WO2012001489A1

WO2012001489A1 - Wire communication system

Info

Publication number: WO2012001489A1
Application number: PCT/IB2011/001506
Authority: WO
Inventors: Hiroyuki Mori; Naoki Matsushita
Original assignee: Toyota Jidosha Kabushiki Kaisha; Nippon Soken, Inc.
Priority date: 2010-06-30
Filing date: 2011-06-28
Publication date: 2012-01-05
Also published as: JP2012015804A

Abstract

Line lengths of communication lines and that are branch connected respectively to a transmission-side node and a reception-side node, which are connected to a branch connector, are set to exhibit line characteristics in which the wavelength of the standing wave generated between the transmission-side node and the reception-side node that receives a signal transmitted from the transmission-side node via the branch connector differs from the wavelength of the standing wave generated between the reception-side node and the branch connector to which the reception-side node is branch connected.

Description

WIRE COMMUNICATION SYSTEM

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The invention relates to a wire communication system in which a plurality of nodes having a signal transmission-reception function are electrically connected via communication lines. 2. Description of Related Art

[0002] Multiplex communication in which a plurality of signals can be transmitted in one transmission channel is generally used in communication systems of factory automation (FA) devices and vehicles. For example, in a vehicle-installed communication system used, a communication line based on one signal line is used as a communication system for low-speed communication at about 33 kps. Further, a communication line using the so-called twist-pair cable as a bus is used as a communication system for high-speed communication at a speed of from several tens of bytes per second (bps) to 10 Mbps. A vehicle-installed local area network (LAN) is constituted by connecting a plurality of nodes by such communication lines. In the vehicle-installed LAN having such a configuration, communication lines branched off from the main bus are wired to each node, and the number of the present branch points corresponds to that of the nodes. Therefore, where characteristic impedances of the branched communication lines differ from each other, a location with a characteristic impedance mismatch is generated. As a result, a reflection wave caused by the characteristic impedance mismatch is generated, and the reflected line causes distortions of signal waveform and communication failures. Further, the presence of the reflected wave is a factor restricting the number of nodes and wiring regions in the communication lines.

[0003] For example, as described in Japanese Patent Application Publication No. 2007-201697 (JP-A-2007-201697), a wire communication system has been heretofore suggested in which the reflected wave generated by the impedance mismatch is attenuated by arranging connectors having a filter circuit in branch points of communication lines. FIG 12 shows a wire communication system described in JP-A-2007-201697.

[0004] As shown in FIG 12, in the communication system 2, a plurality of ECU 4A to 4F are electrically connected via respective communication lines 3A to 3F to a branch connector (JC) 10 provided in the principal communication line 30. Likewise, a plurality of ECUs 4G to 4L are electrically connected via respective communication lines 3G to 3L to a JC 10 provided in the principal communication line 30. The communication lines 3A to 3L are constituted, for example, by twist-pair cables that are obtained by twisting together a pair of communication wires and constitute an equilibrium communication line for differential transmission. Terminal circuits 5A and 5B provided with terminal resistors are attached to both ends of the communication line 30.

[0005] In this case, a JC that incorporates a filter circuit, for example, as described in Japanese Patent Application Publication No. 2008-41287 (JP-A-2008-41287), is used as the JC 10. As shown in FIG 13 by an exploded perspective view of the JC described in JP-A-2008-41287, the JC 10 is obtained, for example, by mating the communication line 4A and the communication line 4D together from the first direction and the second direction opposite to the first direction.

[0006] The JC 40 has a first connector housing 10A and a second connector housing 10B that are joined together by fitting. Receptacle ports 10a for inserting terminal plugs P provided at the end portions of a pair of communication wires 4Aa, 4Ab, 4Da, 4Db constituting the communication line 4 A and communication line 4D are formed in one face side of the first connector housing 10A and second connector housing 10B. Guide ribs 10b that partition regions for accommodating the terminal plugs P are provided at the inner side walls of these receptacle ports 10a, and terminal holes lOd for communication with the terminals 30 of linear shape that are connected to the terminal plugs P are formed in the closed wall 10c serving as a bottom surface for the receptacle ports 10a.

[0007] A substrate 10 having a predetermined wiring pattern formed thereon is accommodated and fixed between the first connector housing 10A and second connector housing 10B having the above-described configuration. As shown in a front structural view in FIG 14, a pair of upper and lower branch wiring patterns 41U and 41D are provided in the left-right direction. A plurality of through holes 42 are formed at positions corresponding to the terminal holes lOd between these branch wiring patterns 41U and 41D, and soldering pads 43 are formed around the through holes 42. The pads 43 are connected to the branch wiring patterns 41U and 41D by a filter circuit F in which a resistor R and a coil L are connected in parallel.

[0008] As shown in a cross-sectional structure in FIG 15 in which the JC 10 is viewed from the side surface, the JC 10 that can branch connect the communication lines 3A to 3L in a star-like configuration is constituted by soldering together the pads 43 and the terminals 30 after the terminals 30 have been inserted into the through holes 42 close to the centers thereof.

[0009] In the JC 10 of such a configuration, the pair of communication wires constituting the communication lines 3A to 3L are connected to the branch wiring patterns 41U and 41D of the substrate 40 via the filter circuit F. Therefore, a digital signal transmitted from a certain ECU is necessarily received by the other ECU via the filter circuit F. As a result, even if a high-frequency noise is generated by impedance mismatch between the communication lines 3A to 3L, the generated high-frequency noise is attenuated each time the noise passes through the filter circuit F, and waveform distortion caused by the high-frequency noise is also reduced.

[0010] However, in a filter circuit such as a low-pass filter, a signal in a predetermined frequency band is by itself also attenuated in a predetermined attenuation amount determined by circuit constants. Therefore, when a signal passes through a filter circuit, not only the distortion component contained in the signal, but also some low-frequency components are attenuated, and a delay can occur in the rising time or falling time of differential voltage.

[0011] Further, in the abovementioned JC 10, a plurality of filter circuits F are disposed integrally in the same JC 10. Therefore, when not all of the channels are used, the filters are still disposed in the locations that are actually not used and the number of filters unnecessarily increases.

SUMMARY OF THE INVENTION

[0012] The invention provides a wire communication system in which waveform distortion in a communication line can be reduced without using a filter circuit, and a wiring region in which communication can be established can be advantageously expanded.

[0013] The first aspect of the invention relates to a wire communication system including: a plurality of nodes; a branch connector connected to the plurality of nodes; and a branch connector connected to the plurality of nodes respectively via communication lines, wherein line characteristics of respective communication lines that are introduced between a transmission-side node connected to the branch connector and a reception-side node receiving a signal transmitted from the transmission-side node via the branch connector are set to exhibit line characteristics in which a wavelength of a standing wave generated between the transmission-side node and the reception-side node differs from a wavelength of a standing wave generated between the reception-side node and the branch connector.

[0014] The signal waveform of the reception-side node is formed by combining the standing wave generated between the transmission-side node and the reception-side node and the standing wave generated between the reception-side node and the branch connector to which the reception-side node is branch connected. The stronger (larger) are these standing waves, the larger is the distortion of the signal waveform received by the reception-side node. Therefore, where line characteristics of communication lines that are branch connected to the transmission side and reception side are set such that the wavelengths of the abovementioned standing waves differ from each other, as in the above-described configuration, when communication is performed between the abovementioned nodes, two standing waves with different wavelengths are generated in the communication line that is branch connected to the reception-side node. As a result, the two generated standing waves that differ from each other in a wavelength weaken each other and the waveform distortion included in the signal waveform is naturally reduced. As a consequence, waveform distortion in the communication line can be reduced without using a filter circuit and a wiring region in which communication can be established can be advantageously expanded.

[0015] In the configuration according to the abovementioned aspect, the plurality of nodes that are branch connected, may be constituted by three or more nodes, and nodes connected to communication lines that are set to exhibit line characteristics, in which a wavelength of a standing wave generated between the transmission-side node and the reception-side node differs, of the communication lines are two nodes connected to the branch connector, a distortion of a signal waveform applied to communication between the two nodes may being larger than in other nodes.

[0016] In a wire communication system in which a plurality of nodes are branch connected to a branch connector, a distortion of signal waveform applied to communication between the nodes varies depending on line characteristics of the communication lines that are branch connected to the nodes. Accordingly, when three or more nodes are present, where the wavelengths of standing waves generated in respective communication lines that are branch connected to the two nodes in which the distortion of signal waveform is larger than in other nodes are made different from each other, as in the abovementioned configuration, the effect of waveform distortion on communication between the nodes with the largest distortion of signal waveform can be advantageously inhibited.

[0017] In the configuration according to the abovementioned aspect, line characteristics of the communication lines that differ from each other in the wavelength of standing waves may be realized as a difference in line lengths between communication lines from the branch connector to two nodes, which are the transmission-side node and the reception-side node.

[0018] The wavelength of a standing wave has an especially strong correlation with the length of the communication line serving as a communication medium for the standing wave. When the lengths of communication lines are the same, the wavelengths of standing waves generated in the communication lines are equal to each other and the standing waves strengthen each other, thereby increasing the reflection distortion contained in the signal distortion. Further, the reflection distortion caused by such standing waves is larger when communication is performed between the nodes via a communication line with a large line length. As a result, where the lengths of communication lines are made different from each other with respect to two nodes for which the lengths of communication lines connected to the branch connector are larger than those for other nodes, as in the abovementioned configuration, the wavelengths of standing waves generated in these communication lines can be easily made different from each other.

[0019] In the configuration according to the abovementioned aspect, the lengths of communication lines from the branch connector to the two nodes may be set such that the line length of the communication line that is branch connected to one node is shorter by 10% or more than the line length of the communication line that is branch connected to the other node.

[0020] When the diameters or material properties of communication lines are the same, the wavelength of the standing wave generated between the transmission-side node and the reception-side node is determined by the sum total value for the communication lines that are branch connected to the nodes on the transmission side and reception side. Further, the wavelength of the standing wave generated between the reception-side node and the branch connector to which the reception-side node is branch connected is determined on the basis of a doubled value of the length of the communication line that is branch connected to the reception-side node. Accordingly, the inventors have confirmed that where the lengths of communication lines from the branch connector to the two nodes are set such that the line length of the communication line that is branch connected to one node is shorter by 10% or more than the line length of the communication line that is branch connected to the other node, as in the above-described configuration, a wavelength difference that is sufficient and necessary for the standing waves to cancel each other is generated. Thus, it is possible to reduce waveform distortion on the basis of a minimum necessary difference in line length between the communication lines. Further, in addition to mutual cancelation of standing waves on the basis of such a difference in line length between the communication lines, this effect has been confirmed to increase with the increase in the difference between the lengths of communication lines.

[0021] In the above-described configuration, all of the communication lines that electrically connect the respective nodes to the branch connector may be set to have mutually different line lengths.

[0022] Where all of the communication lines that electrically connect the nodes to the branch connector are set to have mutually different line lengths, as in the above-described configuration, the wavelengths of two standing waves generated in the communication line that is branched connected to the reception-side node can be made different from each other when transmission and reception of signals is performed between any nodes. As a result, the signal waveform distortion can be reduced between all of the nodes constituting the communication line system and reliability of communication between the nodes can be advantageously increased.

[0023] In the above-described configuration, the line length that is set to be longer from among the line lengths of the communication lines of the two nodes may be equal to or less than 2.0 m, the line length that is set to be longer, by 10% or more, from among the line lengths of the communication lines of the two nodes may be equal to or less than 1.8 m, and the line length of a communication line of a node other than these two nodes may be equal to or less than 1.5 m.

[0024] In a wire communication system such as a vehicle-installed network, the communication lines most often have a line length of equal to or less than 2.0 m. Therefore, with the above-described configuration, waveform distortion of the signal waveform generated in each communication line can be reduced to a range in which feasibility of communication via these communication lines can be maintained even when communication is performed via a communication line with a line length of 2.0 m and a communication line with a line length of 1.8 m as a communication in which the effect of waveform distortion of signal waveform is maximized due to a large length of communication lines, in other words, as a communication between two nodes for which the line lengths of communication lines connected to the branch connector are larger than those for other nodes.

[0025] In the above-described configuration, only two of the branch connectors may be provided, and the plurality of nodes may be connected via the communication lines to each of the two branch connectors.

[0026] The reflection factor and transmission factor of signals transmitted from a transmission-side node via the branch connector correlate with the characteristic impedance of the branch points of the branch connector that are signal reflection points. Further, during transmission and reception of signals between the nodes, the characteristic impedance of each node increases, but the characteristic impedance in the branch points of the branch connector to which these nodes are branch connected decreases with the increase in the number of branch points. The reflection factor of signals with respect to a branch point as a base point increases and the transmission factor decreases with the decrease in the characteristic impedance of the branch point. The signal that has been transmitted from the branch point to another node or the adjacent branch connector on the basis of such a transmission factor is again reflected to the transmission-side node, the other node or the adjacent branch connector serving as a base point for the reflection. The repetition of such reflection events increases the waveform distortion contained in the signal waveform. Therefore, where the number of branch connectors constituting the were communication system is limited to two and a plurality of nodes are separately connected to these branch connectors, as in the abovementioned configuration, the number of connections of nodes, per unit, to the branch connectors increases and the characteristic impedance of branch points of branch connectors decreases accordingly. As a result, the signals transmitted from the transmission-side node are mostly reflected to the transmission-side node, the branch point of the branch connector to which the transmission-side node is branch connected acting as a base point for this reflection. As a result, the transmission amount of the signal to the other node or the adjacent branch connector decreases accordingly. As a result, the reflection wave causing waveform distortion is reduced via the decrease in the transmission amount of signals transmitted from the transmission-side branch connector.

[0027] In the above-described configuration, communication between the nodes connected to the branch connector may be digital communication based on identification of a logical level by a differential voltage.

[0028] In the digital communication based on differential voltage, communication between the nodes is performed by identifying whether the logical level of the signal is logical "H" (high) or logical "L" (low) by using a certain threshold as a criterion. Therefore, with the above-described configuration, the identification of the logical level can be performed correctly and reliability of communication based on the identification of these logical levels can be advantageously increased via the reduction of waveform distortion of signal waveform.

[0029] In the above-described configuration, the identification of the logical level may be performed based on a signal waveform obtained when an amplitude of a combined waveform obtained by combining a standing wave generated between a transmission node that transmits a signal and a reception node that receives the transmitted signal and a standing wave generated between the reception node and the branch connector is at a minimum.

[0030] The amplitude of a signal waveform formed by combining two standing waves having different wavelengths is at a minimum and the distortion of signal waveform caused by these standing waves is also at a minimum at a timing at which phases of the standing waves are opposite to each other. Therefore, with the above-described configuration, communication with higher reliability can be performed by identifying the logical level on the basis of a signal waveform with a minimal effect of waveform distortion.

[0031] In the above-described configuration, the nodes and the communication lines may be nodes and communication lines used in a multiplex communication system constituting a vehicle-installed network.

[0032] In a multiplex communication system constituting such a vehicle-installed network, reliability of received and transmitted signals is very important from the standpoint of avoiding erroneous control and the like. Accordingly, where the abovementioned nodes and the abovementioned communication line are used in a multiplex communication system constituting a vehicle-installed network, high reliability of the wire communication system can be maintained, while expanding the wiring region.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG 1 is a block diagram illustrating a schematic configuration of the wire communication system according to the invention in one embodiment thereof;

FIG 2 A is a block diagram for explaining the principle of distortion reduction in the wire communication system of the embodiment;

FIG 2B shows a transition example of a signal waveform received in the reception node according to the embodiment;

FIG 3 is a block diagram for explaining the principle of distortion reduction in the wire communication system according to the embodiment;

FIG 4A is a block diagram for explaining the principle of distortion reduction in the wire communication system according to the embodiment;

FIG 4B is a graph illustrating a transition example of a standing wave generated between the nodes according to the embodiment;

FIG 5 A is a block diagram for explaining the principle of distortion reduction in the wire communication system according to the embodiment; FIG 5B is a graph illustrating a transition example of a standing wave generated between the nodes according to the embodiment;

FIGS. 6 A and 6B are graphs illustrating a transition example of a standing wave forming a reception waveform in the reception node;

FIG 6C is a graph illustrating a transition example of the reception waveform in the reception node;

FIGS. 7A and 7B are graphs illustrating a transition example of a standing wave forming a reception waveform in the reception node according to the embodiment;

FIG 7C is a graph illustrating a transition example of the reception waveform in the reception node according to the embodiment;

FIG 8A and 8B a graph illustrating a transition example of the reception waveform in the reception node;

FIG 9 is a graph illustrating a transition example of the reception waveform for each node according to the embodiment;

FIGS. 10A and 10B show an example of wiring mode of the JC;

FIG 11 is a graph illustrating a transition example of the reception waveform in the reception node of the embodiment for each of the JC;

FIG 12 is a block diagram illustrating a schematic configuration of the vehicle-installed network according to the related art;

FIG 13 is an exploded perspective view showing an exploded structure of the JC according to the related art;

FIG 14 is a front view illustrating a front structure of the substrate constituting the JC according to the related art; and

FIG 15 is a cross-sectional view illustrating the side surface structure of the JC according to the related art.

DETAILED DESCRIPTION OF EMBODIMENTS

[0034] As shown in FIG 1, the multiplex communication system is configured, for example, according to a Controller Area Network (CAN) standard with a bit rate of 500 kps. This multiplex communication system has a plurality of nodes 100A to 100η and 110A to HOn constituted by electronic control devices controlling various devices, such as an engine, brakes, and power windows, installed on a vehicle. Among the aforementioned nodes, the nodes 100A to 100η are electrically connected, via respective communication lines 200A to 200n, to a JC 300 provided at one end of a main communication line (communication wiring) 220. Likewise, the nodes 110A to 110η constituted by electronic control devices controlling the abovementioned various devices are electrically connected, via respective communication lines 210A to 210n, to a JC 310 provided at the other end of a main communication line (communication wiring) 220.

[0035] The communication lines 200A to 200n and communication lines 210A to 210n are configured, for example, by a twist pair cable obtained by twisting together a pair of communication wires and have predetermined characteristic impedances. A terminal circuit is incorporated in a node serving as an end node among the nodes 100A to 100η and 110A to HOn. As for the line length of the communication lines 200A to 200n and communication lines 210A to 210n, the line length of the first communication line 200A, which is the longest, is about 2.0 m, the line length of the second communication line 200B, which is next in line length to the first communication line 200A, is about 1.8 mm, and the line length of other communication lines 200C to 200n and 210A to 210n is about 1.5 m. The line length of the main communication line 220 is about 5.2 m. In the embodiment, the communication lines 200A to 200n and 210A to 210n are used according to the same specifications in terms of diameter and material properties.

[0036] In the vehicle network configured in the above-described manner, transmission and reception of digital signals is performed based on a differential voltage of each communication wire by using the communication lines 200A to 200n and 210A to 210n as a communication medium with the object of transmitting the desired information between the nodes lOOA to 100η and HOAto HOn. For example, where a digital signal based on a differential voltage is sent from the node 100A, this digital signal is transmitted to other nodes 100B to 100η via the communication line 200A that is branch connected to the node 100A, the JC 300, and the communication lines 200B to 200n in the order of description. A digital signal transmitted from the node 100A is transmitted to other nodes 110A to HOn via the communication line 200A that is branch connected to the node 100A, the JC 300, the main communication line 220, and the communication lines 210A to 210n in the order of description. In the nodes 100B to 100η and 110A to UOn, communication is performed via the determination of a logical level "L" (recessive) or "H" (dominant) based on the digital signal received from the node 100A, that is, the differential voltage. Such determination of the logical level "L" or "H" is performed, for example, on the basis of a signal waveform measured in a sampling point that has been set in the rear-half portion of 1 bit.

[0037] However, in such a configuration in which the communication lines 200A to 200n and 210A to 210n are branch connected to the plurality of nodes 100A to 100η and 110A to UOn, where characteristic impedances of the communication lines 200A to 200n and 210A to 210n differ from each other, an impedance mismatch occurs. A signal is reflected in the locations with impedance mismatch, and where such signal reflections are combined, a distortion occurs in the signal waveform received by the nodes 100 A to 100η and 110A to UOn. As a result, unless this distortion of signal waveform is converged to the abovementioned sampling point, accurate determination of the logical level "L" or "H" based on the differential voltage is difficult to perform in the nodes 100A to 100η and 110A to UOn, and a bit error can also occur.

[0038] Accordingly, in the embodiment, the distortion of signal waveform caused by impedance mismatch is reduced by setting a line length, from among the line characteristics, of the communication lines 200Ato 200n and 210Ato 210n.

[0039] The principle of reducing the signal waveform distortion of the embodiment will be explained below in greater detail with reference to FIGS. 2 to 11. Here, a wire communication system will be assumed in which the first to third nodes 120A to 120C constituted, for example, by the abovementioned electronic control devices are electrically connected to the JC 320 via the first to third communication lines 220A to 220C, as shown in FIG 2A. In such wire communication system, the line length of the communication lines 220A to 220C that are branch connected to the nodes 120A to 120C is about 2.0 m, about 2.0 m, and about 1.8 m, respectively. In this example, the effect of distortion on signal waveform is explained with respect to a period of falling from dominant ("H") to recessive ("L") in which the effect of distortions is especially harmful in a wire communication system such as CAN.

[0040] A transition example LI shown by a broken line in FIG 2B illustrates a transition example of a waveform received by the second node 120B when a digital signal based on a differential voltage is transmitted from the first node 120A. Thus, this transition example LI illustrates the transition of the received waveform when communication between the first node 120A and the second node 120B is performed via the first communication line 220A and the second communication line 220B, which have the same line length, from among the communication lines 220A to 220C. A transition example L2 shown by a solid line in FIG 2B illustrates a transition example of a waveform received by the third node 120C when a digital signal based on a differential voltage is transmitted from the first node 120A. Thus, this transition example L2 illustrates the transition of the received waveform when communication between the first node 120A and the third node 120C is performed via the first communication line 220A and the third communication line 220C, which has a line length by 10% shorter than that of the first communication line 220A.

[0041] As shown by the transition example LI in FIG 2B, the waveform received by the second node 120B is a signal waveform including distortions caused by impedance mismatch between the communication lines 220A to 220C that are branch connected to the JC 320. Therefore, even if the logical level of the signal transmitted from the first node 120A falls from "H" to "L" at a timing tl, the amplitude of the received waveform LI exceeds a threshold Vs, which determines whether the logical level is "H" or "L", due to the effect of waveform distortion before a period T12 elapses.

[0042] Even though the amplitude of the received waveform LI gradually stabilizes and becomes equal to or less than the threshold Vs after the period T12 elapses, when the sampling point of the received waveform is set, for example, at the timing tp, the logical level of the signal transmitted from the first node 120A can be erroneously determined as "H", while it is actually "L", and a bit error can occur.

[0043] By contrast, as shown in a transition example L2 in FIG 2B, although the received waveform of the third node 120C is a signal waveform including distortions caused by the mismatch of characteristic impedance, the effect of waveform distortions is reduced and the amplitude of the received waveform L2 is stabilized and becomes equal to or less than the threshold Vs after a period T13 has elapsed (period T13 < period T12). Therefore, even when sampling of the received waveform L2 is performed at the timing tp, the received waveform L2 is stabilized and becomes equal to or less than the threshold Vs at this time, and the signal with the logical level "L" that has been sent from the first node 120Acan be correctly identified as a signal having the logical level "L".

[0044] Thus, when the communication lines connected between the nodes that communicate with each other have the same length, the effect of signal waveform distortion is large, and when the communication lines connecting the nodes have different lengths, it can be confirmed that the effect of signal waveform distortion can be reduced. Accordingly, in the embodiment the distortion of signal waveforms communicated between the nodes is reduced by setting the lengths of communication lines connecting a plurality of nodes.

[0045] The relationship between the signal waveform and the length of communication lines that are branch connected to a plurality of nodes will be explained below in greater detail with reference to FIGS. 3 to 9. FIG 3 illustrates an example of a wire communication system in which a plurality of nodes are connected to the same JC via communication lines of different lengths. Further, FIGS. 4 to 7 show the transition of a standing wave forming a signal waveform that is received by the receiving node. FIGS. 8 and 9 show a transition example of a signal waveform received by the receiving node.

[0046] In this case, as shown in FIG 3, a wire communication system is assumed in which first to tenth nodes 130A to 130J constituted for example by the abovementioned electronic control devices are electrically connected to the JC 330 via first to tenth communication lines 230A to 230J of different line length. In such wire communication system, the line length of the communication lines 230A to 230J that are branch connected to the nodes 130A to 130J have a length of about 2.0 m, about 2.0 m, about 1.8 m, about 1.6 m, about 1.4 m, about 1.2 m, about 1.0 m, about 0.8 m, about 0.6 m, and about 0.5 m, respectively. In this case, the communication lines 230A to 230J of the same specifications such as diameter and material characteristics are used.

[0047] The distortion effect explained in this example is also that of the distortion of a signal waveform occurring when the signal falls from the dominant level ("H") to the recessive level ("L"), which is especially significant in a wire communication system such as CAN.

[0048] In the wire communication system of such a configuration, the waveform received by the nodes 130A to 130J is formed by combinations of standing waves generated in the communication lines 230 A to 230J. Thus, as shown in FIG 4 A, the received waveform of the second node 130B at the time, for example, of transmission of a digital signal from the first node 130A is formed by a standing wave SWab generated between the first node 130A (transmission side) and the second node 130B (reception side) and a standing wave SWbb generated between the second node 130B (reception side) and the JC 330. These standing wave SWab and SWbb are generated under the effect of traveling waves or reflected waves between the nodes 130Aand 130B.

[0049] Further, as shown in FIG 4B, when the level falls from dominant to recessive, the nodes 130A and 130B that receive and transmit signals are usually at a high impedance. Therefore, these nodes 130A and 130B correspond to the bellies of standing waves SWab and SWbb. Further, in the JC 330, the characteristic impedance decreases with the increase in the number of branches and the characteristic impedance accordingly decreases relative to that of the nodes 130A and 130B. As a result, the branch points of the JC 330 correspond to nodes of the standing waves SWab and SWbb.

[0050] Further, as shown in FIG 5A, the received waveform of the third node 130C at the time, for example, of transmission of a digital signal from the first node 130 A is formed by a standing wave SWac generated between the first node 130A (transmission side) and the third node 130C (reception side) and a standing wave SWcc generated between the third node 130C (reception side) and the JC 330. These standing wave SWac and SWcc are generated under the effect of traveling waves or reflected waves between the nodes 130Aand 130C.

[0051] Further, as shown in FIG 5B, in this case, the nodes 130Aand 130C also correspond to bellies of standing waves SWac and SWcc, and the JC 330 substantially corresponds to nodes of the standing waves SWac and SWcc.

[0052] The wavelength of these standing waves SWab, SWbb, SWac, and SWcc is determined by line characteristics such as diameter and material characteristics of the communication lines 230A to 230C serving as a communication medium. When the line characteristics of the communication lines 230A to 230C are the same, the wavelength is determined by the length of these lines. Thus, in the example shown in FIG 4, the wavelength of the standing wave SWab is determined on the basis of a total value (4 m) of lengths of the communication lines 230A and 230B between the first node 130A and the second node 130B, and the wavelength of the standing wave SWbb is determined on the basis of a doubled value (4 m) of the length of the second communication line 230B between the second node 130B and the JC 330. In the example shown in FIG 5, the wavelength of the standing wave SWac is determined on the basis of a total value (3.8 m) of the lengths of the communication lines 230A and 230C between the first node 130A and the third node 130C, and the wavelength of the standing wave SWcc is determined on the basis of a doubled value (3.6 m) of the length of the third communication line 230C between the third node 130C and the JC 330.

[0053] Further, as shown by a transition example of bellies of standing waves SWab and SWbb in the second node 130B in FIGS. 6A and 6B, the wavelength ab of the standing wave SWab generated in the first communication line 230A and second communication line 230B having the same line length becomes equal to the wavelength Abb of the standing wave SWbb generated in the second communication line 230B between the second node 130B and the JC 330 (Aab = Abb).

[0054] Therefore, as shown in FIG 6C, the waveform received by the second node 130B and formed by the combination of such standing waves SWab and SWbb is a waveform in which the two standing waves SWab and SWbb having the same wavelength are mutually intensified. Thus, in the example, the amplitude V2 of the waveform received by the second node 130B becomes twice as large as the amplitude VI of the standing waves SWab and SWbb and the distortion of signal waveform increases.

[0055] As shown by a transition example of bellies of standing waves SWac and SWcc in the third node 130C in FIGS. 7A and 7B, the wavelength λac of the standing wave SWac generated in the third communication line 230C between the first communication line 230A and the third communication line 230C that have different line lengths is larger than the wavelength cc of the standing wave SWcc generated in the third communication line 230C between the third node 130C and the JC 330.

[0056] Therefore, as shown in FIG 7C, the waveform received by the third node 130C that is formed by a combination of such standing waves SWac and SWcc is a waveform in which the two standing waves SWac and SWcc having different wavelengths are mutually weakened. Close to the timing tl at which the two standing waves SWac and SWcc having different wavelengths are in opposite phases, the amplitude of the combined waveform of the standing waves SWac and SWcc is minimal. As a result, the waveform distortion contained in the signal waveform received by the second node 130B is reduced. After the standing waves SWac and SWcc have been in opposite phases, the waveform distortion again increases as the phases of the standing waves SWac and SWcc come close to each other, but since the signal is attenuated by the resistors constituting the wire communication system, the reflection distortion contained in the signal waveform can be reduced to the allowable range.

[0057] A transition example of the signal waveform received by the second node 130B and third node 130C on the basis of such principle is shown in FIGS. 8A and 8B. In FIGS. 8A and 8B, the transition of the signal waveform received by the nodes 130B and 130C immediately after the logical level of the digital signal transmitted from the first node 130A has made a transition from "H" to "L" is shown in 1 bit units. This signal waveform is a waveform from which the effect of resistor components of the abovementioned communication system has been removed.

[0058] As shown in FIG 8A, the amplitude V2 of the signal waveform received by the second node 130B is twice as large as the amplitude VI of the standing waves SWab and SWbb at all times since the standing waves SWab and SWbb have the same wavelength. For this reason, when communication is performed via the first communication line 230A and second communication line 230B having the same line length, the signal transmitted from the first node 130A is difficult to identify as a signal having the logical level "L" on the basis of the threshold Vs.

[0059] Meanwhile, as shown in FIG 8B, in the reception waveform in 1 bit units of the third node 130C, because the standing waves SWac and SWcc have different wavelengths, the amplitude of the reception waveform becomes about 0 V in the vicinity of timings tl to t3 at which these standing waves SWac and SWcc have opposite phases. Further, in the embodiment, the timings tl to t3 at which the standing waves SWac and SWcc have opposite phases are set as sampling points for measuring a signal waveform for identifying the logical level of the digital signal. Such sampling points are set by computations based on the wavelength of standing waves determined from the length of each communication line or by specifying a timing at which the occurrence frequency of events in which the standing waves have opposite phases is experimentally determined to be high.

[0060] FIG 9 shows an example of the signal waveform received between the nodes in the aforementioned wire communication system shown in FIG 3. A transition example LI 8 shown by a solid line in FIG 9 illustrates a reception wavelength of the third node 130C having branch connected thereto the third communication line 230C with a line length of about 1.8 m, and a transition example L14 shown by a dash-dot line illustrates a reception waveform of a fifth node 130E having branch connected thereto a fifth communication line 230E with a line length of about 1.4 m. Further, a transition example L05 shown by a broken line illustrates a reception waveform of a tenth node 130J having branch connected thereto a tenth communication line 230J with a line length of about 0.5 m. [0061] Thus, as clearly follows from FIG 9, after the logical level, for example, of the digital signal transmitted from the first node 130A has fallen from "H" to "L" at the timing tl, the wavelength distortion of the signal waveform L18 received by the third node 130C via the third communication line 230C, which is next in line length to the first communication line 230A and second communication line 230B, increases. Meanwhile the effect of distortion of the signal waveform LOS received by the tenth node 130J via the tenth communication line 230J that has the smallest line length decreases.

[0062] This is because the time required for the digital signal received from a certain node to propagate between the nodes 130A to 130J, which are the reflection points thereof, and the JC 330 increases and the timing at which the reflection distortion is generated is delayed with the increase in the line length of communication lines 230A to 230J that are branch connected to the nodes 130A to 130J. Another reason is that the difference in wavelength between the standing waves increases and the occurrence frequency of events in which the standing waves have opposite phases also increases with the increase in difference between the line lengths of the communication lines 230 A to 230J that are branch connected to the nodes 130A to 130J. Therefore, it can be confirmed that the distortion of reception waveform transmitted via the communication lines 230A to 230J decreases with the increase in difference between the length of the first communication line 230A, which is the longest among the communication lines 230A to 230J, and the length of other communication lines 230B to 230J. It also follows from FIG 2 above that communication feasibility at the reception side can be ensured when the difference in line length between the first communication line 230A, which is the longest among the communication lines 230A to 230J, and the third communication line 230C, which is next in line length to the first communication line 230A, is ensured to be equal to or greater than 10%.

[0063] The effect of wiring mode of the JC and communication lines on signal waveform will be explained below with reference to FIG 10. In FIG 10, FIG 10A shows a configuration example of wire communication system in which a plurality of nodes are branch connected to three JCs, and FIG 10B illustrates a configuration example of wire communication system in which a plurality of nodes are branch connected to two JCs.

[0064] First, as shown in FIG 10A, seven nodes 140A to 140G are connected via communication lines 240A to 240G, each having a length of about 1.5 m, to a first JC 340 constituting the wire communication system. Then, the first JC 340 is connected to a second JC 350 via a principal communication line (communication wiring) Wl with a line length of about 2.6 m. Two nodes 150A and 150B are connected to the second JC 350 via communication lines 250A and 250B with a line length of about 2.0 m. Furthermore, the second JC 350 is connected to a third JC 360 via the principal communication line (communication wiring) W2 with a line length of about 2.6 m. Seven nodes 160A to 160G are also connected to the third JC 360 via the communication lines 260A to 260G each having a line length of about 1.5 m. Terminal circuits are incorporated in the nodes 140A and 160G serving as terminals.

[0065] In the wire communication system of such a configuration, the number of connections of nodes, per unit, to the second JC 350 is less than that to the first and third JCs 340 and 360. Therefore, the characteristic impedance in the branch point of the second JC 350 is higher than that in the branch points of the first and third JCs 340 and 360. Further, when the node 150A that is branch connected to the second JC 350 is at the transmission side of a digital signal and the node 150B is at the reception side of the same signal, the nodes 150A and 150B, which are the transmission/reception terminals of the digital signal, are higher in characteristic impedance than the first to third JCs 340 to 360. Further, the reflection factor and transmission factor of the digital signal in the branch points of the first to third JCs 340 to 360 vary depending on these characteristic impedances.

[0066] Therefore, between the nodes 150A and 150B, which are the signal transmission/reception terminals, and the second JC 350, the reflection factor in the branch point of the second JC 350 that is viewed from the nodes 150A and 150B assumes a negative value, and the digital signal with a phase inverted according to the reflection factor is reflected to the node 150A which is on the transmission side. Such reflection factor increases with the increase in the number of connections of nodes to the second JC 350 and decreases with the decrease in the number of connections of nodes to the second JC 350. Further, the digital signal that has not been reflected in the branch point of the second JC 350, from among the digital signals transmitted from the node 150A, is transmitted to the adjacent first and third JCs 340, 360 and the node 150B. In the example shown in FIG 10A, the reflection factor and transmission factor in the branch point of the second JC 350 to which the two nodes 150A and 150B are branch connected are 50% each.

[0067] Digital signals transmitted to the first and third JCs 340 and 360 at such reflection factor and transmission factor are reflected in respective branch points, and the reflected waves are again transmitted to the node 150A or node 150B via the second JC 350. The repetition of such signal reflections at the nodes 140A to 140G, 150A and 150B, and 160A to 160G or the JCs 340 to 360 increases the reflection distortion of signal waveform.

[0068] Accordingly, in the embodiment, the reflection distortion of signal waveform is reduced by increasing the number of connections, per unit, to the JCs to which the nodes on the digital signal transmission side and reception side are branch connected, in other words, by decreasing the impedance in the branch points of JCs.

[0069] Thus, the second JC 350 is omitted, as shown in FIG 10B, and the nodes 150A and 150B that have been branch connected to the second JC 350 are branch connected to the first JC 340 via the communication lines 250A and 250B. Therefore, a total of nine nodes 140A to 140G and nodes 150A to 150B are branch connected to the first JC 340. As a result, the reflection factor of the branch point close to the nodes 150A and 150B increases from 50% to 80% and the transmission factor in the same branch point decreases from 50% to 20%. As a result, even when a digital signal is transmitted from the transmission-side node 150A to the reception-side node 150B, the transmission amount of the digital signal in the branch point close to the transmission-side node 150A is greatly reduced. Thus, the reflection wave generated by reflection of the transmitted digital signal in the branch point of the third JC 360 as a base point decreases, and the distortion of signal waveform in the reception-side node 150B caused by the reflection wave is reduced.

[0070] FIG 11 shows the transition of waveform received by the reception-side node 150B when a digital signal is transmitted from the transmission-side node 150A. In FIG 11, a transition example Lc3 represented by a broken line shows the transition of waveform received by the receptions-side node 150B in the wire communication line constituted in the manner shown in FIG 10A, and a transition example Lc2 represented by a solid line shows the transition of waveform received by the reception-side node 150B in the wire communication line constituted in the manner shown in FIG 10B.

[0071] As shown by the transition example Lc3 in FIG 11, the reception waveform of the node 150B obtained when the wire communication system is provided with three JCs 340 to 360 is significantly distorted because the transmission amount in the branch point of the second JC 350 serving as a branch point close to the node 150B is large. Therefore, even when the logical level of the signal transmitted from the transmission-side node 150A falls from "H" to "L" at the timing tl, the amplitude of the reception waveform Lc3 exceeds the threshold Vs that identifies whether the logical level is "H" or "L" under the effect of waveform distortion before the period Tc3 elapses.

[0072] By contrast, as shown by the transition example Lc2 in the same FIG 11, in the reception waveform of the node 150B obtained when the second JC 350 in the wire communication system is omitted, the transmission amount of the branch point in the first JC 340 which is the branch point close to the node 150B is small and therefore the waveform distortion decreases. Therefore, after the period Tc2 elapses (period Tc2 < period Tc3), the amplitude of the reception waveform Lc2 stabilizes and becomes equal to or less than the threshold Vs. Thus, the time interval required for the waveform distortion of signal waveform to decrease is reduced. Further, after the period Tc2 elapses, the logical level of the digital signal transmitted from the transmission-side node 150A can be correctly identified.

[0073] Since the wire communication system is thus configured, the waveform distortion of signal waveform transmitted and received between the nodes is reduced at an early stage by increasing the number of connections of nodes (branch number), per unit, to the JCs.

[0074] On the basis of such a principle, in the configuration shown in FIG 1, (a) the difference between a line length (about 2.0 m) of the first communication line 200A, which is the longest line, and the line length (about 1.8 m) of the second communication line 200B, which is next in line length to the first communication line 200A, is equal to or greater than 10% of the line length of the first communication line 200A.

[0075] (b) The number of JCs in the wire communication system is restricted to two and the number of connections of nodes 100A to 100η and nodes 110A to HOn, per unit, to the JCs 300 and 310 is increased. Where the wire communication system is constituted on the basis of such conditions, the waveform distortion contained in signal waveform transmitted and received between the nodes 100A to 100η and nodes 110A to HOn can be greatly reduced by the synergetic effect of these conditions. Further, since the distortion of signal waveform can be reduced by setting the line lengths in the above-described manner and increasing the number of connections of nodes to JCs, the wire communication system does not require devices such as filter circuits and attenuation of signal waveform caused by filter circuits or the like can be inhibited.

[0076] As explained hereinabove, the following effects can be obtained with the wire communication system according to the embodiment. (1) line characteristics of communication lines 220A and 210 leading to two nodes 100A and 100B for which the lengths of communication lines are larger than those for other nodes are set such as to obtain different wavelengths of two standing waves generated in the communication lines 220A and 210. Therefore, in the communication between the nodes 100A and 100B in which the effect of signal waveform distortion is the largest because of a large line length of communication lines, from among the communications between the nodes 100A to 100η and 110 A to HOn, the reduction of waveform distortion is attained by mutual cancelation of the standing waves. As a result, waveform distortion in the communication lines can be reduced without using a filter circuit, and a wiring region of the wire communication system in which communication can be established can be advantageously expanded.

[0077] (2) A line characteristic of communication lines that creates a difference in wavelength between the standing waves is set as a difference between the line length of the first communication line 200A and the line length of the second communication line 200B, which is next in line length to the first communication line 200A. As a result, the wavelengths of the standing waves generated in the first communication line 200A and second communication line 200B can be easily made different from each other and therefore the reduction of waveform distortion based on the difference between the standing waves can be easily realized.

[0078] (3) The difference between the line length of the first communication line 200A and the line length of the second communication line 200B, which is next in line length to the first communication line 200A, is set to be equal to or greater than 10% of the line length of the first communication line 200A. Therefore, a wavelength difference that is sufficient and necessary for establishing communication between the nodes 100A and 100B, which is performed via these first communication line 200A and second communication line 200B, is generated and the effect of reducing the waveform distortion of signal waveform based on the difference in wavelength between the standing waves can be ensured.

[0079] (4) Among the communication lines 200A to 200n and 210A to 210n, the line length of the first communication line 200A, which has the largest line length, is set to about 2.0 m, the line length of the second communication line 200B, which is next in line length to the first communication line 200A, is set to about 1.8 m, and the line length of other communication lines 200C to 200n and 210A to 210n is set to about 1.5 m. As a result, the waveform distortion of signal waveform generated in each communication line can be reduced to a range in which communication feasibility via these communication lines 200A and 200B can be maintained even when communication via the communication line 200A with a line length of about 2.0 m and the communication line 200B with a line length of about 1.8 m is performed as the communication between the two nodes with line lengths larger than those of other nodes. Further, with the above-described configuration, even when the communication lines have a line length with high utility for communication lines constituting a vehicle-installed network, the distortion of signal waveform generated in the communication lines 200A to 200n and 210Ato 210n can be advantageously reduced.

[0080] (5) The number of JCs in the wire communication system is limited to two JCs 300 and 310, and a plurality of nodes 100A to 100η and 110A to HOn are connected separately to these JCs 300 and 310. As a result, the transmission amount of signals in the branch points of the JCs 300 and 310 is reduced and therefore the waveform distortion caused by the signal transmitted from the branch points is reduced. Further, the synergism of this effect and the reduction effect of signal waveform distortion based on the difference in wavelength between the standing waves makes it possible to perform communication based on the signal waveform with a smaller • waveform distortion.

[0081] (6) Communication between the nodes 100A to 100η and 110A to HOn connected to the JCs 300 and 310 is performed a digital communication based on identification of logical level by a differential voltage. As a result, even when the effect of waveform distortion increases as in the fall period of the logical level of signal, the distortion of signal waveform is confined prior to the sampling point of the signal and reliability of digital communication based on logical level identification is increased.

[0082] (7) The identification of logical level is performed based on the signal waveform obtained when the amplitude of a combined waveform obtained by combining the standing waves is at a minimum. As a result, communication based on the signal waveform with the smallest effect of waveform distortion can be performed and logical level identification can be performed with higher accuracy.

[0083] (8) The abovementioned nodes 100A to 100η and 110A to HOn and also communication lines 200A to 200n and 210A to 210n are used in a multiplex communication system constituting a vehicle-installed network. As a result, high reliability of the wire communication system can be maintained, while expanding the wiring region. [0084] The abovementioned embodiment can be also realized in the below-described modes. Communication between the nodes 100A to 100η and 110A to 11 On connected to the JCs 300 and 310 is performed as digital communication based on identification of logical level on the basis of a differential voltage. However, this configuration is not limiting, and communication between the nodes 100A to 100η and HOA to HOn may be any communication performed via the communication lines 200A to 200n and 210A to 210n that are branch connected thereto. For example, analog communication can be performed.

[0085] In the embodiment, the sampling point for measuring the signal waveform is specified by a timing at which the waveform distortion contained in the reception waveform is at a minimum. However, such a configuration is not limiting, and any communication between the nodes that is based on the signal waveform with the waveform distortion reduced on the basis of difference in wavelength between the standing waves can be performed and the sampling point for measuring the signal waveform can be specified by any timing.

[0086] Further, in the embodiment, the number of JCs constituting the abovementioned wire communication system is limited to two, and the number of connections, per unit, of the nodes 100A to lOOn and 110A to 110ή to two JCs 300 and 310 is increased. However, this configuration is not limiting, and the number of JCs constituting the wire communication system may be one, or three or more, provided that the transmission amount in the branch points of JCs is reduced due to the increase in the number of connections of nodes per unit.

[0087] Further, in the embodiment, among the communication lines 200A to 200n and 210A to 210n constituting the wire communication system, the line length of the first communication line 200A, which has the largest line length, is set to about 2.0 m, the line length of the second communication line 200B, which is next in line length to the first communication line 200A, is set to about 1.8 m, and the line length of other communication lines 200C to 200n and 210A to 210n is set to about 1.5 m. However, such a configuration is not limiting, and any line lengths of the communication lines 200A to 200n and 210A to 210n can be set, provided that the difference in line lengths between the first communication line 200A, which has the largest line length, and the second communication line 200B is ensured to be equal to or greater than 10% of the line length of the first communication line 200A

[0088] Further, the line lengths of all of the communication lines 200n and 210A to 210n may be set to different values. In this case, the wavelengths of two standing waves generated in the communication lines that are branch connected to the reception-side node can be made to differ from each other when signal transmission and reception is performed between any nodes. As a result, the reduction of signal waveform distortion can be ensured among all of the nodes constituting the wire communication system and reliability of communication between the nodes is advantageously increased.

[0089] Further, in the embodiment, the wire communication system is configured to include three or more nodes 100A to 100η and 110 A to 110η. However, such a configuration is not limiting and the wire communication system may be configured to include two nodes on the transmission side and reception side. Essentially, any configuration may be used, provided that the lengths of communication lines that are branch connected to the nodes constituting the wire communication system are set such that the wavelength of standing wave generated between the transmission-side node and the reception-side node differs from the wavelength of standing wave generated between the reception-side node and the JC to which the reception-side node is branch connected.

[0090] Further, in the embodiment, the wavelengths of standing waves are made different from each other by setting the line lengths of communication lines 200A to 200n and 210A to 210n. However, such a configuration is not limiting and the wavelengths of standing waves may be made different from each other on the basis of line characteristics such as diameter and material properties of the communication lines 200A to 200n and 210A to 210n. In this case, the line lengths of the communication lines 200A to 200n and 210A to 210n can be equal to each other.

[0091] Further, in the embodiment, a controller area network (CAN) constituting a vehicle-installed network is considered as the wire communication system, but such a configuration is not limiting, and a vehicle-installed network constituted by FlexRay, local interconnect network (LIN), or the like can also be an application object of the invention. Further, the application of the invention is not limited to the vehicle-installed network, provided it is a wire communication system having communication lines that are branch connected to each of a plurality of nodes.

Claims

1. A wire communication system comprising:

a plurality of nodes; and

a branch connector connected to the plurality of nodes respectively via communication lines, wherein

line characteristics of respective communication lines between a transmission-side node connected to the branch connector and a reception-side node receiving a signal transmitted from the transmission-side node via the branch connector are set to exhibit line characteristics in which a wavelength of a standing wave generated between the transmission-side node and the reception-side node differs from a wavelength of a standing wave generated between the reception-side node and the branch connector .

2. The wire communication system according to claim 1, wherein the plurality of nodes that are branch connected are constituted by three or more nodes, and nodes connected to the communication lines that are set to exhibit the line characteristics, in which a wavelength of a standing wave generated between the transmission-side node and the reception-side node differs, of the communication lines are two nodes connected to the branch connector, a distortion of a signal waveform applied to communication between the two nodes being larger than in other nodes.

3. The wire communication system according to claim 1 or 2, wherein line characteristics, in which a wavelength of a standing wave generated between the transmission-side node and the reception-side node differs, of the communication lines is realized as a difference in line lengths between communication lines from the branch connector to two nodes, which are the transmission-side node and the reception-side node.

4. The wire communication system according to claim 3, wherein the lengths of communication lines from the branch connector to the two nodes are set such that the line length of the communication line that is branch connected to one node is shorter by 10% or more than the line length of the communication line that is branch connected to the other node.

5. The wire communication system according to claim 3 or 4, wherein all of the communication lines that electrically connect the respective nodes to the branch connector are set to have mutually different line lengths.

6. The wire communication system according to any one of claims 3 to 5, wherein the line length that is set to be longer from among the line lengths of the communication lines of the two nodes is equal to or less than 2.0 m, the line length that is set to be longer, by 10% or more, from among the line lengths of the communication lines of the two nodes is equal to or less than 1.8 m, and the line length of a communication line of a node other than these two nodes is equal to or less than 1.5 m.

7. The wire communication system according to any one of claims 1 to 6, wherein only two of the branch connectors are provided, and the plurality of nodes are connected via the communication lines to each of the two branch connectors.

8. The wire communication system according to any one of claims 1 to 7, wherein communication between the nodes connected to the branch connector is digital communication based on identification of a logical level by a differential voltage.

9. The wire communication system according to claim 8, wherein the identification of the logical level is performed based on a signal waveform obtained when an amplitude of a combined waveform obtained by combining a standing wave generated between a transmission node that transmits a signal and a reception node that receives the transmitted signal and a standing wave generated between the reception node and the branch connector is at a minimum.

10. The wire communication system according to any one of claims 1 to 9, wherein the nodes and the communication lines are nodes and communication lines used in a multiplex communication system constituting a vehicle-installed network.