RS232 interface lightning surge protection circuit and method, roadside unit

Abstract

The present disclosure relates to a RS232 interface lightning surge protection circuit and method, and a roadside unit, the circuit comprising: a first protection device for performing first-stage lightning surge protection on a data transceiver end of a RS232 chip; a second protection device for performing second-stage lightning surge protection on the data transceiver end of the RS232 chip; a third protection device for performing third-stage lightning surge protection on the data transceiver end of the RS232 chip; a fourth protection device for performing first-stage lightning surge protection on an internal protected ground; and a fifth protection device for performing second-stage lightning surge protection on the internal protected ground, which can effectively improve the EMC protection level reliability of the RSU while greatly reducing the cost, improving the project development and production assembly and installation efficiency.

Description

Technical Field

[0001] The present disclosure relates to the field of communication technology, and in particular to an RS232 interface lightning surge protection circuit and method, and a roadside unit. Background Art

[0002] C-V2X (Cellular Vehicle-to-Everything), a technology enabling vehicle-road collaboration, can significantly improve traffic efficiency and is currently widely used in the autonomous driving sector. As a key component of C-V2X, the Road Side Unit (RSU) is installed on roadside poles to connect various roadside devices and sensors with the vehicle's On Board Unit (OBU), enabling data forwarding and communication, and carrying out C-V2X services.

[0003] Currently, RSU products in the industry generally include an RS232 interface as an external interface. However, the performance of RS232 interface protection measures varies. One approach involves integrating an SPD (surge protection device) or optoelectronic isolation protector into the RSU, either internally or through external procurement. This solution is costly, inconvenient, and unsightly, reducing product design and project development efficiency. Another approach involves integrating an RS232 interface protection circuit into the RSU circuit board. This circuit typically includes protection components such as a GDT (gas discharge tube), a TSS (thyristor surge suppressor), a TVS (transient voltage suppressor), and a varistor. However, the performance of this circuit design varies, with low or inadequate lightning surge protection often leading to communication anomalies and damage during RSU testing or actual use.

[0004] In the prior art, the RS232 interface lightning surge protection circuit has the following problems:

[0005] First, purchasing a matching SPD not only increases project costs but can also lead to EMC-related issues, such as radiated interference, due to the designer's lack of understanding of the SPD's internal circuit design or inaccurate SPD parameters. (EMC testing is a comprehensive assessment of the electromagnetic interference and interference resistance of electronic products.) In more serious cases, improper selection and matching can lead to RS232 communication anomalies and uneven protection.

[0006] Second, if the first-level protection uses TSS semiconductor discharge tubes with post-stage circuit protection, the protection level is not as high as the first-level protection using GDT gas discharge tubes; GDT with varistor as the first-level protection of RS232 interface will occupy board-level space and cost, and the effect is basically the same as GDT.

[0007] Third, the general practice is to use a gas discharge tube for primary protection, a TVS tube or electrostatic protection tube for secondary protection, and a current-limiting resistor or PTC thermistor in series with the signal line between the two levels. However, lightning surge testing requires multiple microsecond-scale short-term high-voltage and high-current cycles. Without a series resistor, the basic downstream circuit will break down and damage the downstream current during a Level 4 lightning surge test. Similarly, a series resistor solution will also cause breakdown damage due to insufficient resistor power. Using a series PTC thermistor also fails to meet high-level lightning surge testing requirements, as the minimum response time of a PTC that meets the power requirements is in the hundreds of milliseconds. This insufficient response time prevents current limiting, further causing breakdown damage to the downstream circuit.

[0008] Fourth, while the RSU ground wire chassis ground and the device GND are typically isolated, RS232 is asymmetrical, and the data transceiver requires a reference GND line for return current. Therefore, this reference GND line requires protection. Existing solutions either directly connect the reference GND to the PE ground or lack a direct connection between the reference GND line and the device GND. This lack of a low-impedance GND return line can prevent long-distance signal transmission. Existing solutions or lightning surge tests do not test the reference GND line, but this approach is inadequate for practical applications. Summary of the Invention

[0009] In order to solve the above technical problems or at least partially solve the above technical problems, embodiments of the present disclosure provide an RS232 interface lightning surge protection circuit and method, and a roadside unit.

[0010] In a first aspect, an embodiment of the present disclosure provides an RS232 interface lightning surge protection circuit, comprising an RS232 interface and an RS232 chip, the circuit further comprising:

[0011] A first protection device is provided between the data transceiver end of the RS232 interface and the PE, and is used to perform a first level of lightning surge protection on the data transceiver end of the RS232 chip;

[0012] A second protection device is provided between the data transceiver end of the RS232 interface and the data transceiver end of the RS232 chip, and the second protection device is used to perform a second level of lightning surge protection on the data transceiver end of the RS232 chip;

[0013] A third protection device is provided between the data transceiver end of the RS232 interface and the internal protected ground, and is used to perform a third level of lightning surge protection on the data transceiver end of the RS232 chip;

[0014] a fourth protection device, which is provided between the ground terminal of the RS232 interface and the PE, wherein the fourth protection device is used to perform a first level of lightning surge protection on the internal protected ground;

[0015] A fifth protection device is provided between the ground terminal of the RS232 interface and the internal protected ground, wherein the fifth protection device is used to perform second-level lightning surge protection on the internal protected ground.

[0016] In a possible implementation, the second protection device is a transient blocking unit, the fourth protection device is a parallel discharge protection device, and the fifth protection device is a transient blocking unit.

[0017] In a possible implementation manner, the third protection component is a three-terminal transient state diode.

[0018] In a possible implementation, the third protection device is a three-terminal electrostatic resistor.

[0019] In a possible embodiment, the parallel discharge protection device is any one of the following circuits: a parallel circuit of a two-pole gas discharge tube and a 4KV 1nF capacitor, a parallel circuit of a two-pole gas discharge tube and a transient diode, a parallel circuit of a surge suppression thyristor and a 4KV 1nF capacitor, a parallel circuit of a surge suppression thyristor and a transient diode, a parallel circuit of a thyristor surge protector and a 4KV 1nF capacitor, and a parallel circuit of a thyristor surge protector and a transient diode.

[0020] In a possible implementation manner, the first protection device is one of a three-electrode gas discharge tube device, a combination device of two thyristor surge protectors, and a combination device of two surge suppression thyristors.

[0021] In a possible implementation, the internal protected ground is connected to the ground wire via a 1M resistor in parallel with a 4KV 1nF capacitor, wherein the 4KV 1nF capacitor is used to establish a high-frequency path and block low-frequency paths, and the 1M resistor is used to discharge static electricity.

[0022] In a possible implementation, the ground terminal of the RS232 interface transmits the RS232 signal through a shielded cable, wherein the shielded cable is used to enhance the anti-interference capability of the RS232 signal.

[0023] In a second aspect, an embodiment of the present disclosure provides a roadside unit, comprising the above-mentioned RS232 interface lightning surge protection circuit.

[0024] In a third aspect, an embodiment of the present disclosure provides an RS232 interface lightning surge protection method, which is applied to the above-mentioned RS232 interface lightning surge protection circuit, the circuit including an RS232 chip, and the method comprising:

[0025] Using the first protection device to perform the first level of lightning surge protection on the data transceiver end of the RS232 chip;

[0026] A second protection device is used to implement second-level lightning surge protection for the data transceiver end of the RS232 chip;

[0027] Use the third protection device to implement the third level of lightning surge protection for the data transceiver end of the RS232 chip;

[0028] Using the fourth protection device to perform the first level of lightning surge protection on the internal protected ground;

[0029] The fifth protection device is used to implement the second level of lightning surge protection for the internal protected ground.

[0030] The above technical solutions provided by the embodiments of the present disclosure have at least some or all of the following advantages compared to the prior art:

[0031] The RS232 interface lightning surge protection circuit described in the embodiment of the present disclosure includes an RS232 interface and an RS232 chip, and a first protection device, which is arranged between the data transceiver end of the RS232 interface and the PE, and the first protection device is used to perform a first-level lightning surge protection on the data transceiver end of the RS232 chip; a second protection device, which is arranged between the data transceiver end of the RS232 interface and the data transceiver end of the RS232 chip, and the second protection device is used to perform a second-level lightning surge protection on the data transceiver end of the RS232 chip; a third protection device, which is arranged between the data transceiver end of the RS232 interface and the internal The third protection device is used to perform third-level lightning surge protection on the data transceiver end of the RS232 chip between the protection grounds; the fourth protection device is arranged between the ground end of the RS232 interface and the PE, wherein the fourth protection device is used to perform first-level lightning surge protection on the internal protected ground; the fifth protection device is arranged between the ground end of the RS232 interface and the internal protected ground, wherein the fifth protection device is used to perform second-level lightning surge protection on the internal protected ground, which can effectively improve the EMC protection level reliability of the RSU while also greatly reducing the cost and improving the project development and production assembly and installation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0033] In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or related technical descriptions. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0034] Figure 1 The following schematically shows a structural block diagram of an RS232 interface lightning surge protection circuit according to an embodiment of the present disclosure;

[0035] Figure 2 A schematic flow chart of a method for protecting an RS232 interface from lightning surges according to an embodiment of the present disclosure is schematically shown. DETAILED DESCRIPTION

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present disclosure without making any creative efforts shall fall within the scope of protection of the present disclosure.

[0037] To address the need for an external SPD surge protector (SPD) for the RSU and the increased space and cost of the RSU's internal PCBA, embodiments of the present disclosure provide an RS232 interface lightning surge protection circuit. While ensuring long-distance RS232 communication and the normal operation of the RSU, this circuit protects against at least 4kV lightning surge interference. EMC testing must at least pass the EFT test and ESD test level 4 requirements for ITE outdoor information technology equipment, as well as the lightning surge test level 4 requirements. This disclosure effectively improves the reliability of the RSU's EMC protection level while significantly reducing costs and increasing project development, production, assembly, and installation efficiency.

[0038] An embodiment of the present disclosure provides an RS232 interface lightning surge protection circuit, comprising an RS232 interface and an RS232 chip, the circuit further comprising:

[0039] A first protection device is provided between the data transceiver end of the RS232 interface and the PE, and is used to perform a first level of lightning surge protection on the data transceiver end of the RS232 chip;

[0040] A second protection device is provided between the data transceiver end of the RS232 interface and the data transceiver end of the RS232 chip, and the second protection device is used to perform a second level of lightning surge protection on the data transceiver end of the RS232 chip;

[0041] A third protection device is provided between the data transceiver end of the RS232 interface and the internal protected ground, and is used to perform a third level of lightning surge protection on the data transceiver end of the RS232 chip;

[0042] a fourth protection device, which is provided between the ground terminal of the RS232 interface and the PE, wherein the fourth protection device is used to perform a first level of lightning surge protection on the internal protected ground;

[0043] A fifth protection device is provided between the ground terminal of the RS232 interface and the internal protected ground, wherein the fifth protection device is used to perform second-level lightning surge protection on the internal protected ground.

[0044] See also Figure 1 The first protection device is a three-electrode gas discharge tube, the second protection device is a transient blocking unit, the third protection device is a three-terminal transient diode, the fourth protection device is a parallel discharge protection device, and the fifth protection device is a transient blocking unit.

[0045] exist Figure 1 In the embodiment, the ground terminal of the RS232 interface transmits the RS232 signal through a shielded wire, wherein the shielded wire is used to enhance the anti-interference ability of the RS232 signal. In the present embodiment, a shielded wire is used for long-distance transmission of the RS232 signal to enhance the signal anti-interference ability, and a shielded ground braided mesh is used to connect the RS232_GND pin of the RS232 interface. In circuit design, RS232_GND (the ground terminal of the RS232 interface) theoretically needs to be directly connected to the device GND or connected through a 0 ohm resistor to ensure a low-impedance complete RS232 signal long-distance transmission reference ground return, and the device GND (internal protected ground) is a GND that needs to be protected. Therefore, RS232_GND is also protected as a signal line, similar to the protection treatment of RS232_RX (the data receiving end of the RS232 interface) and RS232_TX (the data transmitting end of the RS232 interface):

[0046] In this embodiment, a three-pole GDT with a low DC discharge voltage is used as the first-level differential and common-mode protection on the RS232 signal line. When a lightning surge occurs, the voltage across the GDT increases, the GDT begins to ionize and enter the glow zone, and the current passing through the GDT increases, resulting in an avalanche effect. At this time, the GDT enters a virtual short circuit state, and the arc voltage across the GDT is approximately 10V. Since the time it takes for the GDT to switch from the glow zone to the arc zone is about 0.2us, a transient voltage of tens of volts will still appear after the first-level protection of the GDT. If there is no further protection at the subsequent stage, it may cause damage to the device. The subsequent protection of the RS232 signal line can be designed as follows:

[0047] The existing combination of resistors or PTCs with TVS protection is not suitable. This is because the RS232 chip's current for these two signals during normal communication does not exceed 100mA, and its protection is only up to ESD Level 4, making it unable to withstand the high transient currents of lightning surges. Referring to the 4kV Level 4 requirement of the lightning surge test, ordinary resistors are unable to limit high-level surge currents. As a result, either the large-package resistor fails to provide adequate protection, damaging downstream circuits, or the resistor package is underpowered, causing breakdown damage. PTC devices, on the other hand, have a response time of only about 150ms when protecting against 500mA overcurrent. This millisecond-level transient response speed is inadequate to cope with microsecond-level lightning surge interference. Therefore, transient blocking units (TBUs) are used, offering faster transient response and better dynamic performance. As high-speed, high-voltage overcurrent protection devices, TBUs limit current to a preset value, such as 100mA, within 1µs if a high transient current occurs in the series protection line. For the remainder of the time after the transient, the TBU remains in a protective blocking state, with only approximately 1mA of current flowing. RS232 signals can still communicate normally with a 1mA drive capability. In this blocking state, the TBU has a very high impedance, blocking transient currents. After the lightning surge, the TBU returns to its normal low-impedance state, and RS232 continues to operate normally. Another advantage of using a TBU is that the subsequent TVS diode can be a small package, such as a small three-terminal (TVS) ESD diode with differential and common mode protection. This provides an additional level of ESD protection for subsequent chips while preventing overcurrent or overvoltage from damaging the three-terminal diode.

[0048] The RS232_GND is directly connected to the shielded braided wire harness. The protection for RS232_GND is similar to that for signal lines. The first-level protection uses a "parallel discharge protection device combination." The subsequent protection uses a TBU to connect RS232_GND and the device GND to achieve transient suppression of surge residual current. The reason for connecting the TBU in series has been described and will not be repeated here. The "parallel discharge protection device combination" includes any of the following circuits:

[0049] The parallel circuits of a two-pole gas discharge tube and a 4kV 1nF capacitor, a two-pole gas discharge tube and a transient diode, a surge suppression thyristor and a 4kV 1nF capacitor, a surge suppression thyristor and a transient diode, a thyristor surge protector and a 4kV 1nF capacitor, and a thyristor surge protector and a transient diode are also included. In other words, the parallel discharge protection device combination of this embodiment connects RS232_GND and PE grounds in parallel using two 1812 or SMB package-sized devices, enabling a variety of compatible designs without requiring PCB modifications. There are various primary protection designs that fit the 1812 (SMB) package size, including two-pole GDTs in parallel with 4kV 1nF capacitors, two-pole GDTs in parallel with TVS diodes, TSS semiconductor discharge tubes in parallel with 4kV 1nF capacitors, TSS in parallel with TVS diodes, TISP thyristor surge protectors in parallel with 4kV 1nF capacitors, and TISP in parallel with TVS diodes. Whether using a GDT, TSS, or TISP for primary protection, a certain amount of residual voltage and current will remain during the brief transition from high-voltage to low-voltage range. Therefore, high-voltage capacitors or TVS diodes are needed for further filtering to reduce the burden on the TBU.

[0050] In this embodiment, the internal protected ground is connected to the ground wire through a 1M resistor in parallel with a 4KV 1nF capacitor, wherein the 4KV 1nF capacitor is used to establish a high-frequency path that blocks low frequencies, and the 1M resistor is used to discharge static electricity. It is worth noting that a 1M ohm resistor and a 4KV 1nF capacitor are required to be connected in parallel between the final PE shell ground and the device GND for isolation protection. After protecting the device GND from instantaneous lightning surge interference, the static electricity on the device GND can also be discharged when the PE (ground wire) is well connected to the ground. The lightning surge needs to be discharged or blocked as quickly as possible at the RS232_GND interface, and the clamping voltage after discharge needs to be as low as possible to avoid affecting the level of the device GND, thereby exceeding the effective signal level range of RS232, resulting in RS232 communication abnormalities or damage to the PCBA and lines on the RSU. Therefore, a 1M resistor is not used.

[0051] For the first-level protection device against common-mode and differential-mode high-level lightning surges on the RS232 signal lines in this embodiment, a GDT (Gaseous Discharge Tube) with a rated DC discharge voltage of 90V can be selected. Its transient discharge voltage is 1kV / us and can withstand 600V. Its discharge current is 5kA. The lightning protection trigger point generally begins ionization and enters the glow zone at 300V. Even after the first-level protection of the GDT, transient voltages of approximately 60V and arc voltages of approximately 10V will still occur. Therefore, a second-level transient blocking unit (TBU) current-limiting protection is required. The TBU is generally rated for 300V AC effective voltage and 600V transient voltage withstand. Combined with a three-level TVS protection system, the complete system can protect ITE equipment from high-level lightning surges. For RS232_GND protection, for example, a TSS parallel 4KV 1nF high-voltage capacitor combination can be selected, and a TSS in SMB package with a low trigger voltage can be selected. It can cope with 400A transient pulse current under 8×20us surge waveform and 6KV transient surge voltage under 10×1000us. Combined with high-voltage capacitors and series TBU, it can fully meet the requirements of outdoor level 4 of the national standard 17626.5 lightning surge immunity test.

[0052] In another embodiment, the third protection device may also be a three-terminal electrostatic resistor.

[0053] In another embodiment, the first protection device may also be a device selected from the group consisting of a combination of two thyristor surge protectors and a combination of two surge suppression thyristors.

[0054] An embodiment of the present disclosure further provides a roadside unit, comprising the above-mentioned RS232 interface lightning surge protection circuit.

[0055] The RS232 interface lightning surge protection circuit disclosed in the present invention can ensure that the RSU does not need to purchase an SPD surge protector outside of it, nor does it need to increase the internal PCBA space and cost of the RSU. While ensuring RS232 long-distance communication and normal operation of the RSU, it can protect against at least 4KV lightning surge interference, and the EMC test can at least pass the ITE outdoor information technology equipment immunity type EFT test and ESD test level 4 requirements, as well as the lightning surge Surge test level 4 requirements. Therefore, it can effectively improve the EMC protection level reliability of the RSU while also greatly reducing costs. The circuit disclosed in the present invention has high reliability and an extremely low probability of damage and repair; it avoids or reduces the use of plug-in materials, thereby improving production efficiency; the gas discharge tube uses square materials instead of conventional cylindrical materials to avoid rolling displacement of materials during the production process; the protection is sufficient, and there is no need to assemble and match external protective equipment, and the PCBA space design is standardized to reduce production efficiency, thereby improving the installation efficiency of project development and production assembly. Figure 2The embodiments of the present disclosure further provide a method for protecting an RS232 interface from lightning surges, which is applied to the aforementioned RS232 interface lightning surge protection circuit, the circuit including an RS232 chip, and the method comprising:

[0056] S1, using the first protection device to perform the first level of lightning surge protection on the data transceiver end of the RS232 chip;

[0057] S2, using the second protection device to perform the second level of lightning surge protection on the data transceiver end of the RS232 chip;

[0058] S3, using a third protection device to perform third-level lightning surge protection on the data transceiver end of the RS232 chip;

[0059] S4, using the fourth protection device to perform the first level of lightning surge protection on the internal protected ground;

[0060] S5, using a fifth protection device to perform second-level lightning surge protection on the internal protected ground.

[0061] For the method embodiments, since they basically correspond to the device embodiments, the relevant parts can be referred to the partial description of the device embodiments. The method embodiments described above are merely illustrative. Some or all of the steps can be selected according to actual needs to achieve the purpose of the present invention. Those skilled in the art can understand and implement them without making any creative efforts.

[0062] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0063] The foregoing description is intended only to provide specific embodiments of the present disclosure, intended to enable those skilled in the art to understand and implement the present disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure is not to be limited to the embodiments shown herein, but is to be construed in the broadest manner consistent with the principles and novel features claimed herein.

Claims

1. A RS232 interface lightning surge protection circuit, comprising an RS232 interface and an RS232 chip, characterized in that: The circuit further comprises: A first protection device is provided between the data transceiver end of the RS232 interface and the PE, and is used to perform a first level of lightning surge protection on the data transceiver end of the RS232 chip; A second protection device is provided between the data transceiver end of the RS232 interface and the data transceiver end of the RS232 chip, the second protection device is used to perform second-level lightning surge protection on the data transceiver end of the RS232 chip, the second protection device is a transient blocking unit, the transient blocking unit is used to limit current during a surge and enable normal communication of the RS232 chip; A third protection device is provided between the data transceiver end of the RS232 interface and the internal protected ground, and is used to perform a third level of lightning surge protection on the data transceiver end of the RS232 chip; a fourth protection device, which is provided between the ground terminal of the RS232 interface and the PE, wherein the fourth protection device is used to perform a first level of lightning surge protection on the internal protected ground; A fifth protection device is provided between the ground terminal of the RS232 interface and the internal protected ground, wherein the fifth protection device is used to perform second-level lightning surge protection on the internal protected ground.

2. The circuit according to claim 1, wherein: The fourth protection device is a parallel discharge protection device, and the fifth protection device is a transient blocking unit.

3. The circuit according to claim 2, characterized in that The third protection device is a three-terminal transient diode.

4. The circuit according to claim 2, characterized in that The third protection device is a three-terminal electrostatic resistor.

5. The circuit according to claim 2, characterized in that The parallel discharge protection device is any one of the following circuits: a parallel circuit of a two-pole gas discharge tube and a 4KV 1nF capacitor, a parallel circuit of a two-pole gas discharge tube and a transient diode, a parallel circuit of a surge suppression thyristor and a 4KV 1nF capacitor, a parallel circuit of a surge suppression thyristor and a transient diode, a parallel circuit of a thyristor surge protector and a 4KV 1nF capacitor, and a parallel circuit of a thyristor surge protector and a transient diode.

6. The circuit according to claim 1, wherein: The first protection device is one of a three-electrode gas discharge tube device, a combination device of two thyristor surge protectors, and a combination device of two surge suppression thyristors.

7. The circuit according to claim 1, wherein: The internal protected ground is connected to the ground wire through a 1M resistor in parallel with a 4KV 1nF capacitor, wherein the 4KV 1nF capacitor is used to establish a high-frequency path and block low-frequency paths, and the 1M resistor is used to discharge static electricity.

8. The circuit according to claim 1, wherein: The grounding end of the RS232 interface transmits the RS232 signal through a shielded line, wherein the shielded line is used to enhance the anti-interference capability of the RS232 signal.

9. A roadside unit, characterized in that: The invention comprises the RS232 interface lightning surge protection circuit according to any one of claims 1 to 8.

10. A method for protecting an RS232 interface from lightning surges, applied to an RS232 interface lightning surge protection circuit according to any one of claims 1 to 8, the circuit comprising an RS232 chip, characterized in that: The method comprises: Using the first protection device to perform the first level of lightning surge protection on the data transceiver end of the RS232 chip; A second protection device is used to implement second-level lightning surge protection for the data transceiver end of the RS232 chip; Use the third protection device to implement the third level of lightning surge protection for the data transceiver end of the RS232 chip; Using the fourth protection device to perform the first level of lightning surge protection on the internal protected ground; The fifth protection device is used to implement the second level of lightning surge protection for the internal protected ground.

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