Electronic device

Abstract

The present invention provides an electronic device capable of suppressing the occurrence of malfunction. An electronic device includes: a first connection line capable of being connected to a first signal line for transmitting a first signal between the first connection line and an external device; a first resistance element located between the first connection line and the power supply of the device itself; and a second connection line capable of being connected to a second signal line for transmitting a second signal from the external device. In a state where the first signal line and the second signal line are electrically connected to each other and the second signal is not input from the external device to the second signal line, when the voltage of the operating power supply is input from the first connection line to the second connection line via the external device, the resistance value of the first resistance element is set such that the output voltage from the second connection line is less than a reference value.

Description

[0001] REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the priority of Japanese Patent Application No. 2021-146713, filed on September 9, 2021, and the entire contents of Japanese Patent Application No. 2021-146713 are incorporated herein by reference into the specification of this application. TECHNICAL FIELD

[0003] The present disclosure relates to an electronic device. BACKGROUND ART

[0004] Among electronic devices that operate by receiving a data signal from the outside, there are electronic devices that operate or start by receiving power together with the data signal from the outside via a cable. In such an electronic device, by detecting the input voltage and comparing it with a reference voltage, it is possible to determine whether power is being input.

[0005] Inside the cable, there may be multiple independent signal lines. On the other hand, the signal lines are not necessarily independent in the electronic device at the connection destination and may be connected according to the processing. As a result, when the cable's signal lines connected to the electronic device are in a state where the above processing is not performed, such as during a work stop, the voltage applied to a certain signal line may be transmitted to another signal line. Japanese Unexamined Patent Application Publication No. 2011-164943 describes a technique in which an AV amplifier in a power-off state has a circuit for preventing malfunction caused by the supply power of a display device connected to the AV amplifier via an HDMI (registered trademark) cable being transmitted to the AV amplifier through the HDMI cable. SUMMARY OF THE INVENTION

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] However, in an electronic device connected to such a cable, there is a problem that malfunction may occur because the operating voltage of the device itself is transmitted to other signal lines in the external device and then returns.

[0008] One advantage of the present disclosure is that it is possible to suppress the occurrence of malfunction of an electronic device caused by the connected signal lines.

[0009] MEANS FOR SOLVING THE PROBLEM

[0010] An electronic device includes: a first connection line capable of being connected to a first signal line that transmits a first signal between the first connection line and an external device; a first resistor element located between the first connection line and the power supply of the device itself; and a second connection line capable of being connected to a second signal line that transmits a second signal from the external device. In a state where the first signal line and the second signal line are electrically connected to each other and no second signal is input from the external device to the second signal line, when the voltage of the operating power supply is input from the first connection line to the second connection line via the external device, the resistance value of the first resistor element is set such that the output voltage from the second connection line is less than a reference value.

[0011] According to the present disclosure, there is an effect of being able to more reliably suppress the occurrence of malfunction caused by the connected signal lines in the electronic device. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a diagram for explaining the structure of an image output system including a projection device.

[0013] Figure 2 It is a diagram for explaining the connection state between the projection device and the image data output device.

[0014] Figure 3 It is a diagram for explaining the connection state between the projection device of Modification 1 and the image data output device.

[0015] Figure 4 It is a diagram for explaining the connection state between the projection device of Modification 2 and the image data output device. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] Hereinafter, embodiments of the present disclosure will be described based on the drawings. Figure 1 It is a diagram for explaining the structure of an image output system 100 including a projection device 1 as an electronic device according to the present embodiment.

[0017] The image output system 100 includes a projection device 1 and an image data output device 5 (external device). The projection device 1 and the image data output device 5 operate by receiving power supply from an external power supply P via power supply cables C1 and C2, respectively.

[0018] The image data output device 5 is a device that outputs image data (which may include animations) of a display object, and is, for example, a PC (Personal Computer), a video playback device, or a camera.

[0019] The projection device 1 (projector) has a control unit 15 and a light emitting unit 16. Based on the control of the control unit 15, an image based on the input image data is emitted through the light emitting unit 16 and projected onto a screen or a wall surface of the projection object, etc. The image data output device 5 is connected to the projection device 1 via an HDMI (registered trademark) cable C3.

[0020] Figure 2 This is a diagram illustrating the connection state between the projection device 1 and the image data output device 5. The HDMI cable C3 usually has a connector (connection terminal) with 19 terminals, and 19 corresponding signal lines respectively transmit signals. 12 of these signal lines are signal lines for data related to the output image (including sound). In addition, 2 are signal lines C31 and C32 (the first signal line, signal line pair) of DDC (Display Data Channel) using I2C communication, and 1 is a signal line C33 (the second signal line) that transmits the operating voltage V5 (+5V) according to whether the image data output device 5 is operating.

[0021] The projection device 1 has a signal line connection part 11 and an HDMI receiving part 12 (detection part), and one end of the HDMI cable C3 is connected to the HDMI receiving part 12 via the signal line connection part 11. The image data output device 5 has a signal line connection part 51 and an HDMI transmitting part 52, and the other end of the HDMI cable C3 opposite to the above - mentioned one end is connected to the HDMI transmitting part 52 via the signal line connection part 51.

[0022] The 2 signal lines C31 and C32 related to DDC are used for I2C - based communication. One of them is the signal line C31 (DDCSCL) that transmits the clock signal, and the other is the signal line C32 (DDCSDA) that transmits the data signal which will be identification information related to display from the projection device 1 to the image data output device 5. Here, when power is supplied from the image data output device 5 through the HDMI cable C3 between the projection device 1 and the image data output device 5, the signal lines C31 and C32 are raised to the operating voltage +5V (H level). In the device connected with the HDMI cable C3, the H level and the ground level (L level) are switched by open - drain control to generate and output the data signal. According to the request from the image data output device 5 which is the master device (source), the projection device 1, as the slave device (receiving device), sends the content of the EDID (Extended Display Identification Data) stored in the memory 121 of the HDMI receiving part 12, especially information such as device information, resolution, and refresh rate, to the image data output device 5.

[0023] Based on the power supplied from the external power source P to the image data output device 5, a voltage V5 of a specified voltage value after DC conversion during the operation of the image data output device 5 is input to the signal line C33. Here, it is +5V (VoltageValue, voltage value). In the signal line connection part 51 of the image data output device 5, the power of the voltage V5 after DC conversion is also input in parallel to the wirings 511 and 512 connected to the signal lines C31 and C32 via the resistance elements R21 and R22. As a result, the signal lines C31 and C32 are electrically connected to the signal line C33 via the resistance elements R21 and R22 within the image data output device 5 in a state of being connected to the image data output device 5.

[0024] In the signal line connection part 11 of the projection device 1, when the projection device 1 is operating, a voltage V1 is input from a DC operating voltage source (the power supply of this device) to the wirings 111 and 112 (the first connection lines). Here, it is the same voltage value of 5V as that of the image data output device 5. The wirings 111 and 112 are respectively connected in parallel to the signal lines C31 and C32 via the resistance elements R11 and R12 (the first resistance elements) serving as pull-up resistors.

[0025] A resistance element R41 is inserted in series on the wiring 113 (the second connection line) of the signal line connection part 11 connected to the signal line C33, and a resistance element R42 (the third resistance element) is located between this wiring 113 and the ground plane. Through these resistance elements R41 and R42, a voltage V5a obtained by dividing the input voltage from the signal line C33 is input to the HDMI receiving part 12. For example, when the ratio of the resistance values of the resistance elements R41 and R42 is 1:2, approximately 3.3V of the 5V input from the signal line C33 is input to the HDMI receiving part 12.

[0026] This signal line connection part 11 also has wirings 114 and 115 (the third connection lines) that connect the wiring 113 to the wirings 111 and 112 in parallel respectively. A resistance element R31 is inserted in the wiring 114, and a resistance element R32 (the resistance elements R31 and R32 correspond to the fourth resistance element) is inserted in the wiring 115. In addition, as Figure 2 shown, a diode D is inserted into these wirings 114 and 115 and functions as a rectifying element that blocks the flow of current from the wirings 111 and 112 to the wiring 113 (corresponding to the "on-off operation" and "switching operation" described later). Here, the diode D is a Schottky barrier diode, and the voltage drop of the diode D when the current flows from the wiring 113 to the wirings 111 and 112 is kept small. The diode D can also be a Zener diode or the like.

[0027] When the HDMI receiving unit 12 detects the voltage accompanying the start of the operation of the image data output device 5 via the signal line C33, the operation related to the reception of the image data of the output object or the operation related to the light emission and projection is started in conjunction. The detection of the operating voltage is performed, for example, by comparing a certain reference voltage (reference value) between the assumed voltage V5a and the ground voltage with the input voltage from the wiring 113 to the HDMI receiving unit 12 (the output voltage from the side opposite to the side connected to the signal line C33 of the wiring 113). That is, when the HDMI receiving unit 12 detects the voltage V5a above the reference value, it determines that the image data output device 5 connected to the HDMI cable C3 is operating.

[0028] In addition, for example, in a power saving mode (standby mode) in which only a part of the projection device 1 including the detection of the voltage V5a is selectively performed and the operations of other control units 15 and the light emitting unit 16 are stopped or paused, by detecting an input voltage above the above-mentioned reference voltage (based on the detection result), the HDMI receiving unit 12 can also be linked to release the power saving mode, so as to control the state (normal mode) in which the data reception operation and the image output (light emission, projection) operation become possible through the control unit 15.

[0029] Here, as described above, when the HDMI cable C3 is connected to the image data output device 5, the signal lines C31 and C32 are electrically connected to the signal line C33 inside the image data output device 5. Therefore, in the projection device 1, when the voltage V1 is applied to the wirings 111 and 112 to supply power, even if the image data output device 5 is not operating, the voltage V1 is transmitted from the signal line C33 to the HDMI receiving unit 12 via the resistor elements R11, R12, R21, R22 and the resistor element R41.

[0030] In the case of such a voltage sneak path (Japanese: 回り込み), for example, the input voltage to the HDMI receiving unit 12 via the signal line C31 becomes a voltage obtained by dividing the combined resistance (the sum of the resistance values) of the resistor elements R11, R21, and R41 and the resistance value of the resistor element R42. Usually, the resistance values ​​of the resistor elements R21 and R22 are equal to or more than the resistance value of the resistor element R41 due to current limitation, etc. In contrast, by setting the resistance values ​​of the resistor elements R11 and R12 to be sufficiently larger than the resistance value of the resistor element R41, the input voltage (detected voltage) to the HDMI receiving unit 12 can be sufficiently reduced to be lower than the above-mentioned reference voltage, thereby suppressing the erroneous detection of the operating voltage supplied from the power supply source of the voltage V1 as the operating voltage supplied from the power supply source of the voltage V5 or the reverse erroneous detection.

[0031] On the other hand, if the resistance values of the resistance elements R11 and R12 are too large, the signal followability during the operation of the DDC decreases, and it becomes difficult to receive an appropriate signal. Here, the resistance values of the resistance elements R31 and R32 are determined such that the combined resistance of the resistance elements R31 and R32 related to the power supply from the power supply of voltage V5 and the resistance elements R11 and R12 related to the power supply from the power supply of the above voltage V1 satisfies the conditions of the communication standard of the I2C signal and becomes the level of the resistance values of the original resistance elements R11 and R12.

[0032] Therefore, in the case where the voltage V5 is not applied, the voltage V5a of the latent path is sufficiently reduced. In addition, the voltage V1 will not cause the voltage V5a to rise via the wirings 114 and 115 by the diode D. At the same time, the voltages of the signal lines C31 and C32 are also prevented from becoming intermediate voltages. On the other hand, in the case where the voltage V5 is applied, the voltage is applied with the existing pull-up resistor, and the I2C communication is normally performed.

[0033] [Modification Example]

[0034] A modification example of the signal line connection portion 11 of the projection device 1 will be described. Figure 3 FIG. is a diagram illustrating the connection state between the projection device 1a having the signal line connection portion 11a of the modification example 1 and the image data output device 5.

[0035] The signal line connection portion 11a of the modification example 1 has a switching element S1 as a rectifying element instead of the diode D. The other structures are the same between the projection devices 1 and 1a, so the same reference numerals are attached to the same structures, and the description thereof is omitted.

[0036] The switching element S1 performs an on / off operation according to the voltage of the wiring 113. Here, the switching element S1 is turned on and energized when the input voltage rises above the reference. The reference is determined to perform an on / off operation according to the presence or absence of the power supply from the power supply of voltage V5. That is, the reference is determined to be switched on and off substantially synchronously with the HDMI receiving unit 12 such that the switching element S1 is turned on when there is a power supply from the power supply of voltage V5 and the voltage of the wiring 113 is sufficiently high, and the switching element S1 is turned off regardless of the presence or absence of the power supply from the power supply of voltage V1 when there is no power supply from the power supply of voltage V5. Here, since the input of the voltage that becomes the reference of the switching element S1 is located closer to the connection side with the signal line C33 than the resistance element R41, the reference can be determined to be higher than the above reference voltage of the HDMI receiving unit 12 by the amount of voltage drop caused by the resistance element R41.

[0037] In this way, the behavior of the switching element S1 as a rectifying element is substantially the same as that of the diode D. In addition, since the switching of the operation of the switching element S1 is performed by the voltage of the wiring 113, it is not necessary to separately generate and input a control signal or the like, and the time and power consumption for controlling the operation do not increase.

[0038] Figure 4 FIG. is a diagram showing the connection state of the projection device 1b having the signal line connection portion 11b and the image data output device 5 according to the second modification. In the signal line connection portion 11b of the second modification, a combination (rectifying element) of two transistors T1 and T2 is used instead of the above-described switching element S1. Here, the emitter of the pnp transistor T2 is connected to the wiring 113, and the collector is connected to the resistance elements R31 and R32. In addition, the base of the pnp transistor T2 is connected to the collector of the npn transistor T1 via a resistor. The emitter of the npn transistor T1 is grounded, and the base is connected to the wiring 113.

[0039] According to this structure, when the voltage of the wiring 113 rises above the threshold voltage of the transistor T1, a collector current is also generated due to the base current flowing through the transistor T1, and along with this, a base current of the transistor T2 is also generated. Moreover, by also generating the collector current of the transistor T2, the wiring 113 and the wirings 111 and 112 are energized. When the voltage of the wiring 113 is lower than the threshold voltage of the transistor T1, such a current is not generated, and therefore, no current flows between the wiring 113 and the wirings 111 and 112. That is, as long as the resistance values of the resistance elements R11 and R12 are determined such that the input voltage to the base of the transistor T1 caused by the current flowing from the power supply of the voltage V1 through the latent path signal lines C31 to C33 to the wiring 113 is less than the threshold value.

[0040] That is, in this case, the combination of the transistors T1 and T2 also performs the on / off switching according to the voltage of the wiring 113, similarly to the above-described diode D and switching element S1.

[0041] As described above, the projection device 1 of the electronic device according to the present embodiment includes: wirings 111 and 112 that are respectively connected to signal lines C31 and C32, and the signal lines C31 and C32 transmit a clock signal and a data signal (first signal) between the wirings 111 and 112 and an image data output device 5 as an external device; resistor elements R11 and R12 that are located between the wirings 111 and 112 and the operating voltage source (voltage V1) of the own device (projection device 1); and a wiring 113 that is connected to a signal line C33, and the signal line C33 transmits a voltage signal (second signal) indicating the power supply status in the image data output device 5. The signal lines C31 and C32 and the signal line C33 are electrically connected to each other in a state of being connected to the image data output device 5. The resistance values of the resistor elements R11 and R12 are determined such that, when the voltage V1 of the operating voltage source is input to the signal line C33 via the signal lines C31 and C32 and the image data output device 5 in a state of being connected to the image data output device 5 and without power supply in the image data output device 5, the output voltage from the signal line C33 is less than a reference value. In this way, by setting the resistance values of the resistor elements R11 and R12 higher than before, in the projection device 1, even in a state where the image data output device 5 is not operating, it is possible to avoid misdetection of power by the HDMI reception unit 12 in the image data output device 5, and this misdetection is caused by a latent path of current flowing from the signal lines C31 and C32 to the signal line C33 due to signal wiring. Therefore, the projection device 1 can suppress malfunction caused by such misdetection.

[0042] In addition, the wirings 111 and 112 and the wiring 113 are connected in the following manner: in a state of being connected to the image data output device 5, the signal lines C31 and C32 and the signal line C33 are electrically connected via resistor elements R21 and R22 of the image data output device 5. In this way, since the latent path current flows through the resistor elements in the current path while the voltage drops, by setting the resistor elements R11 and R12 higher than before, it is possible to reliably lower the output voltage from the wiring 113. Thereby, in the projection device 1, it is possible to suppress misdetection of the operating voltage in a state where there is no power supply in the image data output device 5.

[0043] In addition, the wiring 113 is connected to the ground plane via a resistor element R42 in a state of being connected to the image data output device 5. That is, since there is a current flow path including a latent path current from the power supply source of the voltage V1 to the ground plane, by sufficiently lowering the voltage in advance using the resistor elements R11 and R12 before inputting to the wiring 113, it is possible to more reliably suppress misdetection of the operating voltage in a state where there is no power supply in the image data output device 5.

[0044] In addition, the resistance element R42 is connected to the wiring 113. Thus, in the projection device 1, the resistance element R42 with an appropriate resistance value in the signal line connection portion 11 can input a more accurate voltage signal to the HDMI receiving portion 12 with a stable and appropriate current and voltage, taking into account power consumption, voltage dividing resistors, etc.

[0045] Furthermore, the projection device 1 includes an HDMI receiving portion 12 that detects whether the voltage input from the wiring 113 (the output voltage of the wiring 113) is equal to or higher than the above-mentioned reference value. The wiring 113 divides the input voltage from the signal line C33 based on the resistance element R42 (and the resistance element R41), and the HDMI receiving portion 12 detects the output voltage of the divided voltage. Moreover, the resistance elements R11 and R12 are determined such that when the projection device 1 is connected to the image data output device 5 and there is no power supply from the image data output device 5, and the voltage of the operating voltage source of the voltage V1 is input to the wiring 113 via the wirings 111, 112, and the image data output device 5, their resistance values are such that the above-mentioned output voltage detected by the HDMI receiving portion 12 is less than the reference value. In the case of a latent path where current can be generated in such a path, misdetection of the operating voltage of the image data output device 5 can be suppressed. Therefore, even if the connection between the projection device 1 and the image data output device 5 and the start order of power supply to each device are incorrect, it is possible to suppress the occurrence of failures such as the image output system 100 not starting normally.

[0046] In addition, the projection device 1 includes wirings 114 and 115 that are respectively connected to the wirings 111, 112, and 113. The wirings 114 and 115 are respectively connected to the resistance elements R31 and R32, and a diode D, which is an electronic component that blocks the current from the wirings 111 and 112 to the wiring 113, is interposed between the wiring 113 and the wirings 114 and 115. The resistance values of the resistance elements R31 and R32 are determined such that the combined resistance of the resistance values of the resistance elements R11 and R12 and the resistance elements R31 and R32 satisfies the communication standard of the data signal of the I2C communication. Therefore, malfunction due to the above-mentioned latent path can be suppressed, and the DDC signal can be easily transmitted as usual through an HDMI cable or the like.

[0047] Furthermore, the signal lines C31 and C32 are two pairs of signal lines, and the resistance elements R11 and R12, the resistance elements R21 and R22, and the resistance elements R31 and R32 are respectively connected in parallel to each of the signal line pairs. That is, even for two signal lines C31 and C32 located in parallel positions like the DDC signal, they can function properly in the same way as one signal line.

[0048] In addition, signal lines C31 and C32 transmit I2C signals. In the signal lines C31 and C32 that transmit signals generated by dropping from a certain voltage to the ground voltage through an open drain, it is possible to avoid the signal lines C31 and C32 accidentally becoming an intermediate voltage and causing malfunction or bad conditions. Moreover, by appropriately maintaining the resistance value of the pull-up resistor, an appropriate waveform can be obtained, and signals can be transmitted and received between the image data output device 5 and the projection device 1 without any problems.

[0049] In addition, the diode D is a Schottky barrier diode. Thus, the voltage drop when current flows through the diode D can be kept small.

[0050] In addition, the projection device 1 includes a control unit 15 that makes the operation of the projection device 1 linked to the operation of the image data output device 5 based on the detection result of the power supply status of the HDMI reception unit 12 for the power supply from the image data output device 5. As described above, since the voltage signal from the image data output device 5 can be correctly detected without false detection, in the projection device 1, operations such as image projection can be properly prepared and started corresponding to the operation of the image data output device 5. Thereby, the convenience of the operation of the projection device 1 can be improved.

[0051] In addition, the present disclosure is not limited to the above-described embodiments, and various modifications can be made. For example, in the HDMI reception unit 12, as long as it is possible to determine whether the image data output device 5 is operating based on the input voltage, the comparison with the reference voltage can also be indirect.

[0052] Furthermore, in the above-described embodiment, the case where the voltages V1 and V5 are the same has been described. However, in the HDMI reception unit 12, there may be a case where it only corresponds to a 3.3V signal. In this case, the signal line connection unit 11 and the like may have necessary additional electronic components or electronic circuits, etc. Even in this case, it is only necessary to correctly determine whether there is a power supply related to the voltage V5.

[0053] Furthermore, in the above-described embodiment, the case where the signal lines C31 to C33 are part of the HDMI cable C3 has been described, but it is not limited thereto. It may also be another cable using DDC, such as a DVI cable, etc. As long as it is a signal line having the same structure, it may not be a signal line related to the transmission of I2C signals. In this case, it is not necessary for both of the signal lines C31 and C32 to be connected to the signal line C33, and either one can be used.

[0054] In addition, in the above-described embodiments, the case where the electronic device is the projection device 1 has been described, but it is not limited thereto. It may also be an image display device such as a television or an AV amplifier. Alternatively, it may be a device that performs arithmetic processing, communication processing, or various other operations according to an input from an external device regardless of image display. In addition, the specific structures, the contents of the processing operations, the steps, etc. shown in the above-described embodiments can be appropriately changed without departing from the gist of the present disclosure.

[0055] Although several embodiments of the present disclosure have been described, the scope of the present disclosure is not limited to the above-described embodiments, but includes the scope of the disclosure described in the claims and the scope equivalent thereto.

Claims

1. An electronic device, wherein, it includes: A first connection line capable of connecting to a first signal line, and the first signal line transmits a first signal between the first connection line and an external device; A first resistor element located between the first connection line and the power supply of the device itself; A second connection line capable of connecting to a second signal line, and the second signal line transmits a second signal from the external device; A third connection line connecting the first connection line and the second connection line; and A fifth resistor element connected to the second connection line, A fourth resistor element is provided on the third connection line, In a state where the first signal line and the second signal line are electrically connected to each other and no second signal is input from the external device to the second signal line, when the voltage of the power supply is input to the second connection line via the first connection line and the external device, the resistance value of the first resistor element is set such that the output voltage from the second connection line is less than a reference value, and the resistance value of the fourth resistor element is set such that the combined resistance of the resistance value of the first resistor element and the resistance value of the fourth resistor element meets the communication standard of the data signal.

2. The electronic device according to claim 1, wherein, When a second signal is input from the external device to the second signal line, the resistance value of the first resistor element is set such that the output voltage from the second connection line is equal to or higher than the reference value.

3. The electronic device according to claim 1 or 2, wherein, In a state where the device itself is connected to the external device via the first signal line and the second signal line, the first connection line and the second connection line are electrically connected to each other, In a state where the device itself is not connected to the external device, the first connection line and the second connection line are not electrically connected to each other.

4. The electronic device according to claim 1 or 2, wherein, It further includes a detection unit that detects the output voltage output according to the voltage input to the second connection line.

5. The electronic device according to claim 4, wherein, The detection unit determines whether the output voltage is based on a second signal.

6. The electronic device according to claim 1 or 2, wherein, The second connection line is grounded via a second resistor element.

7. The electronic device according to claim 1 or 2, wherein, It further includes a second resistor element, and the second resistor element is connected to the second connection line.

8. The electronic device according to claim 1 or 2, wherein, It further includes: A rectifying element connected to the third connection line.

9. The electronic device according to claim 1 or 2, wherein, It further includes: A third resistor element provided between the third connection line and the first connection line.

10. The electronic device according to claim 9, wherein, The resistance value of the third resistor element is set such that the combined resistance of the resistance value of the first resistor element and the resistance value of the third resistor element meets the communication standard of the first signal.

11. The electronic device according to claim 1 or 2, wherein, The first connection line transmits the first signal including at least one of a data signal and a clock signal.

12. An electronic device, wherein, it includes: a first connection line capable of being connected to a first signal line, the first signal line transmitting a first signal between the first connection line and an external device; a first resistance element located between the first connection line and the power supply of the host; a second connection line capable of being connected to a second signal line, the second signal line transmitting a second signal from the external device; a third connection line connecting the first connection line and the second connection line; and a rectifying element connected to the third connection line, in a state where the first signal line and the second signal line are electrically connected to each other and no second signal is input from the external device to the second signal line, when the voltage of the power supply is input to the second connection line via the first connection line and the external device, the rectifying element does not allow current to flow from the first connection line to the second connection line.

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