CAN bus cascade circuit with built-in nodes

Abstract

The utility model relates to the field of CAN buses, and discloses a CAN bus cascade circuit with built-in nodes, which comprises a power supply circuit, a CAN communication circuit, a filter circuit, an impedance matching circuit and a protection circuit, the power supply circuit comprises a VCC5.0 V power supply and a VCC3.3 V power supply, the filter circuit comprises 30pF capacitors C5 and C6, the impedance matching circuit comprises 22 Omega resistors R4 and R5 and a 120 Omega resistor R6, and the protection circuit is connected with the CAN communication circuit. The protection circuit comprises a protection element Q1, the CAN communication circuit is a CAN transceiver U2, and the CAN transceiver U2 comprises eight pins. Compared with the prior art, the main lines are not provided with any doubling connectors, each main line is only provided with plugs at two ends, and large-scale automatic production is facilitated; the design requirements of almost all vehicle types can be met by only needing the length specifications of several main lines, so that the universality of the wire harness is improved; and a node built-in cascade type design is adopted, so that functional nodes can be expanded at will, and the vehicle type design is enriched.

Description

Technical Field

[0001] This utility model relates to the field of CAN bus, specifically a CAN bus cascade circuit with built-in nodes. Background Technology

[0002] CAN bus (CAN bus) is a widely used vehicle networking standard, short for Controller Area Network. It is a serial communication protocol that allows microcontrollers and devices to communicate without a host computer. The CAN bus was originally designed to meet the high-speed data exchange needs between different control units (ECUs) within a vehicle, and it is also widely used in industrial automation, robotics, medical equipment, and other fields.

[0003] The current CAN bus design involves multiple nodes on a single bus, which presents the following problems: each node's branch line needs to be connected in parallel with the main line; the more nodes there are, the more points of wire breakage and connection occur, increasing the probability of line failure; the location of nodes needs to be pre-designed for each vehicle model, resulting in a different wiring harness standard for each model, which is detrimental to the universality of wiring harnesses and indirectly increases inventory; since the number of wiring harness nodes is fixed, the number of functional modules that can be connected on a finished bus is also fixed, which limits functional expansion.

[0004] Therefore, based on the above problems, this utility model provides a CAN bus cascading circuit with built-in nodes. Utility Model Content

[0005] The purpose of this invention is to provide a CAN bus cascading circuit built into a node to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, this utility model provides the following technical solution: a CAN bus cascade circuit built into a node, comprising a power supply circuit, a CAN communication circuit, a filtering circuit, an impedance matching circuit, and a protection circuit. The power supply circuit includes a VCC 5.0V power supply and a VCC 3.3V power supply. The filtering circuit includes 30pF capacitors C5 and C6. The impedance matching circuit consists of 22Ω resistors R4 and R5 and a 120Ω resistor R6. The protection circuit includes a protection element Q1. The CAN communication circuit is a CAN transceiver U2, which has eight pins. Specifically:

[0007] Pin 1 is connected to the CANTX transmit line of the CAN bus;

[0008] Pin 2 is connected to ground;

[0009] Pin 3 is connected to the VCC 3.3V power supply;

[0010] Pin 4 is connected to the CANRX receive line of the CAN bus;

[0011] Pin 5 is connected to the VCC 3.3V power supply;

[0012] Pin 6 is connected to the CANL low-level line of the CAN bus;

[0013] Pin 7 is connected to the CANH high-level line of the CAN bus;

[0014] Pin 8 is connected to a 30pF capacitor C5;

[0015] The 120Ω R6 resistor is connected between the CANL low-level line and the CANH high-level line.

[0016] Furthermore, the CAN transceiver U2 adopts the TJA105X-S08CAN transceiver.

[0017] Furthermore, the protection element Q1 is an SM24CANA-02HTG protection element.

[0018] Furthermore, a 47μF capacitor C3 is connected between the VCC 5.0V power supply and ground, and a 100nF capacitor C4 is connected between the VCC 3.3V power supply and ground.

[0019] Compared with the prior art, the beneficial effects of this utility model are:

[0020] 1. The TJA1050 CAN bus transceiver chip is used to achieve a data transmission speed of 500KBPS. 5V DC power supply is used, and capacitors C3 and C4 are used to stabilize the power supply.

[0021] 2. Q1, C5, and C6 form an anti-interference circuit to ensure stable communication; R6 is the terminating resistor on the CAN bus, which exists only at the first and last nodes of all devices in the vehicle; R4 and R5 protect the CAN transceiver from overcurrent or overvoltage damage, slow down signal edge changes, and improve signal integrity.

[0022] 3. The CANH and CANL lines are designed according to the PCB circuit layout differential communication line routing specifications;

[0023] 4. CANTX and CANRX are connected to the MCU, accept the protocol, and realize the transmission of relevant functional commands of electric vehicles. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the CAN bus connection method of this utility model.

[0025] Figure 2This is a schematic diagram of the CAN bus cascade circuit of this utility model. Detailed Implementation

[0026] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0027] Example 1: Please refer to Figure 1-2 A CAN bus cascade circuit built into a node includes a power supply circuit, a CAN communication circuit, a filtering circuit, an impedance matching circuit, and a protection circuit. Specifically:

[0028] S100: The power supply circuit includes two power supply sections: VCC5.0V and VCC3.3V. The VCC5.0V power supply is grounded through C3 (47μF capacitor), which acts as a filter to provide a stable 5.0V voltage to some components in the circuit. The VCC3.3V power supply is grounded through C4 (100nF capacitor), which is also a filter capacitor to provide a 3.3V operating voltage to components such as CAN transceivers.

[0029] S200: The CAN communication circuit consists of three parts, specifically including:

[0030] S201: Transmitting section: Pin 1 (TXD) of the TJA105X-S08CAN transceiver (U2) is connected to the transmit line (CANTX) of the CAN bus, and is responsible for transmitting the signals that need to be transmitted to the CAN bus;

[0031] S202: Receiver section: Pin 4 (RXD) is connected to the CAN bus receive line (CANRX) to receive signals transmitted from the CAN bus;

[0032] S203: CAN bus interface section: Pin 6 (CANL) and pin 7 (CANH) are connected to the low-level line (CANL) and high-level line (CANH) of the CAN bus, respectively. A 120Ω terminating resistor (R6) is also connected between CANL and CANH to match the line impedance, reduce signal reflection, and ensure signal transmission quality.

[0033] The specific connection relationship of the eight pins of the TJA105X-S08CAN transceiver (U2) is as follows:

[0034] Pin 1 (TXD) is connected to the CAN bus transmit line (CANTX).

[0035] Pin 2 (GND) is connected to ground;

[0036] Pin 3 (VCC) is connected to a 3.3V power supply;

[0037] Pin 4 (RXD) is connected to the CAN bus receive line (CANRX).

[0038] Pin 5 (VIO) is connected to a 3.3V power supply;

[0039] Pin 6 (CANL) is connected to the low-level line (CANL) of the CAN bus.

[0040] Pin 7 (CANH) is connected to the high-level line (CANH) of the CAN bus.

[0041] Pin 8 (S) is connected to a 30pF capacitor (C5).

[0042] S300: The filtering circuit includes 30pF capacitors (C5 and C6) connected to pins 8 and 5 of the CAN transceiver respectively. These capacitors can filter the signal when the transceiver is working, reduce high-frequency noise interference, and make the signal purer.

[0043] S400: The impedance matching circuit consists of R4, R5 (22Ω resistor), and R6 (120Ω resistor). R4 and R5 are used to match the impedance of the CAN transceiver's output and input signals, while R6 is mainly used to match the CAN bus termination impedance, ensuring minimal energy loss during signal transmission and avoiding signal distortion caused by signal reflection.

[0044] S500: The protection circuit uses Q1 (SM24CANA-02HTG protection element), mainly used to protect the CAN bus from electrostatic discharge (ESD) and other electrical interference. In real-world applications, such as automotive electronic systems or industrial control environments, various electrostatic or electromagnetic interferences may exist. This protection element can effectively prevent these interferences from damaging the CAN communication circuit, ensuring the reliability and stability of the circuit.

[0045] Example 2: Based on the circuit schematic in Example 1, perform PCB layout and routing, place each component reasonably on the PCB board, optimize signal paths, and reduce signal interference and transmission delay;

[0046] Special attention should be paid to the wiring of CANH and CANL differential lines, ensuring that the line lengths are equal and the spacing is consistent, following the principles of differential signal wiring to improve signal integrity.

[0047] Two CAN bus sockets are designed on the node device to connect the upstream and downstream node devices. The sockets are positioned to facilitate wiring and connection of the main harness, while not affecting the layout of other components.

[0048] Create PCB prototypes, perform soldering and assembly, and complete the fabrication of node hardware devices.

[0049] Example 3: Design the PCB connection main harness from Example 2, specifically:

[0050] Wire harness definition and selection: Determine the specifications and definition of the main wire harness, using 4-core wire, defined as CANH (yellow), CANL (green), 12V (red) and GND (black), and select wires with appropriate diameter and insulation performance to meet the requirements of current transmission and anti-interference;

[0051] Plug selection and manufacturing: 4-pin plugs are used at both ends of the main harness to ensure that the plugs match the CAN bus sockets on the node equipment. The plug specifications and definitions are exactly the same to facilitate connection and interchange. The quality and reliability standards of the plugs are determined according to system requirements to ensure that the plugs can work stably under multiple plugging and unplugging and different environmental conditions.

[0052] Harness length determination and processing: Based on the actual application scenario, determine the specifications of main harnesses of different lengths. During the processing, accurately cut the wire length to ensure that the plug and wire are firmly connected and well insulated to avoid short circuits or open circuits. Mark and classify the finished main harnesses to facilitate subsequent installation and maintenance.

[0053] Example 4: Node connection and installation using the fabricated PCB board and wire harness, specifically:

[0054] Node Connection: Connect the fabricated node devices sequentially via the main wiring harness to form a cascaded CAN bus network. Starting with the first node, connect its CAN bus socket to one end of the main wiring harness connector. Then connect the other end of the main wiring harness connector to the CAN bus socket of the next node, and so on, until the last node. Ensure the connection is secure and the connector is fully inserted into the socket to avoid poor contact.

[0055] System wiring and securing: Wiring should be done properly in the vehicle or equipment, and the connected node devices and main wiring harnesses should be secured in appropriate positions to avoid the wiring harnesses being squeezed, worn or pulled. Considering electromagnetic compatibility, the CAN bus should be wired separately from other power lines and signal lines to reduce interference. Critical parts should be protected, such as by using wire channels, corrugated pipes or tape to protect the wiring harnesses, to ensure the stability and reliability of the system during long-term use.

[0056] The working principle of the CAN bus cascade circuit built into the node in this utility model is as follows:

[0057] Step 1: Signal Conversion and Transmission

[0058] Transmission process: When data needs to be transmitted, the logic level signal output by the CAN controller is first transmitted to the TXD pin of the TJA105X-S08CAN transceiver. The internal circuit of the transceiver converts these logic levels into differential signals suitable for transmission on the CAN bus. The differential signals are then transmitted to the CAN bus through the CANH and CANL lines. The differential signals represent the data by the voltage difference between the CANH and CANL lines.

[0059] Reception process: When the CAN transceiver receives the differential signal from the CAN bus through the CANH and CANL lines, its internal circuitry decodes the differential signal and converts it into logic data. Then, it sends the logic data to the CAN controller for further processing through the RXD pin.

[0060] Step Two: Control of Sending and Receiving Process

[0061] The TJA105X-S08CAN transceiver contains internal logic circuitry for precise control of data transmission and reception. For example, it samples, sends, and receives signals at appropriate times according to the rules of the CAN protocol, ensuring the correct transmission order and time synchronization of data on the CAN bus. When the CAN controller needs to send data, the transceiver, under the control of the logic circuitry, accurately converts the logic level output by the controller into the differential level of the CAN bus and sends it out through the CANH and CANL lines at the appropriate time. When receiving data, the transceiver, also under the control of the logic circuitry, decodes the differential signal on the CAN bus and converts it into logic data, then sends it to the CAN controller in a timely manner.

[0062] Step 3: Bus Status Management

[0063] The CAN bus has two states: dominant and recessive. In the dominant state, specific circuits inside the TJA105X-S08 CAN transceiver are turned on, causing the voltage on the CANH line to rise and the voltage on the CANL line to fall, thus creating a voltage difference between CANH and CANL, representing logic 0. When the bus is in the recessive state, these circuits are turned off, CANH and CANL are in a passive state, and the voltage difference is 0, representing logic 1. This mechanism ensures that data on the bus can be transmitted correctly and that multiple nodes can coordinate data transmission and avoid collisions by monitoring the bus status.

[0064] Step 4: Rate and Frame Management

[0065] The TJA105X-S08CAN transceiver is also responsible for managing data transmission and reception based on the configured communication rate and frame ID. The microcontroller or other control device will pre-configure the required communication parameters and instruct the transceiver to perform the corresponding operations. The transceiver generates or parses CAN frames based on these parameters to ensure that data is transmitted on the bus at the correct rate and format, thereby achieving effective communication between different nodes.

[0066] The above description is only a preferred embodiment of the present utility model, but the protection scope of the present utility model is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art within the technical scope disclosed in the present utility model, based on the technical solution and the inventive concept of the present utility model, should be included within the protection scope of the present utility model.

Claims

1. A CAN bus cascade circuit built into a node, characterized in that: It includes a power supply circuit, a CAN communication circuit, a filtering circuit, an impedance matching circuit, and a protection circuit. The power supply circuit includes a VCC 5.0V power supply and a VCC 3.3V power supply. The filtering circuit includes capacitors C5 and C6. The impedance matching circuit consists of resistors R4, R5, and R6. The protection circuit includes a protection element Q1. The CAN communication circuit is a CAN transceiver U2, which has eight pins. Specifically: Pin 1 is connected to the CANTX transmit line of the CAN bus; Pin 2 is connected to ground; Pin 3 is connected to the VCC 3.3V power supply; Pin 4 is connected to the CANRX receive line of the CAN bus; Pin 5 is connected to the VCC 3.3V power supply; Pin 6 is connected to the CANL low-level line of the CAN bus; Pin 7 is connected to the CANH high-level line of the CAN bus; Pin 8 is connected to a capacitor C5; The 120Ω R6 resistor is connected between the CANL low-level line and the CANH high-level line.

2. The CAN bus cascade circuit built into a node according to claim 1, characterized in that: The CAN transceiver U2 is a TJA105X-S08CAN transceiver.

3. The CAN bus cascade circuit built into a node according to claim 1, characterized in that: The protection element Q1 is an SM24CANA-02HTG protection element.

4. The CAN bus cascade circuit built into a node according to claim 1, characterized in that: A 47μF capacitor C3 is connected between the VCC 5.0V power supply and ground, and a 100nF capacitor C4 is connected between the VCC 3.3V power supply and ground.

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