Master-slave communication circuit and method for constructing ring network based on RS485 bus

Abstract

The invention relates to a master-slave communication circuit and method for constructing a ring network based on an RS485 bus, and belongs to the technical field of communication, and the master-slave communication circuit forms the ring network by a host and a plurality of slaves. The host is provided with an RS485 port 1 and an RS485 port 2, the slaves are sequentially connected end to end to form a ring, the head end is connected with the host port 1, and the tail end is connected with the port 2. And the slave circuit comprises two RS485 driving chips, two groups of AB ends are respectively connected in series with the bus, and T / R ends are respectively connected with IO1 / IO2 of the MCU. The RXD1 / RXD2 of the MCU is connected with the RO ends of the two chips, and the TXD1 / TXD2 of the MCU is connected with the DI ends of the two chips. The circuit comprises four diodes, wherein the cathode of D1 is connected with a connection point of RXD1 and RO, and the anode of D1 is connected with a connection point of TXD2 and DI; the cathode of D2 is connected with the RXD2 and RO connection point, and the anode of D2 is connected with the TXD1 and DI connection point; the cathode of D3 is connected with TXD1, and the anode is connected with the connection point of TXD1 and DI; the cathode of D4 is connected with the TXD2, and the anode is connected with the connection point of the TXD2 and the And one ends of the two resistors R1 and R2 are connected with VCC, and the other ends are respectively connected with the two DI ends. The method has the advantages that when the bus breaks down, normal operation of the system is not affected, and the communication distance of the bus is prolonged.

Description

Technical Field

[0001] This application relates to the field of communication technology, and in particular to a master-slave communication circuit and method for constructing a ring network based on an RS485 bus. Background Technology

[0002] In numerous fields such as industrial automation, building automation, and environmental control, data communication needs are widespread, with high requirements for communication reliability, anti-interference capabilities, and transmission distance. The RS485 bus, as a commonly used serial communication interface, possesses strong anti-interference capabilities due to its balanced transmission and differential reception, enabling long-distance data communication. Therefore, it is widely used in communication scenarios between multiple devices.

[0003] Traditional master-slave communication networks based on the RS485 bus typically employ either a bus or star topology. In a bus topology, all slave devices are connected to the master via a single bus. The master controls bus communication and data transmission, while the slaves receive and respond to the master's commands. A star topology connects the slave devices to the master via additional devices.

[0004] Regardless of whether it's a bus or star topology, since communication between slave devices relies on the same bus or is relayed through other devices, a failure in one part will affect the communication of all related devices. Therefore, if a fault occurs in any part of the bus, such as a short circuit or open circuit, it may paralyze the entire network. Moreover, due to the transmission characteristics of the RS485 bus itself, the communication distance between two adjacent nodes is limited. To ensure communication quality, the communication speed often needs to be reduced over long distances, which to some extent limits the system's performance and application scope. Summary of the Invention

[0005] In order to ensure that the normal operation of the system is not affected when the bus fails, and to extend the communication distance of the bus without reducing the communication speed, this application provides a master-slave communication circuit and method for constructing a ring network based on RS485 bus.

[0006] In a first aspect, this application provides a master-slave communication circuit based on an RS485 bus to construct a ring network, employing the following technical solution: A master-slave communication circuit for building a ring network based on an RS485 bus includes: The host includes RS485 port 1 and RS485 port 2; Multiple slave devices are configured and connected to a ring network composed of RS485 port 1 and RS485 port 2, connected end to end in sequence; RS485 port 1 is connected to the beginning of the first slave device, and RS485 port 2 is connected to the end of the last slave device. The slave device's circuitry includes: There are two RS485 driver chips, each with an A terminal, a B terminal, an RO terminal, a DI terminal, and a T / R terminal. The A and B terminals are the bus interface, the RO terminal is the TTL data output of the RS485 driver chip, the DI terminal is the TTL data input of the RS485 driver chip, and the T / R terminal is the control terminal. The A and B terminals of the two RS485 driver chips are connected to the RS485 bus in a serial manner. The microprocessor (MCU) includes IO1, IO2, RXD1, TXD1, TXD2, and RXD2 terminals. IO1 and IO2 are connected to the T / R terminals of two RS485 driver chips, respectively. RXD1 is connected to the RO terminal of one RS485 driver chip, RXD2 is connected to the RO terminal of another RS485 driver chip, TXD1 is connected to the DI terminal of one RS485 driver chip, and TXD2 is connected to the DI terminal of another RS485 driver chip. There are four diodes. The cathode of the first diode D1 is connected to the connection point between the RXD1 terminal and the R0 terminal of the first RS485 driver chip, and the anode is connected to the connection point between the TXD2 terminal and the DI terminal of the second RS485 driver chip. The cathode of the second diode D2 is connected to the connection point between the RXD2 terminal and the R0 terminal of the second RS485 driver chip, and the anode is connected to the connection point between the TXD1 terminal and the DI terminal of the first RS485 driver chip. The cathode of the third diode D3 is connected to the TXD1 terminal, and the anode is connected to the connection point between the TXD1 terminal and the DI terminal of the first RS485 driver chip. The cathode of the fourth diode D4 is connected to the TXD2 terminal, and the anode is connected to the connection point between the TXD2 terminal and the DI terminal of the second RS485 driver chip. There are two resistors: one end of the first resistor R1 and the second resistor R2 are both connected to the power supply VCC, and the other end is connected to the corresponding DI terminal.

[0007] By adopting the above technical solution, when the 485 data stream flows from the first RS485 driver chip IC1 to the second RS485 driver chip IC2, IC1 is in the receiving state and IC2 is in the transmitting state. The RO terminal of IC1 outputs TTL serial data, which can be directly received by the serial interface RXD1 of the microprocessor MCU. The circuit composed of the second resistor R2 and the first diode D1 simultaneously inputs this data signal to the DI terminal of IC2. This realizes that the 485 signal input from the IC1 terminal is retransmitted by IC2 without delay and is also received by the local microprocessor MCU. This enables the 485 communication at the back end of IC2 to be redriven, enhances the communication driving capability, and reduces the possibility of interference. When the 485 data stream flows from IC2 to IC1, IC2 is in receive mode and IC1 is in transmit mode. IC2's RO terminal outputs TTL serial data, which can be directly received by the microprocessor MCU's serial interface RXD2. Simultaneously, this data signal, formed by the first resistor R1 and the second diode D2, is input to IC1's DI terminal. This achieves the 485 signal input from IC2 being retransmitted by IC1 without delay and received by the local microprocessor MCU. This allows the 485 communication behind IC1 to be re-driven, enhancing communication drive capability and reducing the possibility of interference. Through the above circuit, bidirectional drive of the 485 bus is achieved, and the RS485 buses at both ends are isolated in the circuit. A line fault at one end of the slave device does not affect the communication at the other end, thus preventing a paralyzing impact on the entire ring network communication. Each slave device has the ability to re-drive RS485, greatly increasing the communication distance between adjacent nodes, enhancing anti-interference capability, and maintaining the communication speed unchanged or without needing to reduce speed.

[0008] Secondly, this application provides a master-slave communication method for constructing a ring network based on an RS485 bus, employing the following technical solution: A master-slave communication method for constructing a ring network based on an RS485 bus includes: In normal operating mode, RS485 port 2 of the host receives the inspection command sent by RS485 port 1. The inspection command is used to address the slave. At this time, RS485 port 1 of the host is in active transmission state, the first RS485 driver chip of all slaves is in receiving state, and the second RS485 driver chip is in transmission state. The RXD1 terminal of the slave receives the bus information of the first RS485 driver chip, and outputs the response information from the TXD2 terminal of the second RS485 driver chip according to the communication protocol. If the slave machine can continuously receive the inspection instruction of RS485 port 1 within the time T2, all slave machines in the same situation will be kept in the original state, that is, the first RS485 driver chip is set to receive, and the second RS485 driver chip is set to transmit, so as to receive the information sent by the host RS485 port 1; If the slave machine fails to continuously receive the inspection instruction of the host RS485 port 1 within the time T2, all slave machines in the same situation will be switched to the first RS485 driver chip being set to transmit and the second RS485 driver chip being set to receive, so as to receive the information sent by the host RS485 port 2; When the RS485 port 2 fails to receive the inspection instruction of the RS485 port 1 within the time T1, the host switches from the normal working mode to the abnormal working mode, and the abnormal working mode is characterized in that both the RS485 port 1 and the RS485 port 2 can independently and actively send and receive information; T2 is less than T1.

[0009] By adopting the above technical solution, if there is a short circuit or open circuit in a certain place of the ring network, the host RS485 port 2 cannot receive the inspection instruction sent by the RS485 port 1. After multiple judgments through the T1 delay time, the host determines that there is an abnormality in a certain place of the ring network. Because the slave machine circuit has a bus isolation function, the line with a short circuit or open circuit fault will not affect the communication of other normally working lines. That is, the original ring network forms two independent networks due to the problem of the fault point, and will not be paralyzed as a whole once the line is short-circuited like a traditional network. The host changes from the normal working mode where RS485 port 1 sends and RS485 port 2 receives to the abnormal working mode, that is, both RS485 port 1 and RS485 port 2 can independently and actively send and receive. That is, the two 485 ports of the host respectively manage two independent networks and communicate with and control the slave machines on the two networks respectively. When the system is normal, the state of each slave machine is that IC1 receives and IC2 transmits. If the slave machine still continuously receives the inspection instruction of the host RS485 port 1 within the time T2, it means that the slave machine is in front of the line fault point, then all slave machines in this situation still remain in the original state, that is, IC1 receives and IC2 transmits. If the slave machine fails to continuously receive the inspection instruction of the host RS485 port 1 within the time T2, it means that the slave machine is behind the line fault point, then all slave machines in this situation are switched to IC1 transmitting and IC2 receiving, so as to receive the information sent by the host RS485 port 2, thereby splitting the ring network into two independent networks from the fault point and respectively receiving the inspection and control of the host RS485 port 1 and RS485 port 2. Since the time T2 < T1, the slave machine first switches the transmission direction of the 485 bus, and then the host sends the inspection instruction to ensure that the inspection instruction sent by the host can be received by the slave machine, so as to continuously maintain network communication.

[0010] Optionally, after the host switches from normal working mode to abnormal working mode, the host sends a protocol change command from RS485 port 1 and RS485 port 2 respectively, so that the slave can determine the direction of the response information.

[0011] By adopting the above technical solution, each slave device can be notified of network anomalies and the response data flow can be modified accordingly.

[0012] Optionally, the master-slave communication method further includes: All slave devices monitor the communication protocol sent by the master and monitor the network anomaly status bit. When the network anomaly status bit is valid, all slave devices that receive the inspection command sent by RS485 port 1 will set IC1 to transmit state and IC2 to receive state after the master finishes sending a frame of communication data, so that the slave device's response information flows to RS485 port 1. All slave devices that receive information sent from RS485 port 1, after responding according to the communication protocol, will set IC1 to receive mode and IC2 to transmit mode within a preset time, so as to receive the next communication command sent by the host RS485 port 1. When the network abnormal status bit is valid, all slave devices that receive inspection commands sent by RS485 port 2 will set IC1 to receive mode and IC2 to transmit mode after the master finishes sending a frame of communication data, so that the slave device's response information flows to RS485 port 2. All slave devices receiving information from RS485 port 2, after responding according to the communication protocol, will set IC1 to transmit mode and IC2 to receive mode within a preset time, so as to receive the next communication command sent by the host RS485 port 2.

[0013] By adopting the above technical solution, all slave information streams at the front end of the network line fault point are transmitted from the second RS485 driver chip IC2 to the first RS485 driver chip IC1, thereby transmitting slave response information to the host's RS485 port 1; and all slave information streams at the back end of the network line fault point are transmitted from the first RS485 driver chip IC1 to the second RS485 driver chip IC2, thereby transmitting slave response information to the host's RS485 port 2. The slaves on both sides of the fault point are adapted to RS485 bus communication in different directions. Through the host's control of RS485 ports 1 and 2, they respectively inspect the RS485 buses they manage, achieving inspection and control communication with normally functioning slaves unaffected by the fault.

[0014] Optionally, the master-slave communication method further includes: In abnormal working mode, the host RS485 port 1 and RS485 port 2 obtain relevant data of the slave device that is communicating normally through inspection commands; The slave address code in the relevant data is compared with the internally preset slave address list. If there is a slave address code that is not obtained by either RS485 port 1 or RS485 port 2, the slave corresponding to the slave address code that is not obtained is determined to be faulty and an alarm is triggered.

[0015] Optionally, the step of comparing the slave address code in the relevant data with the internally preset slave address list further includes: If the composition of the slave address code obtained by RS485 port 1 and RS485 port 2 matches the slave address list, then RS485 port 1 and RS485 port 2 will determine the slave immediately adjacent to the fault point based on the number of response messages received by the slave from other slaves. The number of response messages received by the slave immediately adjacent to the fault point from other slaves is 0. The fault location is determined based on the physical location corresponding to the address code of the slave device immediately adjacent to the fault point, and an alarm is triggered.

[0016] By adopting the above technical solution, in abnormal operating mode, slave control IC1 and IC2 are in different receiving and transmitting states, resulting in unidirectional network communication. Slave devices responding to RS485 port 1 of the host can only transmit data to RS485 port 1 of the host, and cannot transmit in the reverse direction. For example, information from slave 3's response bus is received by the host and slaves 1 and 2; information from slave 2's response bus is received by the host and slave 1; information from slave 1's response bus cannot be received by any slave device other than the host. That is, slave 1 can receive response information from slaves 2 and 3, slave 2 can receive response information from slave 3, but slave 3 cannot receive response information from any other slave device. The number of other slave response messages each slave can receive is sent to the host. The slave device with the largest number of other slave response messages received is closest to the host, and the slave device with a value of 0 receiving other slave response messages is farthest from the host, i.e., closest to the fault point. The same principle applies to RS485 port 2 on the host. Using the same processing method, the slave address number closest to the fault point on the RS485 port 2 bus side can be found. This method clarifies the order of each slave address code in the ring network (not necessarily the installation order of the slaves), and also identifies the address codes of the two slaves adjacent to the fault point. The host displays this information, and based on the specific physical location corresponding to the address code, the fault location is found for manual intervention.

[0017] Optionally, the master-slave communication method further includes: After the host computer identifies the fault point, it sends control commands to the slave computers on both sides of the fault point. After receiving control commands, the slave devices on both sides of the fault point set the RS485 interface closest to the fault point to receive mode.

[0018] By adopting the above technical solution, it is possible to avoid the slave device sending information to the fault point. In particular, for short circuit faults, it is possible to avoid damage to adjacent RS485 chips caused by external line short circuit faults, thus achieving the isolation of the fault point.

[0019] Optionally, the master-slave communication method further includes: The slave devices on both sides of the fault point periodically send preset communication data for detecting fault recovery in the direction of the fault point; If both slave devices on either side of the fault point can receive the communication data sent by the other, then when the slave devices on either side of the fault point are inspected by the master again, they will send the fault clearing status information to the master. After receiving the fault clearing status information, the host sends a communication command to notify all slave devices on both sides of the fault point to resume normal communication mode.

[0020] By adopting the above technical solution, the slave device on the fault point side can receive a preset data frame from the direction of the fault point for detecting fault recovery, which means that the line fault has been eliminated. When the master inspects each slave device, especially the slave devices on both sides of the original fault point, the slave device sends the detected fault elimination status to the master, and the master knows that the original line fault has been eliminated.

[0021] Optionally, the period for the slave devices on both sides of the fault point to send communication data for detecting fault recovery is randomly adjusted. The adjustment step is n milliseconds, the random multiple is m, and the value of m is randomly adjusted each time. That is, the communication period is randomly differed by n·m milliseconds each time. The ratio of the time for the slave device to send the communication data to the time of the sending period is p:q, where p is less than q and q is at least 200p.

[0022] By adopting the above technical solution, the possibility of two slave devices simultaneously sending fault recovery data to each other is fully avoided, and the shorter communication time also avoids the impact on the communication circuit when the short circuit fault still exists; the random adjustment of the transmission cycle further avoids the possibility of two slave devices simultaneously sending information to each other.

[0023] In summary, this application includes at least one of the following beneficial technical effects: 1. In a ring network built on an RS485 bus, a short circuit or open circuit at any point in the line will not affect the normal operation of the system; 2. Each slave unit is an isolator and signal driver, which can isolate the 485 communication on both sides of the slave unit as needed, so that they do not interfere with each other; it can redrive the 485 signal passing through the slave unit, so that the driving capability between two adjacent slave units is strong and the anti-interference is strong. While maintaining the normal speed, the communication distance between two slave units can exceed 1000 meters, which can extend the distance of the entire ring network. The more slave units there are, the longer the ring bus distance becomes. 3. Automatically identify the location of the fault point and issue an alarm on the host to facilitate manual handling, and automatically determine the position order of each slave unit in the ring network; 4. The system automatically resumes normal operation after the fault is resolved, which improves the intelligence of the system. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the ring network architecture of this application; Figure 2 This is the circuit diagram of the slave device in this application; Figure 3 This is a first flowchart of an embodiment of the method of this application; Figure 4 This is a schematic diagram of the failure point in the ring network architecture of this application; Figure 5 This is a second flowchart of an embodiment of the method of this application. Detailed Implementation

[0025] To make the purpose, technical solution, and advantages of this application clearer, the following description is provided in conjunction with the appendix. Figure 1-5 The present application will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the application.

[0026] The first embodiment of this application discloses a master-slave communication circuit for constructing a ring network based on an RS485 bus.

[0027] Reference Figure 1 The master-slave communication circuit includes a master unit and slave units. The master unit includes RS485 port 1 and RS485 port 2. Multiple slave units are configured, each with its own independent power supply channel. Each slave unit has two RS485 bus terminals, serially connected to a ring bus formed by RS485 ports 1 and 2. Multiple slave units are connected sequentially end-to-end. RS485 port 1 is connected to the beginning of the first slave unit, and RS485 port 2 is connected to the end of the last slave unit. The red lines in the diagram represent the information flow during normal operation.

[0028] Specifically, refer to Figure 2Each slave device has a unique address code. The slave device's circuitry includes two RS485 driver chips, a microprocessor (MCU), four diodes, and two resistors. Other circuitry unrelated to communication is not shown.

[0029] Both RS485 driver chips include A, B, RO, DI, and T / R terminals; the AB terminals (A and B) are bus interfaces, the RO terminal is the TTL data output of the RS485 driver chip, the DI terminal is the TTL data input of the RS485 driver chip, and the T / R terminal is the control terminal for easy communication with the microprocessor MCU; the AB terminals of the two RS485 driver chips are connected to the RS485 bus in a serial manner.

[0030] One RS485 driver chip is represented by IC1, and the other RS485 driver chip is represented by IC2; the specific models are not limited. The microprocessor (MCU) is represented by IC3, which has dual serial ports and can control the communication direction of the two RS485 chips, i.e., whether it is in transmit or receive mode, so as to determine whether the slave response information is sent from the IC1 side or the IC2 side.

[0031] IC3 includes IO1, IO2, RXD1, TXD1, TXD2, and RXD2 terminals. IO1 and IO2 are connected to the corresponding T / R terminals of IC1 and IC2, respectively. RXD1 is connected to the RO terminal of IC1, RXD2 is connected to the RO terminal of IC2, TXD1 is connected to the DI terminal of IC1, and TXD2 is connected to the DI terminal of IC2.

[0032] All four diodes are germanium diodes, which facilitates clamping the potential to 0.3V to achieve a logic low level. The cathode of the first diode D1 is connected to the junction of RXD1 and R0 of IC1, and the anode is connected to the junction of TXD2 and DI of IC2; the cathode of the second diode D2 is connected to the junction of RXD2 and R0 of IC2, and the anode is connected to the junction of TXD1 and DI of IC1; the cathode of the third diode D3 is connected to TXD1, and the anode is connected to the junction of TXD1 and DI of IC1; the cathode of the fourth diode D4 is connected to TXD2, and the anode is connected to the junction of TXD2 and DI of IC2.

[0033] Both resistors are pull-up resistors to achieve a logic high level. One end of the first resistor R1 and the second resistor R2 are both connected to the power supply VCC, and the other end is connected to the corresponding DI terminal. Each communication interface conforms to the UART communication logic, that is, a logic high level when no data is being transmitted, and communication begins with a low level 0 when data is being transmitted.

[0034] When the 485 data stream flows from IC1 to IC2, IC1 is in receive mode and IC2 is in transmit mode. IC1's RO terminal outputs TTL serial data, which can be directly received by IC3's serial interface RXD1. Simultaneously, this data signal, formed by the second resistor R2 and the first diode D1, is input to IC2's DI terminal. This enables the 485 signal input from IC1 to be retransmitted by IC2 without delay and also received by IC3. Consequently, the 485 communication at the IC2 backend is re-driven, enhancing communication driving capability and reducing the possibility of interference. Figure 2 The arrows in the diagram indicate the direction of the data flow for ease of understanding.

[0035] When the 485 data stream flows from IC2 to IC1, IC2 is in receive mode and IC1 is in transmit mode. IC2's RO terminal outputs TTL serial data, which can be directly received by IC3's serial interface RXD2. The circuit consisting of the first resistor R1 and the second diode D2 simultaneously inputs this data signal to IC1's DI terminal. This enables the 485 signal input from IC2 to be retransmitted by IC1 without delay and also received by IC3. Consequently, the 485 communication at the back end of IC1 is re-driven, enhancing communication driving capability and reducing the possibility of interference.

[0036] The above circuit enables bidirectional driving of the RS485 bus, and the RS485 buses at both ends are isolated in the circuit. That is, a line fault (short circuit or open circuit) at one end of the slave device does not affect the communication at the other end, thus preventing paralysis of the entire ring network communication.

[0037] Based on which serial port received the information, IC3 can determine the origin of the 485 information. RXD1 serial port receives information from the 485 bus on the IC1 side, while RXD2 serial port receives information from the 485 bus on the IC2 side. IC3 can control whether the response information is sent from the 485 bus on the IC1 or IC2 side, depending on the host's operating mode. The receive and transmit states of IC1 and IC2 are controlled by IC3's IO1 and IO2 pins.

[0038] When IC3 outputs serial port response data via TXD1, the data passes through the circuit consisting of the first resistor R1 and the third diode D3 and enters the DI terminal of IC1. The communication direction of IC1 is controlled by IO1, and the data enters the 485 network from IC1.

[0039] When IC3 outputs serial port response data via TXD2, the data passes through the circuit consisting of the second resistor R2 and the fourth diode D4 and enters the DI terminal of IC2. The communication direction of IC2 is controlled by IO2, and the data enters the 485 network from IC2.

[0040] The circuits formed by the second resistor R2 and the first diode D1, the first resistor R1 and the second diode D2, the first resistor R1 and the third diode D3, and the second resistor R2 and the fourth diode D4, as described above, serve to ensure the transmission of serial data streams and the correctness of logic levels. This example only illustrates the circuit formed by the second resistor R2 and the first diode D1; the other circuits function similarly and will not be described further.

[0041] The circuit consisting of the second resistor R2 and the first diode D1 has the following characteristics: When the RO terminal of IC1 outputs a high level, the DI terminal of IC2 is pulled up to VCC by the second resistor R2 and is at a high level; when the RO terminal of IC1 outputs a low level, VCC is injected into the RO terminal of IC1 through the second resistor R2 and the first diode D1. Due to the effect of the first diode D1, the DI terminal of IC2 is clamped to 0.3V, that is, the input of the DI terminal of IC2 is low.

[0042] The fourth diode D4, connected to the second resistor R2 and the first diode D1, is unaffected by the circuit consisting of the first diode D1 and the second resistor R2 because its TXD2 terminal is normally at a high level. In this state, the fourth diode D4 can be considered an open circuit. Under the influence of the second resistor R2 and the first diode D1, the R0 port of IC1 is input to the DI terminal of IC2 correctly and without delay, thus ensuring that the 485 bus information is transmitted correctly and without delay from the IC1 terminal to the IC2 terminal.

[0043] The DI interface of IC2 can receive data from both the DO pin of IC1 and the TXD2 pin of IC3. According to the communication protocol, only one port of both chips is transmitting data at any given time; the port not transmitting data is at a high level. When TXD2 is transmitting data, the first diode D1 isolates the DO pin of IC2, and the data transmitted by TXD2 enters the DI interface of IC2, thus enabling IC2 to transmit data from IC3.

[0044] Furthermore, this ring network based on the R485 bus provides a point-to-point connection between adjacent slave devices via the 485 bus, with no other branch lines. The ABI terminal (the terminal corresponding to the AB terminal of IC1, which can also be understood as the aforementioned start terminal) and ABO terminal (the terminal corresponding to the AB terminal of IC2, which can also be understood as the aforementioned tail terminal) of each slave device can be equipped with matching resistors adapted to 485 communication to enhance anti-interference capabilities. This avoids the need to find suitable locations to add matching resistors on-site, simplifying engineering debugging.

[0045] Based on the above circuit embodiments, the second embodiment of this application discloses a master-slave communication method for constructing a ring network based on an RS485 bus.

[0046] Reference Figure 3 The master-slave communication method includes S110-S140: S110, when the host is in normal working mode, RS485 port 2 receives the inspection command sent by RS485 port 1. The inspection command is used to address the slave. At this time, RS485 port 1 of the host is in active transmission state, the first RS485 driver chip of all slaves is in receiving state, the second RS485 driver chip is in transmission state, the RXD1 terminal of the slave receives the bus information of the first RS485 driver chip, and outputs the response information from the second RS485 driver chip from the TXD2 terminal according to the communication protocol. S120, if the slave device can continuously receive the inspection command of RS485 port 1 within the time T2, then all slave devices with the same situation will maintain their original state, that is, the first RS485 driver chip is set to receive and the second RS485 driver chip is set to transmit, so as to receive the information sent by the master RS485 port 1. S130, if the slave device fails to continuously receive the inspection command from the host RS485 port 1 within the T2 time period, then all slave devices with the same situation will be switched to set the first RS485 driver chip to transmit and the second RS485 driver chip to receive, so as to receive the information sent from the host RS485 port 2. S140, when RS485 port 2 fails to receive the inspection command from RS485 port 1 within time T1, the host switches from normal working mode to abnormal working mode. Abnormal working mode is characterized by RS485 port 1 and RS485 port 2 being able to independently and actively send and receive information; T2 is less than T1.

[0047] Specifically, the host's normal operating mode: Normally, host RS485 port 1 is in active transmission mode, while host RS485 port 2 is in receiving mode. Host RS485 port 2 can receive information transmitted by RS485 port 1, thereby monitoring the integrity of the ring network.

[0048] All slave ICs are in receive mode (IC1) and transmit mode (IC2), meaning that RS485 communication information travels from the ABI to the ABO without delay. From the perspective of the ring network, the information flow originates from the master's RS485 port 1 and smoothly reaches RS485 port 2. Slave IC3 receives bus information from the ABI at its RXD1 pin and outputs response information from the ABO pin at its TXD2 pin according to the communication protocol. In this way, the master's RS485 port 2 can also receive data from each responding slave and then process the received data accordingly based on the communication protocol.

[0049] The host's RS485 port 1 sends a frame of communication instruction to address a slave. The addressed slave responds to the information on the bus, which is received by RS485 port 2, and then the host sends the addressing communication instruction for the next address through RS485 port 1, repeating this process. Once RS485 port 2 cannot receive the information from RS485 port 1, it indicates that there is an open or short circuit at a certain node in the ring network, or a certain slave has a fault.

[0050] Host abnormal working mode: If there is a short or open circuit in a certain part of the ring network, the host's RS485 port 2 cannot receive the information sent by RS485 port 1. After multiple judgments with the delay time T1, the host determines that there is an abnormality in a certain part of the ring network. Because the slave has a bus isolation function, the faulty line with a short or open circuit will not affect the communication of other normal lines, that is, the original ring network forms two independent networks due to the problem of the fault point.

[0051] The host changes from the normal working mode where RS485 port 1 sends and RS485 port 2 receives to the abnormal working mode, that is, both 485 ports can independently send and receive actively. That is, the two 485 ports of the host respectively manage two independent networks and communicate with and control the slaves on the two networks respectively.

[0052] Normally, the status of each slave is that IC1 receives and IC2 sends. If a slave still continuously receives the inspection instruction from the host's RS485 port 1 within the time T2, it means that this slave is in front of the line fault point, and all slaves in this situation still maintain the original state, that is, IC1 receives and IC2 sends. If a slave does not continuously receive the inspection instruction from the host's RS485 port 1 within the time T2, it means that this slave is behind the line fault point, and all slaves in this situation switch to IC1 sends and IC2 receives, so as to receive the information sent by the host's RS485 port 2. In this way, the ring network is divided into two independent networks from the fault point and is respectively inspected and controlled by the host's RS485 port 1 and RS485 port 2. This fault point also includes the situation of a certain slave's own fault.

[0053] The above time T2 < T1, that is, the slave first switches the transmission direction of the 485 bus, and then the host sends the inspection instruction to ensure that the inspection instructions sent by the two 485 ports of the host can be received by the slave, so as to continue the network communication.

[0054] In addition, after the host switches from normal working mode to abnormal working mode, the host sends a protocol change command from RS485 port 1 and RS485 port 2 respectively to indicate that the ring network is abnormal, so that each slave can be aware of the network abnormality and make changes to the response data flow.

[0055] Furthermore, the master-slave communication method also includes: All slave devices monitor the communication protocol sent by the master device and monitor the network anomaly status bits within it.

[0056] When the network abnormal status bit is valid, all slave devices that receive inspection commands sent by RS485 port 1 will set IC1 to transmit state and IC2 to receive state after the master finishes sending a frame of communication data, so that the slave device's response information flows to RS485 port 1. All slave devices that receive information sent from RS485 port 1, after responding according to the communication protocol, will set IC1 to receive mode and IC2 to transmit mode within a preset time, so as to receive the next communication command sent by the host RS485 port 1. When the network abnormal status bit is valid, all slave devices that receive inspection commands sent by RS485 port 2 will set IC1 to receive mode and IC2 to transmit mode after the master finishes sending a frame of communication data, so that the slave device's response information flows to RS485 port 2. All slave devices receiving information from RS485 port 2, after responding according to the communication protocol, will set IC1 to transmit mode and IC2 to receive mode within a preset time, so as to receive the next communication command sent by the host RS485 port 2.

[0057] Specifically, all slave devices monitor the communication protocol sent by the master and monitor the network anomaly status bit. When the network anomaly status bit is valid, all slave devices that receive the inspection command sent by the master's RS485 port 1 will set IC1 to transmit state and IC2 to receive state after the master finishes sending a frame of communication data. This ensures that the information flow is transmitted from the ABO end to the ABI end and that the slave device that generates the response transmits the data to the master's RS485 port 1.

[0058] All slave devices receiving information from the host's RS485 port 1, after responding according to the communication protocol, will set IC1 to receive mode and IC2 to transmit mode within a preset time to receive the host's next communication command. This achieves communication between all slave devices and the host at the network line fault point. Figure 4 The line fault between slave 3 and slave 4 is shown. RS485 port 1 communicates with slaves 1 to 3, and data information is transmitted in the purple area shown in the figure.

[0059] When the network abnormal status bit is valid, all slave devices receiving inspection commands sent by the host RS485 port 2 will set IC1 to receive mode and IC2 to send mode after the host finishes sending a frame of communication data. This ensures that the information flow is transmitted from the ABI end to the ABO end and that the slave device that generates the response data is transmitted to the host RS485 port 2.

[0060] All slave devices receiving information from the host's RS485 port 2, after responding according to the communication protocol, will set IC1 to transmit mode and IC2 to receive mode within a preset time to receive the host's next communication command. This enables communication between all slave devices behind the network line fault point and the host. Figure 4 The line fault between slave 3 and slave 4 is shown. RS485 port 2 communicates with slave 4 to N, and data information is transmitted in the cyan area shown in the figure.

[0061] Reference Figure 5 The master-slave communication method also includes S210-S250: S210, in abnormal working mode, the host RS485 port 1 and RS485 port 2 obtain relevant data of the slave device that is in normal communication through inspection commands; S220, compare the slave address code in the relevant data with the internally preset slave address list; S230: If there is a slave address code that is not obtained by either RS485 port 1 or RS485 port 2, then the slave corresponding to the slave address code that is not obtained is determined to be faulty and an alarm is triggered. S240, if the composition of the slave address code obtained by RS485 port 1 and RS485 port 2 matches the slave address list, then RS485 port 1 and RS485 port 2 determine the slave immediately adjacent to the fault point based on the number of response information received by the slave from other slaves. The number of response information received by the slave immediately adjacent to the fault point from other slaves is 0. S250 determines the fault location based on the physical location corresponding to the address code of the slave device immediately adjacent to the fault point, and then issues an alarm.

[0062] Specifically, when a ring network transitions from normal operating mode to abnormal operating mode, there are two possible fault scenarios: 1) A short circuit or open circuit occurs between the two slave devices, but each slave device remains normal. 2) The slave device itself is faulty.

[0063] As described above, when transitioning from normal working mode to abnormal working mode, each slave device relies on whether it receives information from RS485 port 1 within the preset T2 delay time to complete the state switch. This allows the slave devices on both sides of the fault point to adapt to 485 bus communication in different directions. By controlling RS485 port 1 and RS485 port 2, inspection and control communication with the normally working slave device can be achieved.

[0064] A line fault caused the ring network to transition from normal operating mode to abnormal operating mode. Initially, the host did not know which slave devices were located before or after the fault point. Each of the host's two RS485 ports performed a complete inspection of all slave devices. Figure 4 For example, RS485 port 1 can obtain relevant data from slave devices 1-3 through inspection commands, but cannot obtain relevant data from slave devices 4-N, meaning slave devices 1-3 are located before the fault point. RS485 port 2 can obtain relevant data from slave devices 4-N through inspection commands, but cannot obtain relevant data from slave devices 1-3, meaning slave devices 4-N are located after the fault point. The master can obtain relevant data information from all slave devices through the two RS485 ports, but this cannot be used to infer that the fault point is located between slave devices 3 and 4, because the slave device address numbers shown in the diagram are not the actual address codes used for communication commands, and the actual address codes do not necessarily have to be arranged in order.

[0065] Therefore, to facilitate manual handling and locate the specific fault point, the following method is adopted: In abnormal operating mode, slave controllers IC1 and IC2 are in different receive and transmit states, resulting in unidirectional network communication. A slave responding to the master's RS485 port 1 can only transmit data to the master's RS485 port 1, and cannot transmit data in the reverse direction. Figure 4 For example, the information from slave 3's response bus is received by the master and slaves 1 and 2; the information from slave 2's response bus is received by the master and slave 1; the information from slave 1's response bus cannot be received by any slave other than the master. In other words, slave 1 can receive response information from slaves 2 and 3, slave 2 can receive response information from slave 3, but slave 3 cannot receive response information from any other slave. The master receives the number of response messages each slave can receive from other slaves. The slave with the highest number of response messages it can receive is closest to the master, and the slave with a value of 0 is farthest from the master, i.e., closest to the fault point.

[0066] The same principle applies to RS485 port 2 on the host. By using the same processing method, we can find the slave address number that is closest to the fault point on the bus side of RS485 port 2.

[0067] This process uses the slave address code in the communication command for judgment, and the final judgment result is also the slave address code. This method clarifies the order of each slave address code in the ring network and identifies the address codes of the two slaves adjacent to the fault point. The host displays this information, and based on the specific physical location corresponding to the address code, the fault location is found for manual intervention.

[0068] In the event of a fault in the slave device itself, the master device's two 485 ports will each scan all slave devices that can communicate normally. By comparing these scans with the master device's internal preset slave device address list, the master device can determine which slave device address is faulty. The master device will then issue an alarm to prompt manual intervention.

[0069] by Figure 4 For example, suppose slave device 4 malfunctions. The master's RS485 port 1 can obtain relevant data from slave devices 1-3 via a check command, but cannot obtain data from slave devices 4-N. This means slave devices 1-3 are located before the fault point. RS485 port 2 can obtain relevant data from slave devices 5-N via a check command, but cannot obtain data from slave devices 1-4. This means slave devices 5-N are located after the fault point. Since neither of the master's two RS485 ports obtains relevant data from slave device 4, it indicates that slave device 4 has malfunctioned. The master will then issue an alarm and await manual intervention.

[0070] Furthermore, after the host computer locates the fault point, it sends control commands to the slave devices on either side of the fault point. Upon receiving these commands, both slave devices cease outputting information to the fault point, effectively setting their RS485 interfaces closest to the fault point to receive mode. This achieves fault isolation, especially effective against short-circuit faults, preventing damage to adjacent RS485 chips from external line short circuits. In other implementations, a 5-10 ohm resistor can be connected in series at each of the A and B output ports of each RS485 chip. This provides some protection against short circuits without affecting bus communication, further delaying damage to the RS485 chips caused by short circuits. This isolation measure is also effective in the event of a line open circuit, ensuring normal system operation.

[0071] For the slave devices located on either side of the fault point, pre-set communication data for detecting fault recovery is periodically sent in the direction of the fault point to monitor when the fault is eliminated. Once both slave devices on either side of the fault point can receive the communication data sent by the other, it indicates that the fault has been eliminated. When these two slave devices are inspected again by the master, they send the fault-cleared status to the master. After confirming that the fault has been cleared, the master sends a communication command to notify all slave devices on both sides of the original fault point to restore normal communication mode.

[0072] by Figure 4 For example, if a fault occurs between slave devices 3 and 4, IC2 of slave device 3 will be in receive mode, and IC1 of slave device 4 will also be in receive mode. Slave devices 3 and 4 will send preset data frames for fault recovery detection to each other at a certain period, such as once every 20 seconds, using the communication rate of a ring network. Because these data frames are short, transmission can be completed within 20ms. Immediately after transmission, the 485 chip on the side of the device closest to the fault point will be set to receive mode to facilitate receiving the data frames for fault recovery detection sent by the other party.

[0073] If the slave device on the fault point side can receive a data frame from the direction of the fault point to detect fault recovery, it means that the line fault has been eliminated. When the master device inspects each slave device, especially the slave devices on both sides of the original fault point, the slave device sends the detected fault elimination status to the master device, and the master device knows that the original line fault has been eliminated.

[0074] In the above process, if both slave devices simultaneously send data to detect fault recovery towards the fault point, neither can correctly receive the data frames sent by the other. To overcome this problem, the ratio of the time spent by the slave device at the fault point sending the data frame for detecting fault recovery to the transmission cycle time is p:q, where p is less than q and q is at least 200p. In this application, the time ratio can be set to 1:1000 to avoid the possibility of both slave devices simultaneously sending fault recovery detection information to each other. Furthermore, the shorter communication time also avoids the impact on the communication circuit when the short-circuit fault still exists.

[0075] To further avoid the possibility of two slave devices simultaneously sending information to each other, the period for the slave device to send data frames for detecting fault recovery is not fixed. The sending period is randomly adjusted each time, with an adjustment step of n milliseconds and a random multiple of m. The value of m is randomly adjusted each time, that is, the communication period is randomly differed by n·m milliseconds each time. In this application, n can be set to 50, and m ranges from 1 to 100, so as to avoid the possibility of both parties sending data to the fault point at the same time as much as possible.

[0076] After manual processing, the host can also be manually reset. The host will resend the communication protocol, with the network abnormal state being invalid. Notification commands will be sent through RS485 port 1 and RS485 port 2 respectively. All slave devices that receive the communication commands will be set to receive with IC1 and send with IC2, and the system will re-enter normal working mode.

[0077] It should be noted that the time and data communication commands mentioned above can be adjusted according to requirements and are not fixed. This design can also be applied to CAN bus networks; the slave IC1 and IC2 can simply be replaced with CAN drivers.

[0078] Although this application has been described herein in conjunction with various embodiments, those skilled in the art, by reviewing the accompanying drawings, the disclosure, and the appended claims, will understand and implement other variations of the disclosed embodiments in carrying out the claimed application. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude multiple instances. A single processor or other unit can implement several functions listed in the claims. While different dependent claims may recite certain measures, this does not mean that these measures cannot be combined to produce good results.

[0079] The above are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Any feature disclosed in this specification (including the abstract and drawings) may be replaced by other equivalent or similar features unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is only one example of a series of equivalent or similar features.

Claims

1. A master-slave communication circuit for constructing a ring network based on an RS485 bus, characterized in that, include: The host includes RS485 port 1 and RS485 port 2; Multiple slave devices are configured and connected to a ring network composed of RS485 port 1 and RS485 port 2, connected end to end in sequence; RS485 port 1 is connected to the beginning of the first slave device, and RS485 port 2 is connected to the end of the last slave device. The slave device's circuitry includes: There are two RS485 driver chips, each with an A terminal, a B terminal, an RO terminal, a DI terminal, and a T / R terminal. The A and B terminals are the bus interface, the RO terminal is the TTL data output of the RS485 driver chip, the DI terminal is the TTL data input of the RS485 driver chip, and the T / R terminal is the control terminal. The A and B terminals of the two RS485 driver chips are connected to the RS485 bus in a serial manner. The microprocessor (MCU) includes IO1, IO2, RXD1, TXD1, TXD2, and RXD2 terminals. IO1 and IO2 are connected to the T / R terminals of two RS485 driver chips, respectively. RXD1 is connected to the RO terminal of one RS485 driver chip, RXD2 is connected to the RO terminal of another RS485 driver chip, TXD1 is connected to the DI terminal of one RS485 driver chip, and TXD2 is connected to the DI terminal of another RS485 driver chip. Four diodes are provided. The cathode of the first diode D1 is connected to the junction point between the RXD1 terminal and the R0 terminal of the first RS485 driver chip, and the anode is connected to the junction point between the TXD2 terminal and the DI terminal of the second RS485 driver chip. The cathode of the second diode D2 is connected to the junction point between the RXD2 terminal and the R0 terminal of the second RS485 driver chip, and the anode is connected to the junction point between the TXD1 terminal and the DI terminal of the first RS485 driver chip. The cathode of the third diode D3 is connected to the TXD1 terminal, and the anode is connected to the junction point between the TXD1 terminal and the DI terminal of the first RS485 driver chip. The cathode of the fourth diode D4 is connected to the TXD2 terminal, and the anode is connected to the junction point between the TXD2 terminal and the DI terminal of the second RS485 driver chip. There are two resistors: one end of the first resistor R1 and the second resistor R2 are both connected to the power supply VCC, and the other end is connected to the corresponding DI terminal.

2. A master-slave communication method for constructing a ring network based on an RS485 bus, characterized in that, The master-slave communication circuit based on an RS485 bus to construct a ring network, as described in claim 1, is executed, including: In normal operating mode, RS485 port 2 of the host receives the inspection command sent by RS485 port 1. The inspection command is used to address the slave. At this time, RS485 port 1 of the host is in active transmission state, the first RS485 driver chip of all slaves is in receiving state, and the second RS485 driver chip is in transmission state. The RXD1 terminal of the slave receives the bus information of the first RS485 driver chip, and outputs the response information from the TXD2 terminal of the second RS485 driver chip according to the communication protocol. If the slave device can continuously receive the inspection command from RS485 port 1 within time T2, then all slave devices with the same situation will maintain their original state, that is, the first RS485 driver chip will be set to receive and the second RS485 driver chip will be set to transmit, so as to receive the information sent from the master RS485 port 1. If the slave device fails to continuously receive the inspection command from the host's RS485 port 1 within time T2, all slave devices in the same situation will be switched to have the first RS485 driver chip set to transmit and the second RS485 driver chip set to receive, so as to receive the information sent from the host's RS485 port 2. When RS485 port 2 fails to receive the inspection command from RS485 port 1 within time T1, the host switches from normal working mode to abnormal working mode. Abnormal working mode is characterized by RS485 port 1 and RS485 port 2 being able to independently and actively send and receive information; T2 is less than T1.

3. The master-slave communication method for constructing a ring network based on an RS485 bus according to claim 2, characterized in that, After the host switches from normal working mode to abnormal working mode, the host sends a protocol change command from RS485 port 1 and RS485 port 2 respectively, so that the slave can determine the direction of the response information.

4. The master-slave communication method for constructing a ring network based on an RS485 bus according to claim 2, characterized in that, The master-slave communication method further includes: All slave devices monitor the communication protocol sent by the master and monitor the network anomaly status bit. When the network anomaly status bit is valid, all slave devices that receive the inspection command sent by RS485 port 1 will set IC1 to transmit state and IC2 to receive state after the master finishes sending a frame of communication data, so that the slave device's response information flows to RS485 port 1. All slave devices that receive information sent from RS485 port 1, after responding according to the communication protocol, will set IC1 to receive mode and IC2 to transmit mode within a preset time, so as to receive the next communication command sent by the host RS485 port 1. When the network abnormal status bit is valid, all slave devices that receive inspection commands sent by RS485 port 2 will set IC1 to receive mode and IC2 to transmit mode after the master finishes sending a frame of communication data, so that the slave device's response information flows to RS485 port 2. All slave devices receiving information from RS485 port 2, after responding according to the communication protocol, will set IC1 to transmit mode and IC2 to receive mode within a preset time, so as to receive the next communication command sent by the host RS485 port 2.

5. The master-slave communication method for constructing a ring network based on an RS485 bus according to claim 4, characterized in that, The master-slave communication method further includes: In abnormal working mode, the host RS485 port 1 and RS485 port 2 obtain relevant data of the slave device that is communicating normally through inspection commands; The slave address code in the relevant data is compared with the internally preset slave address list. If there is a slave address code that is not obtained by either RS485 port 1 or RS485 port 2, the slave corresponding to the slave address code that is not obtained is determined to be faulty and an alarm is triggered.

6. The master-slave communication method for constructing a ring network based on an RS485 bus according to claim 5, characterized in that, The step of comparing the slave address code in the relevant data with the internally preset slave address list also includes: If the composition of the slave address code obtained by RS485 port 1 and RS485 port 2 matches the slave address list, then RS485 port 1 and RS485 port 2 will determine the slave immediately adjacent to the fault point based on the number of response messages received by the slave from other slaves. The number of response messages received by the slave immediately adjacent to the fault point from other slaves is 0. The fault location is determined based on the physical location corresponding to the address code of the slave device immediately adjacent to the fault point, and an alarm is triggered.

7. The master-slave communication method for constructing a ring network based on an RS485 bus according to claim 6, characterized in that, The master-slave communication method further includes: After the host computer identifies the fault point, it sends control commands to the slave computers on both sides of the fault point. After receiving control commands, the slave devices on both sides of the fault point set the RS485 interface closest to the fault point to receive mode.

8. A master-slave communication method for constructing a ring network based on an RS485 bus according to claim 7, characterized in that, The master-slave communication method further includes: The slave devices on both sides of the fault point periodically send preset communication data for detecting fault recovery in the direction of the fault point; If both slave devices on either side of the fault point can receive the communication data sent by the other, then when the slave devices on either side of the fault point are inspected by the master again, they will send the fault clearing status information to the master. After receiving the fault clearing status information, the host sends a communication command to notify all slave devices on both sides of the fault point to resume normal communication mode.

9. A master-slave communication method for constructing a ring network based on an RS485 bus according to claim 8, characterized in that, The period for the slave devices on both sides of the fault point to send communication data for detecting fault recovery is randomly adjusted. The adjustment step is n milliseconds and the random multiple is m. The value of m is randomly adjusted each time, that is, the communication period is randomly different by n·m milliseconds each time. The ratio of the time for the slave device to send the communication data to the time of the sending period is p:q, where p is less than q and q is at least 200p.

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