JP4574256B2 - Communication apparatus and communication method - Google Patents

Description

  The present invention relates to a communication apparatus and a communication method for performing communication between a plurality of electronic units on a predetermined communication line.

  In recent automobiles, CAN (Controller Area Network) communication has been increasingly adopted as an in-vehicle communication system. Since this CAN communication is a serial bus communication, real-time performance cannot be assured. However, there is a case where high-speed communication is required for automobile communication because it is necessary to perform safe driving. For this reason, in CAN communication, priority is given to each data to perform communication without any trouble.

  That is, in CAN communication, when the unit that first started transmission during bus idle acquires the transmission right, and when two or more units start transmission at the same time, the arbitration field of each message is arbitrated in 1-bit units. A unit that has been given a dominant level for a long time acquires the right to transmit. In this case, the unit that has not acquired the transmission right stops the transmission operation from the next bit and moves to the reception operation.

  Here, the level of a bus in CAN communication (hereinafter referred to as “CAN bus”) includes a relatively preferential dominant level and a relatively receptive recessive level, and the logical value of the dominant level is “0”. And the recessive level is “1”. When one unit outputs a dominant, the CAN bus becomes a dominant level, so that the level of the CAN bus does not become recessive unless all units output a recessive.

  As a prior art regarding CAN communication, there is, for example, Patent Document 1.

JP 2001-119416 A

  An example of the level of the CAN bus in the CAN communication is shown in FIG. FIG. 4 shows a state in which low priority data 1 flows from a certain unit on the CAN bus. In this case, the recessive level is 0V, and the dominant level is 4V.

  Here, consider a case where high priority data 3 is output from another unit to the CAN bus. In this case, the logical value “0” of the high priority data 3 is 0V, and the logical value “1” is 4V.

  In this case, as described above, since the low-priority data 1 has already flowed to the CAN bus, arbitration of the high-priority data 3 cannot be performed, and the high-priority data 3 is postponed. It may become. The cause is as follows. In other words, in a state where the CAN bus is at the dominant level due to the low priority data 1, even if the high priority data 3 outputs a signal of a logical value “1”, the level (dominant level) in the CAN bus is high. There is no change, so arbitration cannot be performed.

  In normal CAN communication, in order for the high-priority data 3 to be output to the CAN bus and arbitrated without any trouble, it is necessary that the data communication on the CAN bus is not performed. . However, in FIG. 4, while the low priority data 1 is flowing through the CAN bus, even if an attempt is made to output the high priority data 3 to the CAN bus, the length of the data 3 necessary for arbitration is set to the CAN bus. The result cannot be reflected, and therefore the result cannot be instantly adjusted. As a result, transmission of high-priority data 3 waits until low-priority data 1 ends on the CAN bus.

  Accordingly, an object of the present invention is to provide a communication apparatus and a communication method in which transmission of a subsequent high priority message is not delayed due to the presence of a first low priority message.

In order to solve the above-mentioned problem, the invention according to claim 1 is a communication device provided for each electronic unit to perform communication between a plurality of electronic units on a predetermined communication line, and the communication line A voltage switching unit that switches at least two different voltage levels as the voltage level of a pulse of data to be transmitted to the high-priority data according to the priority of the data to be transmitted A transmission control unit that controls the voltage switching unit to select the high voltage level; and a voltage determination unit that determines whether or not the voltage state of the communication line is the high voltage level. Means that the voltage determination means determines that the voltage level of the communication line is the high voltage level, and the data flowing in the communication line is not transmitted from the communication device The case, to determine its effect, is to cancel the sending of the data to the communication line.

The invention according to claim 2 is a communication method for performing communication between a plurality of electronic units on a predetermined communication line, and (a) the data sent to the communication line is data other than high priority A step of generating data of a first voltage level and sending it to the communication line; and (b) if the data sent to the communication line is high priority data, Generating a data having a higher second voltage level and sending the data to the communication line, and in either or both of the steps (a) and (b), the voltage state of the communication line is It is determined whether the voltage level is a second high voltage level, it is determined that the voltage state of the communication line is the second voltage level, and the data flowing through the communication line is data from another electronic unit. In some cases, the communication line It is intended to stop the transmission of serial data.

The communication device (communication method) according to the first and second aspects of the present invention generates low voltage level data to the communication line when the data sent to the communication line is data other than high priority. On the other hand, if the data to be sent to the communication line is high priority data, high voltage level data is generated and sent to the communication line, so that non-high priority data is flowing on the communication line. On the way, arbitration can be performed by immediately interrupting high priority data. Therefore, real-time performance can be ensured for high priority data.

Furthermore, the communication device (communication method) according to the first and second aspects of the invention transmits new data to the communication line when high priority and high voltage level data has already been transmitted. Can be prevented. Therefore, it is possible to easily continue the high priority data already flowing in the communication line as it is, and the real-time property of the first high priority data can be maintained.

<Configuration of communication device>
FIG. 1 is a functional block diagram showing a communication apparatus according to an embodiment of the present invention. As shown in FIG. 1, the communication devices (CAN controllers) 10a to 10c have a conventional 4V (first voltage level) system as a voltage source for generating data to be output to a CAN bus 11 as a communication line. In addition to the one voltage source 13, a higher voltage 12V (second voltage level) type second voltage source 15 is also used, and when high priority data is transmitted, the higher voltage 12V is used. When the data generated by the second voltage source 15 of the system is output to the CAN bus 11 and other normal (low priority) data is transmitted, the data generated by the first voltage source 13 of the 4V system is transmitted. The data is output to the CAN bus 11.

  Specifically, as shown in FIG. 1, the communication devices 10 a to 10 c have communication functions such as CAN communication protocol processing when communicating between the electronic units 21 a to 21 c mounted on the automobile through the CAN bus 11. It is in charge and is interposed between each of the electronic units 21 a to 21 c and the CAN bus 11. And each communication apparatus 10a-10c is provided with the transmission part 23 and the receiving part 25, respectively.

  FIG. 1 shows only the internal configuration of the first communication device 10a among the plurality of communication devices 10a to 10c, and omits the internal configuration of the second communication device 10b and the third communication device 10c. However, the internal configuration of each of the communication devices 10a to 10c is the same.

  As shown in FIG. 1, the transmission unit 23 of each of the communication devices 10 a to 10 c includes a 4 V first voltage source 13, a 12 V second voltage source 15 having a higher voltage than the first voltage source 13, A voltage switching unit 31 that switches both voltage sources 13 and 15, and a pulse generation unit 33 that generates a pulse of a signal output to the CAN bus 11 using the voltage (4V or 12V) switched by the voltage switching unit 31. And a transmission control unit 35 that controls the voltage switching unit 31 and the pulse generation unit 33 based on signals output from the electronic units 21a to 21c.

  The first voltage source 13 and the second voltage source 15 are both DC power supply circuits that are conventionally mounted in automobiles, and are not limited to CAN communication, but are used for various electrical components such as other control systems. What is provided to supply power to the system is used as it is.

  The voltage switching unit 31 is a two-contact switching type switch circuit configured to switch between a 4V first voltage source 13 and a 12V second voltage source 15 using, for example, a transistor or the like. It operates based on a switching signal given from the control unit 35.

  The pulse generation unit 33 generates a pulse of data to be output to the CAN bus 11 based on the control by the transmission control unit 35. For example, a MOSFET or the like capable of high speed operation is applied.

  The transmission control unit 35 is a functional element that operates according to a predetermined software program stored in advance in a built-in ROM. The transmission control unit 35 transmits a data signal given from the electronic units 21a to 21c to the CAN bus 11 via CAN communication. A function for controlling the pulse generator 33 so as to convert it into a signal of a protocol suitable for the above and a 12V system for the voltage switching unit 31 when the data given from the electronic units 21a to 21c is of high priority A function of outputting a switching signal so as to select the second voltage source 15 and a first 4V system for the voltage switching unit 31 when the data given from the electronic units 21a to 21c is of low priority. A function for outputting a switching signal so as to select the voltage source 13 and a signal indicating that 12 V data is already flowing from the receiving unit 25 to the CAN bus 11 are given. Re and it has a function of the data to stop the output of data to the CAN bus 11 when it is judged not to be the data that has been voluntarily transmitted from the communication device 10a to 10c. The operation of the transmission control unit 35 will be described later.

  As shown in FIG. 1, the receiving unit 25 of each of the communication devices 10 a to 10 c receives a comparison unit (voltage determination unit) 43 that compares the voltage of the CAN bus 11 with a predetermined reference voltage 41 and data flowing through the CAN bus 11. In addition, when the comparison unit 43 determines that the dominant level of the CAN bus 11 is 12 V, the reception unit 45 outputs the fact to the transmission control unit 35 of the transmission unit 23.

  As the reference voltage 41, a constant voltage source in which a voltage of, for example, 7 to 8V is preset as a threshold level that can distinguish 4V from 12V is applied.

  The comparison unit 43 compares the voltage of the CAN bus 11 with the reference voltage 41, and is a voltage higher than the reference voltage 41 (that is, 12V) or a voltage lower than the reference voltage 41 (that is, 0V or 4V). It is determined whether it exists, and the determination result is output to the receiving circuit 45 as a logical value. For example, when the voltage of the CAN bus 11 is higher than the reference voltage 41 (that is, 12 V), the comparison unit 43 outputs “1” as a logical value to the reception circuit 45, and the voltage of the CAN bus 11 Is a voltage lower than the reference voltage 41 (that is, 0 V or 4 V), “0” is output to the receiving circuit 45 as a logical value.

  The receiving circuit 45 receives the voltage state of the CAN bus 11, and determines whether a dominant level or a recessive level is set for each bit as a clock timing defined by a predetermined clock signal. The determination is made by comparing with the threshold level, and the data flowing in the CAN bus 11 is recognized and subjected to reception processing, and then output to the electronic units 21a to 21c.

  The receiving circuit 45 determines whether the dominant level is 12V or 4V based on the logical value given from the comparison unit 43 at the dominant timing among the data received from the CAN bus 11. When the dominant level is 12V, a signal to that effect is output to the transmission control unit 35 of the transmission unit 23.

  The communication devices 10a to 10c having such a configuration may be configured such that the respective constituent elements are integrated as a single semiconductor integrated circuit, or an electronic circuit component in which the respective constituent elements are individually or only partially integrated. A plurality may be combined and mounted on a predetermined mounting board.

  As the CAN bus 11, for example, a twisted pair cable standardized by ISO11898 or ISO11519 may be used, or a single wire defined by, for example, SAE-J2411 may be used. As described above, each of the 4V pulse and the 12V pulse is appropriately supplied to the CAN bus 11, but, for example, in the single wire defined by SAE-J2411, Since it is allowed to communicate with a pulse of a voltage of 0V to 12V at the time of data transmission, even if there are three kinds of voltage transitions of 0V, 4V and 12V on the CAN bus 11, as described above, The CAN communication can be executed without any trouble in the physical layer standard of the communication protocol.

<Operation example 1: Low priority data communication>
As an operation example of the above configuration, an operation in the case where low priority data is transmitted from the first electronic unit 21a to the second electronic unit 21b through the CAN bus 11 will be described with reference to the flowchart of FIG.

  First, in step S01 in FIG. 2, the first electronic unit 21a outputs low priority data to be transmitted to the first communication device 10a. At this point, the transmission control unit 35 of the first communication device 10a determines that the data is low priority data in step S02 while referring to the header or the like of the low priority data. The transmission control unit 35 then outputs a switching signal to the voltage switching unit 31 to select the 4V first voltage source 13. Then, in step S <b> 03, the voltage switching unit 31 selects the 4V first voltage source 13, and this 4V voltage is applied to the pulse generation unit 33.

  In step S04, the transmission control unit 35 gives a signal to the pulse generation unit 33 so as to convert the data supplied from the first electronic unit 21a into data of a protocol suitable for CAN communication. After generating the transmission data at 33, the data is sent to the CAN bus 11. At this time, in the CAN bus 11, the recessive level is 0V and the dominant level is 4V.

  Here, in the first communication device 10 a that is the data transmission source, the state of the CAN bus 11 is input by the reception unit 25. In step S05, the comparison unit 43 compares the voltage of the CAN bus 11 with a predetermined reference voltage 41 (for example, 7 to 8 V), and determines whether or not a pulse of a voltage of 12 V is flowing through the CAN bus 11. To do. As a result, when the comparison unit 43 determines that the dominant level of the CAN bus 11 is less than the reference voltage 41 (that is, 4 V), the process proceeds to step S06.

  In step S06, the comparison unit 43 outputs a signal (logical value) indicating that the dominant level of the CAN bus 11 is less than the reference voltage 41 (ie, 4V) to the reception circuit 45. In the receiving circuit 45, a signal indicating that the dominant level of the CAN bus 11 is less than the reference voltage 41 is obtained as a determination result in the comparison unit 43, and therefore no special signal is output to the transmission unit 23. For this reason, the transmission unit 23 continues to transmit the low priority data as it is.

  In the subsequent step S07, it is determined whether or not an error has occurred in the transmission data in the communication with the first communication device 10a and the second communication device 10b.

  Specifically, if data communication is not performed on the CAN bus 11 when low priority data is transmitted from the first communication device 10a, the second communication device 10b receives the data. The data flowing in the CAN bus 11 is received without any trouble by the receiving circuit 45 (not shown in FIG. 1) of the unit 25. For this reason, a transmission error does not occur in step S07, the process proceeds to subsequent step S08, and data transmission from the first communication device 10a is continued. In this way, low priority data is transmitted from the first electronic unit 21a to the second electronic unit 21b.

  On the other hand, in step S07, for example, when low priority data of dominant level = 4V is already flowing on the CAN bus 11 at the time of data transmission from the first communication device 10a, for example, The data transmitted from the first communication device 10a is superimposed on the transmission data, and an error occurs in the transmission data. For this reason, it progresses to step S09 and transmission of the data from the 1st communication apparatus 10a is stopped.

<Operation Example 2: High Priority Data Communication>
Next, for example, when the third electronic unit 21c further performs low-priority data communication with another electronic unit (not shown), the first electronic unit 21a to the second electronic unit 21b. A case of transmitting data with high priority to will be described with reference to the flowchart of FIG. Here, reference numeral 51 in FIG. 3 denotes a low-priority data pulse flowing in the CAN bus 11, and reference numeral 53 denotes a high-priority data pulse sent from the first communication device 10a to the CAN bus 11. Respectively.

  When low-priority data is being transmitted from the third electronic unit 21c to another electronic unit through the CAN bus 11, the dominant level is set on the CAN bus 11 as indicated by reference numeral 51 in FIG. Recessive levels appear in various orders depending on the data content. In this case, the recessive level is 0V, and the dominant level is 4V. And 4V which is a dominant level is the data produced | generated using the 1st voltage source of 4V type | system | group in the 3rd communication apparatus 10c (refer the 1st voltage source 13 of the communication apparatus 10a in FIG. 1). Level.

  In such a situation, when high-priority data is sent from the first electronic unit 21a to the CAN bus 11 via the first communication device 10a, in step S01 in FIG. The high priority data is output to the first communication device 10a. In step S02, the transmission control unit 35 of the first communication device 10a determines that the data is high priority data while referring to the header of the high priority data, and the process proceeds to step S10. move on.

  In step S <b> 10, the transmission control unit 35 outputs a switching signal to the voltage switching unit 31 to select the 12V system second voltage source 15. Then, the voltage switching unit 31 selects the 12V system second voltage source 15, and the 12V voltage is supplied to the pulse generation unit 33.

  Then, in the next step S04, the transmission controller 35 gives a signal to the pulse generator 33 so as to convert the data given from the first electronic unit 21a into data of a protocol suitable for CAN communication. High priority data such as reference numeral 53 in FIG. 3 is output from the generation unit 33 to the CAN bus 11. The high priority data at this time is output at a voltage level of 12 V when outputting “1” as its logical value, and is output at a voltage level of 0 V when outputting “0” as its logical value. .

  Then, the dominant level flowing on the CAN bus 11 so far is superimposed on the 4V data, and the data having the dominant level of 12V flows.

  At this time, in the first communication device 10a that is the data transmission source, the data flowing through the CAN bus 11 is input to the reception unit 25, and the voltage of the CAN bus 11 is set to a predetermined reference voltage by the comparison unit 43 in step S05. 41 (e.g. 7-8V). As a result, the comparison unit 43 determines that the dominant level of the CAN bus 11 is higher than the reference voltage 41 (that is, 12 V), and outputs a signal (logical value) to that effect to the reception circuit 45. In the reception circuit 45, a signal indicating that the dominant level of the CAN bus 11 is higher than the reference voltage 41 is obtained as a determination result in the comparison unit 43. In this case, a signal to that effect is output to the transmitter 23, and the process proceeds to the next step S11.

  In step S11, the transmission unit 23 determines that the data on the CAN bus 11 at this time is data transmitted by the first communication device 10a itself, and proceeds to step S06. High priority data continues to be transmitted as it is. In this case, since a transmission error does not occur, the process proceeds from step S07 to step S08, and data transmission is continued.

  In this case, in the second communication device 10b, data flowing through the CAN bus 11 is received by the receiving circuit 45 (not shown in FIG. 1) of the receiving unit 25, and data input processing to the second electronic unit 21b. I do. In this way, high priority data is transmitted from the first electronic unit 21a to the second electronic unit 21b.

  Further, since the third communication device 10c that has sent data to the CAN bus 11 until then detects a voltage level of 12V by the reception circuit 45 (not shown in FIG. 1) of the reception unit, the transmission unit 23 Immediately stop sending low-priority data that was previously sent.

  Further, in other communication apparatuses, even when it is time to transmit new data (dominant level = 4V or 12V), it is detected that data of dominant level = 12V is flowing on the CAN bus 11. By doing so, transmission of the new data is stopped.

  In this way, by outputting the data generated by the 12V system second voltage source 15 of the first communication device 10a to the CAN bus 11, it becomes 12V exceeding the normal dominant level of 4V in the CAN bus 11. Therefore, the arbitration can be performed efficiently using the 12V data.

  When the dominant level = 12V data starts flowing to the CAN bus 11 where the dominant level = 4V data has flown until then, the 12V data is superimposed on the previous 4V data and erased. Therefore, the dominant level = 4V data that has been transmitted from the third communication device 10c until then becomes an error. In this case, general error processing executed in CAN communication is performed between the third communication device 10c and another communication device that is the data transmission destination, and an error occurs without sending a transmission completion interrupt signal. An interrupt is thrown. Therefore, the third communication device 10c that has transmitted the 4V data determines that the 12V high priority data is flowing on the CAN bus 11 when the error processing interrupt signal is given. Then, after waiting for the completion of the high priority data, 4V data is retransmitted.

  In the operation example 2 described above, an example in which high priority data of dominant level = 12V is transmitted from the first communication device 10a when dominant level = 4V data flows on the CAN bus 11 has been described. However, when high-priority data having a dominant level of 12 V is already flowing on the CAN bus 11, the data flowing on the CAN bus 11 is different from the data transmitted from itself. The transmission of data is stopped.

  In this case, in step S05 in FIG. 2, the comparison unit 43 of the reception unit 25 of the first communication device 10a compares the voltage of the CAN bus 11 with a predetermined reference voltage 41 (for example, 7 to 8 V). Then, it is determined that the dominant level of the CAN bus 11 is higher than the reference voltage 41 (that is, 12 V), a signal (logical value) to that effect is output to the receiving circuit 45, and the process proceeds to step S11.

  In step S11 in FIG. 2, the reception circuit 45 of the first communication device 10a obtains a signal indicating that the dominant level of the CAN bus 11 is higher than the reference voltage 41 as a determination result in the comparison unit 43. A signal to that effect is output to the transmitter 23.

  Since the data whose dominant level is 12V at this time is not the data transmitted by itself (for example, the first communication device 10a itself), the process proceeds to step S09, and the transmission unit 23 stops transmitting new data.

  In addition, when high priority data of dominant level = 12V is already flowing on the CAN bus 11, the first communication device 10a also attempts to transmit low priority data of dominant level = 4V. The transmission of data is stopped in the same manner as in the case where the high priority data with the dominant level = 12 V is transmitted.

  As described above, as a voltage source for generating data to be output to the CAN bus 11, in addition to the conventional 4V first voltage source 13, the 12V second voltage source 15 having a higher voltage than this is also provided. When transmitting high priority data, the data generated by the high voltage 12V system second voltage source 15 is output to the CAN bus 11 and other normal (low priority) data is output. In the case of transmission, since the data generated by the 4V system first voltage source 13 is output to the CAN bus 11, low priority data is flowed on the CAN bus 11 as indicated by reference numeral 51 in FIG. Even in the middle of being, arbitration can be performed by immediately interrupting high priority data. Therefore, even if the first low priority data flows on the CAN bus 11, the second high priority data can be immediately transmitted, and the real-time property can be secured for the high priority data. it can.

  In addition, when data having a high priority voltage level is already flowing on the CAN bus 11, it is possible to easily prevent new data from being sent to the CAN bus 11 from the other communication devices 10a to 10c. The high priority data already flowing in the CAN bus 11 can be easily continued as it is, and the real-time property of the first high priority data can be maintained.

  In the above-described embodiment, the configuration includes the two voltage sources, the 4V system first voltage source 13 and the 12V system second voltage source 15. However, arbitration between high priority data is frequently performed. In such a case, arbitration cannot be performed in the above embodiment. For this reason, the voltage level of the data is subdivided, and the voltage level indicating the priority of the data is obtained by using another voltage source having a voltage level different from that of the first voltage source 13 and the second voltage source 15, for example, 8V. May be divided into three stages. In this case, dominant level = 4V data is processed as low priority data, dominant level = 8V data as medium priority data, and dominant level = 12V data as high priority data. In this case, three voltage sources may be provided in the transmission unit 23 of each of the communication devices 10a to 10c, and a dominant level comparison determination may be performed using a plurality of reference voltages and a plurality of comparison units in the reception unit 25. Alternatively, four or more voltage sources may be used to indicate the level of data priority at four or more voltage levels.

  In the above-described embodiment, the CAN communication performed through the CAN bus 11 has been described as an example. However, the present invention may be applied to CSMA / CD communication or CSMA / CA communication.

It is a block diagram which shows the communication apparatus which concerns on one Embodiment of this invention. It is a flowchart which shows operation | movement of the communication apparatus which concerns on one Embodiment of this invention. It is a timing chart which shows the operation example of the communication apparatus which concerns on one Embodiment of this invention. It is a timing chart which shows the operation example of the conventional communication apparatus.

Explanation of symbols

10a to 10c communication device 11 bus 13 first voltage source 15 second voltage source 21a to 21c electronic unit 23 transmission unit 25 reception unit 31 voltage switching unit 33 pulse generation unit 35 transmission control unit 41 reference voltage 43 comparison unit 45 reception circuit

Claims (2)

A communication device provided for each electronic unit in order to perform communication between a plurality of electronic units on a predetermined communication line,
A voltage switching unit that switches at least two different voltage levels as voltage levels of pulses of data sent to the communication line;
A transmission control unit that controls the voltage switching unit so that high priority data selects a higher voltage level than lower priority data according to the priority of the data to be transmitted ;
Voltage determination means for determining whether the voltage state of the communication line is the high voltage level,
The transmission control unit determines that the voltage determination unit is at the high voltage level as the voltage state of the communication line, and when the data flowing through the communication line is not transmitted from the communication device, The communication apparatus is configured to stop the transmission of the data to the communication line . A communication method for performing communication between a plurality of electronic units on a predetermined communication line,
(A) generating data of a first voltage level and sending it to the communication line when the data sent to the communication line is data other than a high priority;
(B) when the data to be sent to the communication line is high-priority data, generating data having a second voltage level higher than the first voltage level and sending the data to the communication line; Prepared,
In either or both of the steps (a) and (b),
It is determined whether the voltage state of the communication line is the second high voltage level, it is determined that the voltage state of the communication line is the second voltage level, and the data flowing through the communication line is A communication method, comprising: stopping transmission of the data to the communication line when the data is from another electronic unit .

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