serial communication path. The output of the return instruction is performed via this serial communication path. Accordingly, in the third ECU 213, the return instruction is output by the return frame reception detection unit 73. The return frame reception detection unit 73 can be mounted as long as it is a CAN transceiver compatible with a partial net, for example.

  Next, the operation of the communication system 200 according to the second embodiment will be described.

  The communication system 200 differs from the first embodiment in operations of the first ECU 11 and the third ECU 213 when the communication protocol is switched from the high-speed protocol to the low-speed protocol. This different operation will be mainly described.

  Based on FIG. 9, FIG. 10, the process performed in 1st ECU11 and 3ECU213 when a communication protocol switches from a high-speed protocol to a low-speed protocol is demonstrated. The first ECU 11 performs S301 shown in FIG. 9 after performing S101 to S104 in the first embodiment. The third ECU 13 performs S401 shown in FIG. 10 after performing S201 to S205 in the first embodiment.

  First, when the communication protocol used for communication via the CAN bus 10 is switched from the high-speed protocol to the low-speed protocol, the first ECU 11 transmits a first return frame for instructing the switching to the CAN bus 10 according to the high-speed protocol (S301). ). As a result, the second ECU 12 receives the first return frame and switches the communication protocol to be used from the high-speed protocol to the low-speed protocol. At this time, since the transceiver 70 of the third ECU 213 is not compatible with the high-speed protocol, a non-compatible signal is output. Therefore, the return frame reception detection unit 73 cannot detect reception of the first return frame.

  Then, the first ECU 11 switches the communication protocol used by itself from the high-speed protocol to the low-speed protocol (S302).

  By the above steps S301 and S302, the first ECU 11 and the second ECU 12 are in a state of using the low speed protocol as the communication protocol.

  Next, the first ECU 11 transmits a second return frame for instructing switching on the CAN bus 10 according to the low-speed protocol (S303). Thus, the receiver 71 of the third ECU 213 receives the second return frame and outputs a signal corresponding to the second return frame to the reception line 91. The return frame reception detection unit 73 receives a signal corresponding to the second return frame via the reception line 91, and detects reception of the second return frame (S401). The return frame reception detection unit 73 that has detected the reception outputs a return instruction to the transmission stop unit 66 and the holding instruction unit 68 (S402). Then, the third ECU 213 transitions to step S207 in FIG.

  With these processes, the first ECU 11 and the third ECU 213 switch the communication protocol used for communication via the CAN bus 10 from the high-speed protocol to the low-speed protocol.

  The subsequent processes of the first ECU 11 and the third ECU 213 are the same as in the first embodiment. After executing step S303, the higher order instruction node 13 executes steps S101 to S104. Then, steps S301 to S303 are executed. The first ECU 11 repeats this.

  The third ECU 213 executes steps S207 to S208 after executing step S402. Thereafter, steps S201 to S205 are executed, and steps S401 to S402 are executed. The third ECU 213 repeats this.

  Next, effects of the communication system 200 according to the second embodiment will be described.

  According to this communication system 200, the first ECU 11 instructs the third ECU 213 to return to the second ECU 213 in accordance with the switching timing at which the communication protocol used for communication via the CAN bus 10 is switched from the high-speed protocol to the low-speed protocol. Send a return frame. Therefore, the first ECU 11 does not need to determine the return timing when transmitting the switching frame. Therefore, the first ECU 11 can determine the return timing for switching the communication protocol from the high-speed protocol to the low-speed protocol after transmitting the switch frame, and can transmit the second return frame according to the determined return timing. Therefore, the first ECU 11 can freely set the return timing.

(Other embodiments)
The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  In the first embodiment, the holding circuit 80 is provided separately from the microcomputer 60, but the present invention is not limited to this and may be built in the microcomputer 60.

  In the first embodiment, each of the first ECU 11, the second ECU 12, and the third ECU 13 is one. However, the present invention is not limited to this, and a plurality of ECUs may be provided.

  In the second embodiment, similarly to the first embodiment, the switching frame reception detection unit 67 detects reception of the switching frame and outputs a switching frame reception instruction to the transmission stop unit 66 and the holding instruction unit 68. It was. However, the present invention is not limited to this, and the return frame reception detection unit 73 detects the reception of the switching frame based on the reception data input from the receiver 71, and holds the switching frame reception instruction and the transmission stop unit 66. You may output to the instruction | indication part 68. FIG.

10 ... CAN bus 11 ... 1st ECU
12 ... 2nd ECU
13 ... 3rd ECU
20 ... microcomputer 22 ... switching instruction unit 30 ... transceiver 31 ... receiver 32 ... transmitter 40 ... microcomputer 50 ... transceiver 51 ... receiver 52 ... transmitter 60 ... · Microcomputer 64 ··· Error counter 65 · · · Error frame generator 66 · · · Transmission stop unit 69 · · · Detection unit 69a · · · Timer 70 · · · Transceiver 71 · · · Receiver 72 · · · Transmitter 73 ... Return frame reception detector 80 ... Holding circuit 100 ... Communication system 200 ... Communication system

Claims (7)

CAN bus (10),
A communication system comprising at least three communication nodes (11, 12, 13) connected to each other via the CAN bus,
Each communication node generates transmission data and processes the reception data, (20, 40, 60),
The transmission data generated by the control unit is input, and the transmission data is sent as a communication frame to the CAN bus (32, 52, 72) and sent from the other communication node as the communication frame. A transceiver (30, 50, 70) having a receiver (31, 51, 71) that receives data and outputs the received data as the received data to the control unit;
The control unit includes an error frame generation unit (65) that generates an error frame indicating an active error as transmission data when the reception data input from the transceiver is an error,
The three communication nodes include two upper nodes (11, 12) and one lower node (13).
The upper node corresponds to the first communication method and the second communication method as the communication method used for communication via the CAN bus, and can communicate by the first communication method and the second communication method.
The lower node corresponds to the first communication method, but does not correspond to the second communication method, and communication by the first communication method is possible.
Of the two upper nodes, at least one upper node (11) is an upper switching node,
The control unit of the upper switching node has a switching frame for instructing the other communication nodes connected to the CAN bus to switch the communication method from the first communication method to the second communication method. Switching instruction means (22) for generating the transmission data is provided, and in the lower node, instead of the transceiver outputting the reception data to the control unit, a signal indicating that the reception data is not present, Alternative output means (80) is provided for executing and stopping execution of an alternative output for outputting a recessive level signal to the control unit,
The alternative output means has stopped the execution of the alternative output when the control unit of the lower node has not received the switching frame, and the control unit of the lower node has received the switching frame A communication system, wherein said alternative output is executed.   The alternative output means is provided in a path through which the transceiver of the lower node outputs the received data to the control unit, and the alternative output means is input from the transceiver when the alternative output is stopped. 2. The reception data is output to the control unit, and a recessive level signal is output to the control unit regardless of the reception data input from the transceiver when the substitute output is executed. The communication system according to 1. The lower node has detection means (69, 73) for detecting that a return condition for switching the communication method from the second communication method to the first communication method is satisfied,
3. The communication system according to claim 1, wherein the alternative output unit stops the execution of the alternative output based on the fact that the detection unit detects that the return condition is satisfied. 4. The control unit of the lower-level node has stop means (66) for executing and canceling the transmission stop that stops outputting the generated transmission data to the transceiver,
The stop means stops transmission when the control unit of the lower node receives the switching frame, and then stops the transmission when the detecting means detects that the return condition is satisfied. The communication system according to claim 3, wherein the communication system is released. The detection means (69) has a timer (69a) that measures an elapsed time from the reception timing of the switching frame when the control unit of the lower node receives the switching frame;
The communication system according to claim 3 or 4, wherein the detection unit detects that the return condition is satisfied based on the elapsed time. The switching instruction means generates a return frame that instructs to switch the communication method from the second communication method to the first communication method as transmission data after generating the switching frame as the transmission data,
The communication system according to claim 3 or 4, wherein when the transceiver receives the return frame, the detection means (73) detects that the return condition is satisfied based on the reception.   The communication system according to any one of claims 1 to 6, wherein the second communication method is a communication method having a higher communication speed than the first communication method.

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