COMMUNICATION FACILITY

Abstract

Communication device (5, 5b) that can be connected to a communication network (7) with a pair of signal lines (71, 72) for transmitting a difference signal, wherein the communication device (5, 5b) comprises: a first transmission part (51) configured to transmit the difference signal to the communication network (7) in accordance with a transmission signal expressed in two values ​​by switching a state of the communication network (7) between a controlled state for supplying power to the communication network (7) and an uncontrolled state for switching off a power supply to the communication network (7) in accordance with the transmission signal, wherein time spans of the controlled state and the uncontrolled state of the first transmission part (51) are assumed to be a dominant time span and a recessive time span, respectively; a second transmission part (52, 52a) configured to be in an uncontrolled state during the dominant time period and in a controlled state during the recessive time period, and to deliver power to the communication network (7) such that the polarity of the difference signal in the recessive time period is opposite to that of the difference signal in the dominant time period; Current monitoring parts (522, 523, 522a, 523a, 526, 527) configured to monitor magnitudes of power supply currents of a first magnitude of a first power supply current supplied by the second transmission part (52, 52a) to a first signal line of the pair of signal lines (71, 72), and a second magnitude of a second power supply current supplied by the second transmission part (52, 52a) to a second signal line of the pair of signal lines (71, 72); and a test section (524, 525) for checking whether a signal collision exists in the communication network (7), based on monitoring results from the current monitoring sections (522, 523, 522a, 523a, 526, 527) of the first and second size, wherein the test part (524, 525) determines that the signal collision in the communication network is present if, during the recessive time period, both the first quantity is greater than a first current threshold and the second quantity is greater than a second current threshold.

Description

[0001] The invention relates to a communication device for communications of a difference signal.

[0002] In recent years, a CAN-FD protocol, developed based on the trademark CAN (Controller Area Network), has been widely used. CAN-FD (CAN with Flexible Data Rate) is a serial bus system with a flexible data rate. In the CAN-FD protocol, a frame being transmitted and received is provided with an arbitration area, which is used for bus arbitration or bus access control, and a non-arbitration area, which is used for data storage. Data transmission occurs faster in the non-decision area than in the decision area.

[0003] To suppress waveform noise in the non-decision region where high-speed communications are performed, US 2014 / 0 330 996 A1 proposes operating a driver to develop a differential voltage with a polarity opposite to that of a dominant in a communication network at the time of outputting a recessive. Since an error frame cannot be detected in the non-decision region in this case, it is proposed to detect the error frame based on a voltage level of the communication network.

[0004] In conventional CAN, however, the output impedance of a transmitter or transceiver is not standardized, i.e., not regulated. In the conventional system proposed in US 2014 / 0 330 996 A1, different potentials are generated in the event of a collision depending on the characteristics of the transmitters connected to the communication network. Consequently, it is impossible to reliably detect the error frame.

[0005] It is therefore an object of the invention to provide a communication device which is capable of stably detecting an error frame.

[0006] According to one aspect, a communication device connectable to a communication network, having a pair of signal lines for transmitting a difference signal, comprises a first transmission part, a second transmission part, power monitoring parts, and a test part. The first transmission part is configured to transmit the difference signal to the communication network according to a transmission signal expressed in two values ​​by switching a state of the communication network between a driven state for supplying power to the communication network and a non-driven state for cutting off power supply to the communication network in accordance with the transmission signal. Driven state and non-driven state periods of the first transmission part are assumed to be a dominant period and a recessive period, respectively.The second transmission part is configured to be in a non-driven state in the dominant period and in a driven state in the recessive period, and to supply power to the communication network such that a polarity of the difference signal in the recessive period is opposite to that of the difference signal in the dominant period. The current monitoring parts are configured to monitor power supply current magnitudes of a first magnitude of a first power supply current supplied by the second transmission part to a first signal line of the pair of signal lines and a second magnitude of a second power supply current supplied by the second transmission part to a second signal line of the pair of signal lines.The checking part checks whether a signal collision occurs in the communication network based on monitoring results of the current monitoring parts of the first and second quantities, wherein the checking part determines that the signal collision occurs in the communication network when both the first quantity is greater than a first current threshold and the second quantity is greater than a second current threshold in the recessive period.

[0007] According to the communication device as described above, the power supply current of the second transmission part is detected, which is also the case with other communication devices connected to the communication network. The detected power supply current is compared with a power supply current normally supplied to detect an abnormality in the detected power supply current, such as an excessive current. Since the excessive current occurs when a signal collision, i.e., an error frame, occurs in the communication network, it is possible to stably detect the error frame. Fig. 1 is a block diagram showing a configuration of a communication system according to a first embodiment; Fig. 2 is a circuit diagram showing a configuration of a transmission circuit in the first embodiment; Fig. 3A and Fig. 3B are explanatory diagrams showing equivalent circuits of a dominant driving part and a recessive driving part, respectively, in the first embodiment; Fig. 4 is a circuit diagram showing a configuration of a current monitoring circuit that monitors a power supply current to CANL in the first embodiment; Fig. 5 is a circuit diagram showing a configuration of a current monitoring circuit that monitors a power supply current to CANH in the first embodiment; Fig. 6 is a timing chart showing an operation of the transmission circuit in the first embodiment; Fig. 7 is a circuit diagram showing the other configuration of a current monitoring circuit that monitors a power supply current to CANL in a modification example of the first embodiment; Fig. 8 is a circuit diagram showing the other configuration of a current monitoring circuit that monitors a power supply current to CANH in the modification example of the first embodiment; Fig. 9 is a circuit diagram showing a configuration of a transmission circuit according to a second embodiment; Fig. 10 is a circuit diagram showing a configuration of a current monitoring circuit that monitors a power supply current to CANL in the second embodiment; Fig. 11 is a circuit diagram showing a configuration of a current monitoring circuit that monitors a power supply current to CANH in the second embodiment; and Fig. 12 is a circuit diagram showing a configuration of a transmission circuit according to a third embodiment.

[0008] A communication device will be described below with reference to embodiments shown in the drawings. [1. First Example][1-1. Configuration]

[0009] Referring to Fig. 1, a communication system is formed from a plurality of electronic control units (ECUs) 3, which are mounted or installed in a vehicle, and a communication network 7, which mutually connects the plurality of ECUs 3.

[0010] Each ECU 3 performs communications via the communication network 7 in accordance with a CAN-FD protocol to provide or acquire various information, and performs various processing based on acquired information to perform assigned functions.

[0011] A communication frame (CAN-FD frame) used in the CAN-FD protocol has an arbitration area and a non-arbitration area. A bit rate of the arbitration area is set to the same bit rate (e.g., 500 kbps) as that of conventional CAN. A bit rate of the non-decision area is selectable up to a maximum of 5 Mbps, which is higher than that of the arbitration area. Arbitration or bus access control is performed in the arbitration area when transmission signals from the multiple ECUs 3 in the communication network 7 collide. In the non-arbitration area, data of the ECU 3 that prevailed in the arbitration or access control is transmitted.In the following description, the decision region and the non-decision region are referred to as a low-speed region and a high-speed region, respectively. [1-2. Communication network]

[0012] The communication network 7 is a bus-like network formed by a pair of signal lines 71 and 72, which are provided for transmitting a differential signal from each ECU 3. The communication network 7 has termination circuits 73 and 74 at both ends to suppress signal reflection. In the following description, one and the other of the pair of signal lines 71 and 72 are referred to as the CANH and CANL lines, respectively. [1-3 ECU]

[0013] Each ECU 3 includes a control section 4 and a transceiver 5 provided as a communication device. The control section 4 mainly consists of a conventional microcomputer including a central processing unit (CPU) 41 and a semiconductor memory 42 such as a RAM, a ROM, and a flash memory. The control section 4 includes a communication controller 43 that performs communications in accordance with the CAN-FD protocol.

[0014] The communication controller 43 supplies the transmitter 5 with transmission data TxD indicating a CAN FD frame and an enable signal EN, which is set to a low level in the low-speed range and a high level in the high-speed range in synchronized relationship with the transmission data TxD. The communication controller 43 receives reception data RxD from the transmitter 5 and, if the reception data RxD is a normal CAN FD frame conforming to the CAN FD protocol, extracts data from the data area. The high signal levels of the transmission data TxD and the reception data RxD are called recessive. The low signal levels of the transmission data TxD and the reception data RxD are called dominant.

[0015] The communication controller 43 is configured to stop transmitting the transmission data TxD as an occurrence of a signal collision, that is, an error frame, when the reception data RxD continues to be dominant for a predetermined upper limit time period or more.

[0016] The CPU 41 executes at least transmission processing for supplying data to be supplied to other ECUs 3 to the communication control device 43 and reception processing for executing various processing using data received from the communication control device 43. [1-4. Transformer]

[0017] The transmitter 5 includes a transmitting circuit 50 and a receiving circuit 60. [1-4-1. Receiving circuit]

[0018] The receiving circuit 60 includes a receiver 62 and a gate circuit 64. The receiver 62 outputs a high level and a low level when the signal level of the difference signal received via the communication network 7 is greater or smaller than a predetermined reception threshold value Vth.

[0019] The gate circuit 64 supplies the communication control device 43 with the output signal of the receiver 62 itself as the received data RxD when the error signal ER output from the transmission circuit 50 is at the low level. The gate circuit 64 supplies the communication control device 43 with the low-level signal (i.e., dominant) as the received data RxD when the error signal ER is at the high level. [1-4-2. Transfer circuit]

[0020] The transmission circuit 50 includes, as shown in Fig. 2 in detail, a first transmission part 51 and a second transmission part 52.

[0021] The first transmission part 51 includes a first driver circuit 511, transistors T11, T12, and diodes D11, D12. The transistor T11 is a P-channel field-effect transistor whose source terminal is connected to a power supply line 53 of a DC voltage VDD. The transistor T12 is an N-channel field-effect transistor whose source terminal is connected to a ground line 54. An anode and a cathode D11 are each connected to a drain terminal of the transistor T11 and the CANH line. An anode and a cathode of the diode D12 are each connected to the CANL line and a drain terminal of the transistor T12.

[0022] In response to the transmission data TxD, the first control circuit 511 generates a non-inverted output signal S11, which is at the same signal level as the transmission data TxD, and an inverted output signal S12, which is the inverted signal level of the transmission data TxD. The first control circuit 511 can, as shown in Fig. 3A, for example, be configured with a buffer circuit L1 and an inverter circuit L2. The non-inverted output signal S11 is applied to a gate terminal of the transistor T11, and the inverted output signal S12 is applied to a gate terminal of the transistor T12.

[0023] That is, when the transmission data TxD is at the high level, transistors T11 and T12 both turn off, i.e., remain in high-impedance states. As a result, no power is supplied to the communication network 7 from the first transmission part 51. When the transmission data TxD is at the low level, transistors T11 and T12 both turn on. As a result, power is supplied from the first transmission part 51 to the communication network 7.

[0024] The second transmission part 52 includes a second drive circuit 521, transistors T21, T22, and diodes D21, D22. The second transmission part 52 further includes current monitoring circuits 522, 523, a gate circuit 524, and a filter 525, all or some of which may be provided outside the second transmission part 52. The transistor T21 is a P-channel field-effect transistor whose source terminal is connected to the DC power supply line 53 via the current monitoring circuit 522. The transistor T22 is an N-channel field-effect transistor whose source terminal is connected to the ground line 54 via the current monitoring circuit 523. An anode and a cathode of the diode D21 are connected to a drain terminal of the transistor T21 and the CANL line, respectively. An anode and a cathode of the diode D22 are each connected to the CANH line and a drain terminal of the transistor T22.

[0025] The second driver circuit 521 generates an inverted driver output signal S21 and a non-inverted driver output signal S22 in response to the transmission data TxD and the enable signal EN. More specifically, when the enable signal EN is at the high level, the inverted output signal S21 is the same as the level-inverted transmission data TxD, and the non-inverted output signal S22 is the same as the signal level of the transmission data TxD. When the enable signal EN is at the low level, the inverted output signal S21 is at the high level, and the non-inverted output signal S22 is at the low level. The second driver circuit 521 can, as in Fig. 3B, for example, a NAND circuit L3 and an AND circuit L4. The non-inverted output signal S21 is applied to a gate terminal of the transistor T21, and the inverted output signal S22 is applied to a gate terminal of the transistor T22.

[0026] The monitoring circuit 522 includes, as in Fig. 4, resistors R11, R12, and a transistor Tr1. The transistor Tr1 is a PNP bipolar transistor. The resistor R11 is connected between a base and an emitter of the transistor Tr1. The emitter and base of the transistor Tr1 are connected to the power supply line 53 and a source terminal of the transistor T21, respectively. A collector of the transistor Tr1 is connected to the ground line 54 via the resistor R12 and is an output terminal of a first detection signal J1.

[0027] The current monitoring circuit 523 includes, as shown in Fig. 5, resistors R21, R22, R23, and transistors Tr2, Tr3. Transistor Tr2 is an NPN bipolar transistor. Resistor R21 is connected between a base and an emitter of transistor Tr2. The emitter and base of transistor Tr2 are respectively connected to ground line 54 and a source terminal of transistor Tr2. Transistor Tr3 is a PNP bipolar transistor. Transistor Tr3 and resistors R22, R23 are connected similarly to transistor Tr1 and resistors R11, R12 of current monitoring circuit 522. However, a base of transistor Tr3 is connected to a collector of transistor Tr2. A collector of transistor Tr3 is an output terminal of a second detection signal J2.

[0028] Here, assume that the power supply currents flowing to the lines CANL and CANH via the second transmission part 53 are Irec1 and Irec2, respectively. The power supply currents Irec1 and Irec2, which flow when the transistors T21 and T22 turn on during normal transmission over the communication network 7, are each referred to as normal currents. The power supply currents Irec1 and Irec2, which flow when the transistors T21 and T22 turn on during a signal collision in the communication network, i.e., when the error frame occurs, and which are larger than the normal currents, are each referred to as error currents.

[0029] The resistance values ​​of resistors R11 and R21 are set such that transistors Tr1 and Tr2 turn on when fault currents flow through resistors R11 and R21, and transistors Tr1 and Tr2 remain off when normal currents flow through resistors R11 and R21. That is, the current threshold values ​​for switching the on and off states of transistors Tr1 and Tr2 are set to be greater than the normal current and less than the fault current.

[0030] In the current monitoring circuit 522 configured as described above, when the power supply current Irec1 is the normal current, the transistor Tr1 turns off, and the first detection signal J1 is at a low level. When the power supply current Irec1 is the fault current, the transistor Tr1 turns on, and the first detection signal J1 is at a high level.

[0031] In the current monitoring circuit 523 configured as described above, when the power supply current Irec2 is the normal current, both of the transistors Tr2 and Tr3 turn off, and the second detection signal J2 is at a low level. When the power supply current Irec2 is the fault current, both of the transistors Tr2 and Tr3 turn on, and the second detection signal J2 is at a high level.

[0032] The gate circuit 524 is a conventional AND circuit which outputs the high-level error signal ER when both the first detection signal J1 and the second detection signal J2 are at the high levels, that is, the error currents are detected on both the lines CANH and CANL.

[0033] Filter 525 is a low-pass filter that, after filtering out radio frequency signals, supplies the communication control device 43 with the error signal ER. That is, filter 525 is provided to prevent the communication control device 43 from operating erratically due to noise superimposed on the error signal ER. [1-5. Operation]

[0034] In the following description, a period during which the transmission data TxD is at the high level and the low level is referred to as a recessive period and a dominant period, respectively. [1-5-1. Operation in the decision area]

[0035] The following describes an operation sequence of the communication control device 43 in the decision area in which the low-level enable signal EN is output. When the enable signal EN is at a low level, both transistors T21 and T22 of the second transmission part 52 turn off regardless of the signal level of the transmission data TxD. For this reason, the signal levels on the lines CANH and CANL, and thus the signal level of the difference signal transmitted via the communication network 7, are determined or ascertained by the first transmission part 51.

[0036] That is, communications are performed in accordance with CAN standards, which are conventional and not described in detail. [1-5-2. Operation in the non-decision area]

[0037] The following describes an operation of the communication control device 43 in the non-decision region in which the high-level enable signal EN is output. In the non-decision region, not only the first transmission part 51 but also the second transmission part 52 operate in accordance with the signal level of the transmission data TxD.

[0038] During the normal time, in which no error frame is generated, the following operation is performed. That is, during the recessive period, in which the transmission data TxD is at the high level, both transistors T11 and T12 turn off, and both transistors T21 and T22 turn on. For this reason, the potentials on the lines CANH and CANL are determined in accordance with the power supply from the second transmission part 52 to the communication network 7. In this situation, as shown in Fig. 6, normal currents flow in transistors T21 and T22. With the normal currents, both the first detection signal J1 and the second detection signal J2 are at low levels, and consequently, the error signal ER is at a low level. In the dominant period in which the transmission data TxD is at a low level, both transistors T11 and T12 turn on, and both transistors T21 and T22 turn off. For this reason, the potentials on the lines CANH and CANL are determined in correspondence with the power supply from the first transmission part 51 to the communication network 7. In this situation, although not shown, normal currents flow in transistors T11 and T12.

[0039] During the error time in which the error frame is generated, the following operation is performed. That is, the transmission data TxD is at the high level, and not only the transistors T21 and T22 in the ECU 3 in question, but also the transistors T11 and T12 in the other ECU 3 outputting the low level, turn on. For this reason, the potentials on the lines CANH and CANL are determined according to the characteristic of the transistor that is turned on, rather than fixed. As a result, the output signal of the receiver 62 constituting the receiving circuit 60 is unstable. Since both the lines CANH and CANL are conductively connected to the power supply line 53 and the ground line 54, an excessive leakage current flows. The leakage current has an upper limit determined by the circuit configuration.With the error current, both the first detection signal J1 and the second detection signal J2 are at high levels. Furthermore, the error signal ER is also at a high level. As a result, the signal level of the received data RxD applied to the communication controller 43 is maintained at a low level (i.e., dominant).

[0040] Upon detecting that the signal level of the received data RxD continues to remain at the low level for a predetermined period of time or more, the communication controller 43 determines that an error occurs and, although not shown, stops transmitting the transmitted data TxD: It is therefore possible to avoid a collision of signals in the communication network 7 and to eliminate error frames.

[0041] When the transmission data TxD is at a low level, the second transmission part 52 is irrelevant with respect to driving the CANH and CANL lines. The operation is the same as when the enable signal EN is at a low level. [1-6. Advantage]

[0042] The communication system 1 described above provides the following advantages.

[0043] (1a) In the non-decision region, even when the transmission data TxD is at the high level, in the recessive period, the power is supplied to the communication network 7 through the second transmission part 52. As a result, it is possible to lower an impedance of the communication network 7 in the recessive period and therefore suppress overshoot that otherwise occurs at the time of transition from the dominant period to the recessive period.

[0044] (1b) During the operation of the second transmission part 52, the current monitoring circuits 522 and 523 detect the fault currents and thereby detect the fault frame. As a result, it is possible to stably detect the generation of the fault frame even in the case where the output impedance of the transformer 5 is not subject to any regulation and the voltage level of the difference signal on the communication network 7 is unstable at the time of fault frame generation.

[0045] (1c) The communication controller 43 detects the error by maintaining the received data RxD supplied to the communication controller 43 as dominant when the error frame is detected. As a result, it is possible to stop outputting the transmitted data TxD and eliminate the error frame by utilizing the existing anti-error function provided in the communication controller 43. [1-7. Modification example]

[0046] In the first embodiment, the current monitoring circuit 522 is formed by the transistor Tr1 and the resistors R11 and R12. However, it can be configured differently. For example, as shown in Fig. 7, a current monitoring circuit 522a may be formed using an operational amplifier OP1 used as a comparator instead of the transistor Tr1 and the resistor R12. In this configuration, an inverting input of the operational amplifier OP1 is connected to the source terminal of the transistor T21, and a non-inverting input of the operational amplifier OP1 is connected to receive a threshold value Vref1 corresponding to the current threshold described above. An output signal of the operational amplifier OP1 is used as the first detection signal J1.

[0047] Furthermore, in the first embodiment, the current monitoring circuit 523 consists of the transistors Tr2, Tr3 and the resistors R21 to R23. However, it can also be configured differently. For example, as in Fig. 8, a current monitoring circuit 523a can be formed using an operational amplifier OP2 used as a comparator instead of the transistors Tr2, Tr3 and the resistors R22, R23. In this configuration, a non-inverting input of the operational amplifier OP2 is connected to the source terminal of the transistor T22, and an inverting input of the operational amplifier OP2 is connected to receive a threshold value Vref2 corresponding to the current threshold described above. An output signal of the operational amplifier OP2 is used as the first and second detection signals J2, respectively. [2. Second Embodiment][2-1. Difference from the First Embodiment]

[0048] A second embodiment is similar in basic configuration to the first embodiment and will be described below with reference to differences. In the following description, the same structural parts as in the first embodiment are denoted by the same reference numerals.

[0049] In the first embodiment described above, the current monitoring circuit 522 of the second transmission part 52 is provided between the source terminal of the transistor T21 and the power supply line 53, and the current monitoring circuit 523 of the second transmission part 52 is provided between the source terminal of the transistor T22 and the ground line 54. The second embodiment differs from the first embodiment in that, as shown in Fig. 9, a current monitoring circuit 526 of a second transmission part 52a is provided between a gate terminal of the transistor T21 and the power supply line 53, and a current monitoring circuit 527 of the second transmission part 52a is provided between a gate terminal of the transistor T22 and the ground line 54. [2-2. Current monitoring circuit]

[0050] The current monitoring circuit 526 includes, as shown in Fig. 10, a transistor T21m, a resistor R14, and an operational amplifier OP3. The transistor T21m is a P-channel field-effect transistor similar to the transistor T21. A gate terminal, a source terminal, and a drain terminal of the transistor T21m are connected to the gate terminal of the transistor T21, the power supply line 53, and the ground line 54, respectively, via the resistor R14. That is, the transistor T21m forms a current mirror circuit with the transistor T21. A non-inverting input terminal of the operational amplifier OP3 is connected to a drain terminal of the transistor T21m, and an inverting input terminal of the operational amplifier OP3 is connected to receive a threshold value Vref3 corresponding to the current threshold value described above. The operational amplifier OP3 is used as a comparator. An output signal of the operational amplifier OP3 is used as the first detection signal J1.

[0051] In current monitoring circuit 526, transistor T21m is provided such that a reference current having the same magnitude as the power supply current Irec1 flowing in transistor T21 flows in resistor R14. Based on a voltage drop caused by resistor R14, the power supply current Irec1 flowing in transistor T21 is determined.

[0052] The current monitoring circuit 527 includes, as shown in Fig. 11, a transistor T22m, a resistor R24, and an operational amplifier OP4. The transistor T22m is an N-channel field-effect transistor similar to the transistor T22. A gate terminal, a source terminal, and a drain terminal of the transistor T22m are connected to the gate terminal of the transistor T22, the ground line 53, and the power supply line 53, respectively, via the resistor R24. That is, the transistor T22m forms a current mirror circuit with the transistor T22. An inverting input terminal of the operational amplifier OP4 is connected to the drain terminal of the transistor T22m, and a non-inverting input terminal of the operational amplifier OP4 is connected to receive a threshold value Vref4 corresponding to the current threshold value described above. The operational amplifier OP4 is used as a comparator. An output signal of the operational amplifier OP4 is used as the second detection signal J2.

[0053] In current mirror circuit 527, transistor T22m is provided so that a reference current of the same magnitude as the power supply current Irec2 flowing in transistor T22 flows in resistor R24. Based on a voltage drop caused by resistor R24, the power supply current Irec2 flowing in transistor T22 is determined. [2-3. Advantage]

[0054] The second embodiment described above also provides the same advantages (1a) to (1c) of the first embodiment. [3. Third Embodiment][3-1. Difference from the First Embodiment]

[0055] A third embodiment is similar in basic configuration to the first embodiment and will be described below with reference to differences. In the following description, the same structural parts as in the first embodiment are denoted by the same reference numerals.

[0056] In the first embodiment, the transmitter 5 is configured to control the signal level of the received data RxD supplied to the communication control device 43 by the error signal ER. A transmitter 5b in the third embodiment differs from that of the first embodiment in that, as shown in Fig. 12, is configured to control the signal level of the enable signal EN, which is supplied from the communication control device 43 to the second transmission part 52, by the error signal ER. [3-2. Transformer]

[0057] The transmitter / receiver 5b includes a transmitting circuit 50b and a receiving circuit 60b. The receiving circuit 60b includes a receiver 62 and is configured to directly supply the communication controller 43 with the output of the receiver 62 as the received data RxD. That is, the gate circuit 64 in the first embodiment is removed from the receiving circuit 60.

[0058] The transmission circuit 50b includes a gate circuit 55 in addition to the first transmission part 51 and the second transmission part 52. The first transmission part 51 and the second transmission part 52 will not be described further. The gate circuit 55 is configured to directly output the enable signal EN supplied from the communication controller 43 to the second transmission part 52 when the error signal ER output from the second transmission part 52 is at the low level. The gate circuit 55 is configured to output the enable signal EN, which is maintained at the low level, to the second transmission part 52 when the error signal ER is at the high level. [3-3. Advantage]

[0059] The third embodiment described above provides the following advantages in addition to the advantages (1a) and (1b) of the first embodiment.

[0060] (3a) When the error frame is detected by or in the second transmission part 52, that is, the error signal ER is changed to the high level, the enable signal EN supplied to the second transmission part 52 is forcibly changed to the low level, thereby stopping the operation of the second transmission part 52. Consequently, it is possible to avoid collision of signals produced in the recessive period, so that only the error frame signal transmitted from other nodes remains in the communication network 7. As a result, the communication control device 43 is enabled to correctly detect the error frame via the receiving circuit 60b and appropriately respond to the error frame. [4. Another embodiment]

[0061] The transmission circuit is not limited to the disclosed embodiments, but can be implemented with various modifications as exemplified below.

[0062] In the above-described embodiments, the AND circuit is used as the gate circuit 524, which generates the error signal ER from the first detection signal J1 and the second detection signal J2. Alternatively, an OR circuit may be used instead of the AND circuit. Using the AND circuit makes it possible to more effectively suppress erroneous operations. Using the OR circuit makes it possible to more effectively improve the response characteristics to the error frame.

[0063] The above-described transmission circuits 50 and 50b can be used in any devices other than the transmitters 5, 5b, the ECU 3, the communication system 1, and the like.

[0064] As described above, when an enable signal EN is at a high level and a transmission data TxD is at a high level, that is, in a recessive period, both transistors (T11 and T12) turn off and both transistors (T21 and T22) turn off. Therefore, potentials of signal lines CANH and CANL are determined by a power supply from a second transmission part (52) to a communication network (7). If an error frame occurs in this state, that is, transistors (T11 and T12) in the other electronic control unit turn on, excessive currents flow in CANH and CANL. When current monitoring circuits (522 and 523) detect error currents, an error signal ER is changed to a high level.

Claims

[1] Communication device (5, 5b) connectable to a communication network (7), having a pair of signal lines (71, 72) for transmitting a difference signal, the communication device (5, 5b) comprising: a first transmission part (51) configured to transmit the difference signal corresponding to a transmission signal expressed in two values ​​to the communication network (7) by switching a state of the communication network (7) between a driven state for supplying power to the communication network (7) and a non-driven state for cutting off power supply to the communication network (7) in accordance with the transmission signal, wherein periods of the driven state and the non-driven state of the first transmission part (51) are assumed to be a dominant period and a recessive period, respectively; a second transmission part (52, 52a) configured to be in a non-driven state in the dominant period and in a driven state in the recessive period, and to supply power to the communication network (7) such that a polarity of the difference signal in the recessive period is opposite to that of the difference signal in the dominant period; Current monitoring parts (522, 523, 522a, 523a, 526, 527) configured to monitor magnitudes of power supply currents of a first magnitude of a first power supply current supplied from the second transmission part (52, 52a) to a first signal line of the pair of signal lines (71, 72) and a second magnitude of a second power supply current supplied from the second transmission part (52, 52a) to a second signal line of the pair of signal lines (71, 72); and a checking part (524, 525) for checking whether a signal collision occurs in the communication network (7) based on monitoring results of the current monitoring parts (522, 523, 522a, 523a, 526, 527) of the first and second sizes, wherein the checking part (524, 525) determines that the signal collision exists in the communication network when, in the recessive period, both the first quantity is greater than a first current threshold and the second quantity is greater than a second current threshold. [2] Communication device (5, 5b) according to claim 1, further comprising: a receiver (62) configured to check a signal level of the difference signal received via the communication network (7); and an error reporting part (64) configured to maintain an output signal of the receiver (62) at a signal level corresponding to the dominant time period when the checking part (524, 525) determines that the signal collision occurs. [3] Communication device (5, 5b) according to claim 1, further comprising: a termination processing part (55) configured to terminate a driving operation of the second transmission part (52) when the checking part (524, 525) determines that the signal collision occurs. [4] Communication device (5, 5b) according to one of claims 1 to 3, wherein: the transmission signal is generated based on a CAN FD protocol; and the second transmission part (52, 52a) is configured to operate in a non-decision area in the CAN FD protocol. [5] Communication device (5, 5b) according to one of claims 1 to 4, wherein: the checking part (524, 525) is configured to determine that the signal collision occurs when the power supply current exceeding a predetermined threshold value is detected in each of the pair of signal lines (71, 72) by the current monitoring parts (522, 523, 522a, 523a, 526, 527). [6] Communication device (5, 5b) according to one of claims 1 to 4, wherein: the checking part (524, 525) is configured to determine that the signal collision occurs when the power supply current exceeding a predetermined threshold value is detected in at least one of the pair of signal lines (71, 72) by the current monitoring parts (522, 523, 522a, 523a, 526, 527). [7] Communication device (5, 5b) according to one of claims 1 to 6, wherein: the communication network (7) includes a first signal line (71) and a second signal line (72); the transmission signal is expressed by a first signal level and a second signal level; the first transmission part (51) includes a first switch (T11) connected between a first power supply line (53) of a predetermined first potential and the first signal line (71), a second switch (T12) connected between a second power supply line (54) of a predetermined second potential lower than the first potential and the second signal line (72), and a first drive circuit (511) configured to turn on the first switch (T11) and the second switch (T12) when the transmission signal is at the first signal level; and the second transmission part (52, 52a) includes a third switch (T21) connected between the first power supply line (53) and the second signal line (72), a fourth switch (T22) connected between the second power supply line (54) and the first signal line (71), and a second drive circuit (521) configured to turn on the third switch (T21) and the fourth switch (T22) when the transmission signal is at the second signal level. [8] Communication device (5, 5b) according to claim 7, wherein: the current monitoring part (522, 523, 522a, 523a, 526, 527) is configured to detect a magnitude of the power supply current flowing in the third switch (T21) and the fourth switch (T22). [9] Communication device (5, 5b) according to claim 7, wherein: the third switch (T21) and the fourth switch (T22) are formed of transistors, each of which forms a current mirror circuit; and the current monitoring parts (522, 523, 522a, 523a, 526, 527) are configured to detect magnitudes of reference currents which have the same magnitudes as the power supply current flowing in the current mirror circuits.

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