CAN bus communication circuit based on RS422

Abstract

The utility model provides a CAN bus communication circuit based on RS422, which comprises a master module and a slave module, the master module comprises a first MCU and a first RS422 circuit connected with the first MCU, the slave module comprises a second MCU and a second RS422 circuit connected with the second MCU, the CAN bus communication protocol is realized by using the RS422 interface circuit, the advantages of the CAN bus and the RS422 are integrated, and the CAN bus communication circuit based on the RS422 has the advantages of being simple in structure and convenient to use. On the basis of ensuring the communication rate and the success rate, the active alarm of the slave is realized, the use condition is stable and reliable, the design requirement is met, the master module or the slave module can initiate communication actively at will in the communication process of the master module and the slave module, the required bus conflict arbitration and conflict avoidance functions are realized by CAN module hardware of the MCU, and the bus conflict arbitration and conflict avoidance functions are realized by the CAN module hardware of the MCU. And additional consideration is not needed.

Description

Technical Field

[0001] The utility model relates to the field of CAN bus communication technology, more specifically to the field of CAN bus communication technology. Background Art

[0002] Controller Area Network (CAN) is a serial communication protocol bus for real-time applications. It can use twisted pair cables to transmit signals and is one of the most widely used field buses in the world. The CAN protocol is used for communication between various components in the car to replace expensive and bulky distribution harnesses. The robustness of the protocol extends its use to other automation and industrial applications. The characteristics of the CAN protocol include complete serial data communication, real-time support, a transmission rate of up to 1Mb / s, and 11-bit addressing and error detection capabilities. The CAN bus uses a serial data transmission method and can run on a 40m twisted pair at a rate of 1Mb / s. It can also be connected using optical cables, and the bus protocol supports multiple master controllers on this bus. However, the existing CAN bus has poor anti-interference ability and is susceptible to electronic interference. Utility Model Content

[0003] The main purpose of the utility model is to solve the above-mentioned problems and provide a CAN bus communication circuit based on RS422.

[0004] The technical solution adopted by the utility model is: a CAN bus communication circuit based on RS422, comprising a master module and a slave module, wherein the master module comprises a first MCU and a first RS422 circuit connected to the first MCU, the slave module comprises a second MCU and a second RS422 circuit connected to the second MCU, the first RS422 circuit has a forward transmitter output, a reverse transmitter output, a forward receiver input, and a reverse receiver input, the second RS422 circuit has a forward receiver input, a reverse receiver input, a forward transmitter output, and a reverse transmitter output, wherein the forward transmitter output of the master module is connected to the forward receiver input of the slave module, the reverse transmitter output of the master module is connected to the reverse receiver input of the slave module, the forward transmitter output of the slave module is connected to the forward receiver input of the master module, and the reverse transmitter output of the slave module is connected to the reverse receiver input of the master module.

[0005] The first RS422 circuit includes a first communication chip, a first transient voltage suppression diode, a second transient voltage suppression diode, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a first magnetic bead inductor, a second magnetic bead inductor, a third magnetic bead inductor and a fourth magnetic bead inductor; the pin of the first communication chip is connected to the CAN_TX pin of the first MCU through the second resistor;

[0006] Pin 1 of the first communication chip is connected to a 5V power supply, a pin of the first communication chip is grounded, pin 2 of the first communication chip is connected to a third resistor, the other end of the third resistor is connected to the 5V power supply, and pin 2 of the first communication chip is also connected to the CAN_RX pin of the first MCU through the first resistor;

[0007] Pin 8 of the first communication chip is connected to the 5V power supply through a fourth resistor, and pin 8 of the first communication chip is also connected to the first magnetic bead inductor, and pin 7 of the first communication chip is grounded through a fifth resistor, the fifth resistor;

[0008] Pin 7 of the first communication chip is also connected to the sixth magnetic bead inductor, the sixth resistor is connected between pin 7 and pin 8 of the first communication chip, the first magnetic bead inductor, the second magnetic bead inductor are connected to the second transient voltage suppression diode, pin 6 of the first communication chip is the reverse transmitter output pin, pin 6 of the first communication chip is connected to the third magnetic bead inductor, pin 5 of the first communication chip is connected to the fourth magnetic bead inductor, and the third magnetic bead inductor, the fourth magnetic bead inductor are connected to the first transient voltage suppression diode.

[0009] The second RS422 circuit includes a second communication chip, a first logic gate chip, a second logic gate chip, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, a fifth magnetic bead inductor, a sixth magnetic bead inductor, a seventh magnetic bead inductor, an eighth magnetic bead inductor, a third transient voltage suppression diode, and a fourth transient voltage suppression diode;

[0010] Pin 1 of the second communication chip is connected to the 5V power supply of the main module, pin 4 of the second communication chip is grounded, pin 2 of the second communication chip is a receiver output pin, pin 2 of the second communication chip is connected to the seventh resistor, and pin 2 of the second communication chip is also connected in parallel to pin 4 of the second logic gate chip;

[0011] Pin 3 of the second communication chip is the transmitter input pin connected to pin 3 of the first logic gate chip, pin 8 of the second communication chip is connected to the eighth resistor, the other end of the eighth resistor is connected to a 5V power supply, and pin 8 of the second communication chip is also connected to the fifth magnetic bead inductor, and pin 7 of the second communication chip is grounded through a ninth resistor;

[0012] Pin 7 of the second communication chip is also connected to the sixth magnetic bead inductor, the tenth resistor is connected to pins 7 and 8 of the second communication chip, the fifth magnetic bead inductor and the sixth magnetic bead inductor are connected to the third transient voltage suppression diode, and pin 6 of the second communication chip is the reverse transmitter output pin connected to the seventh magnetic bead inductor;

[0013] Pin 5 of the second communication chip is connected to the eighth magnetic bead inductor, and the seventh magnetic bead inductor and the eighth magnetic bead inductor are connected to the fourth transient voltage suppression diode.

[0014] The first resistor is a damping resistor, and the resistance value is 100 ohms.

[0015] The second resistor is a damping resistor, and the resistance value is 100 ohms.

[0016] The lead ends of the first magnetic bead inductor, the second magnetic bead inductor, the third magnetic bead inductor and the fourth magnetic bead inductor are respectively the forward receiver input end, the reverse receiver input end, the reverse transmitter output end and the forward transmitter output end of the main module.

[0017] The lead-out ends of the fifth magnetic bead inductor, the sixth magnetic bead inductor, the seventh magnetic bead inductor and the eighth magnetic bead inductor are respectively the forward receiver input end, the reverse receiver input end, the reverse transmitter output end and the forward transmitter output end of the slave module.

[0018] The fifth resistor (R74) is a pull-down resistor with a resistance of 510 ohms.

[0019] The beneficial effects of the utility model are:

[0020] The utility model uses RS422 interface circuit to realize CAN bus communication protocol, combines the advantages of CAN bus and RS422, realizes active alarm of slave machine on the basis of ensuring communication rate and success rate, is safe and reliable in use, and meets the design requirements. In the process of master-slave module communication, the master module or the slave module can actively initiate communication, and the required bus conflict arbitration and conflict avoidance functions are realized by the CAN module hardware of MCU, and no additional consideration is required. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a circuit schematic diagram of the utility model.

[0022] Figure 2 It is a schematic diagram of a first MCU of the present utility model.

[0023] Figure 3 It is a schematic diagram of the circuit principle of the first RS422 of the utility model.

[0024] Figure 4It is a schematic diagram of the second MCU of the present invention.

[0025] Figure 5 A schematic diagram of the circuit principle of the second RS422 of the utility model DETAILED DESCRIPTION

[0026] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0027] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0028] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "leaf flat", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the utility model.

[0029] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present utility model, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0030] See also Figure 1-5 , a CAN bus communication circuit based on RS422 provided by the utility model, comprising a master module (10) and a slave module (20), wherein the master module (10) comprises a first MCU (U3) and a first RS422 circuit (11) connected to the first MCU (U3), and the slave module (20) comprises a second MCU (U5) and a second RS422 circuit (21) connected to the second MCU (U5).

[0031] The first RS422 circuit (11) comprises a first communication chip (U8), a first transient voltage suppressor diode (TVS1), a second transient voltage suppressor diode (TVS2), a first resistor (R11), a second resistor (R12), a third resistor (R13), a fourth resistor (R73), a fifth resistor (R74), a sixth resistor (R49), a first magnetic bead inductor (L5), a second magnetic bead inductor (L6), a third magnetic bead inductor (L7) and a fourth magnetic bead inductor (L8).

[0032] Pin 3 of the first communication chip (U8) is connected to the CAN_TX pin of the first MCU (U3) through the second resistor (R12), and pin 3 is a transmitter input pin. The second resistor (R12) is a damping resistor with a resistance of 100 ohms.

[0033] Pin 1 of the first communication chip (U8) is connected to a 5V power supply (VDD), pin 4 of the first communication chip is grounded (GND), pin 2 of the first communication chip (U8) is a receiver output pin, pin 2 of the first communication chip (U8) is connected to a third resistor (R13), and the other end of the third resistor (R13) is connected to the 5V power supply (VDD). The third resistor (R13) is a pull-up resistor to ensure that pin 2 of the first communication chip (U8) is at a high level when the bus is idle. Pin 2 of the first communication chip (U8) is also connected to the CAN_RX pin of the first MCU (U3) through the first resistor (R11) as an input of the CAN module. The first resistor (R11) is a damping resistor with a resistance of 100 ohms to resist electromagnetic interference.

[0034] Pins 5, 6, 7, and 8 of the first communication chip (U8) correspond to the four bus pins of RS422, wherein pin 8 of the first communication chip (U8) is the in-phase receiver input pin, and pin 7 of the first communication chip (U8) is the reverse receiver input pin. Pin 8 of the first communication chip (U8) is connected to the 5V power supply (VDD) via a fourth resistor (R73), and the resistance value of the fourth resistor is 510 ohms.

[0035] The 8th pin of the first communication chip (U8) is also connected to the first magnetic bead inductor (L5), the first magnetic bead inductor (L5) is for anti-interference, the other end of the first magnetic bead inductor (L5) is directly connected to the external bus, the 7th pin of the first communication chip (U8) is the reverse receiver input pin, and is grounded (GND) through the fifth resistor (R74), the fifth resistor (R74) is a pull-down resistor with a resistance of 510 ohms. The fourth resistor (R73) and the fifth resistor (R74) ensure the voltage difference when the receiving circuit is idle, preventing misjudgment of the received signal;

[0036] Pin 7 of the first communication chip (U8) is also connected to the sixth magnetic bead inductor (L6), the sixth magnetic bead inductor (L6) has an anti-interference effect, and the other end of the sixth magnetic bead inductor (L6) is connected to the external bus. The sixth resistor (R49) is connected between pins 7 and 8 of the first communication chip. The sixth resistor (R49) is a communication matching resistor with a resistance of 120 ohms to prevent the signal from being reflected on the communication line. The first magnetic bead inductor (L5) and the second magnetic bead inductor (L6) are connected to the second transient voltage suppression diode (TVS2), and the second transient voltage suppression diode (TVS2) prevents the chip from being damaged by coupled high-voltage signals on the communication line. Pin 6 of the first communication chip (U8) is a reverse transmitter output pin, and the pin 6 of the first communication chip (U8) is connected to a third magnetic bead inductor (L7), and the third magnetic bead inductor (L7) has an anti-interference function, and the other end is directly connected to an external bus; Pin 5 of the first communication chip (U8) is a forward transmitter output pin, and the pin 5 of the first communication chip (U8) is connected to a fourth magnetic bead inductor (L8), and the fourth magnetic bead inductor (L8) has an anti-interference function, and the other end of the fourth magnetic bead inductor (L8) is directly connected to an external bus; the third magnetic bead inductor (L7) and the fourth magnetic bead inductor (L8) are connected to the first transient voltage suppressor diode (TVS1) to prevent the chip from being damaged by a coupled high-voltage signal on the communication line.

[0037] The lead ends of the first magnetic bead inductor (L5), the second magnetic bead inductor (L6), the third magnetic bead inductor (L7) and the fourth magnetic bead inductor (L8) are respectively the forward receiver input end A, the reverse receiver input end B, the reverse transmitter output end Y and the forward transmitter output end Z of the main module.

[0038] It is worth mentioning that in this embodiment, the signal of the first MCU (U3) is GD32F190C8T6, the model of the second MCU (U3) is M453LG6AE, and the first communication chip (U8) is SP490E.

[0039] The slave module (20) comprises a second MCU (U5) and a second RS422 circuit (11) connected to the second MCU (U5); the second RS422 circuit (21) comprises a second communication chip (U9), a first logic gate chip (U8A), a second logic gate chip (U8B), a seventh resistor (R23), an eighth resistor (R29), a ninth resistor (R32), a tenth resistor (R34), a fifth magnetic bead inductor (L1), a sixth magnetic bead inductor (L2), a seventh magnetic bead inductor (L3), an eighth magnetic bead inductor (L4), a third transient voltage suppressor diode (TVS3) and a fourth transient voltage suppressor diode (TVS4).

[0040] Pin 1 of the second communication chip (U9) is connected to the 5V power supply (VDD) of the above-mentioned main module, pin 4 of the second communication chip (U9) is grounded GND, pin 2 of the second communication chip (U9) is the receiver output pin, pin 2 of the second communication chip (U9) is connected to the seventh resistor (R23), and the seventh resistor (R23) is a pull-up resistor with a resistance of 10k ohms, which ensures that the pin is at a high level when the bus is idle to prevent locking and receiving interruption, and at the same time, pin 2 of the second communication chip (U9) is also connected in parallel to pin 4 of the second logic gate chip (U8B).

[0041] Pin 3 of the second communication chip (U9) is a transmitter input pin connected to pin 3 of the first logic gate chip (U8A); pins 5, 6, 7, and 8 of the second communication chip (U9) correspond to the four bus pins of RS422, wherein pin 8 of the second communication chip (U9) is a common-phase receiver input pin; pin 8 of the second communication chip (U9) is connected to an eighth resistor (R29), which is a pull-up resistor with a resistance of 510 ohms; the other end of the eighth resistor (R29) is connected to a 5V power supply. VDD, and at the same time, the 8th pin of the second communication chip (U9) is also connected to the fifth magnetic bead inductor (L1), the fifth magnetic bead inductor (L1) has an anti-interference effect, and the other end is directly connected to the external bus, the 7th pin of the second communication chip (U9) is the reverse receiver input pin and is grounded (GND) through the ninth resistor (R32), the ninth resistor (R32) is a pull-down resistor with a resistance of 510 ohms, the eighth resistor (R29) and the ninth resistor (R32) ensure the voltage difference when the receiving circuit is idle to prevent misjudgment of the received signal.

[0042] Pin 7 of the second communication chip (U9) is also connected to a sixth magnetic bead inductor (L2), which has an anti-interference function, and the other end of the inductor is connected to an external bus.

[0043] The tenth resistor (R34) is connected to the 7th and 8th pins of the second communication chip (U9). The tenth resistor (R34) is a communication matching resistor with a resistance of 120 ohms to prevent the signal from being reflected on the communication line. The fifth magnetic bead inductor (L1) and the sixth magnetic bead inductor (L2) are connected to the third transient voltage suppressor diode (TVS4). The 6th pin of the second communication chip (U9) is the reverse transmitter output pin and is connected to the seventh magnetic bead inductor (L3). The seventh magnetic bead inductor (L3) has an anti-interference function, and the other end of the inductor is directly connected to the external bus.

[0044] Pin 5 of the second communication chip (U9) is a forward transmitter output pin connected to an eighth magnetic bead inductor (L4), the eighth magnetic bead inductor (L4) has an anti-interference function, and the other end of the eighth magnetic bead inductor (L4) is directly connected to an external bus; the seventh magnetic bead inductor (L3), the eighth magnetic bead inductor (L4) and the fourth transient voltage suppression diode (TVS3) are connected to prevent the chip from being damaged by coupled high-voltage signals on the communication line.

[0045] The lead ends of the fifth magnetic bead inductor (L1), the sixth magnetic bead inductor (L2), the seventh magnetic bead inductor (L3), and the eighth magnetic bead inductor (L4) are respectively connected to the forward receiver input end A1, the reverse receiver input end B1, the reverse transmitter output end Y1, and the forward transmitter output end Z1 of the slave module.

[0046] The forward transmitter output terminal Z of the master module is connected to the forward receiver input terminal A1 of the slave module, the reverse transmitter output terminal Y of the master module is connected to the reverse receiver input terminal B1 of the slave module, the forward transmitter output terminal Z1 of the slave module is connected to the forward receiver input terminal A of the master module, and the reverse transmitter output terminal Y1 of the slave module is connected to the reverse receiver input terminal B of the master module.

[0047] When the main module actively sends a command, the 5th and 6th pins of the first communication chip (U8) send a differential signal, which is sent to the communication line through the Y and Z terminals of the main module. The corresponding communication line is connected to the A1 and B1 terminals of the slave module. After being processed by the second communication chip (U9), the signal is output at its 2nd pin receiver output pin, and is output through the 6th pin of the second logic gate chip (U8B). On the one hand, the output is directly sent to the CAN_RX pin of the first MCU of the main module as the input signal of the CAN module, and the receiving protocol is automatically processed by the hardware module. In addition, the output is also sent through the first Pin 3 of the logic gate chip (U8A) is output to pin 3 of the second communication chip (U9) as the output signal of the transmitter. After being processed by the second communication chip (U9), a differential signal is sent out through its pins 5 and 6. The differential signal is sent to the communication line through the Y1 and Z1 ends of the slave module. The corresponding communication line is connected to the A and B ends of the main module. After being processed by the first communication chip (U8) of the main module, the signal is output at its pin 2 receiver output pin. The signal goes directly to the CAN_RX pin of the first MCU of the main module, completing the closed-loop requirement of self-transmission and self-reception required by the CAN module.

[0048] When the slave module actively initiates communication, the CAN_TX pin of the second MCU sends a signal. There are two pathways for CAN_TX transmission. One pathway is to output the signal to the CAN_RX pin of the second MCU through the 6th pin of the second logic gate chip (U8B), thereby completing the closed-loop requirement of the CAN module for self-transmission and self-reception. The other pathway is to pass through the 3rd pin of the first logic gate chip (U8A) to the 3rd pin of the second communication chip (U9), as the output signal of the transmitter. After being processed by the second communication chip (U9), a differential signal is sent through its 5th and 6th pins. The differential signal is sent to the communication line through the Y1 and Z1 ends of the slave module. The corresponding communication line is connected to the A and B ends of the main module. After being processed by the first communication chip (U8) of the main module, the signal is output at its 2nd pin receiver output pin. The signal is directly sent to the CAN_RX pin of the first MCU of the main module, thereby completing the communication process of the slave module sending the signal and the main module receiving the signal.

[0049] It is worth mentioning that EIA-422 (formerly known as RS-422) is a series of data transmission protocols that stipulate the use of 4-wire, full-duplex, differential transmission, and multi-point communication. It uses balanced transmission and unidirectional / non-reversible transmission lines with or without enable ends. Unlike RS-485, EIA-422 does not allow multiple transmitters but only multiple receivers. In terms of hardware composition, EIA-422 (RS-422) is equivalent to two groups of EIA-485 (RS-485), that is, two half-duplex EIA-485 (RS-485) constitute a full-duplex EIA-422 (RS-422).

[0050] Since the RS-422 four-wire interface uses separate sending and receiving channels, there is no need to control the data direction. Any necessary signal exchange between devices can be done in software (XON / XOFF handshake) or hardware (a pair of separate twisted pairs). The maximum transmission distance of RS-422 is 4000 feet (about 1219 meters), and the maximum transmission rate is 10Mb / s. The length of its balanced twisted pair is inversely proportional to the transmission rate.

[0051] In comprehensive comparison, the advantage of CAN bus is that the communication node can realize multi-master communication, and the following nodes can also actively initiate communication, but the communication rate is relatively low, and from the field test situation, under relatively high-speed communication, there are more communication failures, which affects the response of the equipment; the advantage of RS422 communication is fast speed, the maximum rate can reach 10Mbps, good anti-interference, and the success rate is very high under the communication rate of 1Mbps in industrial environment, and the response speed of the equipment is not affected, but RS422 is a one-master-multiple-slave communication. When the slave device has an alarm message, it cannot be actively sent, and the host can only poll, resulting in a delay in the alarm response. Therefore, the utility model uses the RS422 interface circuit to implement the CAN bus communication protocol, combines the advantages of both CAN bus and RS422, and realizes the active alarm of the slave on the basis of ensuring the communication rate and success rate. The current field use is safe and reliable, and has met the design requirements. In the process of master-slave module communication, the master module or the slave module can be allowed to actively initiate communication. The required bus conflict arbitration and conflict avoidance functions are implemented by the CAN module hardware of the MCU, and no additional consideration is required.

[0052] The embodiment and drawings of the present utility model are only for illustrating the design concept of the present utility model, and the protection scope of the present utility model should not be limited to this embodiment.

[0053] It can be seen from the above description that the design purpose of the utility model can be effectively implemented. The embodiment part shows the purpose of the utility model and the implementation function and structural theme, and includes other equivalent replacements.

[0054] Therefore, the rights of the present utility model include other equivalent implementations, and the specific scope of rights can be found in the claims.

Claims

1. A CAN bus communication circuit based on RS422, characterized in that: The invention comprises a master module and a slave module, wherein the master module comprises a first MCU and a first RS422 circuit connected to the first MCU, the slave module comprises a second MCU and a second RS422 circuit connected to the second MCU, the first RS422 circuit comprises a forward transmitter output, a reverse transmitter output, a forward receiver input, and a reverse receiver input, and the second RS422 circuit comprises a forward receiver input, a reverse receiver input, a forward transmitter output, and a reverse transmitter output, wherein the forward transmitter output of the master module is connected to the forward receiver input of the slave module, the reverse transmitter output of the master module is connected to the reverse receiver input of the slave module, the forward transmitter output of the slave module is connected to the forward receiver input of the master module, and the reverse transmitter output of the slave module is connected to the reverse receiver input of the master module.

2. A CAN bus communication circuit based on RS422 as claimed in claim 1, characterized in that: The first RS422 circuit includes a first communication chip, a first transient voltage suppression diode, a second transient voltage suppression diode, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a first magnetic bead inductor, a second magnetic bead inductor, a third magnetic bead inductor and a fourth magnetic bead inductor; the pin of the first communication chip is connected to the CAN_TX pin of the first MCU through the second resistor; Pin 1 of the first communication chip is connected to a 5V power supply, pin 4 of the first communication chip is grounded, pin 2 of the first communication chip is connected to a third resistor, the other end of the third resistor is connected to the 5V power supply, and pin 2 of the first communication chip is also connected to the CAN_RX pin of the first MCU through the first resistor; Pin 8 of the first communication chip is connected to the 5V power supply through a fourth resistor, and pin 8 of the first communication chip is also connected to the first magnetic bead inductor, and pin 7 of the first communication chip is grounded through a fifth resistor, the fifth resistor; Pin 7 of the first communication chip is also connected to the sixth magnetic bead inductor, the sixth resistor is connected between pin 7 and pin 8 of the first communication chip, the first magnetic bead inductor, the second magnetic bead inductor are connected to the second transient voltage suppression diode, pin 6 of the first communication chip is the reverse transmitter output pin, pin 6 of the first communication chip is connected to the third magnetic bead inductor, pin 5 of the first communication chip is connected to the fourth magnetic bead inductor, and the third magnetic bead inductor, the fourth magnetic bead inductor are connected to the first transient voltage suppression diode.

3. A CAN bus communication circuit based on RS422 as claimed in claim 2, characterized in that: The second RS422 circuit includes a second communication chip, a first logic gate chip, a second logic gate chip, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, a fifth magnetic bead inductor, a sixth magnetic bead inductor, a seventh magnetic bead inductor, an eighth magnetic bead inductor, a third transient voltage suppression diode, and a fourth transient voltage suppression diode; Pin 1 of the second communication chip is connected to the 5V power supply of the main module, pin 4 of the second communication chip is grounded, pin 2 of the second communication chip is a receiver output pin, pin 2 of the second communication chip is connected to the seventh resistor, and pin 2 of the second communication chip is also connected in parallel to pin 4 of the second logic gate chip; Pin 3 of the second communication chip is the transmitter input pin connected to pin 3 of the first logic gate chip, pin 8 of the second communication chip is connected to the eighth resistor, the other end of the eighth resistor is connected to a 5V power supply, and pin 8 of the second communication chip is also connected to the fifth magnetic bead inductor, and pin 7 of the second communication chip is grounded through a ninth resistor; Pin 7 of the second communication chip is also connected to the sixth magnetic bead inductor, the tenth resistor is connected to pins 7 and 8 of the second communication chip, the fifth magnetic bead inductor and the sixth magnetic bead inductor are connected to the third transient voltage suppression diode, and pin 6 of the second communication chip is the reverse transmitter output pin connected to the seventh magnetic bead inductor; Pin 5 of the second communication chip is connected to the eighth magnetic bead inductor, and the seventh magnetic bead inductor and the eighth magnetic bead inductor are connected to the fourth transient voltage suppression diode.

4. A CAN bus communication circuit based on RS422 as claimed in claim 3, characterized in that: The first resistor is a damping resistor, and the resistance value is 100 ohms.

5. A CAN bus communication circuit based on RS422 as claimed in claim 3, characterized in that: The second resistor is a damping resistor, and the resistance value is 100 ohms.

6. A CAN bus communication circuit based on RS422 as claimed in claim 3, characterized in that: The lead ends of the first magnetic bead inductor, the second magnetic bead inductor, the third magnetic bead inductor and the fourth magnetic bead inductor are respectively the forward receiver input end, the reverse receiver input end, the reverse transmitter output end and the forward transmitter output end of the main module.

7. A CAN bus communication circuit based on RS422 as claimed in claim 5, characterized in that: The lead-out ends of the fifth magnetic bead inductor, the sixth magnetic bead inductor, the seventh magnetic bead inductor and the eighth magnetic bead inductor are respectively the forward receiver input end, the reverse receiver input end, the reverse transmitter output end and the forward transmitter output end of the slave module.

8. A CAN bus communication circuit based on RS422 as claimed in claim 3, characterized in that: The fifth resistor (R74) is a pull-down resistor with a resistance of 510 ohms.

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