Vehicle diagnostic instrument

Abstract

The utility model belongs to the technical field of vehicle diagnostic devices, and aims to provide a vehicle diagnostic instrument. According to the technical scheme, the vehicle diagnostic instrument comprises a main control circuit, a disassembly detection circuit, a self-locking circuit, a real-time clock circuit, a data encryption circuit and a data storage circuit, the disassembly detection circuit, the self-locking circuit, the real-time clock circuit, the data encryption circuit and the data storage circuit are electrically connected with the main control circuit, and the output end of the disassembly detection circuit is further electrically connected with the controlled end of the self-locking circuit. According to the utility model, the self-locking of the vehicle diagnostic apparatus can be realized, and the data safety protection of the vehicle diagnostic apparatus can be realized.

Description

Technical Field

[0001] The utility model belongs to the technical field of vehicle diagnostic devices, and in particular relates to a vehicle diagnostic instrument. Background Art

[0002] A vehicle diagnostic instrument, also known as a vehicle fault diagnostic instrument, is a professional instrument used for vehicle testing. It allows users to quickly read and display fault information from the vehicle's electronic control system, allowing them to quickly identify the location and cause of the vehicle fault. During use, the vehicle diagnostic instrument receives vehicle data request commands from a testing client. Upon receiving the vehicle data request command, it sends the vehicle data request command to the vehicle under test, which then returns the vehicle test data corresponding to the request command to the diagnostic instrument. The diagnostic instrument then returns the received vehicle test data to the testing client, allowing the client to diagnose the vehicle's fault based on the vehicle test data.

[0003] With the rapid development of vehicle diagnostic instrument software cracking technology, vehicle diagnostic instrument cracking is becoming a common occurrence, making the security protection of vehicle diagnostic instruments increasingly prominent. To protect vehicle diagnostic instruments, the following methods are currently commonly used: a. Locking the vehicle diagnostic instrument when data anomalies are detected during the interaction between the detection user and the vehicle diagnostic instrument; b. Manually blocking the vehicle diagnostic instrument terminal account when data anomalies are detected during the interaction between the detection user and the vehicle diagnostic instrument.

[0004] However, in the process of using the existing technology, the inventors found that the existing technology has at least the following problems:

[0005] In the existing technology, the vehicle diagnostic instrument itself lacks the self-locking function. It is necessary to actively detect abnormalities in vehicle detection data and other data during the interaction between the detection user terminal and the vehicle diagnostic instrument. Only when abnormalities occur in the data can the vehicle diagnostic instrument be controlled to lock the machine and the terminal account of the vehicle diagnostic instrument be manually blocked, which makes the protection efficiency of the vehicle diagnostic instrument too low. In addition, the protection method of the vehicle diagnostic instrument is too simple to send instructions to the vehicle diagnostic instrument by the detection user terminal so that it can lock and unlock the machine. It can be easily cracked by illegal users, which is not conducive to achieving data security protection of the vehicle diagnostic instrument. Utility Model Content

[0006] In order to solve the above technical problems at least to a certain extent, the present utility model provides a vehicle diagnostic instrument.

[0007] In order to achieve the above purpose, the utility model adopts the following technical solutions:

[0008] A vehicle diagnostic instrument includes a main control circuit, and a disassembly detection circuit, a self-locking circuit, a real-time clock circuit, a data encryption circuit, and a data storage circuit, which are electrically connected to the main control circuit respectively, wherein the output end of the disassembly detection circuit is also electrically connected to the controlled end of the self-locking circuit.

[0009] In a possible design, the main control circuit uses an STM32H743VIT6 single-chip microcomputer and its peripheral circuits.

[0010] In one possible design, the disassembly detection circuit includes a comparator and a photoresistor; wherein, the non-inverting input terminal of the comparator is connected to the power supply circuit through a first resistor and a second resistor in sequence, the junction point of the first resistor and the second resistor is grounded through the photoresistor, the non-inverting input terminal of the comparator is also grounded through a first capacitor, the inverting input terminal of the comparator is electrically connected to its output terminal through a third resistor, the inverting input terminal of the comparator is also grounded through a fourth resistor, the output terminal of the comparator is grounded through a TVS diode and a second capacitor respectively, and the output terminal of the comparator is electrically connected to the controlled end of the main control circuit and the self-locking circuit respectively as the output terminal of the disassembly detection circuit.

[0011] In one possible design, the disassembly detection circuit also includes a first P-type MOS tube, a fifth resistor, a sixth resistor and a third capacitor; wherein, the gate of the first P-type MOS tube is electrically connected to the output end of the comparator through the fifth resistor, the drain of the first P-type MOS tube is electrically connected to the power supply circuit, the drain of the first P-type MOS tube is also electrically connected to its gate through the sixth resistor and the third capacitor, respectively, and the source of the first P-type MOS tube is electrically connected to the main control circuit and the self-locking circuit, respectively.

[0012] In one possible design, the self-locking circuit includes a fuse protection module, which is electrically connected to the main control circuit and the disassembly detection circuit respectively; the fuse protection module includes a second P-type MOS tube, a seventh resistor and a fuse; wherein, the gate of the second P-type MOS tube is electrically connected to the output end of the disassembly detection circuit as the controlled end of the self-locking circuit, the drain of the second P-type MOS tube is connected to the power supply circuit, the drain of the second P-type MOS tube is also grounded through the seventh resistor and the fuse, the source of the second P-type MOS tube is electrically connected to the junction of the seventh resistor and the fuse, and the junction of the seventh resistor and the fuse is also electrically connected to the main control circuit.

[0013] In one possible design, the self-locking circuit also includes a main control drive module, which is electrically connected to the main control circuit and the fuse protection module, respectively; wherein, the main control drive module includes an N-type MOS transistor, an eighth resistor and a ninth resistor, the drain of the N-type MOS transistor is electrically connected to the gate of the second P-type MOS transistor, the source of the N-type MOS transistor is grounded, the gate of the N-type MOS transistor is electrically connected to the main control circuit through the eighth resistor, and the gate of the N-type MOS transistor is also grounded through the ninth resistor.

[0014] In one possible design, the real-time clock circuit uses an SD2506API clock chip and its peripheral circuits.

[0015] In one possible design, the data encryption circuit uses a TMS-T95-102A encryption chip and its peripheral circuits.

[0016] In a possible design, the data storage circuit uses MKDN128GCL-ZA type SDNAND flash memory and its peripheral circuits.

[0017] The beneficial effects of the present invention are mainly reflected in that it can realize the self-locking of the vehicle diagnostic instrument and realize the data security protection of the vehicle diagnostic instrument. Specifically, during the implementation of the present invention, the disassembly detection circuit is used to perform disassembly detection of the vehicle diagnostic instrument and send a disassembly detection signal to the main control circuit so that the main control circuit can detect whether the vehicle diagnostic instrument has been disassembled. The disassembly detection circuit can also send a first self-locking drive signal to the self-locking circuit so that the self-locking circuit can realize the self-locking of the vehicle diagnostic instrument; the main control circuit is used to record the current disassembly time from the real-time clock circuit when receiving the disassembly detection signal, and can encrypt its ID, current disassembly time and vehicle diagnostic data through the data encryption circuit, and then store the encrypted data in the data storage circuit, thereby ensuring that the data cannot be tampered with when the device is disassembled, thereby increasing the security of the vehicle diagnostic instrument. Based on this, the present invention can realize the data security protection of the vehicle diagnostic instrument and avoid the problem of the vehicle diagnostic instrument being cracked. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a control block diagram of a vehicle diagnostic instrument in an embodiment;

[0019] Figure 2 1 is a circuit diagram of the main control circuit in the embodiment;

[0020] Figure 3 1 is a circuit schematic diagram of a disassembly detection circuit in an embodiment;

[0021] Figure 41 is a circuit diagram of a self-locking circuit in an embodiment;

[0022] Figure 5 1 is a circuit diagram of a real-time clock circuit in an embodiment;

[0023] Figure 6 is a circuit schematic diagram of a data encryption circuit in an embodiment;

[0024] Figure 7 4 is a circuit diagram of a data storage circuit in an embodiment. DETAILED DESCRIPTION

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the present invention will be briefly introduced below in conjunction with the drawings and the description of the embodiments or the prior art. Obviously, the following description of the structures of the drawings is only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention.

[0026] It should be understood that although the terms "first," "second," etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are merely used to distinguish one element from another. For example, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element without departing from the scope of the exemplary embodiments of the present invention.

[0027] Example:

[0028] like Figure 1 As shown, this embodiment provides a vehicle diagnostic instrument comprising a main control circuit, and a disassembly detection circuit, a self-locking circuit, a real-time clock circuit, a data encryption circuit, and a data storage circuit, each electrically connected to the main control circuit. The output of the disassembly detection circuit is also electrically connected to the controlled end of the self-locking circuit. It should be understood that in this embodiment, the aforementioned circuit modules are all housed within a sealed enclosure, which is used to implement hardware protection for each circuit.

[0029] In this embodiment, Figure 2As shown, the main control circuit uses the STM32H743VIT6 single-chip microcomputer U6 and its peripheral circuits. It should be noted that the STM32H743VIT6 single-chip microcomputer U6 is a microcontroller based on the ARM Cortex-M7 core, with a main frequency of up to 400MHz, powerful processing power and efficient code execution speed. The chip has built-in 2MB flash memory and 1MB RAM, which can be used to store program data and temporary variables during operation. In addition, the STM32H743VIT6 also provides a rich peripheral interface that can meet the application requirements of various embedded systems. It should also be noted that in this embodiment, the peripheral circuits of the single-chip microcomputer U6, such as including the oscillation module, burning interface and reset module, are not limited here.

[0030] like Figure 3 As shown, the disassembly detection circuit includes a comparator U16B and a photoresistor RL; wherein, the non-inverting input terminal of the comparator U16B is connected to the power supply circuit through the first resistor R55 and the second resistor R56 in sequence, the junction point of the first resistor R55 and the second resistor R56 is grounded through the photoresistor RL, the non-inverting input terminal of the comparator U16B is also grounded through the first capacitor C177, the inverting input terminal of the comparator U16B is electrically connected to its output terminal through the third resistor R54, the inverting input terminal of the comparator U16B is also grounded through the fourth resistor R45, the output terminal of the comparator U16B is grounded through the SMFJ36CA type TVS (Transient Voltage Suppressor) diode D22 and the second capacitor C178 respectively, and the output terminal of the comparator U16B, as the output terminal of the disassembly detection circuit, is electrically connected to the main control circuit and the controlled terminal of the self-locking circuit respectively.

[0031] It should be noted that, in this embodiment, the photoresistor RL constitutes a disassembly detection element for detecting whether there is a disassembly behavior. When the vehicle diagnostic instrument is disassembled, the ambient light will change the resistance of the photoresistor RL, thereby affecting the output signal of the comparator U16B connected thereto; in addition, in the disassembly detection circuit, the first resistor R55, the second resistor R56 and the first capacitor C177 constitute a voltage divider filter module, which helps to stabilize the signal and improve the reliability of the detection circuit. Specifically, the first resistor R55 and the second resistor R56 can divide the 3.3V voltage received from the power supply circuit to drive the photoresistor RL and subsequent circuits. The first capacitor C177 is used to achieve a filtering effect, which can filter out high-frequency noise signals to ensure that the photoresistor signal received by the circuit is more stable and avoid the influence of high-frequency interference or power supply noise on the detection; the comparator U16B, the third resistor R54 and the fourth resistor R45 constitute a power comparison module, which is used to determine whether the transmission signal of the photoresistor RL exceeds the set threshold value, so as to realize Now, the disassembly detection is performed. Specifically, the comparator U16B is used to compare the input voltage signal with a set reference voltage. Its output end can output a disassembly detection signal Open_check to the main control circuit so that the main control circuit can determine whether there is a disassembly behavior. The third resistor R54 and the fourth resistor R45 can form a fixed reference voltage through voltage division and transmit it to the comparator U16B. The reference voltage determines the threshold of the circuit. When the voltage signal generated by the photoresistor RL exceeds or falls below this reference voltage, the disassembly detection signal Open_check output by the comparator U16B will jump to implement a disassembly indication; the TVS diode D22 and the second capacitor C178 are connected in parallel to form a protection filtering module. The TVS diode D22 can implement overvoltage protection to prevent transient high voltage such as electrostatic discharge or surge from damaging the circuit. The second capacitor C178 can filter out high-frequency signals in the disassembly detection signal Open_check to make the output signal of the disassembly detection circuit more stable and avoid false triggering.

[0032] In this embodiment, the disassembly detection circuit also includes a first P-type MOS transistor Q2, a fifth resistor R17, a sixth resistor R53 and a third capacitor C74; wherein, the gate of the first P-type MOS transistor Q2 is electrically connected to the output end of the comparator U16B through the fifth resistor R17, the drain of the first P-type MOS transistor Q2 is electrically connected to the power supply circuit, the drain of the first P-type MOS transistor Q2 is also electrically connected to its gate through the sixth resistor R53 and the third capacitor C74, and the source of the first P-type MOS transistor Q2 is electrically connected to the main control circuit and the self-locking circuit, respectively.

[0033] It should be noted that, in this embodiment, the first P-type MOS transistor Q2, the fifth resistor R17, the sixth resistor R53 and the third capacitor C74 constitute a delayed power-on module, which is used to control the power-on delay and stability of the first self-locking drive signal Cheat_Sig output to the self-locking circuit. Specifically, the fifth resistor R17 is used to implement current limiting protection for the first P-type MOS transistor Q2. The sixth resistor R53 and the third capacitor C74 form an RC delay circuit, which determines the delayed response of the first self-locking drive signal Cheat_Sig. When the vehicle diagnostic instrument is powered on, the third capacitor C74 gradually charges until it reaches a certain voltage, thereby affecting the gate voltage of the first P-type MOS transistor Q2. When the voltage of the third capacitor C74 reaches the threshold voltage of the first P-type MOS transistor Q2, the first P-type MOS transistor Q2 is turned on and outputs the first self-locking drive signal Cheat_Sig to the self-locking circuit, so that the self-locking circuit can achieve self-locking of the vehicle diagnostic instrument. In addition, the RC delay circuit can also filter out transient spike voltages in the power supply, improve the circuit's anti-interference capability, and avoid false triggering.

[0034] like Figure 4 As shown, the self-locking circuit includes a fuse protection module, which is electrically connected to the main control circuit and the disassembly detection circuit respectively; the fuse protection module includes a second P-type MOS transistor Q3, a seventh resistor R91 and a fuse F3; wherein, the gate of the second P-type MOS transistor Q3 is electrically connected to the output end of the disassembly detection circuit as the controlled end of the self-locking circuit, the drain of the second P-type MOS transistor Q3 is connected to the power supply circuit, and the drain of the second P-type MOS transistor Q3 is also grounded through the seventh resistor R91 and the fuse F3, the source of the second P-type MOS transistor Q3 is electrically connected to the junction of the seventh resistor R91 and the fuse F3, and the junction of the seventh resistor R91 and the fuse F3 is also electrically connected to the main control circuit.

[0035] It should be noted that in this embodiment, the fuse protection module is used to lock the vehicle diagnostic instrument. Specifically, during implementation, when disassembly occurs, the voltage of the disassembly detection signal Open_check output by the disassembly detection circuit increases, and the gate voltage of the second P-type MOS transistor Q3 is pulled up to the on-level. At this time, the second P-type MOS transistor Q3 turns on, allowing current to pass through the fuse F3. If the current is large enough, the fuse F3 will melt, physically disconnecting the circuit and locking the device. This achieves hardware-level self-locking of the vehicle diagnostic instrument, ensuring that the vehicle diagnostic instrument cannot be used after detecting disassembly or communication anomalies. In addition, in this embodiment, the fuse protection module can also send a reset signal AD_FUSE_CHECK to the main control circuit through the junction of the seventh resistor R91 and the fuse F3. This resets the main control circuit when an anomaly such as disassembly occurs and prevents it from starting, thereby preventing further use of the vehicle diagnostic instrument.

[0036] In this embodiment, the self-locking circuit further includes a main control driving module, which is electrically connected to the main control circuit and the fuse protection module, respectively. The main control driving module includes an N-type MOS transistor Q7, an eighth resistor R74, and a ninth resistor R75. The drain of the N-type MOS transistor Q7 is electrically connected to the gate of the second P-type MOS transistor Q3, the source of the N-type MOS transistor Q7 is grounded, the gate of the N-type MOS transistor Q7 is electrically connected to the main control circuit via the eighth resistor R74, and the gate of the N-type MOS transistor Q7 is also grounded via the ninth resistor R75.

[0037] It should be noted that in this embodiment, the main control module can send a lock drive signal "Cheat_Ctrl" to the main control driver module. This signal constitutes the second self-lock drive signal of the self-locking circuit, which is used to change the gate voltage of the N-type MOS transistor Q7. The gate voltage is adjusted via the eighth resistor R74 and the ninth resistor R75 to ensure that the N-type MOS transistor Q7 is turned on or off, thereby controlling the fuse protection module. During implementation, the main control module can communicate with external devices such as terminal devices based on the communication circuit connected to it, and perform communication anomaly diagnosis on the communication data. When it determines that the communication status is abnormal, the main control driver module drives the fuse F3 in the fuse protection module to melt, thereby achieving self-locking of the vehicle diagnostic instrument when the communication status is abnormal, such as when a continuous request error occurs.

[0038] like Figure 5As shown, the real-time clock circuit uses the SD2506API clock chip U18 and its peripheral circuits. In this embodiment, the real-time clock circuit is used to record the time when the device is disassembled. When the device is disassembled, the disassembly detection circuit triggers a disassembly event, and the real-time clock circuit records the time of the event.

[0039] It should be noted that the SD2506API clock chip U18 has a built-in crystal oscillator, rechargeable battery, temperature compensation module and standard IIC interface (SCL pin and SDA pin), and has high precision and other characteristics. During implementation, the main control circuit can use the IIC interface of the clock chip U18 to address and read and write 122 bytes of data in the chip (including time register, alarm register, control register, temperature register, battery power register, 70-byte user SRAM register and 8-byte ID code register) through a 7-bit address; in addition, since the clock chip U18 has a built-in crystal oscillator and digital temperature compensation, users do not have to worry about component matching errors, crystal oscillator temperature characteristics and reliability issues caused by external crystal oscillators, resonant capacitors, etc., and can achieve a fully automatic, highly reliable temperature compensation timing function without user intervention within the normal temperature and charging temperature range (-30℃~+80℃), and it can ensure the clock accuracy of ±3.Sppm (at around 25℃), that is, the annual error is less than 2 minutes. In addition, it has a built-in rechargeable battery and charging circuit. When the battery is fully charged at normal temperature, the internal clock will run for about 8 months, which has the advantage of a long service life.

[0040] like Figure 6 As shown, the data encryption circuit uses the TMS-T95-102A encryption chip U20 and its peripheral circuits. This type of encryption chip is designed for data protection and secure communication. It is suitable for a variety of application scenarios, including but not limited to IoT devices, embedded systems, smart cards, mobile payment terminals, etc. It aims to provide efficient data encryption and decryption services and can be used to ensure information security during vehicle diagnostics. The function of the data encryption circuit is to ensure the uniqueness and security of data and prevent unauthorized access or counterfeiting. During the implementation of this embodiment, data encryption is achieved based on the existing encryption scheme of the encryption chip U20. This embodiment only protects the technical solutions related to the circuit structure.

[0041] like Figure 7As shown, the data storage circuit uses the MKDN128GCL-ZA 128GB embedded nano-SDNAND flash memory U21 and its peripheral circuits. It should be noted that the data storage circuit uses the MKDN128GCL-ZA 128GB embedded nano-SDNAND flash memory, which provides an embedded storage design in an LGA package. It consists of NAND flash memory and a high-performance controller. It uses a relatively simple data transmission protocol (compared to EMMC) and has a larger storage space (compared to EEPROM). It integrates the advantages of EMMC and EEPROM, offering high performance, high quality, and low power consumption.

[0042] This embodiment can achieve self-locking of the vehicle diagnostic instrument and simultaneously provide data security protection for the vehicle diagnostic instrument. Specifically, during implementation, the disassembly detection circuit is used to perform disassembly detection on the vehicle diagnostic instrument and transmit a disassembly detection signal, Open_check, to the main control circuit to detect whether the vehicle diagnostic instrument has been disassembled. The disassembly detection circuit can also transmit a first self-locking drive signal, Cheat_Sig, to the self-locking circuit to enable the self-locking circuit to self-lock the vehicle diagnostic instrument. Upon receiving the disassembly detection signal, the main control circuit is used to record the current disassembly time from the real-time clock circuit and encrypt the ID (Identity Document), current disassembly time, and vehicle diagnostic data using a data encryption circuit. The encrypted data is then stored in the data storage circuit. This ensures that data cannot be tampered with when the device is disassembled, thereby enhancing the security of the vehicle diagnostic instrument. Based on this, this embodiment can provide data security protection for the vehicle diagnostic instrument and prevent the vehicle diagnostic instrument from being hacked.

[0043] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A vehicle diagnostic instrument, characterized in that: It includes a main control circuit, and a disassembly detection circuit, a self-locking circuit, a real-time clock circuit, a data encryption circuit and a data storage circuit that are electrically connected to the main control circuit respectively, wherein the output end of the disassembly detection circuit is also electrically connected to the controlled end of the self-locking circuit.

2. A vehicle diagnostic instrument according to claim 1, characterized in that: The main control circuit adopts an STM32H743VIT6 single chip microcomputer (U6) and its peripheral circuits.

3. The vehicle diagnostic instrument according to claim 1, characterized in that: The disassembly detection circuit includes a comparator (U16B) and a photoresistor (RL); wherein the non-inverting input terminal of the comparator (U16B) is connected to a power supply circuit via a first resistor (R55) and a second resistor (R56) in sequence, the junction point of the first resistor (R55) and the second resistor (R56) is grounded via the photoresistor (RL), the non-inverting input terminal of the comparator (U16B) is also grounded via a first capacitor (C177), the inverting input terminal of the comparator (U16B) is electrically connected to its output terminal via a third resistor (R54), the inverting input terminal of the comparator (U16B) is also grounded via a fourth resistor (R45), the output terminal of the comparator (U16B) is grounded via a TVS diode (D22) and a second capacitor (C178), and the output terminal of the comparator (U16B), as the output terminal of the disassembly detection circuit, is electrically connected to the main control circuit and the controlled terminal of the self-locking circuit.

4. A vehicle diagnostic instrument according to claim 3, characterized in that: The disassembly detection circuit further comprises a first P-type MOS transistor (Q2), a fifth resistor (R17), a sixth resistor (R53) and a third capacitor (C74); wherein the gate of the first P-type MOS transistor (Q2) is electrically connected to the output end of the comparator (U16B) via the fifth resistor (R17), the drain of the first P-type MOS transistor (Q2) is electrically connected to the power supply circuit, the drain of the first P-type MOS transistor (Q2) is also electrically connected to its gate via the sixth resistor (R53) and the third capacitor (C74), and the source of the first P-type MOS transistor (Q2) is electrically connected to the main control circuit and the self-locking circuit.

5. The vehicle diagnostic instrument according to claim 1, characterized in that: The self-locking circuit includes a fuse protection module, which is electrically connected to the main control circuit and the disassembly detection circuit respectively; the fuse protection module includes a second P-type MOS tube (Q3), a seventh resistor (R91) and a fuse (F3); wherein the gate of the second P-type MOS tube (Q3) is electrically connected to the output end of the disassembly detection circuit as the controlled end of the self-locking circuit, the drain of the second P-type MOS tube (Q3) is connected to the power supply circuit, the drain of the second P-type MOS tube (Q3) is also grounded through the seventh resistor (R91) and the fuse (F3), the source of the second P-type MOS tube (Q3) is electrically connected to the junction of the seventh resistor (R91) and the fuse (F3), and the junction of the seventh resistor (R91) and the fuse (F3) is also electrically connected to the main control circuit.

6. The vehicle diagnostic instrument according to claim 5, characterized in that: The self-locking circuit further includes a main control drive module, which is electrically connected to the main control circuit and the fuse protection module respectively; wherein the main control drive module includes an N-type MOS transistor (Q7), an eighth resistor (R74) and a ninth resistor (R75); the drain of the N-type MOS transistor (Q7) is electrically connected to the gate of the second P-type MOS transistor (Q3); the source of the N-type MOS transistor (Q7) is grounded; the gate of the N-type MOS transistor (Q7) is electrically connected to the main control circuit via the eighth resistor (R74); and the gate of the N-type MOS transistor (Q7) is also grounded via the ninth resistor (R75).

7. The vehicle diagnostic instrument according to claim 1, characterized in that: The real-time clock circuit adopts the SD2506API clock chip (U18) and its peripheral circuits.

8. The vehicle diagnostic instrument according to claim 1, characterized in that: The data encryption circuit adopts the TMS-T95-102A encryption chip (U20) and its peripheral circuits.

9. The vehicle diagnostic instrument according to claim 1, characterized in that: The data storage circuit adopts MKDN128GCL-ZA type SDNAND flash memory (U21) and its peripheral circuits.

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