Multi-discontinuous register reading method and function code for improving Modbus protocol communication rate

Abstract

The invention provides a multi-discontinuous register reading method for improving Modbus protocol communication rate and a function code. The multi-discontinuous register reading method comprises the following steps: defining a function code 43H in a Modbus protocol; the method comprises the following steps: determining the type, address list and number of discontinuous registers to be read through a master device, assembling a request frame, and sending the request frame to a slave device; after the slave device receives the request frame, address matching and verification are carried out on the request frame, and if the address is not matched or verification fails, the frame is discarded; if the address is matched and the verification is passed, analyzing, judging whether abnormity exists or not, and executing related operation based on a judgment result; the master device receives the response frame returned by the slave device, verifies the response frame, and analyzes a data list in the response frame to obtain data of each register if the response frame passes the verification and is a normal response frame; if verification fails or the frame is responded abnormally, error processing is carried out, and the multi-discontinuous register reading method which can improve the communication rate, reduce the communication overhead and enhance the real-time performance and is high in compatibility is provided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial communication, in particular to a multi-discontinuous register reading method and function code for improving Modbus protocol communication rate. BACKGROUND

[0002] When the register addresses are discontinuous, since the existing function code only supports reading of continuous address registers, the master device can only send a request frame for each discontinuous register or each continuous register, and after the slave device returns the corresponding response frame, the next request is performed.

[0003] For example, if the master device needs to read three discontinuous holding register data of the slave device with addresses 0004H, 0600H and 0100H, according to the prior art, the master device needs to send a request frame with function code 03H three times in turn, each time requesting a register address, and the slave device also needs to return a response frame three times in turn: Q1: 01 03 00 04 00 01 C5 CB; Q2: 01 03 06 00 00 01 84 82; Q3: 01 03 01 00 00 01 85 F6; This multiple request-response interaction mode has obvious defects: on the one hand, it increases the number of communications between the master and slave devices, resulting in long communication link occupation time, especially in the case of a large number of registers and scattered addresses, the communication delay is significantly increased; on the other hand, multiple frame transmissions generate more communication overhead (such as frame header, frame trailer, check field, etc.), reducing the transmission efficiency of effective data, which cannot meet the real-time and high-speed communication requirements in the field of industrial automation.

[0004] Therefore, the existing Modbus protocol has the problems of low communication rate and poor real-time performance when processing multi-discontinuous register reading, and a new technical solution is needed to solve the above-mentioned defects.

[0005] Since the communication time between devices is much longer than the signal processing time, in high-speed communication between the master and slave devices, the system communication period and the number of modbus requests are approximately proportional. Therefore, using the 03H function code of modbus to read discontinuous registers requires sending multiple requests, and the time consumption is proportional to the number of registers. When a large number of registers are to be read, it cannot meet the requirements of high-speed communication. SUMMARY

[0006] In view of the above-mentioned problems, in combination with the first aspect of the present application, the embodiments of the present application provide a multi-discontinuous register reading method for improving the communication rate of the Modbus protocol, which comprises: S1: defining function code 43H in Modbus protocol for reading multiple discontinuous registers; S2: determining the type, address list and number N of discontinuous registers to be read by the master device, assembling a request frame of function code 43H, the request frame at least including slave address, function code 43H, discontinuous register number N, register address list and check field, and sending the request frame to the slave device; S3: after the slave device receives the request frame, performing address matching and checking on the request frame, if the address does not match or the checking fails, discarding the frame; if the address matches and the checking passes, parsing the discontinuous register number N and address table in the request frame, and judging whether there is an exception; S4: if there is an exception, the slave device assembles an exception response frame and sends it to the master device; if there is no exception, the slave device reads the data of each register according to the address list, assembles a response frame of function code 43H and sends it to the master device; S5: the master device receives the response frame returned by the slave device, checks the response frame, if the checking passes and it is a normal response frame, parses the data list in the response frame to obtain the data of each register; if the checking fails or it is an exception response frame, error processing is performed.

[0007] As a further scheme of the application, the method further comprises: In step S2, the discontinuous register number N is 1 byte, wherein N≥1 and N≤64; The register address list is 2×N bytes, and each register address is 2 bytes with the high byte first.

[0008] As a further scheme of the application, the method further comprises: In step S4, the data length field of the response frame is 1 byte, and the data length value is equal to 2×N; The register data list is 2×N bytes, and each register data is 2 bytes with the high byte first.

[0009] As a further scheme of the application, for the process of the master device, comprising: The master device determines the address list and total number N of discontinuous registers to be read; Assembling a request frame of function code 43H according to the request frame format; Sending the request frame to the slave device and starting a timeout timer; Receiving the response frame returned by the slave device, and retransmitting if not received within the timeout; Checking the CRC or LRC of the response frame, if the checking passes, parsing the data of each register according to the data length and data list in the response frame; if the checking fails or an exception response frame is received, performing error processing according to the exception code.

[0010] As a further scheme of the present application, for the slave device flow, comprising: Real-time monitoring the communication bus from the device, receiving the frame data sent by the master device; Parsing the slave station address in the frame, if consistent with the address itself, continue to parse the function code; If the function code is 43H, check CRC or LRC, if the check fails, discard the frame; After the check, parse the number N of discontinuous registers and the address list, judge whether the address is within the register address range of itself, and whether N is out of limit; If there is an exception, assemble an exception response frame and send; if there is no exception, read the current data of each register according to the address list in turn, assemble the data frame according to the response frame format and send.

[0011] In another aspect, the embodiment of the present application also provides a function code for improving the communication rate of Modbus protocol, comprising: In the function code set of Modbus protocol, a new function code 43H is added, which is used to read multiple discontinuous registers; Based on Modbus protocol, Modbus ASCI protocol or Modbus TCP protocol, the request frame, response frame, exception response frame and message frame format of function code 43H are defined.

[0012] As a further scheme of the present application, the request frame format comprises: Slave station address, 1 byte, used to identify the target slave device address; Function code, 1 byte, fixed as 43H; The number N of discontinuous registers, 1 byte, used to represent the total number of discontinuous registers to be read; Register address list, 2×N bytes, wherein each register address occupies 2 bytes, the high byte is in front, and the low byte is in back, and N discontinuous register addresses are listed in order; CRC check, 2 bytes, including cyclic redundancy check and TCP mode without check.

[0013] As a further scheme of the present application, the response frame format comprises: Slave station address, 1 byte, consistent with the slave station address in the request frame; Function code, 1 byte, fixed as 43H; Data length, 1 byte, used to represent the total byte number of subsequent register data, equal to 2×N; Register data list, 2*N bytes, each register address occupies 2 bytes, high byte first, low byte last, N discontinuous register addresses are listed in sequence; CRC check, 2 bytes, including cyclic redundancy check and TCP mode without check.

[0014] As a further scheme of the application, the abnormal response frame format comprises: Slave address, 1 byte, consistent with the slave address in the request frame; Function code, 1 byte, 43H | 80H, indicating the highest position 1, abnormal; Abnormal code, 1 byte, 02H indicating illegal register address, 03H indicating register quantity out of limit; CRC check, 2 bytes, cyclic redundancy check and TCP mode without check.

[0015] As a further scheme of the application, the message frame format comprises: The message frame format comprises the request frame format and the response frame format; The request frame format is represented as 1-node address, 2-function code, 3-register number, 4-register 1 address high byte, 5-register 1 address low byte, 6-register 2 address high byte, 7-register 2 address low byte, …, 9-register n address high byte, 10-register n address low byte, 11-CRC high byte, 12-CRC low byte. The response frame format is represented as 1-node address, 2-function code, 3-register number, 4-register 1 address high byte, 5-register 1 address low byte, 6-register 2 address high byte, 7-register 2 address low byte, …, 9-register n address high byte, 10-register n address low byte, 11-CRC high byte, 12-CRC low byte Compared with the prior art, the application has the following beneficial effects: 1. Significantly improve the communication rate: when the master device reads multiple discontinuous registers, only one request frame needs to be sent, and the slave device only needs to return one response frame, avoiding the multiple request-response interaction process, reducing the communication times and bus occupation time, effectively improving the communication rate, especially in the case of a large number of discontinuous registers, the improvement effect is more obvious.

[0016] 2. Reduce communication overhead: single request-response reduces the transmission amount of redundant information such as frame header, frame tail, and check field, improves the transmission proportion of effective data, and reduces the communication link overhead.

[0017] 3. Enhanced real-time performance: reduced communication delay enables the master device to acquire multi-register data of the slave device faster, meeting the demand for real-time data acquisition in the industrial automation field.

[0018] 4. Strong compatibility: the new function code 43H does not affect the normal use of other function codes in the existing Modbus protocol. The master and slave devices can support this function code through software upgrade without the need to replace hardware, and the compatibility and scalability are strong. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a step flow chart of the multi-non-continuous register reading method of the application for improving the communication rate of the Modbus protocol; DETAILED DESCRIPTION

[0020] The application will be specifically described below in conjunction with the accompanying drawings of the specification. It can be understood that the Modbus protocol is a commonly used serial communication protocol in the industrial communication field and is widely used for data interaction between master and slave devices. In the existing Modbus protocol, when the master device needs to read the multi-register data of the slave device, if the register addresses are continuous, it can be achieved by sending a request frame once through function code 03H (read holding register) or 04H (read input register).

[0021] ; Table 1 is the format of a conventional request frame; It can be understood that the purpose of the application is to overcome the defect of low communication rate caused by the need to send multiple request frames when reading multiple non-continuous registers in the existing Modbus protocol, to provide a new function code and a corresponding implementation method, so that the master device only needs to send a request frame to read the data of multiple non-continuous registers, significantly improving the communication rate and real-time performance between the master and slave devices, and being suitable for the scene of efficiently reading multiple non-continuous register data between the master and slave devices through the Modbus protocol, and can be widely applied in the fields of industrial automation control, intelligent instruments and meters, data acquisition systems, etc.

[0022] As shown in Figure 1 , the multi-non-continuous register reading method for improving the communication rate of the Modbus protocol will be described in detail below.

[0023] Step S1, define function code 43H in the Modbus protocol, which is used to read multiple non-continuous registers.

[0024] Step S2, determine the type, address list and number N of the non-continuous registers to be read through the master device, assemble the request frame with function code 43H, and send the request frame to the slave device. The request frame at least includes the slave station address, function code 43H, the number N of non-continuous registers, the register address list and the check field.

[0025] wherein, in step S2, the number of discontinuous registers N is 1 byte, N≥1 and N≤64, the register address list is 2×N bytes, and each register address is 2 bytes with the high byte first.

[0026] Step S3, after receiving the request frame from the slave device, the address of the request frame is matched and checked, if the address is not matched or the check fails, the frame is discarded; if the address is matched and the check is passed, the number of discontinuous registers N and the address table in the request frame are parsed to determine whether there is an exception.

[0027] Step S4, if there is an exception, the slave device assembles an exception response frame and sends it to the master device; if there is no exception, the slave device reads the data of each register according to the address list, assembles a response frame with function code 43H and sends it to the master device.

[0028] wherein, in step S4, the data length field of the response frame is 1 byte, and the data length value is equal to 2×N; the register data list is 2×N bytes, and each register data is 2 bytes with the high byte first.

[0029] Step S5, the master device receives the response frame returned by the slave device, checks the response frame, if the check is passed and it is a normal response frame, the data list in the response frame is parsed to obtain the register data; if the check fails or it is an exception response frame, error processing is performed.

[0030] In this embodiment, the flow implemented by the master-slave devices includes the master device flow and the slave device flow.

[0031] wherein, for the master device flow, it is specifically: ① The master device determines the address list and the total number N of discontinuous registers to be read.

[0032] ② Assemble a request frame with function code 43H according to the above request frame format.

[0033] ③ Send the request frame to the slave device and start a timeout timer.

[0034] ④ Receive the response frame returned by the slave device, if it is not received within the timeout, resend it (the number of retransmissions can be configured).

[0035] ⑤ Check the CRC (or LRC) of the response frame, if the check is passed, parse the register data according to the data length and data list in the response frame; if the check fails or an exception response frame is received, perform error processing according to the exception code.

[0036] wherein, for the slave device flow, it is specifically ① The slave device listens to the communication bus in real time and receives the frame data sent by the master device.

[0037] ② Analyze the slave address in the frame, if consistent with the own address, continue to analyze the function code.

[0038] ③ If the function code is 43H, check the CRC (or LRC), if the check fails, discard the frame.

[0039] ④ After the check, analyze the number of discontinuous registers N and the address list, judge whether the address is within the own register address range and whether N is out of limit.

[0040] ⑤ If there is an exception, assemble an exception response frame and send; if there is no exception, read the current data of each register according to the address list in turn, assemble the data frame according to the response frame format and send.

[0041] Specifically, the function code for improving the Modbus protocol communication rate includes: Define a new function code: in the function code set of the Modbus protocol, add a function code 43H, the purpose of which is to read multiple discontinuous registers (corresponding to the register type of the original function code 03H).

[0042] Request frame format design: based on the Modbus RTU protocol (which can be extended to the Modbus ASCII and Modbus TCP protocols), the request frame format corresponding to the function code 43H is as follows (the number of bytes is indicated in order): ; Table 2 is the request frame format corresponding to the function code 43H; Response frame format design: after the slave device receives the request frame of the function code 43H and passes the check, the response frame is returned in the following format: ; Table 3 is the response frame format design corresponding to the function code 43H; Exception response frame format: if the slave device receives the request frame, there are address illegal, register quantity out of limit, register type not supported and other exception conditions, return the exception response frame, the format is as follows: ; Table 4 is the exception response frame format corresponding to the function code 43H; The message frame format of the function code 43H includes the request frame format and the response frame format: Request frame format: ; Table 5 is the request frame format in the message frame format of the function code 43H; ; Table 6 is a response frame format in the message frame format of function code 43H; The application will be further described in detail below with reference to specific embodiments.

[0043] Example 1: Reading 3 discontinuous holding registers based on Modbus RTU protocol.

[0044] Suppose that the master device needs to read 3 discontinuous holding registers with addresses 0010H, 0020H and 0030H in a slave device with address 01H, the specific implementation process is as follows: 1. The master device assembles a request frame: (1) Slave address: 01H; (2) Function code: 43H; (3) Number of discontinuous registers N: 03H; (4) Register address list: 0010H (byte 1: 00H, byte 2: 10H), 0020H (byte 3: 00H, byte 4: 20H), 0030H (byte 5: 00H, byte 6: 30H); (5) CRC check: Calculate the CRC value of the first 9 bytes (01H, 43H, 03H, 00H, 10H, 00H, 20H, 00H, 30H), and suppose it is B058H; (6) Final request frame (hexadecimal): 01 43 03 00 10 00 20 00 30 B0 58; 2. The slave device processes the request: (1) The slave device receives frame data and parses the slave address as 01H (consistent with its own address) and the function code as 43H; (2) The CRC is checked as B058H, and the check is passed; (3) The number of discontinuous registers N=03H (not exceeding the limit) and the address list 0010H, 0020H, 0030H are within the range of its own holding register addresses (suppose the slave device holding register address range is 0000H-00FFH); (4) Read the current data of N=3 registers, and suppose they are 1234H, 5678H and 9ABCH respectively; (5) The slave device assembles a response frame: ① Slave address: 01H; ② Function code: 43H; ③ Data length: 06H (2x3=6 bytes); ④ Register data list: 1234H (byte 1: 12H, byte 2: 34H), 5678H (byte 3: 56H, byte 4: 78H), 9ABCH (byte 5: 9AH, byte 6: BCH); 5. CRC check: Calculate the CRC value of the first 9 bytes (01H, 43H, 06H, 12H, 34H, 56H, 78H, 9AH, BCH), and assume it is 6D 73H; 6. Final response frame (hexadecimal): 01 43 06 12 34 56 78 9A BC 6D 73; 3. Master device parses the response: (1) The master device receives the response frame, and the CRC check is 6D 73H, which passes the check; (2) Parse the data length as 06H, which corresponds to 3 register data; (3) According to the address list order, parse the 0010H register data as 1234H, the 0020H register data as 5678H, and the 0030H register data as 9ABCH, and complete the data reading.

[0045] Example 2: Abnormal situation processing.

[0046] Continue with the master-slave device of Example 1, if the master device requests to read the register address 1000H (which is out of the address range of the slave device 0000H-00FFH), then: 1. In the request frame sent by the master device, the register address list is 1000H, 0020H, 0030H; 2. When the slave device parses the address list, it finds that the 1000H address is illegal, and assembles an abnormal response frame: (1) Slave address: 01H; (2) Function code: C3H (43H | 80H); (3) Abnormal code: 02H (address illegal); (4) CRC check: assume it is F131H; (5) Abnormal response frame (hexadecimal): 01 C3 02 F1 31; 3. The master device receives the abnormal response frame, parses the abnormal code as 02H, and judges that it is an illegal address, and performs corresponding error prompt or address correction processing.

[0047] It should be understood that the term "and / or" in this paper is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the existence of A alone, A and B together, and B alone, where A and B can be singular or plural. In addition, the character " / " in this paper generally represents an "or" relationship between the associated objects before and after it, but it can also represent an "and / or" relationship, which can be understood in reference to the context before and after it.

[0048] It should be understood that the size of the sequence number of each process described above in the embodiments of the present application does not mean the order of execution, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0049] The above-described embodiments are only used to illustrate the technical solutions of the present application, but not limit it; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can still be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A method of multi-discontinuous register reading for improving the communication rate of Modbus protocol, characterized in that, The method comprises the following steps: S1: defining function code 43H in Modbus protocol for reading multiple discontinuous registers; S2: determining the type, address list and number N of discontinuous registers to be read by the master device, assembling a request frame of function code 43H, the request frame at least comprising slave address, function code 43H, discontinuous register number N, register address list and check field, and sending the request frame to the slave device; S3: after the slave device receives the request frame, performing address matching and checking on the request frame, if the address does not match or the checking fails, discarding the frame; if the address matches and the checking passes, parsing the discontinuous register number N and address table in the request frame, and judging whether there is an exception; S4: if there is an exception, the slave device assembles an exception response frame and sends it to the master device; if there is no exception, the slave device reads the data of each register according to the address list, assembles a response frame of function code 43H and sends it to the master device; S5: the master device receives the response frame returned by the slave device, checks the response frame, if the checking passes and it is a normal response frame, parses the data list in the response frame to obtain the data of each register; if the checking fails or it is an exception response frame, error processing is performed.

2. The method of multi-discontinuous register read for boosting Modbus protocol communication rate according to claim 1, wherein, The method further comprises: In step S2, the discontinuous register number N is 1 byte, wherein N≥1 and N≤64; The register address list is 2×N bytes, and each register address is 2 bytes, with the high byte first.

3. The method of multi-discontinuous register read for boosting Modbus protocol communication rate according to claim 1, wherein, The method further comprises: In step S4, the data length field of the response frame is 1 byte, and the data length value is equal to 2×N; The register data list is 2×N bytes, and each register data is 2 bytes, with the high byte first.

4. The method of Claim 1, wherein, For the process of the master device, comprising: The master device determines the address list and total number N of discontinuous registers to be read; Assembling a request frame of function code 43H according to the request frame format; Sending the request frame to the slave device and starting a timeout timer; Receiving the response frame returned by the slave device, if the timeout is not received, retransmitting; Checking the CRC or LRC of the response frame, if the checking passes, parsing the data of each register according to the data length and data list in the response frame; if the checking fails or an exception response frame is received, performing error processing according to the exception code.

5. The method of multi-discontinuous register read to boost Modbus protocol communication rate according to claim 1, wherein, For the process of the slave device, comprising: The slave device listens to the communication bus in real time and receives the frame data sent by the master device; Parsing the slave address in the frame, if it is consistent with the address of the slave device, continuing to parse the function code; If the function code is 43H, checking the CRC or LRC, if the checking fails, discarding the frame; After the checking passes, parsing the discontinuous register number N and address list, judging whether the address is within the address range of the slave device and whether N is out of limit; If there is an exception, assembling an exception response frame and sending it; if there is no exception, reading the current data of each register according to the address list, assembling a data frame according to the response frame format and sending it.

6. Function code to increase the Modbus protocol communication rate for implementing the method according to any one of claims 1 to 5, characterized in that, Comprising: In the function code set of Modbus protocol, a new function code 43H is added, the function code 43H is used for reading multiple discontinuous registers; Based on Modbus protocol, Modbus ASCI protocol or Modbus TCP protocol, the request frame, the response frame, the exception response frame and the message frame format of function code 43H are defined.

7. The function code to boost Modbus protocol communication rate according to claim 6, wherein, The request frame format comprises: a slave address, 1 byte, used for identifying the target slave device address; a function code, 1 byte, fixed as 43H; a number of discontinuous registers N, 1 byte, used for indicating the total number of discontinuous registers to be read; a register address list, 2*N bytes, wherein each register address occupies 2 bytes, the high byte is in the front, the low byte is in the back, and N discontinuous register addresses are listed in sequence; a CRC check, 2 bytes, including cyclic redundancy check and no check in TCP mode.

8. The function code to boost Modbus protocol communication rate according to claim 6, wherein, The response frame format comprises: a slave address, 1 byte, consistent with the slave address in the request frame; a function code, 1 byte, fixed as 43H; a data length, 1 byte, used for indicating the total byte number of subsequent register data, equal to 2*N; a register data list, 2*N bytes, wherein each register address occupies 2 bytes, the high byte is in the front, the low byte is in the back, and N discontinuous register addresses are listed in sequence; a CRC check, 2 bytes, including cyclic redundancy check and no check in TCP mode.

9. The function code to boost Modbus protocol communication rate according to claim 6, wherein, The exception response frame format comprises: a slave address, 1 byte, consistent with the slave address in the request frame; a function code, 1 byte, 43H|80H, indicating that the highest position is 1 and abnormal; an exception code, 1 byte, 02H indicating illegal register address and 03H indicating register number out of limit; a CRC check, 2 bytes, cyclic redundancy check and no check in TCP mode.

10. The function code to boost Modbus protocol communication rate according to claim 6, wherein, The message frame format comprises: the message frame format comprises the request frame format and the response frame format; wherein the request frame format is represented as 1-node address, 2-function code, 3-register number, 4-register 1 address high byte, 5-register 1 address low byte, 6-register 2 address high byte, 7-register 2 address low byte, …, 9-register n address high byte, 10-register n address low byte, 11-CRC high byte, 12-CRC low byte; wherein the response frame format is represented as 1-node address, 2-function code, 3-register number, 4-register 1 address high byte, 5-register 1 address low byte, 6-register 2 address high byte, 7-register 2 address low byte, …, 9-register n address high byte, 10-register n address low byte, 11-CRC high byte, 12-CRC low byte.

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