Signal transmission system

Abstract

To provide a signal transmission system in which a connection state of a termination resistor is automatically and certainly optimized with a simple configuration.SOLUTION: A signal transmission system 10B comprises a differential transmission line 20, a first device 30, and three second devices 40-1, 40-2, 40-3. The first device 30 has a first resistor 32 connected between lines. The second devices 40-1, 40-2, 40-3 have a variable resistance unit 42 connected between the lines, and a resistance value control unit 45 which controls a resistance value of the variable resistance unit 42, respectively. The resistance value control unit 45, if voltage between the lines does not fall within a predetermined normal voltage range when random times have elapsed from start, changes the resistance value of the variable resistance unit 42 from a first resistance value equal to the resistance value of a first resistor 32 to a second resistance value (wherein the second resistance value>the first resistance value).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a signal transmission system including a differential transmission line and a first device and at least one second device that transmit signals to each other via the differential transmission line. [Background technology]

[0002] When a first device and a second device connected to a differential transmission line such as a CAN communication line transmit signals to each other, a termination resistor is typically provided in each of the first and second devices to prevent signal reflection. Furthermore, when a differential transmission line extending from a first device branches off and connects to multiple second devices, and these multiple second devices are located relatively close to each other, the termination resistor of one of the second devices is typically enabled, while the termination resistors of all the other second devices are disabled. This enabling / disabling of the termination resistors is performed by the user, for example, by operating a DIP switch.

[0003] Enabling / disabling termination resistors using DIP switches or the like is tedious and prone to operational errors. For this reason, studies are underway to develop systems that do not require users to manually enable / disable termination resistors, i.e., systems that automatically optimize the connection state of termination resistors. For example, in the system described in Patent Document 1, a termination resistor control unit is provided separate from multiple processors that communicate with each other via a multi-bit bus, and this selects the optimal termination resistor from among the multiple termination resistors included in each processor based on the connection information of the multiple processors. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3709329 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the configuration described in Patent Document 1, i.e., a configuration in which a termination resistance control unit receives connection information and centrally controls the termination resistances provided in each of multiple devices (processors), is complex and tends to be expensive.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a signal transmission system that has a simple configuration and yet automatically and reliably optimizes the connection state of termination resistors. [Means for solving the problem]

[0007] In order to solve the above problem, a first signal transmission system according to the present invention is a system including a first device and at least one second device which transmit signals via differential transmission lines, wherein the first device has a first resistor connected between the lines of the differential transmission lines, and the second device has a variable resistance unit connected between the lines of the differential transmission lines and a resistance value control unit which controls the resistance value of the variable resistance unit, and wherein the resistance value control unit changes the resistance value of the variable resistance unit from a first resistance value equal to the resistance value of the first resistor to a second resistance value (where the second resistance value is greater than the first resistance value) if the line-to-line voltage of the differential transmission lines is not within a predetermined normal voltage range when a random time has elapsed since startup.

[0008] In this configuration, in each of at least one second device connected to the differential transmission line, the resistance value of the variable resistance unit connected between the lines is changed by the resistance value control unit on the condition that the line-to-line voltage of the differential transmission line is not within a predetermined normal voltage range. Furthermore, this change is not made simultaneously in all second devices, but is made in each second device when a random time has elapsed since startup. Therefore, with this configuration, the resistance values ​​of the variable resistance units can be changed to the second resistance value one by one (i.e., the termination resistors connected to the differential transmission line can be disabled one by one) until the line-to-line voltage of the differential transmission line falls within the predetermined normal voltage range.

[0009] The variable resistance unit of the first signal transmission system may have a switch and a second resistor connected in series. In this case, the resistance value control unit can change the resistance value of the variable resistance unit from the first resistance value (= the resistance value of the second resistor) to the second resistance value (= infinity) by changing the switch from a closed state to an open state.

[0010] Preferably, the switch of the first signal transmission system is a type of switch that is closed when not controlled by the resistance value control unit, otherwise the resistance value control unit must close the switch when activated.

[0011] In addition, in order to solve the above problem, a second signal transmission system according to the present invention is a signal transmission system including a first device and at least one second device which transmit signals via differential transmission lines, wherein the first device has a first resistor connected between the lines of the differential transmission lines, and the second device has a variable resistance unit connected between the lines of the differential transmission lines and a resistance value control unit that controls the resistance value of the variable resistance unit, and the resistance value control unit is configured to change the resistance value of the variable resistance unit from a first resistance value greater than the resistance value of the first resistor to a second resistance value equal to the resistance value of the first resistor when a random predetermined time has elapsed since startup before the line-to-line voltage of the differential transmission lines falls within a predetermined normal voltage range.

[0012] With this configuration, in each of at least one second device connected to the differential transmission line, if a predetermined time has elapsed since startup before the line-to-line voltage of the differential transmission line falls within a predetermined normal voltage range, the resistance value of the variable resistance unit connected between the lines is changed by the resistance value control unit. Furthermore, this change is not made simultaneously in all second devices, but is made when a randomly set predetermined time has elapsed. Therefore, with this configuration, the resistance values ​​of the variable resistance units can be changed to the second resistance value one by one (i.e., the termination resistors connected to the differential transmission line can be enabled one by one) until the line-to-line voltage of the differential transmission line falls within the predetermined normal voltage range.

[0013] The variable resistance unit of the second signal transmission system may have a switch and a second resistor connected in series. In this case, the resistance value control unit can change the resistance value of the variable resistance unit from the first resistance value (=infinity) to the second resistance value (=resistance value of the second resistor) by changing the switch from an open state to a closed state.

[0014] Preferably, the switch of the second signal transmission system is a type that is open when not controlled by the resistance control unit, otherwise the resistance control unit must open the switch when activated.

[0015] An example of the first device constituting the first and second signal transmission systems is a power conditioner device, and an example of the second device is a power storage device including a storage battery. Also, an example of signal transmission performed via a differential transmission line is CAN communication. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a signal transmission system that has a simple configuration and yet automatically and reliably optimizes the connection state of termination resistors. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram showing a signal transmission system according to a first embodiment and a third embodiment of the present invention. [Figure 2] FIG. 10 is a diagram showing a signal transmission system according to a second embodiment and a fourth embodiment of the present invention. [Figure 3] FIG. 2 is an operation flow diagram of the signal transmission systems according to the first and second embodiments of the present invention. [Figure 4] FIG. 10 is an operation flow diagram of the signal transmission systems according to the third and fourth embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] [First and second examples] First, a signal transmission system according to first and second embodiments of the present invention will be described with reference to FIGS.

[0019] [Configuration of the signal transmission system according to the first embodiment] 1 shows a signal transmission system 10A according to a first embodiment of the present invention. As shown in the figure, the signal transmission system 10A includes a first device 30 and a second device 40 that transmit signals to each other via a differential transmission line 20, which is a CAN communication line.

[0020] The first device 30 is a power conditioner device that is connected to a commercial power grid or a solar power generation system. The first device 30 has a first communication unit 31 connected to one end of the differential transmission line 20, and a 50 Ω first resistor 32 as a termination resistor connected between the lines of the differential transmission line 20. The first resistor 32 is always connected between the lines of the differential transmission line 20. In other words, the termination resistor of the first device 30 is always enabled.

[0021] The second device 40 is a power storage device including a storage battery. The second device 40 has a second communication unit 41 connected to the other end of the differential transmission line 20, a variable resistance unit 42 connected between the lines of the differential transmission line 20, and a resistance value control unit 45 that controls the resistance value of the variable resistance unit 42. The second device 40 is also connected to the first device 30 by a power cable (not shown).

[0022] The variable resistance unit 42 has a switch 44 connected in series with a second 50 Ω resistor 43 as a terminating resistor. The resistance value of the variable resistance unit 42 is 50 Ω when the switch 44 is in a closed state, and is infinite when the switch 44 is in an open state.

[0023] The resistance value control unit 45 sets the resistance value of the variable resistance unit 42 to 50 Ω or infinity by opening and closing the switch 44. When the resistance value control unit 45 opens and closes the switch 44 will be explained later.

[0024] The first communication unit 31 of the first device 30 may be part of a microcontroller (MCU, Micro Controller Unit) that controls each part of the power conditioner. The second communication unit 41, resistance value control unit 45, and switch 44 of the second device 40 may be part of a microcontroller that controls each part of the power storage device.

[0025] The signal transmission system 10A according to this embodiment can transmit signals without reflection when the resistance value of the variable resistance unit 42 is 50Ω, that is, when the termination resistance of the second device 40 is enabled. Note that when the termination resistance of the second device 40 is not enabled, the line-to-line voltage of the differential transmission line 20 indicates a value outside the predetermined normal voltage range.

[0026] [Configuration of a signal transmission system according to the second embodiment] 2 shows a signal transmission system 10B according to a second embodiment of the present invention. As shown in the figure, the signal transmission system 10B includes a first device 30 and three second devices 40-1, 40-2, and 40-3 that transmit signals to each other via a differential transmission line 20, which is a CAN communication line.

[0027] The second devices 40-1, 40-2, and 40-3 are power storage devices including storage batteries. Like the second device 40, the second devices 40-1, 40-2, and 40-3 have a second communication unit 41 connected to the other end of the differential transmission line 20, a variable resistance unit 42 connected between the lines of the differential transmission line 20, and a resistance value control unit 45 that controls the resistance value of the variable resistance unit 42. The second devices 40-1, 40-2, and 40-3 are also connected to the first device 30 by power cables (not shown).

[0028] The signal transmission system 10B according to this embodiment can transmit signals without reflection when the resistance value of any one of the variable resistance units 42 is 50Ω, that is, for example, when the termination resistance of the second device 40-1 is enabled and the termination resistances of all the other second devices 40-2 and 40-3 are disabled. Note that when the number of enabled termination resistances among the three second devices 40-1, 40-2, and 40-3 is zero or two or more, the line-to-line voltage of the differential transmission line 20 indicates a value outside the predetermined normal voltage range.

[0029] [Operation of the signal transmission system according to the first and second embodiments] 3 shows an operation flow diagram of the signal transmission system according to the first and second embodiments of the present invention. When a user connects the second device 40 or the second devices 40-1, 40-2, and 40-3 to the differential transmission line 20 and starts the system, the resistance control units 45 of the second devices 40, 40-1, 40-2, and 40-3 close the switches 44 of the variable resistance units 42 (step S1-1). This enables the termination resistances of all the second devices 40, 40-1, 40-2, and 40-3. Note that if the switches 44 are of a type that are closed when not controlled by the resistance control unit 45, step S1-1 can be omitted.

[0030] Next, the resistance value control units 45 of the second devices 40, 40-1, 40-2, and 40-3 determine whether the line-to-line voltage is within a normal range (step S1-2).

[0031] As described above, the resistance value control unit 45 of the second device 40 according to the first embodiment enables the termination resistor of the second device 40 in step S1-1. Furthermore, the line-to-line voltage of the signal transmission system 10A according to the first embodiment falls within the normal range when the termination resistor of the second device 40 is enabled. Therefore, the resistance value control unit 45 of the second device 40 determines in step S1-2 that the voltage is "within the normal range (Yes)."

[0032] This concludes the termination resistor optimization flow for the signal transmission system 10A according to the first embodiment. This termination resistor optimization flow enables the termination resistor of the second device 40, which is the only second device connected to the differential transmission line 20.

[0033] On the other hand, as described above, the resistance value control units 45 of the second devices 40-1, 40-2, and 40-3 according to the second embodiment enable the termination resistances of the second devices 40-1, 40-2, and 40-3 in step S1-1. Furthermore, the line-to-line voltage of the signal transmission system 10B according to the second embodiment falls within the normal range when the termination resistance of any one of the second devices 40-1, 40-2, and 40-3 is enabled. Therefore, the resistance value control units 45 of the second devices 40-1, 40-2, and 40-3 determine in step S1-2 that the line voltage is "not within the normal range (No)."

[0034] After determining "No" in step S1-2, the resistance value control units 45 of the second devices 40-1, 40-2, and 40-3 according to the second embodiment wait until a random time has elapsed (step S1-3). Here, it is assumed that the standby time of the resistance value control unit 45 of the second device 40-1 is randomly set to "2 ms," the standby time of the resistance value control unit 45 of the second device 40-2 is randomly set to "3 ms," and the standby time of the resistance value control unit 45 of the second device 40-3 is randomly set to "4 ms."

[0035] When 2 ms has elapsed since the start of step S1-3, the resistance value control unit 45 of the second device 40-1 determines whether the line-to-line voltage is within the normal range (step S1-4). Because the termination resistors of the second devices 40-1, 40-2, and 40-3 are still enabled, the resistance value control unit 45 of the second device 40-1 determines that the line voltage is not within the normal range (No) and opens the switch 44 of the second device 40-1 (step S1-5). This disables the termination resistor of the second device 40-1. Note that the time required to execute steps S1-1 and S1-2 is very short. Therefore, the above-mentioned "when 2 ms has elapsed since the start of step S1-3" is essentially the same as "when 2 ms has elapsed since startup."

[0036] When 3 ms has elapsed since the start of step S1-3, the resistance value control unit 45 of the second device 40-2 determines whether the line-to-line voltage is within the normal range (step S1-4). Because the termination resistance of the second device 40-1 was disabled 1 ms ago but the termination resistances of the second devices 40-2 and 40-3 are still enabled, the resistance value control unit 45 of the second device 40-2 determines that the line-to-line voltage is not within the normal range (No) and opens the switch 44 of the second device 40-2 (step S1-5). This also disables the termination resistance of the second device 40-2.

[0037] When 4 ms has elapsed since the start of step S1-3, the resistance value control unit 45 of the second device 40-3 determines whether the line-to-line voltage is within the normal range (step S1-4). Because the termination resistors of the second devices 40-1 and 40-2 were disabled 1 ms and 2 ms ago, and only the termination resistor of the second device 40-3 is enabled, the resistance value control unit 45 of the second device 40-3 determines that the voltage is within the normal range (Yes). As a result, the termination resistor of the second device 40-3 remains enabled.

[0038] This concludes the termination resistor optimization flow for the signal transmission system 10B according to Example 2. According to this termination resistor optimization flow, it is possible to enable a random termination resistor among the three second devices 40-1, 40-2, and 40-3 connected to the differential transmission line 20, and disable the other two termination resistors.

[0039] [Third and fourth examples] Next, a signal transmission system according to a third and fourth embodiment of the present invention will be described with reference to FIGS.

[0040] [Configuration of a signal transmission system according to the third embodiment] Similar to the signal transmission system 10A according to the first embodiment shown in Fig. 1, the signal transmission system according to the third embodiment of the present invention includes a first device 30 and a second device 40 that transmit signals to each other via a differential transmission line 20, which is a CAN communication line. The signal transmission system according to this embodiment is also similar to the signal transmission system 10A in that the line-to-line voltage falls within a predetermined normal voltage range when the termination resistor of the second device 40 is enabled.

[0041] [Operation of the signal transmission system according to the third embodiment] 4 shows an operation flow diagram of a signal transmission system according to a third embodiment of the present invention. When a user connects the second device 40 to the differential transmission line 20 and starts it up, the resistance control unit 45 of the second device 40 opens the switch 44 of the variable resistance unit 42 (step S2-1). This disables the termination resistance of the second device 40. Note that if the switch 44 is a type that opens when not controlled by the resistance control unit 45, step S2-1 can be omitted.

[0042] Next, the resistance value control unit 45 of the second device 40 determines whether the line-to-line voltage is within a normal range (step S2-2).

[0043] As described above, the termination resistor of the second device 40 is disabled in step S2-1. Furthermore, the line-to-line voltage falls within the normal range when the termination resistor of the second device 40 is enabled. Therefore, the resistance value control unit 45 of the second device 40 determines in step S2-2 that the line voltage is "not within the normal range (No)."

[0044] After determining "No" in step S2-2, resistance value control unit 45 of second device 40 waits until the time elapsed since startup reaches a random predetermined time while monitoring whether the line-to-line voltage is within the normal range (steps S2-3 → S2-2 → S2-3 → ...). Here, it is assumed that the predetermined time is set to "2 ms."

[0045] When the time elapsed since startup reaches 2 ms, the resistance value control unit 45 of the second device 40 closes the switch 44 of the second device 40 (step S2-4), thereby enabling the termination resistor of the second device 40.

[0046] Thereafter, the resistance value control unit 45 of the second device 40 again determines whether the line-to-line voltage is within the normal range (step S2-5). Because the termination resistor of the second device 40 was enabled in step S2-4, the resistance value control unit 45 of the second device 40 determines that the line-to-line voltage is within the normal range (Yes).

[0047] This concludes the termination resistor optimization flow for the signal transmission system according to Example 3. This termination resistor optimization flow makes it possible to validate the termination resistor of the second device 40, which is the only second device connected to the differential transmission line 20.

[0048] [Configuration of a signal transmission system according to the fourth embodiment] A signal transmission system according to a fourth embodiment of the present invention, like the signal transmission system 10B according to the second embodiment shown in Fig. 2, includes a first device 30 and three second devices 40-1, 40-2, and 40-3 that transmit signals to each other via a differential transmission line 20 that is a CAN communication line. The signal transmission system according to this embodiment is also similar to the signal transmission system 10B in that when the number of second devices 40-1, 40-2, and 40-3 with an enabled termination resistor is one, the line-to-line voltage falls within a predetermined normal voltage range.

[0049] [Operation of the signal transmission system according to the fourth embodiment] 4 shows an operation flow diagram of a signal transmission system according to a fourth embodiment of the present invention. When a user connects the second devices 40-1, 40-2, and 40-3 to the differential transmission line 20 and starts them up, the resistance control units 45 of the second devices 40-1, 40-2, and 40-3 open the switches 44 of the variable resistance units 42 (step S2-1). This disables the termination resistances of the second devices 40-1, 40-2, and 40-3. Note that if the switches 44 are of a type that are open when not controlled by the resistance control unit 45, step S2-1 can be omitted.

[0050] Next, the resistance value control units 45 of the second devices 40-1, 40-2, and 40-3 determine whether the line-to-line voltages are within a normal range (step S2-2).

[0051] As described above, the termination resistances of the second devices 40-1, 40-2, and 40-3 are disabled in step S2-1. Furthermore, the line-to-line voltage falls within the normal range when the number of the second devices 40-1, 40-2, and 40-3 whose termination resistances are enabled is one. Therefore, the resistance value control units 45 of the second devices 40-1, 40-2, and 40-3 determine in step S2-2 that the line voltage is "not within the normal range (No)."

[0052] After determining "No" in step S2-2, the resistance value control units 45 of the second devices 40-1, 40-2, and 40-3 wait until the time elapsed since startup reaches a random predetermined time while monitoring whether the line-to-line voltage is within the normal range (steps S2-3 → S2-2 → S2-3 → . . .). Here, it is assumed that the predetermined time of the resistance value control unit 45 of the second device 40-1 is set to "2 ms," the predetermined time of the resistance value control unit 45 of the second device 40-2 is set to "3 ms," and the predetermined time of the resistance value control unit 45 of the second device 40-3 is set to "4 ms."

[0053] When the time elapsed since startup reaches 2 ms, the resistance value control unit 45 of the second device 40-1 closes the switch 44 of the second device 40-1 (step S2-4), thereby enabling the termination resistor of the second device 40-1.

[0054] Thereafter, the resistance value control unit 45 of the second device 40-1 again determines whether the line-to-line voltage is within the normal range (step S2-5). Because the termination resistor of the second device 40-1 was enabled in step S2-4, the resistance value control unit 45 of the second device 40-1 determines that the line-to-line voltage is within the normal range (Yes).

[0055] Meanwhile, the resistance value control units 45 of the second devices 40-2 and 40-3, which have been monitoring whether the line-to-line voltage is within the normal range and have been waiting for the time elapsed since startup to reach 3 ms and 4 ms, determine in step S2-2 that the voltage is "within the normal range (Yes)" immediately after the time elapsed since startup reaches 2 ms and the termination resistor of the second device 40-1 is enabled. As a result, the termination resistors of the second devices 40-2 and 40-3 remain disabled.

[0056] This concludes the termination resistor optimization flow for the signal transmission system according to Example 3. According to this termination resistor optimization flow, it is possible to enable a random termination resistor among the three second devices 40-1, 40-2, and 40-3 connected to the differential transmission line 20, and disable the other two termination resistors.

[0057] If the predetermined time of the resistance value control units 45 of two or more of the three second devices 40-1, 40-2, and 40-3 (e.g., the second devices 40-1 and 40-2) is set to the same time (e.g., 2 ms), and the predetermined time of the resistance value control unit 45 of the remaining second device (e.g., the second device 40-3) is set to a time other than 2 ms (e.g., 3 ms), the termination resistances of the second devices 40-1 and 40-2 are simultaneously enabled when the elapsed time from startup reaches 2 ms (step S2-4). This does not achieve optimization of the termination resistances. Therefore, in this embodiment, after the resistance value control units 45 of the second devices 40-1 and 40-2 determine that the resistances are "out of the normal range (No)" (step S2-5), the termination resistances of the second devices 40-1 and 40-2 are disabled (step S2-1). Then, 1 ms later (i.e., when 3 ms has elapsed since startup), the resistance value control unit 45 of the second device 40-3 enables the termination resistor (step S2-4). As a result, only the termination resistor of the second device 40-3 is enabled, and optimization of the termination resistor is achieved.

[0058] [Variations] Although the first to fourth embodiments of the signal transmission system according to the present invention have been described above, the configurations of the present invention are not limited to these.

[0059] For example, the variable resistance section 42 of the second devices 40, 40-1, 40-2, and 40-3 may be a variable resistor whose resistance value changes under the control of the resistance value control section 45. When the resistance value of the first resistor 32 is 50 Ω, it is preferable that the variable resistor can have a resistance value in the range of 50 Ω to infinity.

[0060] Furthermore, the first device 30 may be any device capable of communication other than a power conditioner device.

[0061] Further, second devices 40, 40-1, 40-2, and 40-3 may be any communication-capable devices other than power storage devices.

[0062] Moreover, the differential transmission line 20 may be any differential signal transmission line other than a CAN communication line.

[0063] Furthermore, the signal transmission system 10B according to the second embodiment and the signal transmission system according to the fourth embodiment may not include the second device 40-3, or may further include second devices 40-4, 40-5, etc. (not shown). [Explanation of symbols]

[0064] 10A, 10B signal transmission system 20 Differential transmission lines 30 1st device 31 First Communications Department 32 1st resistor 40 Second device 41 Second Communications Department 42 variable resistor section 43 2nd resistor 44 Switch 45 Resistance control section

Claims

1. A signal transmission system including a first device and at least one second device that transmit signals to each other via a differential transmission line, the first device has a first resistor connected between the lines of the differential transmission line; the second device includes a variable resistor unit connected between the differential transmission lines and a resistance value control unit that controls a resistance value of the variable resistor unit, The resistance value control unit changes the resistance value of the variable resistance unit from a first resistance value equal to the resistance value of the first resistor to a second resistance value (where the second resistance value is greater than the first resistance value) if the line-to-line voltage of the differential transmission line is not within a predetermined normal voltage range when a random time has elapsed since startup. A signal transmission system comprising:

2. the variable resistance unit includes a switch and a second resistor connected in series; a resistance value of the variable resistance unit becomes the first resistance value when the switch is in a closed state, and becomes the second resistance value when the switch is in an open state; The resistance value control unit changes the resistance value of the variable resistance unit from the first resistance value to the second resistance value by changing the switch from a closed state to an open state.

2. A signal transmission system according to claim 1.

3. The switch is in a closed state when not controlled by the resistance value control unit.

3. A signal transmission system according to claim 2.

4. the first device is a power conditioner device, the second device is a power storage device including a storage battery, The first device and the second device perform CAN communication via the differential transmission line.

4. The signal transmission system according to claim 1, wherein the first and second signals are transmitted through the first and second input terminals.

5. A signal transmission system including a first device and at least one second device that transmit signals to each other via a differential transmission line, the first device has a first resistor connected between the lines of the differential transmission line; the second device includes a variable resistor unit connected between the differential transmission lines and a resistance value control unit that controls a resistance value of the variable resistor unit, The resistance value control unit changes the resistance value of the variable resistance unit from a first resistance value greater than the resistance value of the first resistor to a second resistance value equal to the resistance value of the first resistor when a random predetermined time elapses from the start-up before the line-to-line voltage of the differential transmission line falls within a predetermined normal voltage range. A signal transmission system comprising:

6. the variable resistance unit includes a switch and a second resistor connected in series; a resistance value of the variable resistance unit becomes the first resistance value when the switch is in an open state, and becomes the second resistance value when the switch is in a closed state; The resistance value control unit changes the resistance value of the variable resistance unit from the first resistance value to the second resistance value by changing the switch from an open state to a closed state.

6. A signal transmission system according to claim 5.

7. The switch is in an open state when not controlled by the resistance value control section.

7. A signal transmission system according to claim 6.

8. the first device is a power conditioner device, the second device is a power storage device including a storage battery, The first device and the second device perform CAN communication via the differential transmission line.

8. The signal transmission system according to claim 5, wherein:

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