Communication circuit, device, communication system, method for controlling communication circuit, and program

Abstract

Switching between connection and disconnection between a termination resistor of a communication circuit and a transmission path is performed without generating a communication error. A communication circuit (6A) is provided with a communication unit (10), a termination resistor (12), a switch (13), a detection unit (15), and a control unit (16). A communication unit (10) is provided in a device (2) connected to a transmission path (3), and communicates via the transmission path (3) with another communication unit (10) provided in another device (2) connected to the transmission path (3). The termination resistor (12) is connected to the transmission path (3). The switch (13) switches between connection and disconnection between the termination resistor (12) and the transmission path (3). The detection unit (15) detects the total resistance value (R1) of the total resistance connected to the transmission path (3) in a state where the termination resistor (12) is connected to the transmission path (3). The control unit (16) controls the switching between the connection and disconnection between the termination resistor (12) and the transmission path (3) by the switch (13) on the basis of the detection result of the detection unit (15).

Description

Technical Field

[0001] The present disclosure generally relates to a communication circuit, a device, a communication system, a control method and a program for a communication circuit, and more specifically, to a communication circuit having a terminal resistor, a device having the communication circuit, a communication system having the device, and a control method and a program for the communication circuit. Background Art

[0002] The terminal resistance setting device (communication circuit) described in Patent Document 1 includes a control unit, a communication controller, a terminal resistance, and a switch circuit. The control unit controls the communication controller at the start of the operation to send data to the LAN line (transmission path). In addition, when a communication error is received through the communication controller, the control unit recognizes that the data input and output ends of the communication controller are not connected to the terminal resistance, and controls the switch circuit to be connected. In the case of successful data transmission, the control unit recognizes that the data input and output ends of the communication controller are connected to a terminal resistance independent of the above-mentioned terminal resistance, and controls the switch circuit to be disconnected.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 9-326811 Summary of the invention

[0006] In the above-mentioned terminal resistance setting device, since the connection / disconnection of the terminal resistance is switched after a communication error is sensed, communication may be interrupted and become unstable, or the device may malfunction.

[0007] An object of the present disclosure is to provide a communication circuit, an apparatus, a communication system, a communication circuit control method, and a program that can switch between connection and disconnection of a terminal resistor and a transmission path without causing a communication error.

[0008] A communication circuit of one aspect of the present disclosure comprises: a communication unit, a terminal resistor, a switch, a detection unit, and a control unit. The communication unit is provided in a device connected to a transmission path, and communicates with other communication units provided in other devices connected to the transmission path via the transmission path. The terminal resistor is connected to the transmission path. The switch switches the connection and disconnection of the terminal resistor with the transmission path. The detection unit detects the total resistance value of the total resistor connected to the transmission path when the terminal resistor is connected to the transmission path. The control unit controls the switching of the connection and disconnection of the terminal resistor with the transmission path performed by the switch based on the detection result of the detection unit.

[0009] A device according to another aspect of the present disclosure includes the communication circuit and a functional unit. The functional unit is connected to the communication unit of the communication circuit, exchanges signals with the communication unit, and executes a given function.

[0010] A communication system according to another aspect of the present disclosure includes a transmission path and three or more devices. The three or more devices are connected to the transmission path. At least one of the three or more devices is a device according to the above aspect, and the remaining devices include a terminal resistor that is always connected to the transmission path.

[0011] Another method for controlling a communication circuit of the present disclosure is a method for controlling a communication circuit having a communication unit, a terminal resistor, and a switch. The communication unit is provided in a device connected to a transmission path, and communicates with other communication units provided in other devices connected to the transmission path via the transmission path. The terminal resistor is connected to the transmission path. The switch switches the connection and disconnection of the terminal resistor with the transmission path. The method for controlling the communication circuit includes a detection process and a control process. In the detection process, the total resistance value of the total resistor connected to the transmission path is detected in a state where the terminal resistor is connected to the transmission path. In the control process, based on the detection result in the detection process, the switching of the connection and disconnection of the terminal resistor with the transmission path performed by the switch is controlled.

[0012] A program according to another aspect of the present disclosure causes one or more processors to execute the communication circuit control method according to the above aspect.

[0013] According to the present disclosure, there is an advantage that connection and disconnection of the terminal resistor and the transmission path can be switched without causing communication errors. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a structural diagram of a communication system involved in an implementation method.

[0015] Figure 2 This is a flowchart for explaining the operation of the communication circuit of the first device included in the communication system according to the embodiment.

[0016] Figure 3 This is a block diagram of a communication circuit according to variation 2.

[0017] Figure 4 This is a block diagram of a communication circuit according to Modification 3. DETAILED DESCRIPTION

[0018] The following describes the communication circuit, device, communication system, control method of the communication circuit, and program involved in the embodiments. The following embodiments are only examples of various embodiments of the present disclosure. In addition, the following embodiments can be modified in various ways according to the design, etc. as long as the purpose of the present disclosure can be achieved.

[0019] (Implementation Method)

[0020] (1) Summary

[0021] Figure 1 1 is a block diagram of a communication system 1 according to an embodiment of the present invention. Figure 1 As shown, the communication circuit 6A involved in the embodiment includes: a communication unit 10, a terminal resistor 12, a switch 13, a detection unit 15 and a control unit 16. The communication unit 10 is provided in the first device 2A connected to the transmission path 3, and communicates with other communication units 10 provided in other devices 2 connected to the transmission path 3 via the transmission path 3. The terminal resistor 12 is connected to the transmission path 3. The switch 13 switches the connection and disconnection of the terminal resistor 12 to the transmission path 3. The detection unit 15 detects the total resistance value R1 of the total resistor connected to the transmission path 3 when the terminal resistor 12 is connected to the transmission path 3. The control unit 16 controls the switching of the connection and disconnection of the terminal resistor 12 to the transmission path 3 by the switch 13 based on the detection result of the detection unit 15.

[0022] According to this structure, the total resistance value R1 of the total resistance connected to the transmission path 3 (that is, the resistance value of the combined resistance of all the terminal resistors 12) is detected, and based on the detection result, the switching of the connection and disconnection of the terminal resistor 12 and the transmission path 3 by the switch 13 is controlled. Therefore, the connection and disconnection of the terminal resistor 12 and the transmission path 3 can be switched without causing communication errors in the communication unit 10.

[0023] (2) Communication system structure

[0024] Reference Figure 1 The communication system 1 , the first device 2A, and the communication circuit 6A according to the embodiment will be described in detail.

[0025] The communication system 1 is a communication system in which a plurality of devices 2 perform functions of the devices 2 while communicating with each other via a transmission path 3. The plurality of devices 2 are, for example, servo amplifiers and various sensors used in semiconductor manufacturing equipment or industrial robots.

[0026] The communication system 1 includes a transmission path 3 and a plurality of devices 2 .

[0027] The transmission path 3 is, for example, a serial communication cable of the serial communication standard RS485. In more detail, the transmission path 3 is a differential transmission path (also referred to as a differential line) having a characteristic impedance R0 of a differential line (for example, R0 = 100Ω). The transmission path 3 as a differential transmission path has two signal lines 3a and 3b, and uses the potential difference between the two signal lines 3a and 3b to transmit signals. However, the transmission path 3 is not limited to a differential transmission path, and may also be a single-ended transmission path. A single-ended transmission path has one signal line, and uses the potential difference between one signal line and ground to transmit signals. In addition, the transmission path 3 may also be other communication cables such as a LAN (local area network) cable.

[0028] The plurality of (for example, three or more) devices 2 include at least one first device 2A and a second device 2B as the remaining device (i.e., the device 2 other than the first device 2A). In the example shown in the figure, three first devices 2A and one second device 2B are shown. As described later, the plurality of devices 2 each include a communication circuit 6. In the following description, the communication circuit 6 of the first device 2A is sometimes described as a communication circuit 6A, and the communication circuit 6 of the second device 2B is sometimes described as a communication circuit 6B.

[0029] The first device 2A communicates with other devices 2 connected to the transmission path 3 via the transmission path 3, and executes a given function of the first device 2A. The given function of the first device 2A is a function of controlling a servo motor that is a control object of the servo amplifier when the first device 2A is a servo amplifier, and is a function of detecting a given physical quantity when the first device 2A is a sensor that detects a given physical quantity. The first device 2A has a terminal resistor 12, and has a function of automatically switching between connecting and disconnecting the terminal resistor 12 and the transmission path 3.

[0030] The first device 2A includes a functional unit 5 and a communication circuit 6A ( 6 ).

[0031] The functional unit 5 performs the above-mentioned given function. For example, when the first device 2A is a servo amplifier, the functional unit 5 is a control unit that controls the communication with other servo amplifiers and the servo motor. In addition, the terminal resistor 12 described later is also switched between connection and disconnection with the transmission path 3. In addition, when the first device 2A is a sensor that detects a given physical quantity, the functional unit 5 is a detection unit that detects the physical quantity of the detection object. The functional unit 5 is connected to the communication circuit 6A, and performs the above-mentioned given function while sending and receiving signals with the communication circuit 6A. In more detail, the functional unit 5 performs the given function according to the control from the communication circuit 6A. Alternatively, the functional unit 5 performs the given function and sends the execution result from the communication circuit 6A to the other device 2 via the transmission path 3. The above-mentioned given function is not particularly limited, but is a function different from the communication circuit 6A.

[0032] The communication circuit 6A communicates with the communication circuit 6 of the other device 2 via the transmission path 3. The communication circuit 6A includes a power supply circuit 7, two communication terminals 8a and 8b, two wirings 9a and 9b, a communication unit 10, a processing unit 11, a terminal resistor 12, and a switch 13.

[0033] The power circuit 7 generates a DC voltage having a voltage requested by the first device 2A based on a power voltage supplied from an external power source (DC power source or AC power source), and supplies the generated DC voltage to the communication unit 10 and the processing unit 11 .

[0034] The two communication terminals 8a and 8b are respectively connected to the two signal lines 3a and 3b constituting the transmission path 3. More specifically, the two communication terminals 8a and 8b correspond to the two signal lines 3a and 3b constituting the transmission path 3 one by one, and are connected to the corresponding signal lines 3a and 3b via branch signal lines 3c and 3d.

[0035] The communication unit 10 is provided in a device 2 (more specifically, a first device 2A) connected to a transmission path 3. The communication unit 10 communicates with the communication units 10 of other devices 2 via the transmission path 3. In addition, the communication unit 10 exchanges signals with the functional unit 5, is controlled by the functional unit 5, or transmits the execution result of the functional unit 5 to the outside via the transmission path 3. The communication unit 10 is connected to two communication terminals 8a and 8b via two wirings 9a and 9b. That is, the communication unit 10 is connected to the transmission path 3 via two wirings 9a and 9b and two branch signal lines 3c and 3d. When the power of the first device 2A is turned on, the communication unit 10 energizes a current for detection to the transmission path 3 via two wirings 9a and 9b and two branch signal lines 3c and 3d in a connected state of the switch 13 (that is, a state in which the termination resistor 12 is connected to the transmission path 3). The detection current is a current for a detection unit 15 described later to detect a total resistance value R1 of the transmission path 3 described later.

[0036] The termination resistor 12 is a resistor for suppressing a reflected wave of a transmission signal generated at the end of the transmission path 3. The termination resistor 12 is connected across the two wirings 9a and 9b. The termination resistor 12 is connected to the transmission path 3 via two wirings 9a and 9b and two branch signal lines 3c and 3d. The value of the termination resistor 12 is, for example, the same value (e.g., 100 Ω) as the characteristic impedance R0 (e.g., R0 = 100 Ω) of the differential line of the transmission path 3.

[0037] The switch 13 switches the connection and non-connection between the termination resistor 12 and the transmission path 3 according to the control of the processing unit 11 (more specifically, a control unit 16 described later). The switch 13 switches between connection and disconnection according to the control of the processing unit 11. In addition, the switch 13 is connected in series with the termination resistor 12. More specifically, the switch 13 is connected between one wiring 9a and one end of the termination resistor 12. When the switch 13 is switched from disconnection to connection according to the control of the processing unit 11, the termination resistor 12 is connected between the two wirings 9a and 9b, thereby connecting the termination resistor 12 to the transmission path 3. On the other hand, when the switch 13 is switched from connection to disconnection according to the control of the processing unit 11, the termination resistor 12 is disconnected from one wiring 9a, thereby disconnecting the termination resistor 12 from the transmission path 3.

[0038] In addition, the so-called connection of the termination resistor 12 to the transmission path 3 means that the termination resistor 12 is electrically connected between two signal lines 3a and 3b (that is, the termination resistor 12 is connected to the transmission path 3 so as to function as a resistor). The so-called disconnection of the termination resistor 12 from the transmission path 3 means that one end of the termination resistor 12 is disconnected from one wiring 9a (that is, the termination resistor 12 is disconnected from the transmission path 3 so that the termination resistor 12 does not function as a resistor).

[0039] The switch 13 is, for example, a semiconductor switch. Thus, the switch 13 can be miniaturized. More specifically, when the switch 13 is, for example, an N-channel MOSFET, the voltage drop caused by the depletion layer capacity of the N-channel MOSFET can be reduced, and the signal quality of communication in the transmission path 3 can be improved.

[0040] The processing unit 11 detects the above-mentioned total resistance value R1 of the transmission path 3 and performs on / off control of the switch 13. The processing unit 11 includes a detection unit 15, a control unit 16, and a storage unit 17.

[0041] The detection unit 15 detects the resistance value (hereinafter referred to as the total resistance value) R1 of the total resistance (that is, the combined resistance of all the terminal resistances 12 connected to the transmission path 3) connected to the transmission path 3 when the switch 13 is in the connected state (that is, the state in which the terminal resistance 12 is connected to the transmission path 3). More specifically, the detection unit 15 detects the voltage value V1 of the voltage between the two ends of the terminal resistance 12 when the switch 13 is in the connected state, and detects the total resistance value R1 based on the detected voltage value V1. Specifically, the detection unit 15 detects the voltage value V1 of the voltage between the two ends of the terminal resistance 12 when the communication unit 10 supplies the detection current to the transmission path 3. And, the detection unit 15 detects (in more detail, calculates) the total resistance value R1 (= V1 / I1) of the above-mentioned total resistance based on the detected voltage value V1 and the current value I1 of the detection current.

[0042] The control unit 16 controls the switching of the connection and disconnection of the terminal resistor 12 and the transmission path 3 by the switch 13 based on the detection result (total resistance value R1) of the detection unit 15. That is, the total resistance value R1 is compared with the threshold value Rs, and based on the comparison result, the switching of the connection and disconnection of the terminal resistor 12 and the transmission path 3 by the switch 13 is controlled.

[0043] Here, the threshold value Rs is, for example, the same value as the total resistance value of the transmission path 3 when two terminal resistors 12 (i.e., the terminal resistors 12 of each of the two devices 2) are connected to the transmission path 3. When the characteristic impedance R0 of the differential line of the transmission path 3 is 100Ω, in order to optimize the signal quality of the transmission path 3, two 100Ω terminal resistors 12 are sometimes connected in parallel to the transmission path 3. That is, sometimes the terminal resistors 12 of each of the two devices 2 are connected to the transmission path 3. In this case, the total resistance value of the transmission path 3 is 50Ω, which is the parallel connection of two 100Ω. Therefore, in this case, the threshold value Rs is set to 50Ω. When the number of terminal resistors 12 (100Ω) connected to the transmission path 3 is two or less, the total resistance value of the transmission path 3 is 50Ω or more, and when the above number is more than two, the total resistance value of the transmission path 3 is less than 50Ω. In addition, it is preferred that the terminal resistors connected to the line are two located at both ends of the transmission path 3, so that better signal quality can be obtained. In addition, in the present embodiment, the threshold Rs is the same value as the total resistance value of the transmission path 3 when two terminal resistors 12 are connected to the transmission path 3, but can also be set to the same value as the total resistance value of the transmission path 3 when N (N: a natural number) terminal resistors 12 are connected to the transmission path 3.

[0044] More specifically, when the total resistance value R1 detected by the detection unit 15 is greater than the threshold value Rs, the control unit 16 determines that two or less terminal resistors 12 are already connected to the transmission path 3, including the terminal resistor 12 of the first device 2A. And, in the case of this determination result, the control unit 16 controls the switch 13 so that the terminal resistor 12 is connected to the transmission path 3. That is, the control unit 16 sets the switch 13 to be connected. In the present embodiment, since the switch 13 is set to be connected when the communication unit 10 supplies the detection current to the transmission path 3, the connected state is maintained. On the other hand, when the total resistance value R1 detected by the detection unit 15 is less than the threshold value Rs, the control unit 16 determines that more than two terminal resistors 12 are already connected to the transmission path 3, including the terminal resistor 12 of the first device 2A. And, in the case of this determination result, the control unit 16 controls the switch 13 so that the terminal resistor 12 is not connected to the transmission path 3. That is, the control unit 16 sets the switch 13 to be disconnected.

[0045] In addition, as a method for the control unit 16 to read the voltage value V1 of the voltage generated between the communication terminals 8a and 8b (i.e., between the signal lines 3a and 3b) when the detection current is supplied to the transmission path 3, there is, for example, a method of reading the voltage value V1 by an analog-to-digital (AD) converter, or a method of reading the voltage value V1 by determining whether the voltage value V1 is higher than a specified voltage value H (higher) or L (lower) by a comparator.

[0046] The storage unit 17 is, for example, an electrically rewritable nonvolatile semiconductor memory. The storage unit 17 stores information (impedance information) related to the characteristic impedance R0 of the differential line of the transmission path 3. The control unit 16 calculates the threshold value Rs based on the information related to the characteristic impedance R0 of the differential line stored in the storage unit 17, and uses the calculated threshold value Rs to compare the total resistance value R1 with the threshold value Rs as described above.

[0047] In addition, the information on the characteristic impedance R0 of the differential line may be written to the storage unit 17 by, for example, a person using a storage medium (such as a USB memory) from the outside. In this case, the first device 2A has an external connection unit to which the storage medium can be detachably connected. In addition, the first device 2A may be accessed from an external device via the transmission path 3 to write the information on the characteristic impedance R0 of the differential line to the storage unit 17.

[0048] The functional unit 5, the processing unit 11 and the communication unit 10 are respectively mainly composed of a computer system having one or more processors and one or more memories. In addition, the processing unit 11 may be composed of all of its functions by a computer system, or may be composed of a part of its functions by a computer system. In addition, the communication unit 10 may not necessarily be composed of a computer system. In the functional unit 5, the processing unit 11 and the communication unit 10, the functions of the processing unit 11 and the communication unit 10 are realized by executing the program recorded in the memory through one or more processors. The program can be recorded in the memory in advance, or it can be provided through an electric communication line such as the Internet, or it can be recorded in a non-temporary recording medium such as a memory card.

[0049] The second device 2B communicates with other devices 2 connected to the transmission path 3 via the transmission path 3, and executes a given function of the second device 2B. When the second device 2B is a servo amplifier, the given function of the second device 2B is a function of controlling a servo motor that is a control object of the servo amplifier. In addition, when the second device 2B is a sensor that detects a given physical quantity, the function is to detect a given physical quantity. The second device 2B has a terminal resistor 12 that is always connected to the transmission path 3 when connected to the transmission path 3. That is, the second device 2B has a structure in which the switch 13 and the processing unit 11 are omitted in the first device 2A, and does not have a function of supplying a detection current from the communication unit 10 to the transmission path 3.

[0050] The second device 2B includes a functional unit 5 and a communication circuit 6B ( 6 ).

[0051] The functional unit 5 performs a given function of the second device 2B. For example, when the second device 2B is a servo amplifier, the functional unit 5 is a control unit that controls the servo motor. In addition, when the second device 2B is a sensor that detects a given physical quantity, the functional unit 5 is a detection unit that detects the physical quantity of the detection object. The functional unit 5 is connected to the communication circuit 6B, and performs the above-mentioned given function while sending and receiving signals with the communication circuit 6B. In more detail, the functional unit 5 performs the given function according to the control from the communication circuit 6B. Alternatively, the functional unit 5 performs the given function and sends the execution result from the communication circuit 6B to the other device 2 via the transmission path 3. The above-mentioned given function is not particularly limited, but is a function different from the communication circuit 6B.

[0052] The communication circuit 6B communicates with the communication circuit 6 of the other device 2 via the transmission path 3. The communication circuit 6B includes: a power supply circuit 7, two communication terminals 8a, 8b, two wirings 9a, 9b, a communication unit 10, and a terminal resistor 12. That is, the second device 2B has a structure in which the switch 13 and the processing unit 11 are omitted in the first device 2A. In addition, the communication unit 10 of the second device 2B is similarly configured as the communication unit 10 of the first device 2A, except that it does not have the function of supplying a detection current to the transmission path 3. That is, the communication unit 10 of the second device 2B does not supply a detection current to the transmission path 3. The same reference numerals are given to the same structures of the second device 2B as those of the first device 2A, and the description thereof is omitted.

[0053] In the second device 2B, the terminal resistor 12 is always connected between the two wirings 9a and 9b. Therefore, when the second device is connected to the transmission path 3 via the two branch signal lines 3c and 3d, the terminal resistor 12 is automatically always connected to the transmission path 3. The value of the terminal resistor 12 of the second device 2B is set to the same value as the characteristic impedance R0 of the differential line of the transmission path 3, for example, similarly to the case of the terminal resistor 12 of the first device 2A.

[0054] (3) Operation of the communication circuit of the first device

[0055] Reference Figure 2 The operation of the communication circuit 6A of the first device 2A will be described. Figure 2 This is a flowchart for explaining the operation of the communication circuit 6A of the first device 2A included in the communication system 1 according to the embodiment.

[0056] When the power of the first device 2A is turned on (S1), the control unit 16 sets the switch 13 to be connected (S2). As a result, the terminal resistor 12 is connected to the transmission path 3. In addition, when the power is turned on, the communication unit 10 supplies a detection current (current value I1) to the transmission path 3 via the wiring 9a, 9b and the branch signal lines 3c, 3d, and the detection unit 15 detects the voltage value V1 of the voltage between the two ends of the terminal resistor 12 generated by the energization (S3). And, based on the detected voltage value V1 and the current value I1 of the detection current, the detection unit 15 detects the total resistance value R1 (=V1 / I1) of the total resistance connected to the transmission path 3 (S4).

[0057] Furthermore, the control unit 16 controls the switching of the connection and disconnection of the terminal resistor 12 and the transmission path 3 by the switch 13 based on the detection result (total resistance value R1) of the detection unit 15 (S5). More specifically, when the total resistance value R1 detected by the detection unit 15 is greater than the threshold value Rs (S5: Yes), the control unit 16 determines that two or less terminal resistors 12 are connected to the transmission path 3. Furthermore, in the case of this determination result, the control unit 16 controls the switch 13 to be connected so that the terminal resistor 12 is connected to the transmission path 3. That is, the control unit 16 maintains the connection of the switch 13 (S6). On the other hand, when the total resistance value R1 detected by the detection unit 15 is less than the threshold value Rs (S5: No), the control unit 16 determines that more than two terminal resistors 12 are connected to the transmission path 3. Furthermore, in the case of this determination result, the control unit 16 controls the switch 13 to be disconnected so that the terminal resistor 12 and the transmission path 3 are disconnected (S7). Furthermore, the processing ends.

[0058] (4) Communication circuit control methods and procedures, etc.

[0059] The same functions as those of the communication circuit 6A according to the above-described embodiment may be embodied by a control method of the communication circuit 6A, a computer program (program), or a non-transitory recording medium recording the computer program.

[0060] A control method for a communication circuit according to one embodiment controls the switching of the connection and disconnection of the terminal resistor 12 and the transmission path 3 by the switch 13 in the communication circuit 6A. The communication circuit 6A includes a communication unit 10, a terminal resistor 12, and a switch 13. The communication unit 10 is provided in a device 2 connected to the transmission path 3, and communicates with other communication units 10 provided in other devices 2 connected to the transmission path 3 via the transmission path 3. The terminal resistor 12 is connected to the transmission path 3. The control method for the communication circuit includes a detection step and a control step. In the detection step, in a state where the terminal resistor 12 is connected to the transmission path 3, the total resistance value R1 of the total resistance connected to the transmission path 3 is detected. In the control step, based on the detection result in the detection step, the switching of the connection and disconnection of the terminal resistor 12 and the transmission path 3 by the switch 13 is controlled.

[0061] A program according to one aspect causes one or more processors to execute the above-mentioned communication circuit control method.

[0062] A non-transitory recording medium according to one aspect records a program for causing one or more processors to execute the method for controlling the communication circuit.

[0063] (5) Modification

[0064] A modification of the above embodiment is described. In the following description, the description is centered on the parts different from the above embodiment, and the same parts as the above embodiment are given the same symbols, and sometimes the drawings and descriptions are omitted. In addition, the above embodiment and the following modification can be implemented in combination.

[0065] (Variant 1)

[0066] In the communication circuit 6A of the above-mentioned embodiment, when the power of the first device 2A is turned on, the connection and disconnection of the terminal resistor 12 and the transmission path 3 are switched by the switch 13. In contrast, in the communication circuit 6A of the modification 1, the connection and disconnection of the terminal resistor 12 and the transmission path 3 are switched by the switch 13 periodically. More specifically, in the modification 1, the detection unit 15 periodically detects the total resistance value R1 of the transmission path 3 in a state where the terminal resistor 12 and the transmission path 3 are connected. Each time the detection unit 15 detects the total resistance value R1 of the transmission path 3, the control unit 16 controls the switching of the connection and disconnection of the terminal resistor 12 and the transmission path 3 by the switch 13 based on the detection result of the detection unit 15.

[0067] According to variation 1, the connection and disconnection of the terminal resistor 12 with the transmission path 3 by the switch 13 can be periodically switched. As a result, even if the second device 2B that does not have the function of disconnecting the terminal resistor 12 is connected to the transmission path 3 after the first device 2A having the communication circuit 6A of the present disclosure is connected to the transmission path 3, the number of terminal resistors 12 connected to the transmission path 3 can be adjusted to the optimal number by switching the connection and disconnection of the terminal resistor 12 in the communication circuit 6A of the present disclosure with the transmission path 3.

[0068] (Variant 2)

[0069] Figure 3 6A is a block diagram of a communication circuit according to a second modification. Figure 3 As shown, the communication circuit 6A according to the second modification is further provided with a manual switch 18 for switching between the automatic mode and the forced mode in addition to the communication circuit 6A according to the first embodiment.

[0070] In the automatic mode, as described in the above embodiment, the control unit 16 controls the switching of the connection and disconnection between the terminal resistor 12 and the transmission path 3 by the switch 13 based on the detection result of the detection unit 15. In the forced mode, the control unit 16 forcibly controls the switch 13 to be connected so that the terminal resistor 12 is connected to the transmission path 3.

[0071] That is, in the automatic mode, the communication unit 10 supplies the detection current to the transmission path 3 via the wirings 9a, 9b and the branch signal lines 3c, 3d. Furthermore, the detection unit 15 detects the voltage value V1 of the voltage generated in the terminal resistor 12 by the energization, and detects the total resistance value R1 of the transmission path 3 based on the detected voltage value V1 and the current value I1 of the detection current. Furthermore, the control unit 16 compares the total resistance value R1 with the threshold value Rs, and controls the connection and disconnection of the switch 13 based on the comparison result. In contrast, in the forced mode, the above-mentioned processing of the communication unit 10, the detection unit 15 and the control unit 16 is not performed, and the control unit 16 controls the switch 13 to be connected, so that the terminal resistor 12 is connected to the transmission path 3.

[0072] According to variation 2, the operation mode of the communication circuit 6A can be switched between the automatic mode and the forced mode by the manual switch 18. By switching the operation mode of the communication circuit 6A to the forced mode, the terminal resistor 12 can be forcibly connected to the transmission path 3. Thus, when the first device 2A having the communication circuit 6A of the present disclosure is connected to the end of the transmission path 3, the terminal resistor 12 can be forcibly connected to the transmission path 3 by the manual switch 18. That is, the terminal resistor 12 of the first device 2A connected to the end of the transmission path 3 can be forcibly connected to the transmission path 3.

[0073] (Variant 3)

[0074] Figure 4 6A is a block diagram of a communication circuit 6A according to a modification example 3. The communication circuit 6A of the above embodiment includes a terminal resistor 12 (see Figure 1 ), but if Figure 4 As shown, the communication circuit 6A of the modification example 3 includes a plurality of terminal resistors 12a, 12b, and 12c having different resistance values. Furthermore, the switch 13D of the modification example 3 selects one of the plurality of terminal resistors 12a to 12c based on the control of the control unit 16, and switches the selected terminal resistor to be connected to and disconnected from the transmission path 3.

[0075] In more detail, each terminal resistor 12a to 12c is connected in parallel between two wirings 9a and 9b. The switch 13D is composed of a plurality of switches 13a to 13c corresponding to the plurality of terminal resistors 12a to 12c. The switch 13a, the switch 13b, and the switch 13c are provided between the corresponding terminal resistor 12a, the terminal resistor 12b, and the terminal resistor 12c and one wiring 9a. By connecting and disconnecting the switches 13a to 13c, the corresponding terminal resistors 12a to 12c and one wiring 9a are connected and disconnected. Thus, the switches 13a to 13c respectively switch the connection and disconnection of the corresponding terminal resistors 12a, 12b, or 12c with the transmission path 3.

[0076] When the power of the first device 2A is turned on, the control unit 16 of this modified example controls the multiple switches 13a to 13c to select a terminal resistor to be used from the multiple terminal resistors 12a to 12c. More specifically, the control unit 16 sets the switch corresponding to the terminal resistor to be used among the multiple switches 13a to 13c to be connected, and sets the switches corresponding to the remaining terminal resistors not to be used to be disconnected. As a result, only the terminal resistor to be used among the multiple terminal resistors 12a to 12c is connected to the transmission path 3.

[0077] The control unit 16 selects, as one terminal resistor to be used, a terminal resistor having a resistance value closest to the resistance value specified by the impedance information (information related to the characteristic impedance R0 of the differential line) stored in the storage unit 17 from among the plurality of terminal resistors 12a to 12c. In other words, the terminal resistor that matches the characteristic impedance R0 of the differential line of the transmission path 3 is automatically selected from among the plurality of terminal resistors 12a to 12c.

[0078] According to Modification 3, the optimal terminal resistor among the plurality of terminal resistors 12a to 12b can be connected to the transmission path. Thus, the communication circuit 6A of the present disclosure can be adapted to various transmission paths 3 having different characteristic impedances R0 of differential lines.

[0079] (Variant 4)

[0080] In the communication circuit 6A of the above embodiment, the control unit 16 compares the total resistance value R1 of the transmission path 3 with the threshold value Rs, and based on the comparison result, controls the switching of the connection and disconnection of the terminal resistor 12 to the transmission path 3 by the switch 13. In contrast, in the communication circuit 6A of the modification 4, the control unit 16 compares the number N1 of the terminal resistors 12 connected to the transmission path 3 with the threshold value Ns, and based on the comparison result, controls the switching of the connection and disconnection of the terminal resistor 12 to the transmission path 3 by the switch 13. In addition, the structure of the communication circuit 6A of the modification 4 is the same as the structure of the communication circuit 6A of the above embodiment.

[0081] In more detail, in variant example 4, the control unit 16 calculates the number N1 of terminal resistors 12 connected to the transmission path 3 (i.e., the number of terminal resistors 12 connected to the transmission path 3 among the terminal resistors 12 of the device 2) based on the detection result (total resistance value R1) of the detection unit 15.

[0082] In addition, in this calculation, it is assumed that the resistance value of each terminal resistor 12 connected to the transmission path 3 is the same as the characteristic impedance R0 of the differential line of the transmission path 3. In addition, each terminal resistor 12 connected to the transmission path 3 is connected across the two signal lines 3a and 3b of the transmission path 3, and is connected in parallel with each other. Based on these prerequisites and knowledge of electromagnetics, the above-mentioned number N1 can be calculated based on the detection result (total resistance value R1) of the detection unit 15. The details of the calculation of the number N1 are omitted here.

[0083] Then, the control unit 16 compares the calculated number N1 with a threshold value Ns. The threshold value Ns is, for example, two, but is not limited to two. When the result of the size comparison is that the number N1 is less than the threshold value Ns, the control unit 16 determines that less than Ns (for example, two) terminal resistors 12 are already connected to the transmission path 3, including the terminal resistor 12 of the first device 2A. And, in the case of this determination result, the control unit 16 controls the switch 13 so that the terminal resistor 12 is connected to the transmission path 3. That is, the control unit 16 sets the switch 13 to be connected. In the modification 4, similarly to the above-mentioned embodiment, since the switch 13 is set to be connected when the communication unit 10 energizes the detection current to the transmission path 3, the connection is maintained. On the other hand, when the result of the above-mentioned size comparison is that the number N1 exceeds the threshold value Ns, the control unit 16 determines that more than Ns (for example, two) terminal resistors 12 are already connected to the transmission path 3, including the terminal resistor 12 of the first device 2A. Then, in the case of this determination result, the control unit 16 controls the switch 13 so that the terminal resistor 12 is disconnected from the transmission path 3. That is, the control unit 16 turns off the switch 13.

[0084] The threshold Ns may be used to set the optimal number of terminal resistors 12 connected to the transmission path 3. In this case, the switching of connection and disconnection of the terminal resistors 12 to the transmission path 3 is controlled so that the transmission path 3 is connected to the optimal number of terminal resistors 12.

[0085] According to Modification 4, by comparing the number N1 of terminal resistors 12 connected to the transmission path 3 with the threshold value Ns (ie, by simple control), it is possible to control the connection and disconnection of the terminal resistor 12 to the transmission path 3 by the switch 13 .

[0086] (Way)

[0087] As is apparent from the above-described embodiment and modified examples, the following aspects are disclosed in this specification.

[0088] The communication circuit (6A) of the first mode comprises: a communication unit (10), a terminal resistor (12), a switch (13), a detection unit (15) and a control unit (16). The communication unit (10) is provided in a device (2) connected to a transmission path (3), and communicates with other communication units (10) provided in other devices (2) connected to the transmission path (3) via the transmission path (3). The terminal resistor (12) is connected to the transmission path (3). The switch (13) switches between connection and disconnection of the terminal resistor (12) and the transmission path (3). The detection unit (15) detects the total resistance value (R1) of the total resistance connected to the transmission path (3) when the terminal resistor (12) is connected to the transmission path (3). The control unit (16) controls the switching of connection and disconnection of the terminal resistor (12) and the transmission path (3) performed by the switch (13) based on the detection result of the detection unit (15).

[0089] According to this structure, the total resistance value (R1) of the total resistance connected to the transmission path (3) is detected, and based on the detection result, the switching of the connection and disconnection of the terminal resistor (12) and the transmission path (3) by the switch (13) is controlled. Therefore, the connection and disconnection of the terminal resistor (12) and the transmission path (3) can be switched without causing communication errors in the communication unit (10).

[0090] In the communication circuit (6A) of the second embodiment, in the first embodiment, when the total resistance value (R1) detected by the detection unit (15) is greater than the threshold value (Rs), the control unit (16) controls the switch (13) so that the terminal resistor (12) is connected to the transmission path (3). When the total resistance value (R1) detected by the detection unit (15) is less than the threshold value (Rs), the control unit (16) controls the switch (13) so that the terminal resistor (12) and the transmission path (3) are disconnected.

[0091] According to this structure, by comparing the total resistance value (R1) with the threshold value (Rs) (i.e., by simple control), it is possible to control the connection and disconnection of the terminal resistor (12) and the transmission path (3) by the switch (13).

[0092] The communication circuit (6A) of the third aspect further comprises, in the second aspect, a storage unit (17) for storing impedance information related to the characteristic impedance (R0) of the differential line of the transmission path (3). The control unit (16) sets the threshold value (Rs) based on the impedance information stored in the storage unit (17).

[0093] According to this configuration, the optimum threshold value (Rs) can be automatically set simply by setting the impedance information in the storage unit (17).

[0094] In a communication circuit (6A) of a fourth aspect, in the first aspect, the control unit (16) calculates the number (N1) of terminal resistors (12) connected to the transmission path (3) based on the detection result of the detection unit (15). When the calculated number (N1) is less than a threshold value (Rs), the control unit (16) controls the switch (13) so that the terminal resistor (12) is connected to the transmission path (3). When the calculated number (N1) exceeds the threshold value (Rs), the control unit (16) controls the switch (13) so that the terminal resistor (12) and the transmission path (3) are disconnected.

[0095] According to this structure, by comparing the number (N1) of terminal resistors (12) connected to the transmission path (3) with the threshold value (Rs) (i.e., by simple control), it is possible to control the connection and disconnection of the terminal resistor (12) and the transmission path (3) by the switch (13).

[0096] In a fifth aspect of the communication circuit (6A), in any one of the first to fourth aspects, the communication unit (10) supplies a detection current to the transmission path (3). The detection unit (15) calculates a total resistance value (R1) of the transmission path (3) based on a voltage value (V1) of a voltage generated in the terminal resistor (12) by the detection current and a current value (I1) of the detection current when the terminal resistor (12) is connected to the transmission path (3).

[0097] According to this structure, the total resistance value (R1) of the total resistance connected to the transmission path (3) can be calculated by a simple method. In addition, since the above-mentioned total resistance is detected by passing a detection current through the transmission path (3), the communication circuit (6A) of the present disclosure is compatible with the device (2) that operates by passing a current with high impedance as the above-mentioned device (2).

[0098] In a communication circuit (6A) of a sixth aspect, in the fifth aspect, the communication unit (10) supplies a detection current to the transmission path (3) when the power of the device (2) is turned on.

[0099] According to this configuration, when the power of the device (2) is turned on, the connection and non-connection of the terminal resistor (12) and the transmission path (3) can be switched by the switch (13).

[0100] In a seventh aspect of the communication circuit (6A), in any one of the first to sixth aspects, the detection unit (15) periodically detects the total resistance value (R1) of the transmission path (3) in a state where the terminal resistor (12) is connected to the transmission path (3). Each time the detection unit (15) detects the total resistance value (R1) of the transmission path (3), the control unit (16) controls the switching of the terminal resistor (12) and the switch (13) to be connected or disconnected, which is performed by the switch (13), based on the detection result of the detection unit (15).

[0101] According to this structure, the connection and disconnection of the terminal resistor (12) and the transmission path (3) by the switch (13) can be periodically switched. As a result, even if a device (2A) having a communication circuit (6A) of the present disclosure is connected to the transmission path (3) and then a device (2B) that does not have a function of switching the terminal resistor (12) to disconnect is connected, the number (N1) of terminal resistors (12) connected to the transmission path (3) can be appropriately adjusted by switching the connection and disconnection of the terminal resistor (12) and the transmission path (3) in the device (2A) of the present disclosure.

[0102] The communication circuit (6A) of the eighth aspect is, in any one of the first to seventh aspects, further comprising: a manual switch (18) for switching between an automatic mode and a forced mode. In the automatic mode, the control unit (16) controls the switching of the connection and disconnection of the terminal resistor (12) and the transmission path (3) by the switch (13) based on the detection result of the detection unit (15). In the forced mode, the control unit (16) forcibly controls the switch (13) so that the terminal resistor (12) is connected to the transmission path (3).

[0103] According to this structure, it is possible to switch between the automatic mode and the forced mode by means of a manual switch (18). By switching the operation mode of the communication circuit (6A) to the forced mode, the terminal resistor (12) can be forcibly connected to the transmission path (3). Thus, when a device (2A) having the communication circuit (6A) disclosed herein is connected to the end of the transmission path (3), the terminal resistor (12) can be forcibly connected to the transmission path (3) by means of the forced mode. That is, the terminal resistor (12) of the device (2) (device (2) having the communication circuit (6A) disclosed herein) connected to the end of the transmission path (3) can be forcibly connected to the transmission path (3).

[0104] A ninth aspect of the communication circuit (6A) is characterized in that, in any one of the first to ninth aspects, it comprises a plurality of terminal resistors (12). The plurality of terminal resistors (12) have resistance values ​​different from each other. The switch (13) selects one of the plurality of terminal resistors (12) and switches between connecting and disconnecting the selected terminal resistor (12) and the transmission path (3).

[0105] According to this structure, the optimal termination resistor (12) among a plurality of termination resistors (12) can be connected to the transmission path (3). Thereby, the communication circuit (6A) of the present disclosure can be made to correspond to various transmission paths (3) having a characteristic impedance (R0) different from that of the differential line.

[0106] The apparatus (2) of the tenth aspect includes the communication circuit (6A) and the functional unit (5) according to any one of the first to ninth aspects. The functional unit (5) is connected to the communication unit (10) of the communication circuit (6A), exchanges signals with the communication unit (10), and executes a given function.

[0107] According to this structure, it is possible to provide an apparatus (2) that is used by being connected to the transmission path (3) and includes the communication circuit (6A) of the present disclosure.

[0108] The communication system (1) of the eleventh aspect includes a transmission path (3) and three or more apparatuses (2). The three or more apparatuses (2) are connected to the transmission path (3). At least one of the three or more apparatuses (2) is the apparatus (2A) of the tenth aspect, and the remaining apparatuses (2) include termination resistors (12) that are always connected to the transmission path (3).

[0109] According to this structure, it is possible to provide a communication system (1) including the apparatus (2) of the present disclosure.

[0110] The control method of the communication circuit (6A) of the twelfth aspect is a control method of a communication circuit (6A) including a communication unit (10), a termination resistor (12), and a switch (13). The communication unit (10) is provided in an apparatus (2) connected to the transmission path (3) and communicates with another communication unit (10) provided in another apparatus (2) connected to the transmission path (3) via the transmission path (3). The termination resistor (12) is connected to the transmission path (3). The switch (13) switches between connecting and not connecting the termination resistor (12) to the transmission path (3). The control method of the communication circuit (6A) includes a detection step and a control step. In the detection step, the total resistance value (R1) of the total resistance connected to the transmission path (3) is detected in a state where the termination resistor (12) is connected to the transmission path (3). In the control step, based on the detection result in the detection step, the switching between connecting and not connecting the termination resistor (12) to the transmission path (3) by the switch (13) is controlled.

[0111] According to this structure, the total resistance value (R1) of the total resistance connected to the transmission path (3) is detected, and based on the detection result, the switching of the connection and disconnection of the terminal resistor (12) and the transmission path (3) by the switch (13) is controlled. Therefore, the connection and disconnection of the terminal resistor (12) and the transmission path (3) can be switched without causing communication errors.

[0112] The program according to the thirteenth aspect causes one or more processors to execute the control method of the communication circuit (6A) according to the twelfth aspect.

[0113] According to this configuration, it is possible to provide a program for causing one or more processors to execute a method for controlling a communication circuit (6A).

[0114] Industrial Applicability

[0115] The communication circuit, device, communication system, control method and program of the communication circuit disclosed in the present invention have the advantage of being able to switch between connection and disconnection of the terminal resistor and the transmission path without causing communication errors. Therefore, the communication circuit, device, communication system, control method and program of the communication circuit disclosed in the present invention are useful in industry.

[0116] -Explanation of symbols-

[0117] 1 Communication system

[0118] 2 Devices

[0119] 2A 1st device

[0120] 2B Second Device

[0121] 3 Transmission Path

[0122] 6, 6A, 6B Communication circuit

[0123] 10 Ministry of Communications

[0124] 12, 12a, 12b, 12c terminal resistance

[0125] 13, 13a, 13b, 13c, 13D Switch

[0126] 15. Inspection Department

[0127] 16 Control Unit

[0128] 17 Storage

[0129] 18 Manual switch

[0130] I1 current value

[0131] N1 number

[0132] Ns threshold

[0133] R0 Characteristic impedance of differential line

[0134] R1 Total resistance value

[0135] Rs Threshold

[0136] V1 voltage value.

Claims

1. A communication circuit comprising: a communication unit provided in a device connected to a transmission path, and communicating with another communication unit provided in another device connected to the transmission path via the transmission path; A terminal resistor connected to the transmission path; A switch for switching connection and disconnection between the terminal resistor and the transmission path; a detection unit, which detects a total resistance value of a total resistor connected to the transmission path in a state where the terminal resistor is connected to the transmission path; and The control unit controls switching of connection and disconnection of the terminal resistor and the transmission path by the switch based on the detection result of the detection unit.

2. The communication circuit according to claim 1, in, When the total resistance value detected by the detection unit is greater than a threshold value, the control unit controls the switch so that the terminal resistor is connected to the transmission path. When the total resistance value detected by the detection unit is smaller than the threshold value, the control unit controls the switch so that the terminal resistor and the transmission path are disconnected.

3. The communication circuit according to claim 2, in, The communication circuit further includes: a storage unit storing impedance information related to the characteristic impedance of the differential line of the transmission path; The control unit sets the threshold value based on the impedance information stored in the storage unit.

4. The communication circuit according to claim 1, in, The control unit calculates the number of terminal resistors connected to the transmission path based on the detection result of the detection unit, When the calculated number is less than a threshold value, the control unit controls the switch so that the terminal resistor is connected to the transmission path. When the calculated number exceeds the threshold value, the control unit controls the switch so that the terminal resistor and the transmission path are disconnected.

5. The communication circuit according to claim 1, in, The communication unit supplies a detection current to the transmission path, The detection unit calculates the total resistance value of the transmission path based on a voltage value of a voltage generated in the terminal resistance by the detection current and a current value of the detection current in a state where the terminal resistance is connected to the transmission path.

6. The communication circuit according to claim 5, in, The communication unit supplies the detection current to the transmission path when the power of the device is turned on.

7. The communication circuit according to claim 1, in, The detection unit periodically detects the total resistance value of the transmission path in a state where the terminal resistor is connected to the transmission path, The control unit controls switching of connection and disconnection of the terminal resistor to the switch by the switch based on a detection result of the detection unit every time the detection unit detects the total resistance value of the transmission path.

8. The communication circuit according to claim 1, in, The communication circuit also has a manual switch for switching between automatic mode and forced mode. In the automatic mode, The control unit controls switching of connection and disconnection of the terminal resistor and the transmission path by the switch based on the detection result of the detection unit, In the forced mode, The control unit forcibly controls the switch so that the terminal resistor is connected to the transmission path.

9. The communication circuit according to claim 1, in, The communication circuit includes a plurality of terminal resistors. The plurality of terminal resistors have resistance values ​​different from each other, The switch selects one of the plurality of terminal resistors and switches between connection and disconnection of the selected terminal resistor with the transmission path.

10. A device comprising: The communication circuit of claim 1; and The functional unit is connected to the communication unit of the communication circuit, exchanges signals with the communication unit, and executes a given function.

11. A communication system comprising: transmission path; and Three or more devices are connected to the transmission path, At least one of the three or more devices is the device according to claim 10, and the remaining devices include a terminal resistor that is always connected to the transmission path.

12. A method for controlling a communication circuit, the communication circuit comprising: a communication unit provided in a device connected to a transmission path, communicating with other communication units provided in other devices connected to the transmission path via the transmission path; a terminal resistor connected to the transmission path; and a switch for switching between connection and disconnection of the terminal resistor and the transmission path, The control method of the communication circuit comprises: a detection step of detecting a total resistance value of a total resistor connected to the transmission path in a state where the terminal resistor is connected to the transmission path; and The control step controls switching of connection and disconnection between the terminal resistor and the transmission path by the switch based on the detection result in the detection step.

13. A program for causing one or more processors to execute the communication circuit control method according to claim 12.

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