WO2016084647A1

WO2016084647A1 - Communication system

Info

Publication number: WO2016084647A1
Application number: PCT/JP2015/082175
Authority: WO
Inventors: 坪内　利康
Original assignee: 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: 2014-11-27
Filing date: 2015-11-17
Publication date: 2016-06-02
Also published as: JP2016103693A

Abstract

Provided is a communication system in which few constraints are imposed on a cable routing configuration, and with which it is possible to reduce the impact of ringing without giving rise to an increase in manufacturing costs. The communication system is provided with: two first communication devices (which are not shown in the drawings) connected to end portions of a trunk line comprising a pair of communication lines; a branch line 4 comprising a pair of communication lines, connected respectively to the pair of communication lines (which are not shown in the drawings) of the trunk line; and one or a plurality of second communication devices 1 having conductor patterns 27c provided on a circuit board 27 for installation of a termination resistor, and having a communication unit 16 connected to the branch line 4. The first communication device and the second communication device 1 each perform communications. The second communication device 1 is provided with a non-terminating circuit 17a, 17b for reducing ringing, interposed between the pair of communication lines of the branch line 4, with the interposition of the conductor patterns 27c.

Description

Communications system

The present invention relates to a trunk line having a pair of communication lines, two first communication devices having a terminal resistor interposed between the pair of trunk communication lines and connected to each end of the trunk line, and a pair of trunk lines. The present invention relates to a communication system including a branch line having a pair of communication lines connected to each communication line and one or a plurality of second communication devices having a communication unit connected to the branch lines.

In a vehicle, a large number of mounted electronic devices are connected via a communication line and communicate with each other to perform cooperative operation, thereby realizing vehicle travel control, vehicle interior environmental control, and the like. In mounted electronic devices, CAN (Controller Area として Network) is widely adopted as a communication protocol (see Non-Patent Document 1).

In general, in a communication system that employs a CAN communication protocol, a twisted pair cable in which a pair of communication lines are more combined is used. . Each electronic device performs communication using a differential signal, and a dominant is detected when a potential difference between a pair of communication lines exceeds a threshold value, and a recessive is detected when the potential difference is equal to or less than the threshold value.

In general, a communication system employing a CAN communication protocol adopts a bus type network topology. In the bus-type network topology, each electronic device is connected to a branch line that branches from a main line used for communication in common with other electronic devices. For example, each electronic device performs data transmission / reception with a dominant corresponding to data 0 and a recessive corresponding to data 1.

In a communication system employing the CAN communication protocol, ringing occurs when an electronic device transmits to another electronic device. Ringing is caused by multiple reflection of a signal due to impedance mismatch at a branching portion that branches from a main line to a branch line, impedance mismatch of a communication device connected to the branch line, and the like.

When the influence of ringing increases, the communication system causes a failure in communication because the dominant signal transmitted from one communication device is judged to be recessive on the received communication device side. May fall out of communication.
For this reason, in a communication system using the CAN communication protocol, the degree of freedom of twisted-pair cable routing is limited so that the influence of ringing does not increase, and a filter such as ferrite is provided at the branch part of the main line and branch line. It is necessary to adopt a method of mounting a resistor or a filter on a non-terminal portion.

Patent Document 1 discloses a data communication system in which transmission lines connected to individual subscriber terminal stations are connected to one passive network node in a star shape. The transmission line has a frequency dependent attenuating element, for example a ferrite bead. Good characteristic impedance matching of the high-frequency noise signal can be performed by simultaneously and freely selecting system parameters set in a steady data symbol state.

JP 7-700463 Gazette

As described above, in a communication system adopting the CAN communication protocol, a filter is interposed at the branch portion between the main line and the branch line, or a resistor or a filter is interposed at the non-terminal portion so that the influence of ringing does not increase. In order to do so, it is necessary to remanufacture from the conductor pattern of the circuit board, and there is a problem that the manufacturing cost increases.

The present invention has been made in view of the above-described circumstances, and provides a communication system capable of reducing the influence of ringing without a large degree of freedom in cable routing and without causing an increase in manufacturing cost. With the goal.

A communication system according to the present invention includes a trunk line having a pair of communication lines, a termination resistor, and a conductor pattern provided on a circuit board for mounting the termination resistor between the pair of communication lines. Two first communication devices that are connected to each end of the main line, a branch line having a pair of communication lines connected to the pair of communication lines, and a termination resistor. And a first communication device and a second communication device, each having a conductor pattern provided on a circuit board for mounting and having a communication unit connected to the branch line. In the communication system in which each communicates, the second communication device is provided between the pair of communication lines of the branch line via the conductor pattern, and includes a non-termination circuit for reducing ringing. It is characterized by.

In this communication system, the trunk line has a pair of communication lines, and the two first communication devices are terminated between the pair of communication lines via a conductor pattern provided on a circuit board for mounting a termination resistor. A resistor is interposed and connected to each end of the main line. The branch line has a pair of communication lines connected to the pair of communication lines of the trunk line, and one or a plurality of second communication devices are provided with a conductor pattern provided on a circuit board for mounting a termination resistor. And having a communication unit connected to the branch line, each of the first communication device and the second communication device communicates.
In the second communication device, a non-termination circuit for reducing ringing is interposed between a pair of communication lines of a branch line via a conductor pattern for mounting a termination resistor.

The communication system according to the present invention is characterized in that the non-terminal circuit is a low-pass filter.

The communication system according to the present invention is characterized in that the low-pass filter is a resistor and a capacitor connected in series between a pair of communication lines of the branch line through the conductor pattern.

In this communication system, in a low-pass filter that is a non-terminal circuit, a resistor and a capacitor are connected in series between a pair of communication lines included in a branch line via a conductor pattern for mounting a terminal resistor.

In the communication system according to the present invention, the resistor has a resistance value equal to or higher than a characteristic impedance of the communication line and lower than an input impedance value of the communication unit, and the capacitor has a capacitance value of 50 to 300 pF. It is characterized by having.

According to the communication system according to the present invention, it is possible to realize a communication system capable of reducing the influence of ringing without incurring an increase in manufacturing cost with a high degree of freedom in cable routing.

1 is a circuit diagram showing a schematic configuration of an embodiment of a communication system according to the present invention. It is a block diagram which shows typically the structural example of ECU. It is a block diagram which shows typically the structural example of terminal ECU. It is a circuit diagram which shows the other schematic structure of embodiment of the communication system which concerns on this invention.

Hereinafter, the present invention will be described in detail with reference to the drawings showing embodiments thereof.

FIG. 1 is a circuit diagram showing a schematic configuration of an embodiment of a communication system according to the present invention.
This communication system includes ECUs (Electronic Control Units) 1a, 1b, and 1c mounted on a vehicle, and

terminal ECUs

2a and 2b that are also mounted on the vehicle. The terminal ECU 2a is connected to one end of the trunk line 3 having a communication line, and the terminal ECU 2b is connected to the other end of the trunk line 3.

The ECU 1a is connected to a branch line 4a branched from a branch point A in the middle of the trunk line 3, the ECU 1b is connected to a branch line 4b branched from a branch point B in the middle of the trunk line 3, and the ECU 1c is connected to a branch point in the middle of the trunk line 3 It is connected to a branch line 4c branched from C. The branch point B is closer to the end ECU 2b than the branch point A, and the branch point C is closer to the end ECU 2b than the branch point B. The

branch lines

4a, 4b, and 4c are configured to have communication lines.

Since the

ECUs

1a, 1b, and 1c have the same configuration, they are also collectively referred to as ECU1 below. Since the

end ECUs

2a and 2b have the same configuration, they are also collectively referred to as the end ECU 2 below. Since the

branch lines

4a, 4b, and 4c have the same configuration, they are also collectively referred to as branch lines 4 below. The ECU 1 corresponds to the second communication device of the present invention, and the terminal ECU 2 corresponds to the first communication device of the present invention.
Here, the trunk line 3 and the branch line 4 are twisted pair cables having the characteristic impedance of a CAN (Controller Area Network) bus.

In the communication system having such a configuration, communication is performed between the ECU 1 and the terminal ECU 2 using the main line 3 as a common communication line. For example, when a signal is output to the branch line 4b by the ECU 1b, this signal reaches the ECU 1a from the branch line 4b through the trunk line 3 and the branch line 4a, and a reflected wave reflected by the connection portion etc. at which the ECU 1a connects to the branch line 4a. appear. The reflected wave reaches the ECU 1b via the branch line 4a, the trunk line 3, and the branch line 4b (see the broken arrow in FIG. 1).

The reflected wave that has reached the ECU 1b is reflected again at the connection portion where the ECU 1b connects to the branch line 4a again. In this way, ringing occurs in the communication system due to repeated signal reflection. Since the ringing becomes longer and the ringing time becomes longer as the length of the branch line or the trunk line becomes longer, the range of the ringing is limited. Moreover, although illustration is abbreviate | omitted in FIG. 1, the same reflected wave generate | occur | produces also in ECU1c. Further, the terminal ECU 2 may generate a similar reflected wave depending on the characteristic impedance values of the main line and the branch line.

FIG. 2 is a block diagram schematically illustrating a configuration example of the ECU 1.
The ECU 1 is individually mounted on a circuit board 27, and 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 driver 16, and a connection circuit 17. Etc. are provided. The control unit 11 is configured by using an arithmetic processing device such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit), and by reading and executing a control program stored in the ROM 12, various control units 11 can be used. Perform control processing.

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 transmits / receives information generated with the processing of the control unit 11 and other ECUs 1. Information and the like 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 the vehicle, or various switches for operation disposed 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 driver 16 transmits / receives information to / from other ECUs 1 according to the CAN protocol, and is connected to the branch line 4 via the connection circuit 17. The driver 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 16a.
The transmission unit 16a outputs a signal to the branch line 4 according to the value of each bit of the given transmission data (0 (dominant) or 1 (recessive)).

In the CAN protocol, the trunk line 3 and the branch line 4 are twisted pair cables formed by twisting a pair of communication lines. The transmitter 16 a outputs a differential signal to the branch line 4 connected via the connection circuit 17. When transmitting a dominant signal, the transmission unit 16a outputs a differential signal in which the potential difference between the pair of communication lines of the branch line 4 is 2V. When transmitting a recessive signal, the potential difference is 0V. A differential signal is output. The driver 16 corresponds to the communication unit of the present invention.

Further, the driver 16 detects the signal level of the branch line 4 to determine whether the signal transmitted on the branch line 4 is a signal corresponding to dominant or recessive, and each bit is dominant or recessive. It has the receiving part 16b which receives the data represented. The signal level of the branch line 4 refers to a potential difference between a pair of communication lines included in the branch line 4. The driver 16 gives the data received by the receiving unit 16b to the control unit 11.

Further, the driver 16 receives the data transmitted by the transmission unit 16a at the reception unit 16b, and if the transmission data and the reception data do not match (the recessiveness of the transmission data has changed to dominant in the reception data). In other words, it is detected that data is being transmitted by the other ECU 1 or the terminal ECU 2, and 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.

The connection circuit 17 is interposed in the branch line 4 and is configured to suppress a reflected wave due to a signal input from the branch line 4 to the driver 16. The connection circuit 17 is a filter, and a series circuit of a resistor 17a and a capacitor 17b is interposed between a pair of communication lines of the branch line 4 via

conductor patterns

27c, 27c, and 27c provided on the surface of the circuit board 27. It is intervened. The connection circuit 17 corresponds to a non-terminal circuit of the present invention.
The conductor pattern 27c is provided for mounting a termination resistor 27a (FIG. 3), which will be described later. Conventionally, the circuit board 27 for mounting the ECU 1 can be changed to the termination ECU 2 by any ECU 1. It is also provided on the surface.

The resistor 17a has a resistance value equal to or higher than the characteristic impedance of the branch line 4 and lower than the value of the input impedance to the driver 16, and the capacitor 17b desirably has a capacitance value of 50 to 300 pF. .
In general, the input impedance value of the driver 16 of the communication device corresponding to the ECU 1 is extremely higher than the characteristic impedance value of the communication line corresponding to the branch line 4. The signal level of the reflected wave is high when the degree of impedance mismatch is large, that is, when the difference in impedance between the two media transmitting signals is large.

When the length of the branch line or the main line becomes longer, the ringing tends to be longer and the ringing frequency becomes lower, and the difference from the frequency of the communication waveform becomes smaller. Therefore, when it is desired to take a wide wiring range, a filter constant that cuts even in a low frequency band is selected. By setting the capacitor to 50 pF or more, the filter effect is enhanced at such a low ringing frequency.
On the other hand, if the capacitor is made too large, the time constant becomes large, and the waveform fall or rise time tends to increase.

Therefore, since the resistance 17a has the above-described resistance value in the ringing occurrence frequency band, the impedance difference is reduced, so that signal reflection can be suppressed.
On the other hand, if the resistance value of the resistor 17a is made smaller than the impedance of the communication line, the impedance mismatch becomes large, so it is desirable to make it equal to or higher than the impedance of the communication line.
In addition, since the connection circuit 17 can remove high-frequency ringing components because the resistor 17a and the capacitor 17b function as a low-pass filter, ringing can be suppressed and communication stability can be improved.

FIG. 3 is a block diagram schematically illustrating a configuration example of the terminal ECU 2.
The termination ECU 2 is individually mounted on the circuit board 27, and includes a control unit 21, a ROM 22, a RAM 23, an input unit 24, an output unit 25, a driver 26, a connection circuit 28, and the like. Here, the control unit 21, ROM 22, and RAM 23 operate in the same manner as the control unit 11, ROM 12, and RAM 13 in FIG. The input unit 24, the output unit 25, and the driver 26 operate in the same manner as the input unit 14, the output unit 15, and the driver 16 in FIG. Note that the driver 26 of the terminal ECU 2 is connected to the main line 3 via the connection circuit 28.

In the connection circuit 28, a series circuit composed of two resistors 27a is interposed between a pair of communication lines of the main line 3 via

conductor patterns

27c, 27c, 27c provided on the surface of the circuit board 27. Yes. The connection circuit 28 includes a capacitor 27b. One end of the capacitor 27b is connected to the common connection node of the two resistors 27a via the conductor pattern 27c, and the other end is grounded via the conductor pattern 27c. ing.

The connection circuit 27 having such a configuration is a so-called split termination in the CAN protocol, and matches the input impedance to the driver 26 and the characteristic impedance of the main line 3. Note that the connection circuit 28 may be a termination resistor and may be configured other than the split termination.

In the communication system having the above configuration, the difference between the characteristic impedance of the branch line 4 and the input impedance of the driver 16 can be reduced by the resistor 17a of the connection circuit 17 of the ECU 1, and the resistor 17a and the capacitor 17b function as a low-pass filter. Therefore, communication with low influence of ringing can be performed. Therefore, even when communication at a higher data rate than the CAN protocol being studied as a next generation communication protocol, for example, communication at 1 Mbps or more and 8 Mbps or less is performed, communication with less influence of ringing may be performed. it can.

In the communication system according to the present embodiment, the

ECUs

1a, 1b, and 1c have been described using the bus type (FIG. 1) connected to the

branch lines

4a, 4b, and 4c branched from different branch points A, B, and C, respectively. As shown in FIG. 4, even if the

ECUs

1a, 1b, 1c are connected to the

branch lines

4a, 4b, 4c branched from one branch point D, the same effect can be obtained.

The embodiment disclosed herein is illustrative in all respects and should not be considered as restrictive. The scope of the present invention is defined not by the above-mentioned meaning but by the scope of claims for patent, and is intended to include all modifications within the scope and meaning equivalent to the scope of claims for patent.

The present invention can be used in a communication system that performs communication between electronic devices mounted on a vehicle.

1a, 1b, 1c ECU (second communication device)
2a, 2b Terminal ECU (first communication device)
3

Trunk line

4a, 4b,

4c Branch line

16, 26 Driver (communication part)
17 Connection circuit (non-terminal circuit)
17a Resistance (non-termination circuit)
17b Capacitor (non-termination circuit)
27 Circuit board 27a Resistance (termination resistor)

27b Capacitor

27c Conductor pattern 28 Connection circuit

Claims

The termination resistor is interposed between the pair of communication lines via a trunk line having a pair of communication lines and a conductor pattern provided on a circuit board for mounting the termination resistor. A circuit board for mounting two first communication devices connected to each end of the trunk line, a branch line having a pair of communication lines connected to the pair of communication lines, and a termination resistor, respectively. 1 or a plurality of second communication devices each having a conductor pattern provided and having a communication unit connected to the branch line, wherein each of the first communication device and the second communication device performs communication. ,
The second communication device includes a non-termination circuit for reducing ringing, which is interposed between the pair of communication lines of the branch line via the conductor pattern.
The communication system according to claim 1, wherein the non-terminal circuit is a low-pass filter.
The communication system according to claim 2, wherein the low-pass filter is a resistor and a capacitor connected in series between a pair of communication lines of the branch line via the conductor pattern.
4. The resistance according to claim 3, wherein the resistance is equal to or higher than a characteristic impedance of the communication line and has a resistance value lower than a value of an input impedance of the communication unit, and the capacitor has a capacitance value of 50 to 300 pF. Communications system.