RS485 interface protection circuit and industrial equipment

Abstract

The application discloses a RS485 interface protection circuit and industrial equipment, and belongs to the technical field of electronic circuits. The circuit comprises a first protection circuit, a second protection circuit and a decoupling circuit. The first protection circuit is connected with a wiring terminal and is used for eliminating surge energy. The decoupling circuit is used for limiting a surge current. The second protection circuit is connected with the first protection circuit through the decoupling circuit and is used for clamping a surge voltage to a safe voltage. The second protection circuit is also connected with a differential bus input end of a RS485 chip. The application can effectively improve the anti-surge capability of the RS485 interface by designing two-stage protection, eliminating surge energy by the first protection circuit and clamping the surge voltage to the safe voltage by the second protection circuit, so as to maintain the reliability and stability of the equipment.

Description

Technical Field

[0001] This application relates to the field of electronic circuit technology, and in particular to an RS485 interface protection circuit and industrial equipment. Background Technology

[0002] Currently, RS485, as a commonly used serial communication standard, is widely used in industrial control, automation equipment, and remote data transmission. However, the most common failure phenomenon in RS485 systems is the burnout of the series resistor on the AB differential line, which leads to the inability of devices to connect and transmit data normally, or even damage to the RS485 chip.

[0003] In related technologies, surge protection circuits are typically used. However, in practical applications, it has been found that existing surge protection circuits have low protection levels and cannot withstand high surge voltages.

[0004] In summary, the technical problems existing in the relevant technologies need to be improved. Utility Model Content

[0005] This application provides an RS485 interface protection circuit and industrial equipment that can improve the surge protection capability of the RS485 interface to maintain the reliability and stability of the equipment.

[0006] On the one hand, this application provides an RS485 interface protection circuit, which includes: a primary protection circuit, a secondary protection circuit, and a decoupling circuit; The primary protection circuit is connected to the wiring terminal to eliminate surge energy; The decoupling circuit is used to limit inrush current; The secondary protection circuit is connected to the primary protection circuit through the decoupling circuit, and is used to clamp the surge voltage to a safe voltage; The secondary protection circuit is also connected to the differential bus input terminal of the RS485 chip.

[0007] Optionally, the primary protection circuit includes: a first varistor, a second varistor, and a third varistor; One end of the first varistor is connected to the first pin of the terminal block; the other end of the first varistor is connected to the chassis ground. One end of the second varistor is connected to the first pin of the terminal block; the other end of the second varistor is connected to the second pin of the terminal block. One end of the third varistor is connected to the second pin of the terminal block; the other end of the third varistor is connected to the chassis ground.

[0008] Optionally, the decoupling circuit includes: a first common-mode inductor; One end of the first winding of the first common-mode inductor is connected to the first-level protection circuit; the other end of the first winding of the first common-mode inductor is connected to the second-level protection circuit. One end of the second winding of the first common-mode inductor is connected to the primary protection circuit; the other end of the second winding of the first common-mode inductor is connected to the secondary protection circuit.

[0009] Optionally, the secondary protection circuit includes: a TVS diode, a first resistor, and a second resistor; One end of the TVS diode is connected to the first resistor; the other end of the TVS diode is connected to the second resistor. One end of the first resistor is connected to the decoupling circuit; the other end of the first resistor is connected to the positive terminal of the differential bus of the RS485 chip. One end of the second resistor is connected to the decoupling circuit; the other end of the second resistor is connected to the negative terminal of the differential bus of the RS485 chip.

[0010] Optionally, the RS485 interface protection circuit further includes: a third resistor; One end of the third resistor is connected to the first resistor; the other end of the third resistor is connected to the second resistor.

[0011] Optionally, the RS485 interface protection circuit further includes: a first ESD protection diode and a second ESD protection diode; One end of the first ESD protection diode is connected to the first resistor; the other end of the first ESD protection diode is connected to digital ground. One end of the second ESD protection diode is connected to the second resistor; the other end of the second ESD protection diode is connected to digital ground.

[0012] Optionally, the RS485 interface protection circuit further includes: The first pin of the terminal block is connected to the differential signal line A. The second pin of the terminal block is connected to the differential signal line B. The third pin of the terminal block is connected to digital ground.

[0013] Optionally, a fourth resistor and a first capacitor are provided between the digital ground and the chassis ground of the RS485 interface protection circuit; The fourth resistor is connected in parallel with the first capacitor.

[0014] On the other hand, embodiments of this application provide an industrial device, including: an RS485 interface protection circuit as described in any of the above embodiments.

[0015] This application embodiment designs a two-level protection system. The first-level protection circuit eliminates surge energy, and the second-level protection circuit clamps the surge voltage to a safe voltage, which can effectively improve the surge protection capability of the RS485 interface to maintain the reliability and stability of the equipment. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of an RS485 interface protection circuit provided in an embodiment of this application. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit it. In the following description, when referring to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with those of this application; they are merely examples of apparatuses and methods consistent with some aspects of the embodiments of this application as detailed in the appended claims.

[0018] It is understood that the terms “first,” “second,” etc., used in this application may be used herein to describe various concepts, but unless otherwise stated, these concepts are not limited by these terms. These terms are only used to distinguish one concept from another. For example, without departing from the scope of the embodiments of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the words “if,” “when,” or “in response to a determination” as used herein may be interpreted as “when…” or “when…” or “in response to a determination.”

[0019] As used in this application, the terms "at least one", "multiple", "each", "any", etc., "at least one" includes one, two or more, "multiple" includes two or more, "each" refers to each of the corresponding multiples, and "any" refers to any one of the multiples.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit this application.

[0021] Currently, RS485, as a commonly used serial communication standard, is widely used in industrial control, automation equipment, and remote data transmission. However, the most common failure phenomenon in RS485 systems is the burnout of the series resistor on the AB differential line, which leads to the inability of devices to connect and transmit data normally, or even damage to the RS485 chip.

[0022] In related technologies, surge protection circuits are typically used. However, in practical applications, it has been found that existing surge protection circuits have low protection levels and cannot withstand high surge voltages.

[0023] In view of this, this application provides an RS485 interface protection circuit and industrial equipment. By designing two levels of protection, the first-level protection circuit eliminates surge energy, and the second-level protection circuit clamps the surge voltage to a safe voltage, which can effectively improve the surge protection capability of the RS485 interface to maintain the reliability and stability of the equipment.

[0024] The specific implementation of the embodiments of this application will be described in detail below with reference to the accompanying drawings. First, an RS485 interface protection circuit provided in an embodiment of this application will be described with reference to the accompanying drawings.

[0025] Please refer to Figure 1 , Figure 1 This is a schematic diagram of an RS485 interface protection circuit provided in an embodiment of this application. The circuit includes: a primary protection circuit, a secondary protection circuit, and a decoupling circuit. The primary protection circuit is connected to terminal J1 to eliminate surge energy; The decoupling circuit is used to limit inrush current; The secondary protection circuit is connected to the primary protection circuit through the decoupling circuit, and is used to clamp the surge voltage to a safe voltage; The secondary protection circuit is also connected to the differential bus input terminal of the RS485 chip.

[0026] In this embodiment, the RS485 interface protection circuit mainly includes a primary protection circuit, a secondary protection circuit, and a decoupling circuit.

[0027] The primary protection circuit is connected to terminal J1, which is used to connect the differential signal lines A and B of the RS485 chip. The primary protection circuit is mainly used to resist common-mode surges and differential-mode surges.

[0028] Furthermore, a decoupling circuit is provided between the primary protection circuit and the secondary protection circuit. After most of the energy in the surge is discharged through the primary protection circuit, the residual energy flows through the decoupling circuit and provides current limiting capability for surge overcurrent.

[0029] Furthermore, the secondary protection circuit protects the subsequent RS485 transceiver chip by clamping the surge voltage to a safe voltage. For example, Figure 1 As shown, the secondary protection circuit is also connected to the differential bus input terminal of the RS485 chip. The differential bus input terminal of the RS485 chip includes a differential bus positive terminal and a differential bus negative terminal. The differential bus positive terminal corresponds to differential signal line A, RS485A, and the differential bus negative terminal corresponds to differential signal line B, RS485B.

[0030] Optionally, the first pin of the terminal J1 is connected to the differential signal line A; The second pin of terminal J1 is connected to differential signal line B; The third pin of terminal J1 is connected to digital ground GND.

[0031] In the embodiments of this application, such as Figure 1 As shown, the first pin of terminal J1 is connected to differential signal line A, the second pin is connected to differential signal line B, and the third pin is connected to digital ground GND, thereby connecting the external RS485 differential line to the PCB where the RS485 interface protection circuit is located.

[0032] Therefore, the RS485 interface protection circuit provided in this application is designed with two levels of protection. The entire protection process is that the surge voltage passes through the first-level protection circuit, the decoupling circuit and the second-level protection circuit from the RS485 terminal. This can effectively prevent the surge signal from being transmitted to the RS485 chip and avoid damage to the devices on the line and the chip caused by the surge signal.

[0033] Specifically, as an optional implementation, the primary protection circuit includes: a first varistor RV1, a second varistor RV2, and a third varistor RV3; One end of the first varistor RV1 is connected to the first pin of the terminal J1; the other end of the first varistor RV1 is connected to the chassis ground EGND. One end of the second varistor RV2 is connected to the first pin of the terminal J1; the other end of the second varistor RV2 is connected to the second pin of the terminal J1. One end of the third varistor RV3 is connected to the second pin of the terminal J1; the other end of the third varistor RV3 is connected to the chassis ground EGND.

[0034] In the embodiments of this application, such as Figure 1As shown, the primary protection circuit mainly consists of three varistors. One end of the first varistor RV1 and the third varistor RV3 are connected to the A line and B line of the RS485 differential bus, respectively, corresponding to the first pin and the second pin of the terminal J1. The other end of the first varistor RV1 and the third varistor RV3 are connected to the chassis ground EGND. The parallel terminal of the second varistor RV2 is connected between the A and B lines.

[0035] In practical applications, the first varistor RV1 and the third varistor RV3 are mainly used to resist common-mode surges, while the second varistor RV2 is mainly used to resist differential-mode surges. When a surge voltage occurs, the voltage across the first varistor RV1 and the third varistor RV3 will rise and exceed their nominal rated voltage, causing the first varistor RV1 and the third varistor RV3 to be quickly broken down and connected, changing from a high-resistance state to a low-resistance state. At this time, the current flowing through the first varistor RV1 and the third varistor RV3 will increase sharply, so that most of the surge energy is discharged through the chassis ground EGND after passing through the first varistor RV1 and the third varistor RV3 respectively.

[0036] Optionally, the chassis ground EGND can be electrically connected to the nearest screw hole on the PCB where the RS485 interface protection circuit is located, and the equipment chassis is connected to the ground through the ground wire, which can ensure that the surge energy of the PCB has a discharge path, so that the surge energy is discharged into the ground, and the surge voltage is limited to a lower amplitude that the subsequent circuit devices can withstand after flowing through the first-level protection circuit.

[0037] Furthermore, after the surge voltage passes, the surge voltage across the first varistor RV1 and the third varistor RV3 is less than their nominal rated voltage, causing the resistance of the first varistor RV1 and the third varistor RV3 to return to a high resistance state, with almost no current flowing through them.

[0038] In practical applications, the first varistor RV1, the second varistor RV2, and the third varistor RV3 can all be varistors with the same parameters.

[0039] Therefore, this application constructs a primary protection circuit using multiple varistors, which can effectively eliminate surge energy in its initial stage.

[0040] Specifically, as an optional implementation, the decoupling circuit includes: a first common-mode inductor L1; One end of the first winding of the first common-mode inductor L1 is connected to the first-level protection circuit; the other end of the first winding of the first common-mode inductor L1 is connected to the second-level protection circuit. One end of the second winding of the first common-mode inductor L1 is connected to the first-level protection circuit; the other end of the second winding of the first common-mode inductor L1 is connected to the second-level protection circuit.

[0041] In the embodiments of this application, such as Figure 1 As shown, the decoupling circuit is mainly composed of a first common-mode inductor L1. The first common-mode inductor L1 has two sets of windings, which are used to correspond to the A line and B line of the RS485 differential signal line, respectively. Specifically, one end of the first winding is connected to the first-level protection circuit, and the other end of the first winding is connected to the second-level protection circuit. One end of the second winding is connected to the first-level protection circuit, and the other end of the second winding is connected to the second-level protection circuit.

[0042] In practical applications, the first common-mode inductor L1 exhibits low impedance to the differential signals on lines A and B due to magnetic flux cancellation. Ideally, this does not affect the transmission of the differential signals. However, when a surge occurs, most of the energy in the surge is discharged to the ground through the varistor in the first-stage protection circuit. The remaining energy flows through the first common-mode inductor L1. Since the surge currents on lines A and B are in the same direction, the first common-mode inductor L1 exhibits high impedance to the surge currents on lines A and B due to magnetic flux superposition. This effectively provides sufficient current limiting capability for surge overcurrent.

[0043] Optionally, the minimum reference value of the inductance of the first common-mode inductor L1 can be calculated based on the highest clamping voltage and maximum current carrying capacity of the varistor in the first-level protection circuit and the highest clamping voltage of the TVS diode V1 in the second-level protection circuit, under the surge current of 8 / 20us.

[0044] Specifically, L = (U1-U2)*(T2-T1) / (I / 2), where U1 is the highest clamping voltage of the varistor, U2 is the highest clamping voltage of the TVS diode V1, I is the maximum current carrying capacity of the varistor, T1 is the wavefront rise time, i.e. 8us, and T2 is the half-peak time, i.e. 20us.

[0045] Therefore, by adding a decoupling circuit design, this application can limit the surge current of the RS485 line, prevent excessive residual surge current from damaging the TVS diode in the secondary protection circuit, further damaging the series resistance of the AB differential line and causing communication failure, and even potentially damaging the downstream RS485 chip.

[0046] Optionally, the secondary protection circuit includes: a TVS diode V1, a first resistor R1, and a second resistor R2; One end of the TVS diode V1 is connected to the first resistor R1; the other end of the TVS diode V1 is connected to the second resistor R2. One end of the first resistor R1 is connected to the decoupling circuit; the other end of the first resistor R1 is connected to the positive terminal of the differential bus of the RS485 chip. One end of the second resistor R2 is connected to the decoupling circuit; the other end of the second resistor R2 is connected to the negative terminal of the differential bus of the RS485 chip.

[0047] In the embodiments of this application, such as Figure 1 As shown, the secondary protection circuit mainly includes a TVS diode V1, a first resistor R1, and a second resistor R2.

[0048] In this circuit, one end of the TVS diode V1 is connected to the first resistor R1, and the other end is connected to the second resistor R2. One end of the first resistor R1 is connected to the decoupling circuit, and the other end is connected to the positive terminal of the differential bus of the RS485 chip, which corresponds to RS485 differential signal line A (RS485A). One end of the second resistor R2 is connected to the decoupling circuit, and the other end is connected to the negative terminal of the differential bus of the RS485 chip, which corresponds to RS485 differential signal line B (RS485B).

[0049] In practical applications, the surge transient peak pulse current that flows out after being current-limited by the decoupling circuit will flow through the TVS diode V1. The current in the TVS diode V1 changes from the original reverse leakage current to the reverse breakdown current. The voltage across its terminals rises from the rated reverse turn-off voltage VRWM to the breakdown voltage VBR, which causes the TVS diode V1 to break down. This clamps the voltage across its terminals to below the predetermined maximum clamping voltage (i.e., the safe voltage). The safe voltage can be preset to be less than the withstand voltage of the positive and negative terminals of the differential bus of the RS485 chip.

[0050] Furthermore, as the pulse current decays exponentially, the voltage across the TVS diode V1 continuously decreases until it returns to its initial state. The first resistor R1 and the second resistor R2 in the secondary protection circuit serve as the last layer of protection, sharing some of the energy during transients and limiting the surge current from entering the RS485 chip. They can also be used as dampers to reduce ringing.

[0051] Optionally, the RS485 interface protection circuit further includes: a third resistor R3; One end of the third resistor R3 is connected to the first resistor R1; the other end of the third resistor R3 is connected to the second resistor R2.

[0052] In the embodiments of this application, such as Figure 1 As shown, a third resistor R3 is also provided in the RS485 interface protection circuit. The third resistor R3 is mainly used as the terminating resistor on the RS485 differential bus. It can be used to match the impedance of the cable end to the output impedance of the driver, eliminate signal reflection, and improve signal quality during high-speed transmission.

[0053] Specifically, as an optional implementation, the RS485 interface protection circuit further includes: a first ESD protection diode D1 and a second ESD protection diode D2; One end of the first ESD protection diode D1 is connected to the first resistor R1; the other end of the first ESD protection diode D1 is connected to digital ground GND. One end of the second ESD protection diode D2 is connected to the second resistor R2; the other end of the second ESD protection diode D2 is connected to digital ground GND.

[0054] In the embodiments of this application, such as Figure 1 As shown, the RS485 interface protection circuit also includes a first ESD protection diode and a second ESD protection diode. One end of the first ESD protection diode is connected to the first resistor and the other end is connected to digital ground. One end of the second ESD protection diode is connected to the second resistor and the other end is connected to digital ground.

[0055] Among them, the first ESD protection diode and the second ESD protection diode are electrostatic protection diodes, which are used to safely conduct electrostatic current to digital ground GND by quickly responding to electrostatic pulses, so as to avoid electrostatic voltage breakdown or damage to RS485 chip and effectively protect internal circuits.

[0056] Specifically, as an optional implementation, a fourth resistor R4 and a first capacitor C1 are provided between the digital ground GND and the chassis ground EGND of the RS485 interface protection circuit. The fourth resistor R4 is connected in parallel with the first capacitor C1.

[0057] In the embodiments of this application, such as Figure 1 As shown, the fourth resistor R4 is connected in parallel with the first capacitor C1, and its two ends are connected to the chassis ground EGND and the digital ground GND, respectively. The first capacitor C1 can be used to provide a low impedance discharge path for high frequency transients, so that the instantaneous high frequency energy can be quickly discharged to ground through the chassis. The fourth resistor R4 is used to limit the low frequency DC leakage current and provide damping.

[0058] Therefore, this application ensures that a large amount of charge will not accumulate on the digital ground (GND) to cause electrostatic high voltage to break down components by adding a circuit connecting the chassis ground and digital ground through resistors and capacitors. Furthermore, the chassis ground (EGND) is electrically connected to the PCB screw holes nearby, and the equipment casing is connected to the earth through a ground wire. This ensures that the surge energy of the circuit board has a discharge path, high-frequency signals have a stable grounding point, and electromagnetic radiation is reduced.

[0059] Specifically, in one possible implementation, this application embodiment also provides an industrial device, which includes the aforementioned RS485 interface protection circuit.

[0060] For example, industrial equipment can be different types of industrial equipment such as industrial automation equipment, security monitoring equipment, and smart home equipment.

[0061] This application provides an RS485 interface protection circuit and industrial equipment. By designing two levels of protection, the first-level protection circuit eliminates surge energy, and the second-level protection circuit clamps the surge voltage to a safe voltage, which can effectively improve the surge protection capability of the RS485 interface and maintain the reliability and stability of the equipment.

[0062] The embodiments described in this application are for the purpose of more clearly illustrating the technical solutions of the embodiments of this application, and do not constitute a limitation on the technical solutions provided by the embodiments of this application. As those skilled in the art will know, with the evolution of technology and the emergence of new application scenarios, the technical solutions provided by the embodiments of this application are also applicable to similar technical problems.

[0063] Those skilled in the art will understand that the technical solutions shown in the figures do not constitute a limitation on the embodiments of this application, and may include more or fewer steps than shown, or combine certain steps, or different steps.

[0064] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0065] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0066] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0067] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0068] The preferred embodiments of the present application have been described above with reference to the accompanying drawings, but this does not limit the scope of the claims of the present application. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and substance of the embodiments of the present application shall be within the scope of the claims of the present application.

Claims

1. An RS485 interface protection circuit, characterized in that, The circuit includes: a primary protection circuit, a secondary protection circuit, and a decoupling circuit; The primary protection circuit is connected to the wiring terminal to eliminate surge energy; The decoupling circuit is used to limit inrush current; The secondary protection circuit is connected to the primary protection circuit through the decoupling circuit, and is used to clamp the surge voltage to a safe voltage; The secondary protection circuit is also connected to the differential bus input terminal of the RS485 chip.

2. The RS485 interface protection circuit according to claim 1, characterized in that, The primary protection circuit includes: a first varistor, a second varistor, and a third varistor; One end of the first varistor is connected to the first pin of the terminal block; the other end of the first varistor is connected to the chassis ground. One end of the second varistor is connected to the first pin of the terminal block; the other end of the second varistor is connected to the second pin of the terminal block. One end of the third varistor is connected to the second pin of the terminal block; the other end of the third varistor is connected to the chassis ground.

3. The RS485 interface protection circuit according to claim 1, characterized in that, The decoupling circuit includes: a first common-mode inductor; One end of the first winding of the first common-mode inductor is connected to the first-level protection circuit; the other end of the first winding of the first common-mode inductor is connected to the second-level protection circuit. One end of the second winding of the first common-mode inductor is connected to the primary protection circuit; the other end of the second winding of the first common-mode inductor is connected to the secondary protection circuit.

4. The RS485 interface protection circuit according to claim 1, characterized in that, The secondary protection circuit includes: a TVS diode, a first resistor, and a second resistor; One end of the TVS diode is connected to the first resistor; the other end of the TVS diode is connected to the second resistor. One end of the first resistor is connected to the decoupling circuit; the other end of the first resistor is connected to the positive terminal of the differential bus of the RS485 chip. One end of the second resistor is connected to the decoupling circuit; the other end of the second resistor is connected to the negative terminal of the differential bus of the RS485 chip.

5. The RS485 interface protection circuit according to claim 4, characterized in that, The RS485 interface protection circuit also includes: a third resistor; One end of the third resistor is connected to the first resistor; the other end of the third resistor is connected to the second resistor.

6. The RS485 interface protection circuit according to claim 4, characterized in that, The RS485 interface protection circuit further includes: a first ESD protection diode and a second ESD protection diode; One end of the first ESD protection diode is connected to the first resistor; the other end of the first ESD protection diode is connected to digital ground. One end of the second ESD protection diode is connected to the second resistor; the other end of the second ESD protection diode is connected to digital ground.

7. The RS485 interface protection circuit according to claim 1, characterized in that, The RS485 interface protection circuit also includes: The first pin of the terminal block is connected to the differential signal line A. The second pin of the terminal block is connected to the differential signal line B. The third pin of the terminal block is connected to digital ground.

8. The RS485 interface protection circuit according to claim 1, characterized in that, A fourth resistor and a first capacitor are provided between the digital ground and the chassis ground of the RS485 interface protection circuit. The fourth resistor is connected in parallel with the first capacitor.

9. An industrial device, characterized in that, include: The RS485 interface protection circuit as described in any one of claims 1-8.

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