CN109050444B - CAN circuit structure and vehicle diagnosis equipment thereof - Google Patents

Abstract

The invention relates to a CAN circuit structure and vehicle diagnosis equipment thereof. The CAN circuit structure comprises: a pair of data buses having differential signals transmitted thereon; and the CAN transceiver is used for receiving and transmitting the differential signals and is connected with the data bus and works in a first voltage domain. The clamping circuit is arranged between the CAN transceiver and the data bus and is used for clamping the high level or the low level of the differential signal so as to enable the voltage difference of the differential signal to be matched with the CAN transceiver; and the CAN controller is connected with the CAN transceiver and is used for communicating with the CAN transceiver, and the signal isolation circuit is arranged between the CAN transceiver and the CAN controller and is used for isolating the first voltage domain and the second voltage domain. The circuit allows the use of standard CAN transceiver chips of common standards in special CAN circuit structures such as a CAN network protocol system of a 24V trailer, thereby effectively reducing the manufacturing cost of related equipment.

Description

CAN circuit structure and vehicle diagnosis equipment thereof

[ Field of technology ]

The invention relates to the technical field of vehicle diagnosis, in particular to a CAN circuit structure and vehicle diagnosis equipment thereof.

[ Background Art ]

In the automotive industry, automobile manufacturers have developed a variety of different electronic control systems for many reasons, including safety, comfort, convenience, low pollution, and low cost. Because of the difference in the data types and reliability required for communication between these electronic control systems, the number of wiring harnesses increases, which brings about certain difficulties in manufacturing and designing automobiles.

To accommodate the need for "reducing the number of wiring harnesses", "high-speed communication of large amounts of data over multiple LANs", german electric Shang Boshi corporation developed an automobile-oriented CAN communication protocol in 1986.

CAN is an acronym for controller area network (Controller Area Network, CAN). After being standardized by ISO11898 and ISO11519, the system is one of the most widely used field buses internationally, and provides powerful technical support for realizing real-time and reliable data communication among nodes of a distributed control system.

In carrying out the invention, the inventors have found that the prior art has at least the following problems: the logic level signal specification of the existing automotive CAN network protocol specification still exists in a number of different versions, such as the common CAN network protocol specification and the 24V trailer CAN network protocol specification.

Different versions require the use of CAN transceiver chips conforming to corresponding standards to enable communication with the CAN network and read information from the car. Therefore, the limited range of use of standard CAN transceiver chips also results in some non-standard or common CAN networks requiring the use of a custom made CAN transceiver chip, thereby increasing its manufacturing cost.

[ Invention ]

In order to solve the technical problems, embodiments of the present invention provide a CAN circuit structure and a vehicle diagnostic apparatus thereof, which CAN be adapted to a specific CAN network specification.

In order to solve the technical problems, the embodiment of the invention provides the following technical scheme: a CAN circuit structure. The CAN circuit structure comprises:

A pair of data buses, wherein differential signals are transmitted on the data buses; the CAN transceiver is used for receiving and transmitting the differential signals and is connected with the data bus; the clamping circuit is arranged between the CAN transceiver and the data bus and used for clamping the high level or the low level of the differential signal so as to enable the voltage difference of the differential signal to be matched with the CAN transceiver; a CAN controller operating in a second voltage domain, the CAN controller is connected with the CAN transceiver and is used for communicating with the CAN transceiver; and the signal isolation circuit is arranged between the CAN transceiver and the CAN controller and is used for isolating the first voltage domain and the second voltage domain.

In some embodiments, the CAN circuit structure further comprises: and the power supply circuit is used for providing the first voltage domain and the second voltage domain for the CAN transceiver and the CAN controller.

In some embodiments, the power supply circuit forms a first ground terminal and a second ground terminal isolated from each other, and outputs a first power supply voltage and a second power supply voltage;

The CAN transceiver is respectively connected with the first power supply voltage and the first grounding end, and the CAN controller is respectively connected with the second power supply voltage and the second grounding end.

In some embodiments, the power supply circuit includes an input power source and an isolated power source; the input end of the isolation power supply is connected with the input power supply;

The output end of the isolation power supply forms the first power supply voltage and a first grounding end; the isolated power supply is connected with the CAN transceiver and provides a first power supply voltage and a first grounding end for the CAN transceiver.

In some embodiments, the power supply circuit further comprises a low dropout linear regulator; the input end of the low-dropout linear voltage regulator is connected with the input power supply;

the output end of the low dropout linear voltage regulator forms a second power supply voltage and a second grounding end; the low dropout linear regulator is connected with the CAN controller and provides a second power supply voltage and a second grounding end for the CAN controller.

In some embodiments, the clamp circuit is comprised of a first diode and a second diode; the pair of data buses consists of a first data line and a second data line;

the positive electrode of the first diode is connected with the first data line, and the positive electrode of the second diode is connected with the second data line; and the cathodes of the first diode and the second diode are connected with the first grounding end.

In some embodiments, the clamping circuit is configured to limit a low level of the differential signal to a ground of the first voltage domain; the high level of the differential signal is comparable to the operating voltage of the first voltage domain.

In some embodiments, a first connection terminal of the signal isolation circuit is connected to the CAN transceiver, and a second connection terminal of the signal isolation circuit is connected to the CAN controller for isolating and converting signals transmitted between the first voltage domain and the second voltage domain.

In some embodiments, the CAN transceiver is a CAN transceiver that meets the common standard ISO 11898; the differential signal transmitted on the data bus is a CAN signal conforming to the ISO11992 standard.

In order to solve the technical problems, the embodiment of the invention also provides the following technical scheme: a vehicle diagnostic apparatus. The vehicle diagnostic apparatus includes:

the CAN transceiver is connected with a CAN bus of the vehicle to be detected and used for receiving and transmitting differential signals; the clamping circuit is arranged between the CAN transceiver and the data bus and used for clamping the differential signals; a CAN controller operating in a second voltage domain, the CAN controller is connected with the CAN transceiver and is used for communicating with the CAN transceiver; the signal isolation circuit is arranged between the CAN transceiver and the CAN controller and is used for isolating the first voltage domain and the second voltage domain; and the power supply circuit is used for providing the first voltage domain and the second voltage domain for the CAN transceiver and the CAN controller.

Compared with the prior art, the CAN circuit structure of the embodiment of the invention CAN use the standard CAN transceiver chip of the common standard in the special CAN circuit structure such as the CAN network protocol system of the 24V trailer, thereby effectively reducing the manufacturing cost of related equipment.

[ Description of the drawings ]

One or more embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements, and in which the figures of the drawings are not to be taken in a limiting sense, unless otherwise indicated.

FIG. 1 is a schematic diagram of a typical CAN circuit configuration;

FIG. 2 is a logic diagram of the CAN physical layers CAN_H and CAN_L of the common standard;

FIG. 3 is a logic diagram of CAN physical layers CAN_H and CAN_L of a 24V trailer;

fig. 4 is a structural block diagram of a CAN circuit structure provided by an embodiment of the present invention;

Fig. 5 is a schematic circuit diagram of a CAN circuit structure according to an embodiment of the present invention;

fig. 6 is a schematic diagram of an application example of a CAN circuit structure according to an embodiment of the present invention.

[ Detailed description ] of the invention

In order that the invention may be readily understood, a more particular description thereof will be rendered by reference to specific embodiments that are illustrated in the appended drawings. It will be understood that when an element is referred to as being "fixed" to another element, it can be directly on the other element or one or more intervening elements may be present therebetween. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or one or more intervening elements may be present therebetween. The terms "upper," "lower," "inner," "outer," "bottom," and the like as used in this specification are used in an orientation or positional relationship based on that shown in the drawings, merely to facilitate the description of the invention and to simplify the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the invention. Furthermore, the terms "first," "second," "third," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

Unless defined otherwise, 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 invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and/or" as used in this specification includes any and all combinations of one or more of the associated listed items.

In addition, the technical features mentioned in the different embodiments of the invention described below can be combined with one another as long as they do not conflict with one another.

The CAN technical specification 2.0 is formulated and issued in 1991 and is divided into an A part and a B part. The 2.0A part gives the standard format of the CAN message, and the 2.0B part is an extension part. In 2000, the J1939 protocol based on the CAN2.0B specification was proposed.

Fig. 1 is a typical CAN circuit block diagram. As shown in fig. 1, the CAN circuit block diagram includes a pair of data buses (represented by can_h and can_l in fig. 1, respectively), a CAN transceiver 110, a CAN controller 120, and a power supply 130.

Wherein CAN transceiver 110 acts as a transmission intermediary for enabling conversion between different data forms. That is, the binary code stream is converted into a differential signal to be transmitted into the data bus, and the differential signal is converted into a binary code stream to be received.

The CAN controller 120 is a control core for implementing a protocol bottom layer and a data link layer of the CAN bus. It may generate a CAN frame and send it to the CAN transceiver 110 in the form of a binary code stream, which is converted to a corresponding differential signal by the CAN transceiver or may parse and receive the binary code stream received from the CAN transceiver.

Of course, in the transmitting process of the CAN controller, tasks such as bit filling, CRC check adding, response detection (corresponding to performing transmit-receive comparison, bit removal filling, CRC check executing in the receiving process of the CAN controller) or performing tasks such as collision judgment, error processing and the like may also be performed in the receiving process.

The power supply 130 may be any type of power management system for outputting a stable and reliable dc voltage to power the CAN transceiver 110 and the CAN controller 120. Specifically, the power supply 130 may be a power management system consisting of a low dropout linear regulator, and outputs an operating voltage VCC required by the CAN transceiver and the CAN controller.

In the CAN circuit block diagram shown in fig. 1, differential signals transmitted on the data buses typically represent different information by a difference in high and low levels between the two buses. For example, when the data line can_h is at a low level and the data line can_l is at a high level, binary information "0" is indicated. And when the data line can_h is at a high level and the data line can_l is at a low level, binary information "1" is indicated.

Although the logic settings may be similar, there is a distinction for CAN networks that follow different standards, due to voltage specifications, etc. Thus, the voltage differences between the differential signals that are typically transmitted on the data bus are not the same.

For example, fig. 2 is a logic diagram of CAN physical layers can_h and can_l of a general standard. FIG. 3 is a logic diagram of CAN physical layers CAN_H and CAN_L of a 24V trailer.

As CAN be seen from a comparison of fig. 2 and 3, when in the dominant state (representing information "0"), the highest level of can_l of the common standard is maintained at about 5V, whereas the highest level of can_l of the 24V trailer may reach about 32V.

Therefore, CAN standards having different maximum levels (voltage differences between differential signals) are also different in terms of the usage requirements of the CAN transceiver 11. In order to accommodate different CAN network protocols, it is often necessary to design and use an adapted CAN transceiver.

For example, as shown in fig. 2 and 3, since the voltage difference of the differential signal is large in the voltage specification standard of the 24V trailer, the CAN transceiver of the general standard cannot be used in the CAN network of the 24V trailer, but only a dedicated CAN transceiver adapted to the 24V trailer standard CAN be used.

The CAN transceiver of a 24V trailer is specially adapted with a special CAN version relative to a normal standard CAN transceiver. The number of the devices on the market is small, the price is relatively high, and the cost of related devices for accessing the CAN network of the 24V trailer is high.

The CAN circuit structure provided by the embodiment of the invention CAN be still applied to CAN buses of other special standards under the condition of selecting a CAN transceiver chip meeting the common standard. This reduces the need for a special standard CAN transceiver chip and reduces the manufacturing costs of the associated device.

Fig. 4 is a CAN circuit structure provided in an embodiment of the present invention. As shown in fig. 4, the CAN circuit structure may be composed of: a pair of data buses, CAN transceiver 410, clamp 440, CAN controller 420, signal isolation 450, and power supply 430.

Wherein a pair of data buses are denoted can_h and can_l, respectively. Differential signals corresponding to the CAN network protocol are transmitted on the data bus, and information is transmitted through the corresponding relation between CAN_H and CAN_L and high level and low level.

The CAN transceiver 410 is connected to the data buses can_h and can_l, and is configured to receive and transmit the differential signal, so as to implement conversion between the differential signal and a binary digital signal. The first voltage domain consists of a ground terminal and a corresponding operating voltage. The ground may not be a zero potential reference point for the entire system.

The voltage difference between the high and low levels of the differential signal that CAN be received and transmitted by the CAN transceiver is constant according to different standards that it is designed to meet. Here, the voltage difference of the differential signal that CAN be received and transmitted by the CAN transceiver 410 is denoted by "operating in the first voltage domain".

In some embodiments, the CAN transceiver 410 may be selected to meet common standards. For example, CAN transceivers that meet the ISO11898 standard to have lower hardware implementation costs.

The clamp circuit 440 is a functional circuit that keeps the top or bottom of a periodically varying waveform signal at a certain level. The clamp circuit 440 is provided between the CAN transceiver 410 and the data buses can_h and can_l, and CAN limit the high level or the low level of the differential signal to a specific level. The voltage difference of the differential signals transmitted on the data bus CAN be changed in such a way that it corresponds to the standard that CAN transceiver 410 meets.

The CAN controller 420 may specifically be any suitable CAN controller, and may perform one or more functions (such as performing operations of bit stuffing, adding CRC check, and detecting response) disclosed in the foregoing embodiments during information sending and information receiving.

Because CAN transceiver 410 needs to be adapted to the differential signal on the data bus, CAN controller 420 operates in a normal voltage environment. Thus, the CAN controller 420 is distinguished from the CAN transceiver 410 by a reference voltage point in the voltage environment.

Here, "operating in the second voltage domain" means that the operating voltage and the ground used when the CAN controller 420 operates are different from the voltage environment in which the CAN transceiver 410 operates.

A signal isolation circuit 450 is disposed between the CAN transceiver 410 and the CAN controller 420. The signal isolation circuit CAN be any type of circuit or chip capable of exerting a signal isolation effect, so that the CAN transceiver 410 and the CAN controller 420 CAN operate normally, and signals between the two CAN be converted correspondingly without being influenced by voltage domain changes.

The power supply circuit 430 is a functional module that performs a power supply management function, and specifically any power supply management chip or the like that can satisfy dual-voltage output can be used. Which may be coupled to CAN transceiver 410 and CAN controller 420 to provide corresponding first and second voltage domains for CAN transceiver 410 and CAN controller 420, respectively.

In this embodiment, the power supply circuit 430 CAN be used as a separate power management system, and has a plurality of different output terminals, so as to meet the power supply requirements of the CAN transceiver 410 and the CAN controller 420.

In other embodiments, the power supply circuit 430 may be integrated into the CAN circuit structure as part of the CAN circuit structure, with two outputs providing a first voltage domain and a second voltage domain, respectively.

Taking the differential signal used in a 24V trailer system as an example, the differential signal would have a high level of about 35V if referenced to a low level of zero potential.

Thus, in an actual CAN circuit configuration, the operating voltage of the first voltage domain may be set to be about 25V, which corresponds to the high level of the differential signal. Meanwhile, the voltage difference between the grounding end of the first voltage domain and the working voltage is kept at about 5V, so that the CAN transceiver CAN be used.

And the working voltage of the second voltage domain is normal working voltage, the grounding end of the second voltage domain is also zero potential reference, and the normal working of the CAN controller is kept.

According to the CAN circuit structure provided by the embodiment of the invention, on one hand, the voltage difference between the high level and the low level on the data bus is limited to be within the voltage difference range with the common standard through the additionally arranged clamping circuit, so that the CAN transceiver meeting the common standard CAN be used in some CAN protocols of specific versions.

On the other hand, the CAN transceivers working in two different voltage domains are connected with the CAN receivers through the signal isolation circuit, and the voltage domain isolation and the signal conversion between the two are realized by the signal isolation circuit, so that the signal CAN be effectively transmitted between the two.

Fig. 5 is a specific example of a CAN circuit structure provided in an embodiment of the present invention. As shown in fig. 5, the CAN circuit structure has two isolated first ground GND1 and second ground CND2.

The CAN transceiver 510 is connected to the first ground GND1 and operates at a first voltage VCC1. The CAN controller 520 is connected to the second ground GND2 and operates at the second voltage VCC2.

The CAN transceiver 510 and the CAN controller 520 are connected through the signal isolation chip 540, the signal isolation chip 540 isolates two different voltage domains where the CAN transceiver 510 and the CAN controller 520 are located, and the conversion of signals between the two voltage domains is realized.

The first ground GND1, the second ground CND2, the first voltage VCC1 and the second voltage VCC2 are all provided by the power supply circuit 530.

In some embodiments, the power supply circuit 530 is composed of two parts of an isolated power supply 531 and a low dropout linear regulator 532, each having a corresponding output port to provide a first ground GND1, a second ground CND2, a first voltage VCC1, and a second voltage VCC2.

The access terminal of the power supply circuit 530 is connected to the input power Vin, and receives the voltage provided by the input power Vin. The ground terminal of the input power Vin is also the second ground terminal GND2, which is used as a zero voltage point.

On the other hand, the input terminal of the isolated power supply 531 is connected to the input power supply, and after the input power supply is converted, the first voltage VCC1 and the first ground GND1 are output at the output terminal thereof. Since an isolated power supply is used. Therefore, the first ground GND1 and the second ground GND2 outputted at the output terminal are isolated from each other.

On the other hand, the input terminal of the low dropout linear regulator 532 is also connected to the input power supply, and a well-stabilized output voltage VCC2 (second voltage) is provided to the CAN controller 520 by the low dropout linear regulator 532. Of course, in the low dropout linear regulator 532, the ground terminal is the same as the ground terminal of the input power supply, and is also the second ground terminal GND2.

In the above power supply circuit, the first voltage domain (i.e., the first ground GND1 and the first operating voltage VCC 1) is provided to the CAN transceiver 510 through the isolated power supply 531, and the second voltage domain (i.e., the second ground GND2 and the second operating voltage VCC 2) is provided to the CAN controller 530 through the low dropout linear regulator 532.

With continued reference to fig. 5, in order to ensure that the voltage difference of the differential signals transmitted on the data bus is matched to the CAN transceiver 510, the CAN circuit structure further includes a clamping circuit 540. The CAN transceiver 510 is connected to the data bus via the clamp circuit 540, and the clamp circuit controls the voltage difference of the differential signal.

As shown in fig. 5, in some embodiments, the clamping circuit 540 may be comprised of a first diode D1 and a second diode D2. A pair of data buses are represented by a first data line can_h and a second data line can_l, respectively.

The positive electrode of the first diode D1 is connected to the first data line can_h, and the positive electrode of the second diode D2 is connected to the second data line can_l. The cathodes of the first diode D1 and the second diode D2 are both connected to the first ground GND 1.

By the clamp circuit, the low level on the first data line can_h and the second data line can_l CAN be clamped at the first ground GND1. While the high level of the differential signal corresponds to the first operating voltage VCC1 of the CAN transceiver 31. Thereby enabling the voltage difference of the differential signal transmitted on the data lines to be adapted to the CAN transceiver 510.

In actual operation, although the voltage difference between the high level and the low level of the differential signal transmitted on the data bus may be greater than the voltage specification standard satisfied by the CAN transceiver 510. For example, on a 24V trailer system, the level value of the high level is as high as about 32V.

However, by the clamping action of the clamping circuit 35, after the low level (the initial level value is zero potential reference point, that is, the second ground GND 2) on the first data line can_h or the second data line can_l is clamped at the first ground GND1 (which is consistent with the ground of the CAN transceiver 510), only the high level of the differential signal is required to be kept equal to the first operating voltage VCC1, so that the CAN transceiver which CAN only meet the common standard CAN also be applied to a 24V trailer system to receive or output the differential signal which meets the CAN standard of the 24V trailer, so as to reduce the corresponding cost requirement.

The CAN circuit structure provided by the embodiment of the invention CAN be widely applied to a plurality of different related devices. Fig. 6 is an application example of a CAN circuit structure provided in an embodiment of the present invention. As shown in fig. 6, the CAN circuit structure may be applied to a diagnostic device 62 for making a diagnosis of the trailer system 61.

The trailer system 61 is a typical vehicle control system that uses a CAN bus to enable real-time data communication between a plurality of functional nodes within the trailer. In general, all data structures required for vehicle control, such as throttle control, etc., are transmitted on the CAN bus.

The diagnostic device 62 is a data information reading device used during a fault maintenance or service. The diagnostic device 62 may communicate with a CAN bus within the trailer system 10 via a communication interface provided by the trailer system 61 to obtain relevant data information transmitted on the bus to assist in completing a diagnosis of a vehicle fault.

As shown in fig. 6, the CAN circuit structure disclosed in the above embodiment is applied to the diagnostic device 62, and includes a clamp circuit 621, a CAN transceiver 622, a signal isolation circuit 623, a CAN controller 624, and a power supply circuit 625.

The diagnostic device establishes a connection with the CAN bus of the trailer system 61 through a connection interface extending from the clamp 621, and reads one or more associated vehicle information transmitted in the CAN bus via the CAN transceiver 622, the CAN controller 624, and the like.

Of course, the diagnostic device 62 may also add or subtract one or more functional modules as may be desired in the actual situation. For example, the diagnostic device may be provided with control keys for receiving control instructions from a user, or a portable power source such as a lithium battery may be provided to power the entire diagnostic device 62.

In the present embodiment, although the CAN bus in the trailer system 61 uses a specific version of CAN protocol such as 24V or 12V trailers. However, the diagnostic device 62 may still use a relatively low cost, more commercially available CAN receivers that meet the common standard as converters for differential signals to receive and transmit differential signals that meet a particular version of the CAN protocol.

In this embodiment, since there is a specific CAN circuit structure design, the manufacturing cost of the diagnostic device CAN be effectively reduced and the need for a special CAN receiver CAN be reduced.

In particular, the diagnostic device 20 may use a diagnostic device that is applied to vehicle device diagnostics of a 24V trailer system. The device is connected into a CAN bus of the 24V trailer through the CAN circuit structure to carry out relevant equipment diagnosis operation. The CAN transceiver provided in the diagnostic device 20 is a CAN transceiver chip that satisfies ISO11898 of a general standard.

Those skilled in the art will further appreciate that the individual steps of an exemplary CAN circuit network described in connection with the embodiments disclosed herein CAN be implemented as electronic hardware, computer software, or combinations of both, and that the individual exemplary components and steps have been described generally in terms of functionality in the foregoing description to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the solution.

Those skilled in the art may implement the described functionality using different approaches for each particular application, but such implementation is not intended to be limiting. The computer software may be stored in a computer readable storage medium, and the program, when executed, may include the flow of the embodiments of the methods described above. The storage medium may be a magnetic disk, an optical disk, a read-only memory, a random access memory, or the like.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; the technical features of the above embodiments or in the different embodiments may also be combined within the idea of the invention, the steps may be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims (9)

1. A CAN circuit structure comprising:

a pair of data buses, wherein differential signals are transmitted on the data buses;

the CAN transceiver is used for receiving and transmitting the differential signals and is connected with the data bus; the first voltage domain consists of a first grounding end and a first working voltage;

The clamping circuit is arranged between the CAN transceiver and the data bus and used for clamping the low level of the differential signal so as to enable the voltage difference of the differential signal to be matched with the CAN transceiver;

a CAN controller operating in a second voltage domain, the CAN controller is connected with the CAN transceiver and is used for communicating with the CAN transceiver; the second voltage domain consists of a second grounding end and a second working voltage;

The signal isolation circuit is arranged between the CAN transceiver and the CAN controller and is used for isolating the first voltage domain and the second voltage domain;

the clamping circuit is used for limiting the low level of the differential signal to the first grounding end; the high level of the differential signal is equivalent to the first working voltage; the second ground terminal is isolated from the first ground terminal.

2. The CAN circuit structure of claim 1, further comprising: and the power supply circuit is used for providing the first voltage domain and the second voltage domain for the CAN transceiver and the CAN controller.

3. The CAN circuit structure of claim 2, wherein the power supply circuit forms the first ground and the second ground isolated from each other and outputs the first operating voltage and the second operating voltage;

the CAN transceiver is respectively connected with the first working voltage and the first grounding end, and the CAN controller is respectively connected with the second working voltage and the second grounding end.

4. The CAN circuit structure of claim 3 wherein the power supply circuit includes an input power supply and an isolated power supply; the input end of the isolation power supply is connected with the input power supply;

the output end of the isolation power supply forms the first working voltage and a first grounding end; the isolation power supply is connected with the CAN transceiver and provides a first working voltage and a first grounding end for the CAN transceiver.

5. The CAN circuit arrangement of claim 4, wherein the power supply circuit further comprises a low dropout linear regulator; the input end of the low-dropout linear voltage regulator is connected with the input power supply;

The output end of the low dropout linear voltage regulator forms a second working voltage and a second grounding end; the low dropout linear regulator is connected with the CAN controller and provides a second working voltage and a second grounding end for the CAN controller.

6. The CAN circuit structure of claim 3, wherein the clamp circuit is comprised of a first diode and a second diode; the pair of data buses consists of a first data line and a second data line;

the positive electrode of the first diode is connected with the first data line, and the positive electrode of the second diode is connected with the second data line; and the cathodes of the first diode and the second diode are connected with the first grounding end.

7. The CAN circuit structure of claim 1, wherein a first connection terminal of the signal isolation circuit is connected to the CAN transceiver and a second connection terminal of the signal isolation circuit is connected to the CAN controller for isolating and converting signals transmitted between the first voltage domain and the second voltage domain.

8. The CAN circuit structure of claim 1, wherein the CAN transceiver is a CAN transceiver that meets a common standard ISO 11898; the differential signal transmitted on the data bus is a CAN signal conforming to the ISO11992 standard.

9. A vehicle diagnostic apparatus, characterized by comprising:

The CAN transceiver is connected with a CAN bus of the vehicle to be detected and used for receiving and transmitting differential signals; the first voltage domain consists of a first grounding end and a first working voltage;

the clamping circuit is arranged between the CAN transceiver and the CAN bus and used for clamping the differential signals;

a CAN controller operating in a second voltage domain, the CAN controller is connected with the CAN transceiver and is used for communicating with the CAN transceiver; the second voltage domain consists of a second grounding end and a second working voltage;

The signal isolation circuit is arranged between the CAN transceiver and the CAN controller and is used for isolating the first voltage domain and the second voltage domain;

a power supply circuit for providing the first voltage domain and the second voltage domain to the CAN transceiver and the CAN controller;

The clamping circuit is used for limiting the low level of the differential signal to the first grounding end; the high level of the differential signal is equivalent to the first working voltage; the second ground terminal is isolated from the first ground terminal.