WO2013051677A1

WO2013051677A1 - Communication system, communication device, communication method, and communication parameter determining method

Info

Publication number: WO2013051677A1
Application number: PCT/JP2012/075883
Authority: WO
Inventors: 大祐梅原; 石河　伸一; 坪内　利康
Original assignee: 国立大学法人京都工芸繊維大学; 株式会社オートネットワーク技術研究所; 住友電装株式会社; 住友電気工業株式会社
Priority date: 2011-10-06
Filing date: 2012-10-05
Publication date: 2013-04-11

Abstract

　Provided are a communication system, communication device, communication method and communication parameter determining method enabling higher speed communication and a reduction in the impact of ringing. If transmission data is dominant, a transmission unit (17) in an ECU (1) outputs, to a communication line (5), a signal having a specific signal level spanning a pulse width (Tp) which is shorter than the transmission time for one bit, and then stops the output of the signal to the communication line (5), creating a high impedance state, and if the transmission data is recessive, the transmission unit (17) creates a high impedance state without the output of the signal to the communication line (5). Also, a reception unit (18) in the ECU (1) samples the signal level of the communication line (5) across a sampling period (Td), calculates the average value of the sampled signal levels, and makes a dominant/recessive determination according to whether the calculated average exceeds a threshold value or not.

Description

COMMUNICATION SYSTEM, COMMUNICATION DEVICE, COMMUNICATION METHOD, AND COMMUNICATION PARAMETER DETERMINING METHOD

The present invention relates to a communication system, a communication apparatus, a communication method, and a communication parameter capable of detecting a collision of information transmission with respect to a communication line while a plurality of communication apparatuses connected to a common communication line can mutually transmit and receive information. Regarding the determination method.

Conventionally, a CAN (ControllerＣＡArea Network) communication protocol has been widely adopted for communication between a plurality of electronic devices (communication devices) mounted on a vehicle (see Non-Patent Documents 1 and 2). In the CAN communication protocol, since a plurality of communication devices are connected to a common CAN bus, when a plurality of communication devices transmit information simultaneously and a collision occurs, an arbitration process ( Arbitration) is performed, and information transmission with a high priority is executed. In order to perform arbitration, each communication device outputs a transmission signal to the CAN bus and simultaneously detects the signal level of the CAN bus, and the signal level of the detected signal relative to the transmission signal output by itself is detected. When it changes from recessive (inferior value) to dominant (dominant value), it judges that information transmission with high priority has occurred, and stops transmission processing. Since signals on the CAN bus are dominant over recessive signals, electronic devices that output dominant signals can continue to perform transmission processing even if simultaneous transmissions from a plurality of communication devices occur.

Generally, in a communication system adopting a CAN communication protocol, a twisted line is used as a communication line, and each communication device performs communication using a differential signal, and a case where a potential difference between twisted lines exceeds a threshold is dominant. And a recessive case where the potential difference does not exceed the threshold value. In the digital processing in the communication apparatus, the dominant is associated with data 0 and the recessive is associated with data 1. 26 and 27 are schematic diagrams showing examples of signal waveforms in a conventional communication system, in which the vertical axis represents the potential difference V between the twist lines and the horizontal axis represents time t. The signal waveforms shown in FIGS. 26 and 27 are waveforms when the signal is changed from dominant to recessive on the CAN bus. As shown in the figure, when the transmission signal output from the communication device to the CAN bus is changed from dominant to recessive, a waveform that oscillates while the signal level (potential difference) on the CAN bus gradually attenuates is generated. This is because it is necessary to provide many branch portions in the CAN bus in order to connect many communication devices, and signal reflection is repeated due to factors such as impedance mismatch in this branch portion. Called ringing.

When such ringing occurs, each communication device cannot make a dominant / recessive determination until the ringing signal level is attenuated to some extent. The time during which the ringing signal level attenuates varies depending on the length of the branch line that branches the CAN bus. The ringing signal level varies depending on the number of communication devices connected to the CAN bus. For this reason, each communication device needs to make a dominant / recessive decision after waiting for a time period during which ringing is considered to be sufficiently attenuated in consideration of the number of communication devices in the communication system, the length of the branch line, and the like. In addition, the conventional communication system using the CAN protocol has a problem in that speeding up of communication is hindered by the influence of ringing.

The present invention has been made in view of such circumstances, and its object is to reduce the influence of ringing and realize a communication system, communication apparatus, communication method, and communication parameter capable of realizing high-speed communication. To provide a decision method.

The communication system according to the present invention includes a plurality of communication devices connected via a common communication line, and each communication device is represented by a binary value of a dominant value or an inferior value via the communication line. In the communication system having communication means for transmitting and receiving a plurality of consecutive bits of information, the communication means is predetermined over a predetermined time Tp shorter than the information transmission time of 1 bit with respect to the superiority value of the information to be transmitted. After outputting a pulse signal of a signal level to the communication line, the signal output to the communication line is not performed, and the signal output to the communication line is not performed for the inferior value of the information to be transmitted. It is characterized by.

In addition, the communication system according to the present invention includes a plurality of communication devices connected via a common communication line, and each communication device has a binary value with each bit being a dominant value or an inferior value via the communication line. In the communication systems each having communication means for transmitting and receiving continuous plural bits of information, the communication means has a first predetermined time shorter than the information transmission time for one bit with respect to the superiority value of the information to be transmitted. Information that outputs a signal having a second signal level lower than the first signal level over a second predetermined time Th that is shorter than the information transmission time after outputting a signal having the first signal level over Tp A signal output to the communication line is not performed with respect to the inferior value.

In the communication system according to the present invention, the communication device connects / disconnects the other end of the resistor, one end of which is connected to a fixed potential, with respect to the communication line, and the information for one bit. And switching control means for controlling the switching unit to connect the resistor after the first predetermined time Tp has elapsed in the transmission time.

In the communication system according to the present invention, the first predetermined time Tp and the second predetermined time Th satisfy the conditions of Tp + Th ≦ Tb and Th ≧ 2 × L × A (where Tb is 1 bit of information transmission time, L is the shortest distance of the communication line interposed from one communication apparatus to another communication apparatus, and A is signal transmission per unit length of the communication line It is time.)

In the communication system according to the present invention, when the communication device outputs information related to the superiority value or the inferiority value to the communication line, the signal level in the communication line over a predetermined sampling period Td. A plurality of times of sampling, and calculating means for calculating an average value of the signal level in the predetermined sampling period Td, and a signal transmitted to the communication line according to the average value calculated by the calculating means Determining means for determining which of the recessive values, and detecting means for detecting information transmission from other communication devices when the determining means determines that it is a dominant value after transmitting the information of the recessive value It is characterized by having.

In the communication system according to the present invention, when the communication device outputs information related to the superiority value or the inferiority value to the communication line, the signal level in the communication line over a predetermined sampling period Td. The comparison means for performing sampling of a plurality of times and comparing the signal level of each sampling result with a threshold value, and based on the comparison result of the comparison means, the number of samples whose signal level exceeds the threshold value and the signal level exceeds the threshold value A determination unit that determines whether a signal transmitted to the communication line is a dominant value or an inferior value according to the number of samples that is not present, and the determination unit is a dominant value after transmitting information on the recessive value And a detection unit that detects transmission of information from another communication device when the determination is made.

In the communication system according to the present invention, the communication device sequentially transmits information of a plurality of dominant values having different predetermined times Tp, and different predetermined sampling periods with respect to the information transmitted by the test transmission unit. Sampling over Td and making a determination by the determination means, evaluating means for evaluating the reception result for a combination of the predetermined time Tp and the predetermined sampling period Td, and each predetermined time based on the evaluation result by the evaluation means Selecting means for selecting a predetermined sampling period Td having a high evaluation with respect to Tp, wherein one communication apparatus performs transmission by the test transmission means, and each communication apparatus performs evaluation by the evaluation means and by the selection means. The process of selecting is performed for all communication devices in order, and based on the selection result by the selecting means of each communication device, a predetermined time Characterized in that you have to determine the p and a predetermined sampling period Td.

Further, the communication system according to the present invention is characterized in that the test transmission means transmits the information of the dominant value and the information of the inferior value alternately.

In the communication system according to the present invention, the evaluation unit calculates an evaluation value corresponding to the number of the dominant value information determined as the dominant value, the number of the recessive value information determined as the dominant value, and the sampling number. It is characterized by being.

Further, in the communication system according to the present invention, the plurality of communication devices include one master communication device and a plurality of slave communication devices, and the slave communication device corresponds to the evaluation unit corresponding to the sorting result of the sorting unit. Evaluation result transmission means for transmitting the evaluation result to the master communication device, wherein the master communication device receives the evaluation result transmitted by the plurality of slave communication devices, and receives the evaluation result. A predetermined time determining means for determining the predetermined time Tp based on a plurality of evaluation results received by the means; and a predetermined time for transmitting information on the predetermined time Tp determined by the predetermined time determining means to the plurality of slave communication devices. And the slave communication device further includes a predetermined time information receiving unit for receiving information of the predetermined time Tp transmitted by the predetermined time information transmitting unit, and the predetermined time information receiving unit receives the information. Place At time Tp, characterized in that are to perform the subsequent signal output by said communication means.

In the communication system according to the present invention, the main communication device includes predetermined sampling period determining means for determining the predetermined sampling period Td in accordance with the predetermined time Tp determined by the predetermined time determining means. Subsequent sampling is performed in the predetermined sampling period Td determined by the sampling period determining means, and the slave communication device is configured to perform the predetermined sampling period according to the predetermined time Tp received by the predetermined time information receiving means. It has a predetermined sampling period determining means for determining Td, and the subsequent sampling is performed in the predetermined sampling period Td determined by the predetermined sampling period determining means.

Further, the communication device according to the present invention is connected to another device via a common communication line, and each bit is represented by two or more consecutive bits represented by a binary value of a dominant value or a recessive value via the communication line. In a communication apparatus including a communication unit that transmits and receives information, the communication unit outputs a pulse signal having a predetermined signal level over a predetermined time Tp shorter than an information transmission time of 1 bit with respect to a superiority value of information to be transmitted. After output to the communication line, signal output to the communication line is not performed, and signal output to the communication line is not performed for the inferior value of the information to be transmitted.

Further, the communication device according to the present invention is connected to another device via a common communication line, and each bit is represented by two or more consecutive bits represented by a binary value of a dominant value or a recessive value via the communication line. In a communication apparatus comprising a communication means for transmitting and receiving information, the communication means has a first signal level over a first predetermined time Tp shorter than an information transmission time for one bit with respect to a superiority value of information to be transmitted. After outputting a signal, a signal having a second signal level lower than the first signal level is output for a second predetermined time Th shorter than the information transmission time, and the communication with respect to the inferior value of the information to be transmitted The signal output to the line is not performed.

Further, the communication device according to the present invention performs sampling of the signal level in the communication line a plurality of times over a predetermined sampling period Td when the communication means outputs information relating to the dominant value or the inferior value to the communication line. And calculating means for calculating an average value of the signal level during the predetermined sampling period Td, and depending on the average value calculated by the calculating means, the signal transmitted to the communication line is either a dominant value or a recessive value. A determination unit that determines whether or not there is a detection unit that detects transmission of information from another communication device when the determination unit determines that the determination is a dominant value after transmitting the information of the recessive value. And

Further, the communication device according to the present invention performs sampling of the signal level in the communication line a plurality of times over a predetermined sampling period Td when the communication means outputs information relating to the dominant value or the inferior value to the communication line. And comparing means for comparing the signal level of each sampling result with a threshold, and based on the comparison result of the comparing means, the number of samples whose signal level exceeds the threshold and the number of samples whose signal level does not exceed the threshold And determining means for determining whether the signal transmitted to the communication line is a dominant value or an inferior value, and determining that the determining means is a dominant value after transmitting the information of the inferior value, And detecting means for detecting information transmission from another communication device.

The communication apparatus according to the present invention also includes a test transmission unit that sequentially transmits information of a plurality of dominant values having different predetermined times Tp, and sampling over different predetermined sampling periods Td with respect to the information transmitted by the test transmission unit. Evaluation is performed by the determination means, and evaluation means for evaluating the reception result for the combination of the predetermined time Tp and the predetermined sampling period Td, and the evaluation is high for each predetermined time Tp based on the evaluation result by the evaluation means And a selecting means for selecting a predetermined sampling period Td.

Further, the communication method according to the present invention is a communication method for transmitting and receiving information of a plurality of consecutive bits each represented by a binary value of a dominant value or a recessive value via a common communication line. Information to be transmitted without outputting a signal to the communication line after outputting a pulse signal of a predetermined signal level to the communication line over a predetermined time Tp shorter than the information transmission time of 1 bit with respect to the dominant value. The signal output to the communication line is not performed with respect to the inferior value.

Further, the communication method according to the present invention is a communication method for transmitting and receiving information of a plurality of consecutive bits each represented by a binary value of a dominant value or a recessive value via a common communication line. After outputting the signal of the first signal level over the first predetermined time Tp shorter than the information transmission time for 1 bit with respect to the dominant value, over the second predetermined time Th shorter than the information transmission time. A signal having a second signal level lower than the first signal level is output, and signal output to the communication line is not performed for the inferior value of information to be transmitted.

The communication parameter determination method according to the present invention is a communication parameter determination method for determining the predetermined time Tp and the predetermined sampling period Td in the communication system described above, wherein the predetermined time Tp is determined by one communication apparatus. Information of a plurality of different dominant values is transmitted in order, the information transmitted by the one communication device is sampled over a different predetermined sampling period Td and determined by the determination means, and the predetermined time Tp and the predetermined sampling period The reception result for the combination of Td is evaluated, and based on the evaluation result, a predetermined sampling period Td that is highly evaluated for each predetermined time Tp is selected, and transmission of one communication device is performed. The process of selecting is performed in order for all communication devices, and based on the selection result of each communication device, the predetermined time Tp and the predetermined And determining a sampling period Td.

In the present invention, when the information to be transmitted is dominant (dominant value), the communication apparatus has a high level (predetermined signal level) over a predetermined time Tp shorter than this time with respect to the information transmission time of 1 bit. The signal is output to the communication line, and then the signal output to the communication line is stopped (becomes a high impedance state). When the information to be transmitted is recessive (inferior value), the communication device does not output a signal to the communication line (becomes a high impedance state).
As a result, when a dominant transmission and a recessive transmission collide, a signal corresponding to the dominant is transmitted over a predetermined time Tp on the communication line, so the communication device that has transmitted the recession detects the signal on the communication line. By doing so, the signal of the dominant value transmitted by another communication apparatus can be detected.
When the communication device transmits a dominant signal, ringing occurs in the communication line after the signal is output for a predetermined time Tp. By setting the signal output time to be shorter than the information transmission time for one bit, The ringing can be attenuated after the signal output until the transmission of the next bit information starts. Further, no ringing occurs even when the communication device transmits a recessive signal.
As a result, the influence of ringing on the next bit to which the communication apparatus has transmitted a dominant can be reduced, so that dominant / recessive determination can be performed at an early timing for each bit. Therefore, high-speed communication can be realized.

In conventional CAN, ringing as shown in FIGS. 26 and 27 occurs when transmission of the communication apparatus is changed from dominant to recessive. The communication device outputs a high level signal (a signal having a predetermined potential difference) to the communication line as a dominant transmission, and then becomes recessive and enters a high impedance state. The signal change from dominant to recessive by one communication device is reflected by another communication device in recessive (high impedance state), and this reflection is further reflected by the one communication device that has transitioned to recessive. Reflection occurs and ringing occurs.
Therefore, in the present invention, when the information to be transmitted is a dominant (dominant value), the communication apparatus performs the first signal level over a first predetermined time Tp shorter than this time with respect to the information transmission time of 1 bit. After the signal is output, a signal of the second signal level (<first signal level) over the second predetermined time Th is output to the communication line. That is, the communication apparatus outputs a pulse-like signal that changes from the first signal level to the second signal level in response to the dominant. When the information to be transmitted is recessive (inferior value), the communication device does not output a signal to the communication line (becomes a high impedance state).
As a result, when dominant transmission and recessive transmission exist simultaneously, a pulse-like signal changing from the first signal level to the second signal level is observed on the communication line. By detecting a signal on the communication line, the device can detect the presence of the communication device that has transmitted the dominant. In addition, the communication apparatus which transmitted recessive can suppress generation | occurrence | production of a reflected signal by performing impedance matching in the area of a 2nd signal level after the time of a 1st signal level passes.
When the information transmitted by the communication apparatus is changed from dominant to recessive, the signal level is lowered from the first signal level to the second signal level, and then the state is shifted to the high impedance state. For this reason, the amplitude of the signal reflected by the communication line can be reduced, and further, by setting the second signal level to approximately 0V, the amplitude of the reflected signal can be approximately 0V. Can be suppressed.
As a result, the influence of ringing on the next bit to which the communication apparatus has transmitted a dominant can be reduced, so that dominant / recessive determination can be performed at an early timing for each bit. Therefore, high-speed communication can be realized.

In a system in which a plurality of communication devices communicate via a common communication line, a main communication line (main line) is branched to provide a branch line, and the communication apparatus is connected to the end of the main line or branch line. In the present invention, a switching unit such as a switch for connecting / cutting off a resistor connected to a fixed potential such as a ground potential is provided for a communication line to which each communication device is connected. Each communication apparatus controls the switching unit to connect the resistor after the first predetermined time TP in the 1-bit transmission time has elapsed. Thereby, each communication device in the communication system can connect the resistor to the communication line after the elapse of the first predetermined time Tp in the 1-bit transmission time, and perform impedance matching by the resistor. As a result, impedance mismatching, which is a cause of ringing, can be eliminated, and ringing can be suppressed.

Since ringing occurs when a signal output from one communication device is reflected by another communication device, the ringing is the closest to one communication device (the distance of the communication line through which the signal propagates is the shortest). The communication device has a great influence on the occurrence of ringing.
Therefore, in the present invention, when the shortest distance of the communication line interposed between two communication devices included in the communication system is L and the transmission time per unit length of the communication line is A, the second predetermined time. Th is Th ≧ 2 × L × A
Set to satisfy the conditions. Note that 2 × L is a round trip distance between two communication devices, and 2 × L × A is a time until a signal output from one communication device is reflected by another communication device and returned to the one communication device. It is. By setting the second predetermined time Th to be equal to or longer than this time, the impedance matching by the resistor is performed before the reflected wave returns to the one communication device, so that the one communication device shifts to the high impedance state. And ringing can be reliably suppressed.
Further, the first predetermined time Tp is, when the information transmission time for 1 bit is Tb,
Tp + Th ≦ Tb
It is necessary to set so as to satisfy the conditions.

Further, in the present invention, when the communication apparatus outputs the above signal to the communication line, the communication line performs sampling of the signal level of the communication line a plurality of times over a predetermined sampling period Td, and the signal level is obtained from the sampling results of the plurality of times. The average value of is calculated. For example, the communication apparatus performs sampling over a time that is about the same as the output time (predetermined time Tp) of the signal output as the dominant. Accordingly, when the signal on the communication line is dominant, the communication apparatus can calculate a value approximately equal to the signal level of the signal output as the dominant as the average value of the signal level. When the signal on the communication line is recessive, the communication device can calculate a value in the vicinity of 0 V as the average value of the signal level. Even when ringing occurs on the communication line, the ringing repeats positive and negative amplitudes, so that the influence of the ringing can be eliminated by calculating the average value of the signal level.
The communication device determines whether the signal on the communication line is dominant / recessive, for example, depending on whether the average value of the calculated signal level exceeds a threshold value, and transmits communication information by itself. When the signal on the communication line is later determined to be dominant, it is detected that the information transmission has collided. As a result, the communication device can reduce the influence of ringing and detect a signal transmitted by another communication device.

In the present invention, when the communication apparatus outputs the above signal to the communication line, the signal level of the communication line is sampled a plurality of times over a predetermined sampling period Td, and the signal level and threshold value of each sampling result are obtained. Compare with. From the result of this comparison, the number of samples whose signal level exceeds the threshold is compared with the number of samples whose signal level does not exceed the threshold, and it is determined whether the signal on the communication line is dominant or recessive by so-called majority decision. To do.
For example, the communication apparatus performs sampling over a time that is about the same as the output time (predetermined pulse width) of a signal output as a dominant. The comparison between the sampling result and the threshold value can be easily performed by inputting the signal level of the sampling result to a simple CMOS (Complementary Metal Oxide Semiconductor) circuit and acquiring the output binary signal.
When the communication device determines that the signal on the communication line is dominant after transmitting the recessive information, the communication device can detect that another communication device has transmitted the dominant signal.

In order to perform communication as described above, it is necessary to appropriately set communication parameters for a predetermined time Tp and a predetermined sampling period Td necessary for performing communication processing in each communication device. Since the communication characteristics are affected by the length of the communication line and the number of communication devices, these communication parameters must be set appropriately for each communication system. Although it is possible to measure communication characteristics in a communication system and determine these communication parameters in advance, there is a possibility that the communication characteristics change due to factors such as increase or decrease of communication devices or aging in the communication system.
Therefore, in the present invention, for example, when the communication system is shipped, maintained, or when the number of communication devices is increased or decreased, each communication device of the communication system transmits and receives experimental information, and the predetermined time Tp and the predetermined sampling period. Th communication parameters are determined.

One communication apparatus sequentially transmits information of a plurality of dominant values having different predetermined times Tp. Each communication apparatus performs information reception processing by sampling information transmitted in sequence by one communication apparatus a plurality of times at different predetermined sampling periods Td. For example, one communication apparatus sequentially transmits information of dominance values by changing the predetermined time Tp such as predetermined times Tp1, Tp1, Tp1, Tp2, Tp2, Tp2, Tp3, Tp3, and Tp3. On the other hand, for example, each communication apparatus performs sampling in order by changing the predetermined sampling period Td like the predetermined sampling periods Td1, Td2, Td3, Td1, Td2, Td3, Td1, Td2, and Td3. In this example, there are nine combinations of the predetermined time Tp and the predetermined sampling period Td by the three predetermined times Tp and the three predetermined sampling periods Td. Each communication apparatus evaluates the reception result of each combination, and selects a predetermined sampling period Td having a high evaluation for each predetermined time Tp based on the evaluation result. In the above example, one predetermined sampling period Td1, Td2, Td3 that is highly evaluated for each predetermined time Tp1, Tp2, Tp3 is selected, and three combinations of the predetermined time Tp and the predetermined sampling period Td are selected as the sorting results. can get.
The communication devices that perform trial information transmission as one communication device are sequentially changed, the same processing is performed for all the communication devices, and finally, the predetermined time Tp and the predetermined sampling period Td are determined from these processing results. .
Accordingly, transmission / reception of trial information between communication devices of the communication system can be performed under various conditions of communication parameters, and each communication device can determine which condition is suitable.

Also, in the present invention, when transmitting / receiving experimental information as described above, one communication apparatus alternately transmits dominant value information and inferior value information. Thereby, trial information is transmitted and received under an unfavorable condition in which ringing is likely to occur, and a more appropriate communication parameter can be determined.

In the present invention, for a combination of the predetermined time Tp and the predetermined sampling period Td, the number (D0) in which the information on the dominant value is determined as the dominant value (D0) and the number in which the information on the inferior value is determined as the dominant value ( R0) and an evaluation value (for example, (D0−R0) / Pd) corresponding to the number of samplings (Pd) performed during the sampling period are calculated. Each communication device can select a predetermined sampling period Td suitable for the predetermined time Tp according to the calculated evaluation value.

In the present invention, the communication system includes one master communication device and a plurality of slave communication devices. The slave communication device performs the evaluation and selection as described above, and transmits an evaluation result corresponding to the selection result to the main communication device. The main communication device receives the evaluation result from each slave communication device, and determines one predetermined time Tp as the predetermined time Tp used in the subsequent communication based on the evaluation result. The master communication device transmits the determined predetermined time Tp to each slave communication device. Each slave communication device outputs a signal for subsequent information transmission at a predetermined time Tp received from the master communication device.
As a result, the evaluation results of the respective slave communication devices can be aggregated in the main communication device to determine the predetermined time Tp, and all communication devices can perform subsequent communication at the common predetermined time Tp.

In the present invention, each slave communication device determines a predetermined sampling period Td according to the predetermined time Tp received from the main communication device. Since each slave communication device has already selected a predetermined sampling period Td that is highly evaluated with respect to the predetermined time Tp, by selecting the predetermined sampling period Td corresponding to the predetermined time Tp from the selection result, the predetermined sampling period Td Can be determined. The predetermined sampling period Td may be different for each communication device.

According to the present invention, by adopting a configuration in which a signal shorter than the information transmission time for one bit is output as a dominant, the influence of ringing on the next bit of information to be transmitted can be reduced. Since recessive determination can be performed at an early timing, communication that requires arbitration such as the CAN protocol can be speeded up.

According to the present invention, the communication apparatus outputs a signal having the second signal level for the second predetermined time Th after the first signal level signal output for the first predetermined time Tp for the dominant information transmission. Since the output configuration can suppress the occurrence of ringing within one bit of transmission data, it is possible to perform dominant / recessive determination at each bit at an early timing, as in the CAN protocol. Communication that performs arbitration can be accelerated.

Further, according to the present invention, when each communication device transmits and receives experimental information and determines the communication parameters for the predetermined time Tp and the predetermined sampling period Td, for example, when the number of communication devices increases or decreases, or Even when the communication characteristics change due to secular change or the like, communication parameters suitable for the changed communication characteristics can be automatically determined.

It is a schematic diagram which shows one structural example of a communication system. It is a block diagram which shows the structure of a communication apparatus. It is a schematic diagram for demonstrating the signal which each ECU transmits / receives in the communication system which concerns on this invention. It is a schematic diagram for demonstrating the structure of the communication system evaluated by simulation. It is a schematic diagram for demonstrating the structure of the communication system evaluated by simulation. It is a graph which shows a simulation result. It is a flowchart which shows the procedure of the transmission process by a transmission part. It is a flowchart which shows the procedure of the reception process by a receiving part. 10 is a table showing simulation results of the second embodiment. 10 is a flowchart illustrating a procedure of reception processing by a reception unit according to the second embodiment. 10 is a flowchart illustrating a procedure of reception processing by a reception unit according to the second embodiment. It is a schematic diagram for demonstrating the test signal output by an automatic setting process. It is a schematic diagram for demonstrating the sampling performed in an automatic setting process. It is a schematic diagram which shows an example of the selection result memorize | stored in RAM. It is a flowchart which shows the procedure of the automatic setting process which master ECU performs. It is a flowchart which shows the procedure of the automatic setting process which a slave ECU performs. It is a flowchart which shows the procedure of a test signal transmission process. It is a flowchart which shows the procedure of a test signal reception process. FIG. 10 is a schematic diagram for explaining signals transmitted and received by each ECU in a communication system according to a fourth embodiment. FIG. 10 is a schematic diagram for explaining impedance matching by a CAN communication control unit according to a fourth embodiment. It is a schematic diagram for demonstrating the 1st predetermined time and 2nd predetermined time which concern on data transmission. 10 is a flowchart illustrating a procedure of transmission processing by a CAN communication control unit according to the fourth embodiment. 10 is a flowchart illustrating a procedure of transmission processing by a CAN communication control unit according to the fourth embodiment. 10 is a flowchart illustrating a procedure of reception processing by a CAN communication control unit according to the fourth embodiment. 10 is a flowchart illustrating a procedure of reception processing by a CAN communication control unit according to the fourth embodiment. FIG. 10 is a schematic diagram for explaining an effect of a communication system according to a fourth embodiment. It is a schematic diagram which shows an example of the signal waveform in the conventional communication system. It is a schematic diagram which shows an example of the signal waveform in the conventional communication system.

(Embodiment 1)
Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof. FIG. 1 is a schematic diagram illustrating a configuration example of a communication system. The communication system according to the present embodiment includes, for example, a plurality of ECUs (Electronic Control Units) 1 mounted on a vehicle (not shown) as a communication device, and the plurality of ECUs 1 are connected via a common communication line 5. is there. In FIG. 1, the plurality of ECUs 1 are distinguished from each other by being denoted by reference numerals 1a to 1e, and the communication line 5 is distinguished into a trunk line 5a and branch lines 5b to 5d. That is, the illustrated communication system has a configuration in which

ECUs

1a and 1e are connected via a trunk line 5a, and ECUs 1b to 1d are connected to three branch lines 5b to 5d branched from the trunk line 5a of the communication line 5, respectively.

For example, when a signal is output to the branch line 5b of the communication line 5 by the ECU 1b, this signal passes from the branch line 5b to the ECU 1c via the trunk line 5a and the branch line 5c, and the reflected wave reflected by the terminal portion of the ECU 1c or the like Then, it reaches the ECU 1b via the trunk line 5a and the branch line 5b (see the broken arrow in FIG. 1). Although not shown in FIG. 1, a similar reflected wave is also generated in the ECU 1d. By repeating such signal reflection, ringing as shown in FIGS. 26 and 27 occurs. As the distance between the branch lines 5b to 5d becomes longer, the time until the reflected wave returns to the signal output source becomes longer. Therefore, the period of ringing becomes longer, and the time for ringing to continue (the time required for attenuation) becomes longer. Become. Further, when the number of branch lines 5b to 5d of the communication line 5 increases (the number of ECUs 1 increases), the number of reflected wave generation points increases, so that the ringing amplitude increases and the time required for the ringing to attenuate is increased. become longer.

FIG. 2 is a block diagram showing the configuration of the communication device (ECU 1). The ECU 1 includes a control unit 11, a ROM (Read Only Memory) 12, a RAM (Random Access Memory) 13, an input unit 14, an output unit 15, a CAN communication control unit 16, and the like. The control unit 11 is configured by using an arithmetic processing unit such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit), and performs various controls by reading and executing a control program stored in the ROM 12. Processing can be performed.

The ROM 12 is composed of a nonvolatile memory element such as an EEPROM (Electrically Erasable Programmable ROM) or a flash memory, for example, and a control program executed by the control unit 11 and information necessary for processing performed by the control unit 11. Etc. are stored in advance. The RAM 13 is configured by a memory element such as SRAM (Static RAM) or DRAM (Dynamic RAM), for example, and information generated by processing of the control unit 11 and information transmitted to and received from other ECUs 1. Etc. are stored.

The input unit 14 receives a signal from an input device such as a sensor such as a vehicle speed sensor or a temperature sensor of a vehicle, or various switches for operation arranged inside and outside the vehicle, and performs sampling of the input signal or A / Information obtained by performing processing such as D conversion is given to the control unit 11. The output unit 15 is connected to a load such as a motor or a lamp, and outputs a drive signal for driving these loads in response to an instruction from the control unit 11. Note that the ECU 1 does not necessarily need to include both the input unit 14 and the output unit 15, and may be configured to include only one of them.

The CAN communication control unit 16 has a terminal connected to the communication line 5, and transmits / receives information to / from another ECU 1 according to the CAN protocol via the communication line 5 connected to the terminal. Is. The CAN communication control unit 16 converts the transmission information given from the control unit 11 into transmission data (frame) according to the CAN protocol and gives the data to the transmission unit 17. The transmission unit 17 of the CAN communication control unit 16 outputs a signal to the communication line 5 according to the value of each bit of the given transmission data (0 (dominant) or 1 (recessive)). In the CAN protocol, a twist line is used as the communication line 5, and the transmission unit 17 outputs a differential signal to the communication line 5. The transmission unit 17 sequentially processes each bit of the transmission data composed of a plurality of bits, and when the value of the processing target bit is dominant, outputs a short signal of a predetermined signal level, and then sets the terminal to a high impedance state. When the value of the processing target bit is recessive, the terminal is set to a high impedance state.

Further, the CAN communication control unit 16 determines whether the signal transmitted on the communication line 5 is a signal corresponding to dominant / recessive by detecting the signal level of the communication line 5 (potential difference of the twist line). The receiving unit 18 receives data in which each bit is represented by a dominant / recessive binary value. The CAN communication control unit 16 gives the data received by the receiving unit 18 to the control unit 11. Further, the CAN communication control unit 16 receives the data transmitted by the transmission unit 17 at the reception unit 18, and when the transmission data and the reception data do not match (the recessiveness of the transmission data changes to dominant in the reception data). In the case where a collision has occurred with the transmission of another ECU 1 connected to the communication line 5, arbitration processing is performed. The arbitration process performed by the ECU 1 is the same as that performed by the conventional CAN protocol, and thus detailed description thereof is omitted.

FIG. 3 is a schematic diagram for explaining a signal transmitted and received by each ECU 1 in the communication system according to the present invention. The vertical axis represents a potential difference [V] between twist lines of the communication line 5 and the horizontal axis represents time [n. [Second]. Further, in FIG. 3, the transmission signal is shown in the upper part and the reception signal is shown in the lower part. In the illustrated example, it is assumed that the ECU 1 performs a communication according to the CAN protocol at a communication speed of 1 Mbps, that is, a communication system with a 1-bit data transmission time of 1000 ns. In the example shown in the figure, waveforms are shown when the transmission unit 17 outputs a signal corresponding to dominant from 0 ns to 1000 ns and outputs a signal corresponding to recessive from 1000 ns to 2000 ns.

When transmitting the dominant data, the transmission unit 17 of the ECU 1 outputs a signal (pulse signal) of a predetermined signal level (2 V) during a period from the start time to 400 ns in the 1-bit transmission time 1000 ns, and then 400 ns. During a period of ˜1000 ns, no signal is output and the terminal is in a high impedance state. Further, when performing the recessive data transmission, the transmission unit 17 sets the terminal in a high impedance state without outputting a signal for the entire transmission time of 1 bit (period of 1000 ns to 2000 ns in FIG. 3).

When the transmitter 17 outputs the above signal to the communication line 5, the signal on the communication line 5 has a waveform as shown in the lower part of FIG. During the period from 0 ns to 400 ns when the transmitter 17 outputs a signal of a predetermined signal level, the signal on the communication line 5 has a distorted waveform in the vicinity of the predetermined signal level. Further, during a period of 400 ns to 2000 ns in which the transmission unit 17 puts the terminal in a high impedance state, the signal on the communication line 5 vibrates around about 0V and gradually attenuates over time, that is, a ringing waveform. Become.

The reception unit 18 of the ECU 1 samples the signal level of the communication line 5 at a cycle of 5 ns, for example, over a predetermined period (for example, 400 ns) from the start time of the transmission time 1000 ns of each bit. The receiving unit 18 calculates an average value of the signal level from the sampling result of a predetermined period, and performs dominant / recessive determination according to whether or not the calculated average value exceeds a predetermined threshold value. In the example shown in the lower part of FIG. 3, the average signal level from 0 ns to 400 ns is about 1.7 V, and the receiving unit 18 performs determination using, for example, 1 V as a threshold, so that dominant transmission is performed during the period from 0 ns to 1000 ns. It is determined that The average of the signal levels from 1000 ns to 1400 ns is about 0 V, and the receiving unit 18 determines that recessive transmission is performed during this period.

Next, an evaluation result by simulation of the communication system according to the present invention will be described. In this simulation, it is assumed that the communication speed is 1 Mbit / s (that is, 1-bit data transmission time is 1000 ns), and the receiving unit 18 samples the signal level at a cycle of 5 ns. For each sampling result, the standard deviation of noise σ = 1 V / sample was considered. The threshold for comparison with the average value of the sampling results was set to 0.85V. In this simulation, the dominant → recessive data with the largest ringing effect was transmitted. Under this condition, when the signal width of the signal output from the transmitter 17 during dominant transmission is Tp and the period during which the receiver 18 samples the signal level is Td, the communication error (bit error rate) is minimized. Consider a combination of Tp and Td.

4A and 4B are schematic diagrams for explaining the configuration of the communication system evaluated by simulation. This simulation was performed in consideration of two conditions that are severe for communication. Condition 1 shown in FIG. 4A is a condition in which the distance from the transmission-side ECU 1 to the reception-side ECU 1 is long and signal propagation delay is severe. In condition 1, the distance between the transmission-side and reception-side ECU 1 (the length of the communication line 5) is 15 m (the longest distance of the communication line 5 in the vehicle), and the load impedance in the transmission-side and reception-side ECU 1 is 120Ω. did. Condition 2 shown in FIG. 4B is a condition in which ringing is severe. Under condition 2, the ECU 1 receives a signal transmitted by itself, the length of the branch line of the communication line 5 to which the ECU 1 is connected is 2 m, and the load impedance of the ECU 1 is 40 kΩ. The bit error rate BER is calculated by the following equation (1). In the equation (1), A1 indicates an average value of the signal level calculated by the receiving unit 18 with the signal corresponding to the dominant, and A0 indicates an average value of the signal level calculated by the receiving unit 18 with the signal corresponding to the recessive. , Ts indicates the sampling time, and erfc () is a complementary error function.

FIG. 5 is a graph showing the simulation results, in which the horizontal axis is the pulse width Tp and the vertical axis is the bit error rate. In the illustrated graph, the simulation result under condition 1 is indicated by a broken line, the simulation result under condition 2 is indicated by a one-dot chain line, and the average of both conditions is indicated by a solid line. In the illustrated graph, the simulation results are plotted at intervals of 100 ns from 100 ns to 1000 ns with respect to the pulse width Tp of the signal output to the dominant. From the graph shown, the pulse width Tp = 400 ns has the smallest bit error rate average value. Although illustration of the simulation result is omitted, the sampling period Td = 345 ns in which the average value of the bit error rate is the smallest with respect to the pulse width Tp = 400 ns. Therefore, when the communication system of the present embodiment performs communication at a communication speed of 1 Mbps, the pulse width Tp of the signal output from the transmitter 17 to the dominant is set to 400 ns, and the sampling period Td by the receiver 18 is set to 345 ns. Therefore, it is possible to realize highly accurate communication with a minimum bit error rate.

FIG. 6 is a flowchart showing a procedure of transmission processing by the transmission unit 17. The transmission unit 17 of the CAN communication control unit 16 first acquires 1-bit information to be transmitted from the data to be transmitted (step S1), and determines whether or not this 1-bit is dominant (step S1). Step S2). If 1 bit to be transmitted is dominant (S2: YES), the transmission unit 17 outputs a signal at a predetermined signal level to the communication line 5 (step S3). Next, the transmitter 17 further determines whether or not a time (predetermined time Tp) corresponding to the pulse width Tp determined from the start of output of this signal has passed (step S4), and the time corresponding to the pulse width Tp. If it has not elapsed (S4: NO), the process returns to step S3 to continue signal output.

When the time corresponding to the determined pulse width Tp has elapsed (S4: YES), the transmission unit 17 stops signal output and places the terminal in a high impedance state (step S5). Similarly, when 1 bit to be transmitted is not dominant (S2: NO), that is, in the case of recessive, similarly, the transmission unit 17 sets the terminal in a high impedance state without performing signal output (step S5). Thereafter, the transmission unit 17 determines whether or not the 1-bit transmission time has elapsed (step S6). If the 1-bit transmission time has not elapsed (S6: NO), the process proceeds to step S5. Return and continue high impedance state. When the transmission time of 1 bit has elapsed (S6: YES), the transmission unit 17 further determines whether or not to end transmission by determining whether or not transmission of all the bits of the transmission data has been completed. (Step S7). When it determines with not complete | finishing transmission (S7: NO), the transmission part 17 returns a process to step S1, and performs the same process about the next bit of transmission data. When it is determined that the transmission is to be ended (S7: YES), the transmission unit 17 ends the transmission process.

FIG. 7 is a flowchart showing a procedure of reception processing by the reception unit 18. The receiving unit 18 of the CAN communication control unit 16 determines whether or not the signal level of the communication line 5 has exceeded a predetermined threshold (step S20), and if the signal level does not exceed the threshold (S20: NO), Wait until the signal level exceeds the threshold. When the signal level exceeds the threshold (S20: YES), the receiving unit 18 samples the signal level of the communication line 5 (step S21), and determines whether the sampling period Td has elapsed since the start of sampling (step S21). Step S22). If it is determined that the sampling period Td has not elapsed (S22: NO), the receiving unit 18 returns the process to step S21 and repeats sampling of the signal level.

When it is determined that the sampling period Td has elapsed (S22: YES), the receiving unit 18 calculates an average value of a plurality of signal levels sampled in the sampling period Td (step S23), and the calculated average value is determined in advance. It is determined whether or not the determined threshold value is exceeded (step S24). When it determines with the average value of a signal level exceeding a threshold value (S24: YES), the receiving part 18 determines with the received signal corresponding to a dominant (step S25), and advances a process to step S27. When it is determined that the average signal level does not exceed the threshold (S24: NO), the receiving unit 18 determines that the received signal corresponds to recessive (step S26), and the process proceeds to step S29. Proceed.

In addition, after determining that the signal received in step S25 is dominant, the reception unit 18 determines whether or not the transmission unit 17 was performing recessive transmission during the period during which the signal was sampled (step S25). S27). When the transmission unit 17 is performing recessive transmission (S27: YES), since the transmitted recessive has changed to dominant, the reception unit 18 detects that another ECU 1 has transmitted a signal (step S28). ), The process proceeds to step S29. If the transmission unit 17 is not performing recessive transmission (S27: NO), the reception unit 18 proceeds to step S29 without detecting the signal transmission of the other ECU1.

Thereafter, the receiving unit 18 determines whether or not the 1-bit transmission time has elapsed (step S29). If the 1-bit transmission time has not elapsed (S29: NO), this time has elapsed. Wait until. When the transmission time of 1 bit has elapsed (S29: YES), the reception unit 18 returns the process to step S20 and performs the same reception process for the next bit.

In the communication system configured as described above, the transmission unit 17 of the ECU 1 outputs a signal of a predetermined signal level over the pulse width Tp shorter than the transmission time of 1 bit to the communication line 5 when the transmission data is dominant, and then Stops the signal output to the communication line 5 to be in a high impedance state, and when the transmission data is recessive, does not output a signal to the communication line 5 to be in a high impedance state. As a result, even if ringing occurs after the signal corresponding to the dominant is output, the ringing can be attenuated until the transmission time of the next bit, so that the dominant / recessive determination in each bit can be performed quickly. It is possible to perform at the timing, and it is possible to realize high speed communication.

Further, the receiving unit 18 of the ECU 1 samples the signal level of the communication line 5 over the sampling period Td, calculates an average value of the sampled signal levels, and depending on whether the calculated average value exceeds a threshold value. By adopting a configuration that performs dominant / recessive determination, it is possible to reduce the influence of ringing that repeats positive and negative amplitudes in the vicinity of 0 V, and to perform processing such as data reception and arbitration with high accuracy.

In the present embodiment, the communication system is mounted on the vehicle, but the present invention is not limited to this. The configuration of the communication system shown in FIG. 1 (the number of ECUs 1, the connection form of the ECU 1, etc.) is merely an example, and the present invention is not limited to this. Further, although the twisted line is used as the communication line 5, the present invention is not limited to this, and other structures such as using one cable as the communication line 5 may be used.

(Embodiment 2)
In the communication system according to the first embodiment described above, the receiving unit 18 of the ECU 1 samples the signal level of the communication line 5, calculates the average value of the signal level of the sampling result, and whether or not this average value exceeds the threshold value. In this configuration, dominant / recessive determination is performed. On the other hand, the communication system according to the second embodiment is similar in that the reception unit 18 of the ECU 1 samples the signal level of the communication line 5, but the subsequent dominant / recessive determination method is different. In the communication system according to the second embodiment, the receiving unit 18 compares the signal level of each sampling result with a threshold value, and depends on the number of samples whose signal level exceeds the threshold value and the number of samples whose signal level does not exceed the threshold value. The configuration is such that a majority decision is made and a dominant / recessive decision is made.

The receiving unit 18 of the ECU 1 according to the second embodiment sets the signal level of the communication line 5 over a predetermined period (for example, 400 ns) from the start point in the transmission time of each bit (for example, 1000 ns) for a predetermined period (for example, 5 ns period). The signal level is compared with the threshold value at a predetermined cycle. For example, the receiving unit 18 can be configured such that the signal of the communication line 5 is input to the CMOS circuit, and acquires the signal output from the CMOS circuit at a predetermined period.

The receiving unit 18 includes two counters that count the comparison result between the signal level and the threshold value. The number of samples whose signal level exceeds the threshold value and the number of samples whose signal level does not exceed the threshold value are respectively set. It counts with the counter. For example, the receiving unit 18 can be configured to count up one of the two counters in accordance with the output signal of the CMOS circuit.

After the elapse of a predetermined period, the receiving unit 18 compares the values of the two counters. If the number of samples whose signal level exceeds the threshold is greater than the number of samples not exceeding the threshold, dominant transmission is performed during this period. It is determined that Further, when the number of samples whose signal level exceeds the threshold is smaller than the number of samples that does not exceed the threshold, the receiving unit 18 determines that recessive transmission has been performed during this period.

Next, evaluation results by simulation of the communication system according to Embodiment 2 will be described. In this simulation, the amplitude (potential difference between twisted cables) of signals transmitted and received on the communication line 5 is set to 2.0 V, the determination level of the CMOS circuit of the receiving unit 18 is set to 0.9 V, and the maximum signal delay is set to 0. 5 μs, and the receiver 18 samples the signal level (output of the CMOS circuit) at a cycle of 100 ns. Similarly to the simulation of the communication system according to the first embodiment, the simulation of the communication system according to the second embodiment is performed for the two conditions shown in FIGS. 4A and 4B (where the distance between transmission and reception in the condition 2 is 0 m). Went. Under this condition, when the signal width (pulse width) of the signal output from the transmission unit 17 during dominant transmission is Tp and the period during which the reception unit 18 samples the signal level is Td, the communication error by majority decision is determined. Consider (success / failure).

FIG. 8 is a table showing the simulation results of the second embodiment. The table shown in the figure shows each combination of Tp and Td when the pulse width Tp is changed from 0.1 μs to 1.0 μs at intervals of 0.1 μs and the sampling period Td is changed from 0.1 μs to 0.5 μs. The simulation result is described as “correct” when communication can be performed without error and as “error” when an error occurs. Note that the combinations indicated by “−” in the table are not simulated (since the sampling period Td cannot be set longer than the pulse width Tp). In the simulation results, for each combination of Tp and Td, “Positive” indicates that no error has occurred in the determination of both dominant and recessive values under both

conditions

1 and 2, and there is an error in either case. What happened is called "false".

From the simulation results shown in the figure, it can be seen that, when the pulse width Tp is long, the influence of ringing appears, so that an error occurs in the determination of dominant / recessive communication. On the other hand, the occurrence of errors can be suppressed by increasing the sampling period Td.

FIG. 9 and FIG. 10 are flowcharts showing a procedure of reception processing by the reception unit 18 of the second embodiment. In this processing, it is assumed that the receiving unit 18 performs processing using two counters, a D counter and an R counter. The receiving unit 18 of the CAN communication unit 16 according to the second embodiment first initializes two counters, a D counter and an R counter (step S41). Next, the receiving unit 18 determines whether or not the signal level of the communication line 5 has exceeded a predetermined threshold (step S42), and if the signal level does not exceed the threshold (S42: NO), the signal level exceeds the threshold. Wait until it exceeds.

When the signal level exceeds the threshold (S42: YES), the reception unit 18 samples the signal level of the communication line 5 (step S43), and determines whether the signal level of the sampled signal exceeds the threshold. (Step S44). Note that the threshold value in step S42 and the threshold value in step S44 may be the same value. When the signal level exceeds the threshold value (S44: YES), the reception unit 18 counts up the D counter (step S45). When the signal level does not exceed the threshold value (S44: NO), the reception unit 18 counts up the R counter. (Step S46).

After counting up the D counter or the R counter, the receiving unit 18 determines whether or not the sampling period Td has elapsed from the start of sampling (step S47). When it is determined that the sampling period Td has not elapsed (S47: NO), the receiving unit 18 returns the process to step S43, and repeatedly performs sampling of the signal level and comparison with the threshold value.

When it is determined that the sampling period Td has elapsed (S47: YES), the receiving unit 18 compares the values of the two counters and determines whether or not the value of the D counter exceeds the value of the R counter (step S48). ). If it is determined that the value of the D counter exceeds the value of the R counter (S48: YES), the receiving unit 18 determines that the received signal corresponds to a dominant (step S49), and the process proceeds to step S51. Proceed. If it is determined that the value of the D counter does not exceed the value of the R counter (S48: NO), the receiving unit 18 determines that the received signal corresponds to recessive (step S50), and proceeds to step S53. Proceed with the process.

Further, after determining that the signal received in step S49 is dominant, the reception unit 18 determines whether or not the transmission unit 17 is performing a recessive transmission during the period during which the signal was sampled (step S49). S51). When the transmission unit 17 is performing recessive transmission (S51: YES), since the transmitted recessive has changed to dominant, the reception unit 18 detects that another ECU 1 has transmitted a signal (step S52). ), The process proceeds to step S53. If the transmission unit 17 is not performing recessive transmission (S51: NO), the reception unit 18 proceeds to step S53 without detecting the signal transmission of the other ECU1.

Thereafter, the receiving unit 18 determines whether or not the 1-bit transmission time has elapsed (step S53). If the 1-bit transmission time has not elapsed (S53: NO), this time has elapsed. Wait until. When the transmission time of 1 bit has elapsed (S53: YES), the reception unit 18 returns the process to step S41, and performs the same reception process for the next bit.

In the communication system according to Embodiment 2 configured as described above, the receiving unit 18 of the ECU 1 samples the signal level of the communication line 5 over the sampling period Td, and the sampled signal level compares the threshold value with the threshold value. Thus, the dominant / recessive determination is performed according to the number of samples whose signal level exceeds the threshold and the number of samples whose signal level does not exceed the threshold. Since the configuration of the communication system according to the second embodiment can facilitate the circuit configuration of the receiving unit 18 as compared with the configuration of the communication system according to the first embodiment, the price of the ECU 1 can be reduced. Can be realized.

In the second embodiment, the receiving unit 18 is configured to perform determination using two counters, but is not limited thereto, and may be configured to perform determination using one counter. For example, the counter can be counted up only when it is determined that the signal level exceeds the threshold, and it can be determined whether or not the value of the counter exceeds half of the total number of samplings. Further, for example, the counter can be counted up when it is determined that the signal level exceeds the threshold, and the counter can be counted down when it is determined that the signal level does not exceed the threshold. In addition, the comparison between the signal level of the communication line 5 and the threshold value is performed by the CMOS circuit. However, the configuration is not limited to this, and the comparison may be performed by another circuit.

(Embodiment 3)
In the communication systems according to the above-described first and second embodiments, as shown in FIGS. 5 and 8, etc., the pulse width Tp (predetermined time Tp) of the pulse signal output at the time of dominant transmission, and at the time of reception The value of the sampling period Td (predetermined sampling period Td) for sampling the signal level has a great influence on the communication performance. The optimum pulse width Tp and sampling period Td are set in advance in each ECU 1 by measuring the characteristics of the communication system and calculating the optimum values before shipping the communication system (vehicle equipped with) to the factory, for example.

However, the pulse width Tp and the sampling period Td calculated and set in advance are optimal values, for example, when the number of ECUs 1 is increased / decreased due to addition / deletion of optional equipment of the vehicle, and the characteristics of the communication system change. There is a possibility of disappearing. Further, the communication characteristics may change due to the secular changes of the ECU 1 and the communication line 5 and the like, and the pulse width Tp and the sampling period Td calculated and set in advance may not be optimal values.

The communication system according to Embodiment 3 solves the above problem by providing an automatic setting function of the pulse width Tp and the sampling period Td. This automatic setting process is performed at a vehicle dealer or factory, for example, when a vehicle equipped with a communication system is shipped from the factory, when the vehicle is inspected, or when the ECU 1 is added / deleted. . During the automatic setting process, each ECU 1 of the communication system stops the normal communication process.

In the communication system according to the third embodiment, in the automatic setting process of the pulse width Tp and the sampling period Td, one ECU 1 serves as a master ECU and the remaining ECU 1 serves as a slave ECU. The function as the master ECU may be provided only in one ECU 1 in the communication system, or provided in a plurality of ECUs 1 and any one ECU 1 operates as a master ECU depending on the situation. Also good.

In the following description, in the configuration of the communication system in FIG. 1, the ECU 1a is a master ECU, and the other ECUs 1b to 1e are slave ECUs. For example, the master ECU 1a is provided with an operation unit (not shown) for operating the automatic setting processing of the pulse width Tp and the sampling period Td, and an operator can operate the operation unit at a vehicle dealer or factory. By performing an operation on, automatic setting processing is started.

The master ECU 1a transmits an automatic setting process start command to the slave ECUs 1b to 1e via the communication line 5. The slave ECUs 1b to 1e that have received this stop normal control processing and communication processing, and start automatic setting processing. Note that the automatic setting process start command transmitted by the master ECU 1a may be transmitted as data conforming to the CAN protocol, for example, and a specific signal different from the CAN protocol is output to the communication line 5, for example. The slave ECUs 1b to 1e may be configured to detect the signal.

Thereafter, the master ECU 1 a outputs a test signal to the communication line 5. FIG. 11 is a schematic diagram for explaining a test signal output in the automatic setting process. The master ECU 1a outputs a signal in which dominant and recessive are alternately connected as a test signal. As shown in the upper part of FIG. 11, the test signal has a configuration in which N signal sequences from the Tp1 signal sequence to the TpN signal sequence are separated by a delimiter. The delimiter is a signal sequence determined in advance as a delimiter. For example, the delimiter can be a signal in which a predetermined number of recessive signals are continuous. The signal sequence of Tpn (n = 1, 2,..., N) has a configuration in which M dominant and recessive 2-bit sequences are continued.

Further, as shown in the lower part of FIG. 11, the pulse widths of the pulse signals output as dominants are different in the Tpn signal sequence. That is, the dominant pulse width in the Tp1 signal train is Tp1, the dominant pulse width in the Tp2 signal train is Tp2,..., And the dominant pulse width in the TpN signal train is TpN.

Thus, the master ECU 1a outputs a test signal including L × N 2-bit strings of dominant and recessive to the communication line 5. On the other hand, the master ECU 1a and the slave ECUs 1b to 1e (that is, all the ECUs 1a to 1e in the communication system) sample the test signal output to the communication line 5. FIG. 12 is a schematic diagram for explaining the sampling performed in the automatic setting process. As shown in the upper part of FIG. 12, in the Tpn signal sequence of the test signal, there are M consecutive dominant and recessive 2-bit sequences in which the dominant pulse width is set to Tpn.

In contrast, each of the ECUs 1a to 1e samples the test signal while changing the sampling period Tdm (m = 1, 2,..., M). Each of the ECUs 1a to 1e samples one dominant and recessive 2-bit string in the same sampling period Tdm, and samples the next 2-bit string in another sampling period Tdm. Accordingly, each of the ECUs 1a to 1e performs sampling twice in the same sampling period Tdm, like the sampling periods Td1, Td1, Td2, Td2,..., TdM, TdM. Since the test signal is a signal in which dominant and recessive are alternately repeated, by performing sampling twice in the same sampling period Tdm, each ECU 1a to 1e can perform dominant and recessive sampling in the same sampling period Tdm. it can.

Each of the ECUs 1a to 1e repeatedly samples the voltage value of the communication line 5 with a predetermined period of, for example, 5 ns during each sampling period Tdm, and a plurality of sampling results obtained by a plurality of samplings are obtained. Whether the signal on the communication line 5 is dominant or recessive based on (for example, based on the average value of the sampling results in the first embodiment and based on the majority decision of the sampling results in the second embodiment). Is judged. In the automatic setting process, each of the ECUs 1a to 1e calculates an evaluation value according to the following equation (2) from a plurality of sampling results obtained during each sampling period Tdm.

Evaluation value = (D0-R0) / Pd (2)

Note that the evaluation value is calculated for the dominant and recessive sampling results performed in the same sampling period Tdm. In the equation (2), D0 is the number of sampling results in which the dominant signal is determined to be dominant, R0 is the number of sampling results in which the recessive signal is determined to be dominant, and Pd is the number of samplings of dominant or recessive. is there. The evaluation value ranges from −1 to +1. If the evaluation value is greater than 0, dominant or recessive can be correctly determined by majority decision.

When the above sampling and evaluation value calculation are performed on a signal sequence having one pulse width Tpn of the test signal, each of the ECUs 1a to 1e can calculate M evaluation values. Each of the ECUs 1a to 1e selects the sampling period Tdm having the highest evaluation value. Since the test signal includes a signal sequence having N kinds of pulse widths Tpn, each ECU 1a to 1e can select one sampling period Tdm for each pulse width Tpn. The sampling period Tdm is stored in the RAM 13 together with the pulse width Tpn and the evaluation value.

FIG. 13 is a schematic diagram showing an example of the sorting result stored in the RAM 13. After the output of the test signal by the master ECU 1a and the sampling and evaluation of the test signal by the ECUs 1a to 1e are completed, for example, the slave ECU 1b outputs the same test signal, and the ECU 1a to 1e Evaluate etc. In this way, all ECUs 1a to 1e in the communication system sequentially output test signals, and each ECU 1a to 1e performs sampling, evaluation, and the like on all the test signals output from all ECUs 1a to 1e. For example, when the number of ECUs mounted in the communication system is L, the selected L × N sampling periods Tdm are stored in the RAM 13.

Note that the output order of the test signals by the ECUs 1a to 1e may be any order. In the above description, the master ECU 1a first outputs the test signal, but it is not always necessary to start outputting the test signal from the master ECU 1a. For example, the test signals may be output according to a predetermined order for each of the ECUs 1a to 1e. For example, the ECUs 1a to 1e may output the test signals at random. In the configuration in which the test signals are output at random, when the plurality of ECUs 1a to 1e output the test signals simultaneously, for example, the output of the test signals may be stopped and the output may be performed again after a random waiting time has elapsed.

After the output of test signals by all the ECUs 1a to 1e is completed, the master ECU 1a sequentially requests the slave ECUs 1b to 1e to transmit the information stored in the RAM 13. In response to this request, the slave ECUs 1b to 1e read out the information stored in the RAM 13 and transmit it to the master ECU 1a. The master ECU 1a receives information from all the slave ECUs 1b to 1e and stores it in the RAM 13. As a result, the RAM 13 of the master ECU 1a stores information such as L × L × N sampling periods and evaluation values including information created by itself.

Next, the master ECU 1a determines the pulse width used in the subsequent communication based on the information stored in the RAM 13. The master ECU 1a selects one pulse width from the N pulse widths Tpn based on the evaluation values included in the L × L × N pieces of information, but any selection method may be used. For example, for the L × L × N pieces of information, the master ECU 1a first excludes the pulse width Tpn whose evaluation value is equal to or less than the threshold from the selection target, and selects the pulse width Tpn having the largest average evaluation value of each pulse width Tpn. be able to. The master ECU 1a notifies the selected one pulse width Tpn to the slave ECUs 1b to 1e by broadcast or the like.

Each of the slave ECUs 1b to 1e notified of the pulse width Tpn from the master ECU 1a determines a sampling period Tdm suitable for the pulse width Tpn based on the information stored in the RAM 13 (see FIG. 13). The information stored in the RAM 13 stores L pieces of sampling period Tdm and evaluation value information corresponding to the notified pulse width Tpn, and the slave ECUs 1b to 1e select one sampling period Tdm from these. select. However, any selection method may be used. For example, for the L pieces of information, the slave ECUs 1b to 1e can first exclude the sampling period Tdm whose evaluation value is equal to or less than the threshold from the selection target and select the sampling period Tdm having the largest evaluation value. Similarly, the master ECU 1a determines the sampling period Tdm with respect to the pulse width Tpn determined by itself based on the information created by itself among the information stored in the RAM 13.

Next, the ECUs 1a to 1e store the pulse width Tpn determined by the master ECU 1a and the sampling period Tdm determined by the ECU 1a in a non-volatile memory for storing a set value provided in the CAN communication control unit 16, for example. Store and update communication parameters. Thereafter, communication by each of the ECUs 1a to 1e is performed using a newly set pulse width and sampling period. That is, the ECUs 1a to 1e perform dominant transmission processing with a common pulse width determined by the master ECU 1a. Each of the ECUs 1a to 1e performs reception processing in a sampling period determined by itself. The sampling periods of the ECUs 1a to 1e may be different.

FIG. 14 is a flowchart showing a procedure of automatic setting processing performed by the master ECU 1a. First, the master ECU 1a transmits an automatic setting process start command to all the slave ECUs 1b to 1e in the communication system (step S61). Next, the master ECU 1a performs a test signal transmission process (step S62) and a test signal reception process (step S63). The test signal transmission process in step S62 and the test signal reception process in step S63 are performed in parallel. The detailed procedure of steps S62 and S63 will be described later.

Based on information such as a sampling period and an evaluation value obtained by the test signal reception process, the master ECU 1a selects a sampling period suitable for the pulse width (step S64), and stores the selection result in the RAM 13 (step S65). ). Next, the master ECU 1a determines whether or not all the ECUs 1a to 1e of the communication system have finished transmitting test signals (step S66). If all the ECUs 1a to 1e have not finished transmitting the test signals (S66: NO), the master ECU 1a returns the process to step S63, and the test signal receiving process and the test signals for the slave ECUs 1b to 1e are transmitted. The sampling period is selected (in this case, the master ECU 1a does not perform the test signal transmission process).

When all the ECUs 1a to 1e have finished transmitting the test signals (S66: YES), the master ECU 1a gives a request for transmitting the selection result of the sampling period to one of the slave ECUs 1b to 1e (step S67). The selection results transmitted from the slave ECUs 1b to 1e are received (step S68), and the received selection results are stored in the RAM 13 (step S69). The master ECU 1a determines whether or not the selection results of all the ECUs 1a to 1e are stored in the RAM 13 (step S70). If the selection results of all the ECUs 1a to 1e are not stored (S70: NO), the process proceeds to step S67. And sends a transmission request to another slave ECU 1b to 1e.

When the selection results of all the ECUs 1a to 1e are stored (S70: YES), the master ECU 1a determines one pulse width based on the evaluation value of the information stored in the RAM 13 (step S71), and determines the determined pulse width. All the slave ECUs 1b to 1e are notified (step S72). Next, the master ECU 1a determines a sampling period suitable for the pulse width determined in step S71 based on the information stored in the RAM 13 (step S73). The master ECU 1a updates the setting by storing the pulse width determined in step S71 and the sampling period determined in step S73 in, for example, a memory in the CAN communication control unit 16 (step S74), and ends the process. To do.

FIG. 15 is a flowchart showing a procedure of automatic setting processing performed by the slave ECUs 1b to 1e. The slave ECUs 1b to 1e determine whether or not an automatic setting process start command is received from the master ECU 1a (step S81). If no start command is received (S81: NO), the slave ECU 1b-1e receives the start command. Wait until

When the start command is received (S81: YES), the slave ECUs 1b to 1e determine whether or not the transmission order is their own (step S82). When the slave ECUs 1b to 1e are in their own transmission order (S82: YES), the slave ECUs 1b to 1e perform a test signal transmission process (step S83), and when they are not in their own transmission order (S82: NO), perform the test signal transmission process. Absent. The slave ECUs 1b to 1e perform a test signal reception process (step S84). When the slave ECUs 1b to 1e perform the test signal transmission process in step S83, the test signal transmission process and the test signal reception process in step S84 are performed in parallel.

Based on information such as the sampling period and the evaluation value obtained by the test signal reception process, the slave ECUs 1b to 1e select a sampling period suitable for the pulse width (step S85), and store the selection result in the RAM 13 (step S85). Step S86). Next, the slave ECUs 1b to 1e determine whether or not all the ECUs 1a to 1e of the communication system have finished transmitting the test signals (step S87). If all the ECUs 1a to 1e have not finished transmitting the test signals (S87: NO), the slave ECUs 1b to 1e return the process to step S82 and repeat the above process.

When all the ECUs 1a to 1e have finished transmitting the test signals (S87: YES), the slave ECUs 1b to 1e determine whether or not a selection result transmission request from the master ECU 1a has been received (step S88). When the transmission request for the sorting result has not been received (S88: NO), the slave ECUs 1b to 1e stand by until the transmission request is received. When the selection result transmission request is received (S88: YES), the slave ECUs 1b to 1e transmit the selection result stored in the RAM 13 to the master ECU 1a (step S89).

Next, the slave ECUs 1b to 1e determine whether or not the pulse width determined and notified by the master ECU 1a has been received (step S90). When the pulse width is not received from the master ECU 1a (S90: NO), the slave ECUs 1b to 1e stand by until the pulse width is received. When the pulse width is received (S90: YES), the slave ECUs 1b to 1e determine a sampling period suitable for the pulse width received in step S90 based on the information stored in the RAM 13 (step S91). The slave ECUs 1b to 1e update the settings by storing the pulse width received in step S90 and the sampling period determined in step S91 in, for example, a memory in the CAN communication control unit 16 (step S92), and processing Exit.

FIG. 16 is a flowchart showing the procedure of the test signal transmission process, which is a process performed by the ECU 1 (master ECU 1a or slave ECUs 1b to 1e) in step S62 of the flowchart shown in FIG. 14 and step S83 of the flowchart shown in FIG. . In the illustrated flowchart, variables i and j for counting the number of processing loops are used. These variables are secured in a storage area such as a register in the control unit 11 of the ECU 1 or the RAM 13. The constant N is the number of types of pulse widths in the test signal, and the constant M is the number of consecutive 2-bit strings of dominant and recessive output for one pulse width in the test signal.

In the test signal transmission process, first, the ECU 1 initializes the values of the variables i and j to 1 (step S101). Next, the ECU 1 sets the pulse width to the i-th pulse width Tpi (step S102), outputs a dominant with this pulse width (step S103), outputs recessive (step S104), and sets the value of the variable j to 1. Are added (step S105). The ECU 1 determines whether or not the value of the variable j exceeds the constant M (step S106). If the value of the variable j does not exceed the constant M (S106: NO), the process returns to step S103, and the dominant and Repeat the recessive output.

When the value of the variable j exceeds the constant M (S106: YES), the ECU 1 initializes the value of the variable j to 1 (step S107) and adds 1 to the value of the variable i (step S108). Next, the ECU 1 determines whether or not the value of the variable i exceeds a constant N (step S109). When the value of the variable i does not exceed the constant N (S109: NO), the ECU 1 outputs a delimiter (step S110), returns the process to step S102, and repeats signal output with the next pulse width. When the value of the variable i exceeds the constant N (S109: YES), the ECU 1 ends the test signal transmission process.

FIG. 17 is a flowchart showing the procedure of the test signal reception process, and is a process performed by the ECU 1 (master ECU 1a or slave ECUs 1b to 1e) in step S63 of the flowchart shown in FIG. 14 and step S84 of the flowchart shown in FIG. . The variables i and j and the constants M and N are the same as those in the flowchart shown in FIG.

In the test signal reception process, first, the ECU 1 initializes the values of the variables i and j to 1 (step S121). Next, the ECU 1 sets the sampling period to the j-th sampling period Tdj (step S122), performs dominant sampling in this sampling period (step S123), and performs recessive sampling (step S124). The ECU 1 calculates an evaluation value based on the expression (2) based on the sampling results of steps S123 and S124, and stores it in the RAM 13 (step S125). Next, the ECU 1 adds 1 to the value of the variable j (step S126), and determines whether or not the value of the variable j exceeds the constant M (step S127). When the value of the variable j does not exceed the constant M (S127: NO), the ECU 1 returns the process to step S122 and repeats sampling in the next sampling period.

When the value of the variable j exceeds the constant M (S127: YES), the ECU 1 initializes the value of the variable j to 1 (step S128) and adds 1 to the value of the variable i (step S129). Next, the ECU 1 determines whether or not the value of the variable i exceeds a constant N (step S130). When the value of the variable i does not exceed the constant N (S130: NO), after receiving the delimiter (step S131), the ECU 1 returns the process to step S122 and repeats the above process. When the value of the variable i exceeds the constant N (S130: YES), the ECU 1 ends the test signal reception process.

The communication system according to Embodiment 3 configured as described above has a function of automatically setting a pulse width and a sampling period necessary for performing communication processing. As a result, even when the number of ECUs 1 is increased or decreased, or when a secular change occurs, for example, when the number of ECUs 1 is increased or decreased or when maintenance is performed on the communication system, the changed communication is performed. Communication can be performed with communication parameters suitable for the characteristics. Therefore, the communication system can maintain high-quality and high-speed communication.

When automatically setting communication parameters, one ECU 1 transmits test signals in order, and all ECUs 1 perform processing to receive the test signals. The test signal is transmitted while changing the dominant pulse width, and the test signal is received while changing the sampling period. Thereby, the transmission / reception results can be evaluated for a plurality of combinations of the pulse width and the sampling period, and the pulse width and the sampling period suitable for the communication characteristics of the communication system can be determined from these evaluation results.

Also, the evaluation results of the slave ECUs 1b to 1e are collected in the master ECU 1a, and the master ECU 1a determines the pulse width based on all the evaluation results and notifies each slave ECU 1b to 1e. As a result, all ECUs 1 can perform subsequent communication with a common pulse width. Further, each ECU 1 determines the sampling period according to the pulse width determined by the master ECU 1a and its own evaluation result. Thereby, the sampling period suitable for each ECU 1 can be determined.

In the present embodiment, the evaluation value based on the expression (2) is calculated to determine the pulse width and the sampling period. However, the present invention is not limited to this, and the evaluation value is calculated based on other calculation expressions. It may be calculated. In addition, the above processing for determining the pulse width and the sampling period is performed by the control unit 11 of each ECU 1, but the present invention is not limited to this, and the CAN communication control unit 16 may perform the processing.

(Embodiment 4)
The communication system according to the fourth embodiment is slightly different from that of the communication system according to the first to third embodiments described above, with respect to the signal that each ECU 1 outputs as a dominant. The transmission unit 17 of the ECU 1 according to the fourth embodiment sequentially processes each bit of transmission data composed of a plurality of bits. When the value of the processing target bit is dominant, the transmission unit 17 performs the first predetermined time Tp. After outputting the signal of the first signal level, the signal of the second signal level (<first signal level) is output for the second predetermined time Th. In addition, when the value of the processing target bit is recessive, the transmission unit 17 sets the terminal in a high impedance state.

FIG. 18 is a schematic diagram for explaining signals transmitted and received by each ECU 1 in the communication system according to the fourth embodiment. The vertical axis represents the potential difference V between the twist lines of the signal line 5, and the horizontal axis represents time t. It is a graph. The illustrated example is a signal when transmission data changes from dominant to recessive. When transmitting the dominant data, the transmission unit 17 of the ECU 1 outputs a signal of the first signal level (V1) in the period from the start time to the first predetermined time Tp in the 1-bit transmission time Tb. The signal of the second signal level (0 V) is output over the second predetermined time Th. Note that Tp + Th ≦ Tb may be satisfied. When Tp + Th <Tb, the transmission unit 17 does not output a signal until the 1-bit transmission time Tb is reached after the second predetermined time Th has elapsed. Set to high impedance state. Further, in the case of performing recessive data transmission, the transmission unit 17 sets a terminal in a high impedance state without outputting a signal for the entire transmission time Tb of 1 bit.

The reception unit 18 of the ECU 1 samples the signal level of the communication line 5 at a predetermined cycle over a first predetermined time Tp from the start time in the transmission time Tb of each bit. The receiving unit 18 calculates the average value of the signal level from the sampling result over the first predetermined time Tp, and determines the dominant / recessive depending on whether the calculated average value exceeds a predetermined threshold value. Do.

Further, the CAN communication control unit 16 has a function of dynamically performing impedance matching of the communication line 5 when performing communication. FIG. 19 is a schematic diagram for explaining impedance matching by the CAN communication control unit 16 according to the fourth embodiment, and a circuit in the CAN communication control unit 16 is schematically shown. The CAN communication control unit 16 has two terminals 16a to which twist lines are connected. In the CAN communication control unit 16, for example, two internal wirings connected to the two terminals 16a are laid on a circuit board or the like.

The two internal wirings are respectively connected to two output terminals of the output differential amplifier of the transmission unit 17 and two input terminals of the input differential amplifier of the reception unit 18. Each internal wiring is connected to one end of a resistor R via a switch SW, and the other end of the resistor R is connected to a ground potential. The resistance value of each resistor R is set to 60Ω, for example (this resistance value is a half value of 120Ω defined as the termination resistance value of the transmission line by the CAN protocol). The switching unit 19 having two switches SW connected to two internal wirings turns on the two switches SW according to a control signal output from a control circuit (not shown) in the CAN communication control unit 16. / Switch off (connect / block) simultaneously.

The CAN communication control unit 16 turns off the two switches SW of the switching unit 19 during the period from the start of transmission of each bit until the first predetermined time Tp elapses in the 1-bit transmission time Tb shown in FIG. The resistor R is disconnected from the internal wiring. The CAN communication control unit 16 turns on the two switches SW of the switching unit 19 and connects the resistor R to the internal wiring after the first predetermined time Tp ends until the 1-bit transmission time Tb ends. To do. The connection / disconnection of the resistor R by the CAN communication control unit 16 is performed at the same timing regardless of whether the transmission data is dominant / recessive, and is the same timing when data is not transmitted (only reception operation). Done in In addition, the same processing is performed in the CAN communication control unit 16 of all ECUs 1 in the communication system, thereby realizing dynamic impedance matching.

FIG. 20 is a schematic diagram for explaining the first predetermined time Tp and the second predetermined time Th related to data transmission. The two ECUs 1b and 1c included in the communication system shown in FIG. The communication line 5 (the trunk line 5a and the

branch lines

5b and 5c) is extracted. Since ringing occurs when a signal output from one ECU 1 is reflected by another ECU 1, the other ECU 1 that is closest to one ECU 1 (with the shortest signal propagation distance) causes the ringing to occur. The impact is great. Here, it is assumed that the two ECUs 1b and 1c are closest to each other in the communication system shown in FIG. 1 (that is, the distance between the ECUs 1b and 1c is the shortest in the communication system).

When the length of the

branch lines

5b and 5c branched from the trunk line 5a of the communication line 5 is LS and the length between the branch points of the

branch lines

5b and 5c branched from the trunk line 5a is LP, the distance between the two ECUs 1b and 1c L is
L = 2 × LS + LP
It is. Thus, for example, the time T from when the signal output from the ECU 1b is reflected by the ECU 1c to return to the ECU 1b is A as the transmission time of the signal per unit length of the communication line 5 (the transmission speed of the communication line 5). If
T = 2 × L × A
It is. The transmission time A per unit length is defined as 5 nsec / m in the CAN protocol, for example.

Therefore, by setting the second predetermined time Th to be equal to or longer than the transmission time T, the 0V signal output and impedance matching are performed during the second predetermined time Th, so that ringing can be suppressed. That is, the second predetermined time Th is
Th ≧ 2 × L × A
It is necessary to satisfy the conditions. As described above, the first predetermined time Tp and the second predetermined time Th are
Tp + Th ≦ Tb
It is necessary to satisfy the conditions.

FIGS. 21 and 22 are flowcharts showing the procedure of the transmission process by the CAN communication control unit 16 of the fourth embodiment. The CAN communication control unit 16 acquires 1-bit information to be transmitted from the data to be transmitted (step S201), and determines whether the 1-bit is dominant (step S202).

If the transmission target bit is dominant (S202: YES), the CAN communication control unit 16 outputs a signal at the first signal level to the communication line 5 (step S203), and proceeds to step S204. In addition, when one bit to be transmitted is not dominant and is recessive (S202: NO), the CAN communication control unit 16 advances the process to step S204 without performing signal output. Next, the CAN communication control unit 16 starts a timer (step S204), and determines whether or not a first predetermined time Tp has elapsed from the start of the bit transmission process (step S205). When the first predetermined time Tp has not elapsed (S205: NO), the CAN communication control unit 16 continues the time measurement by the timer and waits until the first predetermined time Tp elapses.

When the first predetermined time Tp has elapsed (S205: YES), the CAN communication control unit 16 outputs a signal of the second signal level (0 V) to the communication line 5 (step S206). Thereafter, the CAN communication control unit 16 determines whether or not the second predetermined time Th has elapsed since the first predetermined time Tp has elapsed (step S207), and the second predetermined time Th has not elapsed. In the case (S207: NO), a signal of the second signal level is output and waits until the second predetermined time Th has elapsed. When the second predetermined time Th has elapsed (S207: YES), the CAN communication control unit 16 stops signal output (step S208).

Next, the CAN communication control unit 16 determines whether or not the 1-bit transmission time Tb has elapsed (step S209). If the 1-bit transmission time Tb has not elapsed (S209: NO), the transmission is performed. Wait until time Tb has elapsed. When the 1-bit transmission time Tb has elapsed (S209: YES), the CAN communication control unit 16 stops the timer (step S210), and determines whether or not transmission of all bits of transmission data has been completed. Then, it is determined whether or not to end the transmission (step S211). If it is determined not to end the transmission (S211: NO), the CAN communication control unit 16 returns the process to step S201, and performs the same process for the next bit of the transmission data. If it is determined that the transmission is to be ended (S211: YES), the CAN communication control unit 16 ends the transmission process.

FIG. 23 and FIG. 24 are flowcharts showing a procedure of reception processing by the CAN communication control unit 16 according to the fourth embodiment. First, the CAN communication control unit 16 sets the terminal to a high impedance state without performing signal output (step S221), and disconnects the resistor R by turning off the two switches SW of the switching unit 19 (step S222). .

Next, the CAN communication control unit 16 determines whether or not the signal level of the communication line 5 exceeds a predetermined threshold value (step S223). If the signal level does not exceed the threshold value (S223: NO), the signal level is Wait until the threshold is exceeded. If the signal level exceeds the threshold (S223: YES), the CAN communication control unit 16 samples the signal level of the communication line 5 (step S224), and whether or not the first predetermined time Tp has elapsed since the start of sampling. Is determined (step S225). If the first predetermined time Tp has not elapsed (S225: NO), the CAN communication control unit 16 returns the processing to step S224, and repeats sampling of the signal level until the first predetermined time Tp has elapsed.

When the first predetermined time Tp has elapsed (S225: YES), the CAN communication control unit 16 connects the resistor R by turning on the two switches SW of the switching unit 19 (step S226).

Next, the CAN communication control unit 16 determines whether or not the second predetermined time Th has further elapsed from the elapse of the first predetermined time Tp (step S227), and the second predetermined time Th has not elapsed. (S227: NO), it waits until the second predetermined time Th elapses. When the second predetermined time Th has elapsed (S227: YES), the CAN communication control unit 16 disconnects the resistor R by turning off the two switches SW of the switching unit 19 (step S228), and stops signal output. Thus, the terminal is set to a high impedance state (step S229).

Thereafter, the CAN communication control unit 16 determines whether or not the 1-bit transmission time Tb has elapsed (step S230). If the 1-bit transmission time Tb has not elapsed (S230: NO), Wait until time has passed. When the transmission time Tb of 1 bit has elapsed (S230: YES), the CAN communication control unit 16 determines whether or not to end the reception by determining whether or not the reception of all the bits of the reception data has been completed. Determination is made (step S231). When it is determined that the reception is not terminated (S231: NO), the CAN communication control unit 16 returns the process to step S223 to perform the same process for the next bit of the received data, and performs the processes from step S223 to S231. Do. If it is determined that the reception is to be ended (S231: YES), the CAN communication control unit 16 ends the reception process.

FIG. 25 is a schematic diagram for explaining the effect of the communication system according to the fourth embodiment, and is a graph in which the vertical axis represents a potential difference between twist lines and the horizontal axis represents time. The example shown in the figure is a waveform when 1-bit information transmission time Tb = 1000 ns, dominant transmission is performed from 0 ns to 1000 ns, and recessive transmission is performed from 1000 ns to 2000 ns. In the dominant transmission, signal output is performed for the first predetermined time Tp = 800 ns and the first signal level = 2V, the second predetermined time Th = 200 ns and the second signal level = 0V.

25, it can be seen that the ringing signal level (amplitude) is reduced in the communication system of the present invention compared to the waveform of the conventional communication system shown in FIG. In the conventional communication system, the maximum ringing signal level exceeds 4V, whereas in the communication system of the present invention, the maximum ringing signal level is about 0.8V. Therefore, in the communication system of the present invention, it is possible to determine dominant / recessive by determining the signal level on the communication line 5 with a threshold value such as 0.9V or 1.0V.

In the communication system according to the fourth embodiment having the above-described configuration, when the transmission unit 17 of the ECU 1 transmits dominant data, the signal at the first signal level is transmitted to the communication line 5 over the first predetermined time Tp. When the transmission data is recessive and the signal level of the communication line 5 is recessive and the signal of the second signal level (0V) is output for the subsequent second predetermined time Th. When the signal is not output to the communication line 5 for the time Tp and the second predetermined time Th and the transmission data is recessive and the signal level of the communication line 5 is dominant, the first predetermined time Tp The signal is not output to the communication line 5 over a long period of time, and is set in a high impedance state, and then a signal of the second signal level (0 V) is output over a second predetermined time Th. The CAN communication control unit 16 of the ECU 1 is configured to be able to connect / disconnect the resistor R to the communication line 5 by switching connection / disconnection of the switch SW of the switching unit 19. The resistor R is connected after the elapse of the first predetermined time Tp at the time Tb. With these configurations, the occurrence of ringing in the communication line 5 in the communication system can be suppressed, so that high-speed communication can be realized.

Further, when the shortest distance between two ECUs 1 in the communication system is L and the transmission time per unit length of the communication line 5 is A, the first predetermined time Tp and the second predetermined time Th are:
Tp + Th ≦ Tb
Th ≧ 2 × L × A
Set to satisfy the conditions. As a result, the signal output from one ECU 1 is reflected by the other ECU 1 and the one ECU 1 does not enter the high impedance state before the reflected wave returns to the one ECU 1. It can suppress more reliably.

The first predetermined time Tp and the second predetermined time Th need only satisfy Tp + Th ≦ Tb. Therefore, when Tp + Th <Tb, the transmission time Tb of 1 bit from the end of the second predetermined time Th is There is time to elapse. In the present embodiment, the switch SW of the switching unit 19 is turned on during this time. However, the present invention is not limited to this, and the switch SW may be turned off. 21 and 22 assume that Tp + Th <Tb. However, the present invention is not limited to this, and Tp + Th = Tb may be used. If the transmission data is dominant, step S212 is performed. And S213 may not be performed. In addition, the signal level is sampled in the reception process over the first predetermined time Tp. However, the present invention is not limited to this, and the time is shorter than the first predetermined time Tp (predetermined sampling period Th). It may be configured to perform sampling.

1, 1a to 1e ECU (communication device)
5 communication line 5a trunk line 5b to 5d branch line 11 control unit (evaluation means, selection means, predetermined time determination means, predetermined sampling period determination means)
16 CAN communication control unit (communication means, calculation means, determination means, detection means, switching control means)
17 Transmitter (test transmission means, evaluation result transmission means, predetermined time information transmission means)
18 Receiver (Evaluation result receiving means, predetermined time information receiving means)
19 Switching part R Resistor SW Switch

Claims

A plurality of communication devices connected via a common communication line, and each communication device receives information of a plurality of consecutive bits each represented by a binary value of a dominant value or a recessive value via the communication line. In a communication system having communication means for transmitting and receiving,
The communication means includes
A pulse signal having a predetermined signal level is output to the communication line for a predetermined time Tp shorter than the information transmission time for one bit with respect to the superiority value of the information to be transmitted, and then no signal is output to the communication line. ,
A communication system, wherein a signal output to the communication line is not performed for an inferior value of information to be transmitted.
A plurality of communication devices connected via a common communication line, and each communication device receives information of a plurality of consecutive bits each represented by a binary value of a dominant value or a recessive value via the communication line. In a communication system having communication means for transmitting and receiving,
The communication means includes
A second predetermined time shorter than the information transmission time after outputting a signal of the first signal level over a first predetermined time Tp shorter than the information transmission time of 1 bit with respect to the dominant value of the information to be transmitted Outputting a signal of a second signal level lower than the first signal level over Th;
A communication system, wherein a signal output to the communication line is not performed for an inferior value of information to be transmitted.
The communication device
A switching unit for connecting / blocking the other end of the resistor, one end of which is connected to a fixed potential, with respect to the communication line;
The switching control means for controlling the switching unit so as to connect the resistor after the first predetermined time Tp has elapsed in the information transmission time for the one bit. The communication system described.
The first predetermined time Tp and the second predetermined time Th are:
Tp + Th ≦ Tb
Th ≧ 2 × L × A
Where Tb is the information transmission time for 1 bit, L is the shortest distance of the communication line interposed from one communication device to another communication device, and A is (This is the signal transmission time per unit length of the communication line.)
The communication system according to claim 2 or claim 3, wherein
The communication device
When the communication means outputs information relating to the dominant value or the inferior value to the communication line, the signal of the predetermined sampling period Td is sampled a plurality of times over the predetermined sampling period Td and the signal level in the communication line is sampled. A calculation means for calculating an average value of the levels;
Determining means for determining whether a signal transmitted to the communication line is a dominant value or a recessive value according to the average value calculated by the calculating means;
5. A detection unit that detects information transmission from another communication device when the determination unit determines that it is a dominant value after transmitting information of a recessive value. The communication system according to any one of the above.
The communication device
When the communication means outputs information relating to the dominant value or the inferior value to the communication line, the signal level in the communication line is sampled a plurality of times over a predetermined sampling period Td, and the signal level of each sampling result A comparison means for comparing the threshold value;
Based on the comparison result of the comparison means, the signal transmitted to the communication line is either a dominant value or a recessive value depending on the number of samples whose signal level exceeds the threshold and the number of samples whose signal level does not exceed the threshold. Determination means for determining whether there is,
5. A detection unit that detects information transmission from another communication device when the determination unit determines that it is a dominant value after transmitting information of a recessive value. The communication system according to any one of the above.
The communication device
Test transmission means for sequentially transmitting information of a plurality of dominant values having different predetermined times Tp;
Evaluation means for performing sampling over different predetermined sampling periods Td on the information transmitted by the test transmission means, making a determination by the determination means, and evaluating a reception result for a combination of the predetermined time Tp and the predetermined sampling period Td When,
Screening means for selecting a predetermined sampling period Td having a high evaluation for each predetermined time Tp based on the evaluation result by the evaluation means;
One communication apparatus performs transmission by the test transmission means, and each communication apparatus performs processing for evaluation by the evaluation means and selection by the selection means in order for all communication apparatuses,
The communication system according to claim 5 or 6, wherein a predetermined time Tp and a predetermined sampling period Td are determined based on a selection result obtained by the selection unit of each communication device.
The communication system according to claim 7, wherein the test transmission unit is configured to alternately transmit dominant value information and recessive value information.
The evaluation means calculates the evaluation value according to the number of the dominant value information determined as the dominant value, the number of the recessive value information determined as the dominant value, and the sampling number. 9. The communication system according to 8.
The plurality of communication devices include one master communication device and a plurality of slave communication devices,
The slave communication device has an evaluation result transmission unit that transmits an evaluation result of the evaluation unit corresponding to a selection result of the selection unit to the main communication device,
The main communication device is:
Evaluation result receiving means for receiving the evaluation results transmitted by the plurality of slave communication devices;
Predetermined time determining means for determining the predetermined time Tp based on a plurality of evaluation results received by the evaluation result receiving means;
Predetermined time information transmitting means for transmitting information on the predetermined time Tp determined by the predetermined time determining means to the plurality of slave communication devices,
The slave communication device is:
A predetermined time information receiving means for receiving information on the predetermined time Tp transmitted by the predetermined time information transmitting means;
The communication according to any one of claims 7 to 9, wherein the communication means performs subsequent signal output at the predetermined time Tp received by the predetermined time information receiving means. system.
The main communication device is:
Predetermined sampling period determining means for determining the predetermined sampling period Td according to the predetermined time Tp determined by the predetermined time determining means;
The subsequent sampling is performed in the predetermined sampling period Td determined by the predetermined sampling period determining means,
The slave communication device is:
Predetermined sampling period determining means for determining the predetermined sampling period Td according to the predetermined time Tp received by the predetermined time information receiving means;
The communication system according to claim 10, wherein the subsequent sampling is performed in the predetermined sampling period Td determined by the predetermined sampling period determining means.
A communication device connected to another device via a common communication line, and comprising a communication means for transmitting and receiving information of a plurality of consecutive bits each represented by a binary value of a dominant value or an inferior value via the communication line In
The communication means includes
A pulse signal having a predetermined signal level is output to the communication line for a predetermined time Tp shorter than the information transmission time for one bit with respect to the superiority value of the information to be transmitted, and then no signal is output to the communication line. ,
A communication apparatus characterized by not outputting a signal to the communication line for an inferior value of information to be transmitted.
A communication device connected to another device via a common communication line, and comprising a communication means for transmitting and receiving information of a plurality of consecutive bits each represented by a binary value of a dominant value or an inferior value via the communication line In
The communication means includes
A second predetermined time shorter than the information transmission time after outputting a signal of the first signal level over a first predetermined time Tp shorter than the information transmission time of 1 bit with respect to the dominant value of the information to be transmitted Outputting a signal of a second signal level lower than the first signal level over Th;
A communication apparatus characterized by not outputting a signal to the communication line for an inferior value of information to be transmitted.
When the communication means outputs information relating to the dominant value or the inferior value to the communication line, the signal of the predetermined sampling period Td is sampled a plurality of times over the predetermined sampling period Td and the signal level in the communication line is sampled. A calculation means for calculating an average value of the levels;
Determining means for determining whether a signal transmitted to the communication line is a dominant value or a recessive value according to the average value calculated by the calculating means;
14. A detection means for detecting information transmission from another communication device when the determination means determines that it is a dominant value after transmitting the information of the recessive value. The communication apparatus as described in.
When the communication means outputs information relating to the dominant value or the inferior value to the communication line, the signal level in the communication line is sampled a plurality of times over a predetermined sampling period Td, and the signal level of each sampling result A comparison means for comparing the threshold value;
Based on the comparison result of the comparison means, the signal transmitted to the communication line is either a dominant value or a recessive value depending on the number of samples whose signal level exceeds the threshold and the number of samples whose signal level does not exceed the threshold. Determination means for determining whether there is,
14. A detection means for detecting information transmission from another communication device when the determination means determines that it is a dominant value after transmitting the information of the recessive value. The communication apparatus as described in.
Test transmission means for sequentially transmitting information of a plurality of dominant values having different predetermined times Tp;
Evaluation means for performing sampling over different predetermined sampling periods Td on the information transmitted by the test transmission means, performing determination by the determination means, and evaluating a reception result for a combination of the predetermined time Tp and the predetermined sampling period Td;
The communication device according to claim 14, further comprising: a selection unit that selects a predetermined sampling period Td that is highly evaluated for each predetermined time Tp based on an evaluation result by the evaluation unit.
In a communication method of transmitting and receiving information of a plurality of consecutive bits each represented by a binary value of a dominant value or a recessive value via a common communication line,
A pulse signal having a predetermined signal level is output to the communication line for a predetermined time Tp shorter than the information transmission time for one bit with respect to the superiority value of the information to be transmitted, and then no signal is output to the communication line. ,
A communication method characterized by not outputting a signal to the communication line with respect to an inferior value of information to be transmitted.
In a communication method of transmitting and receiving information of a plurality of consecutive bits each represented by a binary value of a dominant value or a recessive value via a common communication line,
A second predetermined time shorter than the information transmission time after outputting a signal of the first signal level over a first predetermined time Tp shorter than the information transmission time of 1 bit with respect to the dominant value of the information to be transmitted Outputting a signal of a second signal level lower than the first signal level over Th;
A communication method characterized by not outputting a signal to the communication line with respect to an inferior value of information to be transmitted.
The communication parameter determination method for determining the predetermined time Tp and the predetermined sampling period Td in the communication system according to claim 5 or 6,
A plurality of dominant values with different predetermined times Tp are transmitted in order in one communication device,
Sampling over different predetermined sampling periods Td on the information transmitted by the one communication device to make a determination by the determination means, evaluating a reception result for a combination of the predetermined time Tp and the predetermined sampling period Td,
Based on the evaluation result, a predetermined sampling period Td having a high evaluation for each predetermined time Tp is selected,
One communication device is transmitted, and the processing in which each communication device performs evaluation and selection is performed sequentially for all communication devices,
A communication parameter determining method, wherein a predetermined time Tp and a predetermined sampling period Td are determined based on a selection result of each communication device.