CN117742714A - PLC batch read-write transmission method based on MQTT and S7 protocol - Google Patents

Abstract

The invention relates to a PLC batch read-write transmission method based on MQTT and S7 protocols, which specifically comprises the following steps: determining the structure of an XML file; writing the parameter information into an XML file; analyzing the data blocks of the XML file; obtaining parameter information of an XML file, and reading all data into a memory in a byte form; performing deserialization on the obtained byte sequence to obtain the required data; and the obtained PLC data are sent to the corresponding theme of the MQTT server, and the client subscribing the theme can receive the PLC data. The system adopts XML files, loosens the coupling degree of programs, increases the expansibility of a read-before-read PLC system, can complete read-write work with the least number of read-write times, improves the stability and efficiency of the system, and can provide real-time reliable PLC data transmission service for remote other devices with few codes and limited bandwidth by utilizing the MQTT lightweight communication protocol.

Description

PLC batch read-write transmission method based on MQTT and S7 protocol

Technical Field

The invention relates to the technical field of Internet of things sensing in an industrial Internet digital workshop, in particular to a batch read-write transmission method of a remote PLC based on MQTT and S7 protocols.

Background

Along with the continuous development of the manufacturing industry to intellectualization and digitalization, the intelligent manufacturing is one of hot topics for the manufacturing industry, wherein the PLC has the advantages of stable operation, programmable logic control and the like, and plays an important role in the field of intelligent manufacturing. In the production scene of intelligent manufacturing, whether the reading and writing of PLC data relate to the production scene can be intelligently and intensively controlled or not, in the general industrial production scene, the PLC directly controls the operation of lower production equipment, and an upper system can control and regulate the whole production flow by obtaining and writing the data in the PLC. The second method is to install special communication programming on the PLC, and the method has a certain technical threshold and cannot be popularized.

Disclosure of Invention

In view of this, the invention provides a method for implementing the reading and writing of the PLC data by the upper computer by adopting the open source S7 protocol, and the existing S7 related function is directly utilized to implement the batch reading and writing of the PLC data by the upper computer.

The technical scheme adopted by the invention for achieving the purpose is as follows:

a PLC batch reading transmission method based on MQTT and S7 protocol includes the following steps:

1) Constructing an XML file structure when PLC data are read, and writing parameter information of the PLC into the XML file;

2) Analyzing the XML file, judging the integrity of the analysis result, if the analysis result is complete, performing the step 3), otherwise returning to the step 1);

3) Distributing a new thread for the analysis result of the XML file, and in the new thread, utilizing the analysis result of the XML file to read all the PLC data into the memory according to the byte sequence;

4) Performing deserialization on the byte sequence in the memory to obtain PLC original data;

5) And transmitting the PLC original data by utilizing the MQTT.

The XML file has the structure specifically that:

an XML file is provided with only one root node, all primary child nodes of the root node are used as dividing basis of data blocks, the XML file is divided into a plurality of data blocks, each data block corresponds to a section of continuous data point in a PLC, each data block is divided into three layers of nested structures, the first layer of nested structures is a device label, the attribute of the device label comprises necessary information required by the connection of the PLC, and the necessary information comprises: the IP address of the PLC, the CPU type of the PLC, the name of the PLC and fixed parameters when the PLC is connected; the second layer of nested structure is a data block label, the attribute of the data block label comprises an address block of a target address to be monitored of the PLC, and the starting address of bytes and the number of bytes need to be read in the address block; the nested structure of the third layer is a data point tag, and the attribute of the data point tag comprises detailed information of all the operated data points, wherein the detailed information comprises a specific address of the data point, a specific type of the data point, an ordinal number of the data point and a specific meaning of the data point.

The step 3) is specifically as follows:

and opening a new thread through the analysis result of the XML file, calling the byte reading method provided by the S7 protocol by the thread, reading data in the PLC at a start address, and calling the S7 protocol for a plurality of times when the number of bytes to be read is larger than N bytes until all the byte numbers are read.

The step 4) is specifically as follows:

4.1 Converting the specific address into the offset of a byte list, and completely extracting bytes of the data according to the number of bytes occupied by each data type;

4.2 The bytes are rearranged and then the reordered byte sequence is de-serialized into the original data in the PLC.

The step 5) is specifically as follows:

and packaging the original data into a Key-Value format through a function, wherein the Key Value represents the IP address of the PLC, the Value is the data in the PLC, and triggers the corresponding theme of the MQTT to transmit the data to the remote client.

A PLC batch writing method based on MQTT and S7 protocol includes the following steps:

1) Constructing an XML file structure when writing PLC data, and writing the parameter information of the PLC and the data to be written into the XML file;

2) Analyzing the XML file, judging the integrity of the analysis result, if the analysis result is complete, performing the step 3), otherwise returning to the step 1);

3) And distributing a new thread for the analysis result of the XML file, and writing data into the PLC bit by bit in the new thread by utilizing the analysis result of the XML file.

The nesting structure of the XML file is specifically as follows:

an XML file is provided with only one root node, all primary child nodes of the root node are used as dividing basis of data blocks, the XML file is divided into a plurality of data blocks, each data block corresponds to one PLC, each data block is divided into three layers of nested structures, the first layer of nested structures is an equipment label, the attribute of the equipment label contains necessary information required by connection of the PLCs, and the necessary information comprises: the IP address of the PLC, the CPU type of the PLC, the name of the PLC and fixed parameters when the PLC is connected; the second layer of nested structure is a data block label, and the attribute of the data block label comprises an address block of a target address to be monitored of the PLC; the nested structure of the third layer is a data point label, the attribute of the data point label comprises detailed information of all the operated data points, the detailed information comprises a specific address of the data point, a specific type of the data point, an ordinal number of the data point, data to be written of the data point and a specific meaning of the data point

The step 3) is specifically as follows:

and opening a new thread through the analysis result of the XML file, calling the bit-by-bit writing method provided by the S7 protocol by the thread, and writing the data bit by bit according to the specific address of the data point.

The invention has the following beneficial effects and advantages:

1. the coupling degree is low, the XML file is adopted to store data, the coupling degree of a program is reduced, and the data of the XML file can be changed under the condition of changing source codes;

2. the method has strong expansibility, adopts XML files to configure the access list, can flexibly and conveniently carry out addition and deletion, and has high expansibility;

3. the invention directly uses the S7 protocol package provided by Siemens, does not need to install any service in the development of an upper computer, and reads the required data with the least reading times when reading the data, thereby greatly reducing the utilization of resources.

Drawings

FIG. 1 is an overall flow chart of the present invention;

FIG. 2 is a schematic diagram of XML file data block partitioning when reading PLC data;

fig. 3 is a schematic diagram of XML file data block division when writing PLC data.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples.

A PLC batch read-write transmission method based on MQTT and S7 protocol includes the following steps:

PLC batch reading and transmission: constructing an XML file structure when PLC data are read, and writing parameter information such as addresses of PLC soft elements of a programmable controller into the XML file; analyzing the data blocks of the XML file; obtaining detailed address provided by XML file and parameter information such as byte number read; according to the S7 protocol supported by the PLC, the PLC data are all read out according to byte sequences by the detailed address, byte number and other parameter information provided by the XML file; and analyzing the obtained bytes according to other parameter information provided by the XML file to obtain the required data. The obtained PLC data is sent to the corresponding theme of the MQTT server, and other clients subscribing the theme under the server can receive the PLC data, specifically: and obtaining the PLC original data, packaging the original data into a Key-Value format, wherein a Key Value represents the address of a PLC soft element, the Value is in the PLC, and triggering the corresponding theme of the MQTT to transmit the data.

The PLC batch writing, namely constructing an XML file structure when writing PLC data, writing the PLC data according to the data type one by one, mainly adding the data value to be written in a nested structure, designing entity classes to store the data to be written, and forming an object of the entity class by each data value to be written, the type of the data to be written and the soft element address, storing the objects by using an operation data list, traversing the operation data list, and writing the data to be written into a data block of the PLC, thereby realizing the batch writing function.

The XML structure is determined, one XML file is provided with only one root node, all primary child nodes of the root node are used as dividing basis of data blocks, the XML file is divided into a plurality of data blocks, each data block corresponds to a continuous data point in a section of PLC, and simultaneously corresponds to one thread, so that the system can read and write a plurality of PLCs in parallel by utilizing the characteristic of multithreading. Each data block corresponds to a continuous data point in one PLC: dividing each data block into three layers of nested structures, wherein the first layer of nested structure is an equipment tag, attribute information of the equipment tag comprises necessary information required by connection of a PLC, the second layer of nested structure is a data block tag, the attribute information of the data block tag comprises an address block of a target address to be written of the PLC, and the necessary information comprises: the IP address of the PLC, the CPU type of the PLC, the name of the PLC and fixed parameters when the PLC is connected; the third layer of nested structure is a data point label, and the attribute information of the data point label comprises detailed information of all the operated data points, wherein the detailed information comprises a specific address of the data point, a specific type of the data point, an ordinal number of the data point, a specific meaning of the data point and data to be written. The three-layer label has the structural characteristics of father- > son- > grandson.

The method comprises the steps of writing parameter information such as an address to be detected of a Programmable Logic Controller (PLC) into an XML file, and specifically comprises the following steps: and respectively corresponding the designed XML data blocks to each PLC, and respectively corresponding the three-layer nested structure of the data blocks to the detailed information under the PLC.

The data block of the XML file is analyzed, and the detailed address provided by the XML file, the number of bytes read and other parameter information are obtained as follows: according to the characteristics of the XML file, a plurality of data blocks are processed in parallel by a plurality of threads, each data block is provided with a father- > son- > Sun Tedian, entity classes are respectively set for corresponding storage, and if a plurality of data are stored, the list data structure is utilized to store instantiation information.

According to the S7 communication protocol supported by the PLC, the PLC data is completely read out according to the byte sequence by the detailed address, byte number and other parameter information provided by the XML file, and the method comprises the following steps: according to the S7 communication protocol supported by the PLC, one thread reads one PLC in batches, all the read data are stored in a byte list in a byte form and are stored in a memory to wait for the next operation.

The obtained bytes are deserialized according to other parameter information provided by an XML file to obtain the required data, and the software implementation flow is as follows: and converting the address provided by the XML third layer tag attribute into an offset in a byte list, determining the storage size end of data in the PLC and the occupied byte number of the PLC data, and deserializing the data into original data in the PLC by using a left shift operator of a high-level programming language.

The obtained PLC data is sent to the corresponding theme of the MQTT server, and other clients subscribing the theme under the server can receive the collected PLC data, and the implementation method is as follows: after the program obtains the data in the PLC soft element, the data is packaged into a Key-Value format, the Key Value represents the address of the PLC soft element, the Value is the data in the PLC, and the corresponding theme of the MQTT is triggered, so that the data is uploaded to the MQTT software service.

The XML file structure when the PLC is designed to write is as follows: the first layer nested structure is a device tag, the attribute of the device tag contains necessary information required by connection of the PLC, the second layer nested structure is a data block tag, the attribute of the data block tag contains an address block of a target address to be monitored of the PLC, and the necessary information comprises: the IP address of the PLC, the CPU type of the PLC, the name of the PLC and fixed parameters when the PLC is connected; the nested structure of the third layer is a data point label, and the attribute of the data point label comprises detailed information of all the operated data points, wherein the detailed information comprises a specific address of the data point, a specific type of the data point, an ordinal number of the data point, data to be written of the data point and a specific meaning of the data point.

Fig. 1 shows a PLC batch read-write transmission method based on MQTT and S7 protocols, comprising the steps of:

(1) File structure design and initialization of XML file

Fig. 2 is a schematic diagram of data block division of an XML file when PLC data is read in the embodiment of the present invention, in fig. 2, one data block in the XML file, and in the embodiment of the present invention, one XML file should include a plurality of data blocks, each data block corresponds to a continuous data point in a section of PLC, and determines a nested structure in the data block, and in an attribute of a first layer of nested node tag, basic information of the PLC should be included, where the basic information includes: the specific contents of the IP number, the port number, the type of the PLC, the number of the PLC, the name corresponding to the PLC, the fixed parameters required by the S7 protocol and the like are shown in the table one.

List one

Wherein the CupType includes a plurality of types, such as S7200, S7300, S7400, S71200, S71500, and each PLC is different in model, and the corresponding Rack and Solt are also different, such as rack=0, solt=1, corresponding to S7200.

Under the first layer of nested node labels, there is a second layer of nested node labels, and the layer of label attributes have data point information to be read, including: the PLC data block numbers, the start address, the number of bytes to be read, and the information of the data points are shown in the following table two, and the tag attribute of the third layer records other information of the data points according to the address sequence, such as the real address of the data points, the data type, the specific meaning, the ordering sequence, and the like, and is organized into the following table three according to fig. 1 to be described in detail.

Watch II

1	Block	PLC data block numbering
			2	BeginAddress	Address of start reading
3	ReadCount	Number of bytes to be read

Watch III

1	Address	Real address of data point
			2	DataType	Data type of data point
3	Desc	Specific meaning of data points
			4	Pos	Ordered sequence of data points

The DataType comprises Bit, byte, char, word, int, DWord, DInt, real, string, and the number of occupied bytes in the PLC is 1/8,1,1,2,2,4,4,4, 256, respectively. It should be noted that if the data type of the data point is Bit type, the start address is backward fetch, and if the start address is 1.1, the start address may be planned to be 1.

Fig. 3 is a schematic diagram showing the division of XML file data blocks when writing PLC data in the embodiment of the present invention, and it can be known that only the data to be written needs to be added to the read XML file when writing.

The XML file is configured, so that decoupling of the program can be realized, operability of non-program personnel is reduced, the program is flexible and changeable, and in addition, the XML file is configured, data point addresses can be placed in one data block continuously as much as possible, the reading and writing times are reduced, and the reading and writing efficiency is improved.

(2) Analysis of XML file and read-write analysis of PLC by dynamic thread mechanism

After the XML file is configured, analyzing the data block of the XML file to obtain the detailed address and the number of bytes read provided by the XML file, detecting whether the information provided by the XML file is complete or not by a program, if the information is complete, continuing to execute, if the information is incomplete, redesigning the XML file, then reading all PLC data into a memory according to the detailed address and the number of bytes read provided by the XML file according to the S7 communication protocol supported by the PLC, and storing the byte sequences into a list according to the sequence. And deserializing the obtained byte sequence according to other parameter information of the data points provided by the XML file to obtain the required data. Specific reading and de-serialization may include the steps of:

by obtaining the data point information provided by the XML file, a new thread is opened up for reading the data point data of the continuous address under the PLC, the thread calls the method provided by the S7 protocol for reading the data in the PLC at the starting address, and the method provided by the S7 protocol for reading the PLC bytes can only read data less than or equal to 200 bytes at one time, so if the number of bytes required to be read is greater than 200 bytes, the method is called for a plurality of times, the 200 bytes data read each time are all stored in a byte list, and if the number of the last bytes is less than 200, the data are read according to the actual number of bytes and stored in the byte list until all the byte numbers are read. Because the byte list is obtained instead of the original data of the PLC, the bytes are deserialized, the original data in the PLC is obtained, the specific address of each data point, the data type and other information are recorded in detail according to the third-layer tag attribute description of the data block in the XML file as shown in fig. 2, the specific address is firstly converted into the offset of the byte list, the bytes of the data are all taken out according to the number of bytes occupied by each data type, then the bytes are rearranged according to the characteristics of the large end storage of the PLC, and then the byte sequence is deserialized into the original data in the PLC. It should be noted that, in the storage feature of the String type in the siemens PLC, the String type occupies 256 bytes in the siemens PLC, the first byte stores the total number of characters, and the second byte stores the current number of characters, so that in the reverse serialization process, the first two bytes need to be removed, and a messy code phenomenon can not occur. Because the number of write operations of the upper computer to the PLC is less, batch write can be separately executed by using the single-point write method provided by the S7 protocol, and the specific operation steps are as follows:

by obtaining the data point information provided by the XML file, a new thread is opened up for writing data, whether the information provided by the XML file is complete or not needs to be detected before writing, the thread calls the single-point writing method provided by the S7 protocol, different methods are called through the specific address and the data type of the data point, the data is written into the PLC, and the feedback of successful data writing can be realized.

(3) MQTT data transmission

The obtained PLC data is sent to the corresponding theme of the MQTT server, and other clients subscribing the theme under the server can receive the collected PLC data, and the specific operation steps are as follows:

obtaining PLC original data, encapsulating the original data into Key-Value format through a function, wherein Key Value represents an IP address of the PLC, value is data in the PLC, value is a combination of a group of Key-Value format character strings, the combination is specifically shown in the following table IV, and corresponding topics of MQT are triggered to transmit the data to a remote client.

Table four

Key	Value	Meaning of the concrete
			Address	DB1.4.0	Specific address of the data
Data	1	The true content of the data
			DataType	Int	Data type of the data
Desc	Switching threshold value	Specific meaning of the data

。

Claims (8)

1. The PLC batch reading transmission method based on the MQTT and the S7 protocol is characterized by comprising the following steps of:

1) Constructing an XML file structure when PLC data are read, and writing parameter information of the PLC into the XML file;

2) Analyzing the XML file, judging the integrity of the analysis result, if the analysis result is complete, performing the step 3), otherwise returning to the step 1);

3) Distributing a new thread for the analysis result of the XML file, and in the new thread, utilizing the analysis result of the XML file to read all the PLC data into the memory according to the byte sequence;

4) Performing deserialization on the byte sequence in the memory to obtain PLC original data;

5) And transmitting the PLC original data by utilizing the MQTT.

2. The method for batch reading and transmitting of PLCs based on MQTT and S7 protocol according to claim 1, wherein the XML file structure specifically comprises:

an XML file is provided with only one root node, all primary child nodes of the root node are used as dividing basis of data blocks, the XML file is divided into a plurality of data blocks, each data block corresponds to a section of continuous data point in a PLC, each data block is divided into three layers of nested structures, the first layer of nested structures is a device label, the attribute of the device label comprises necessary information required by the connection of the PLC, and the necessary information comprises: the IP address of the PLC, the CPU type of the PLC, the name of the PLC and fixed parameters when the PLC is connected; the second layer of nested structure is a data block label, the attribute of the data block label comprises an address block of a target address to be monitored of the PLC, and the starting address of bytes and the number of bytes need to be read in the address block; the nested structure of the third layer is a data point tag, and the attribute of the data point tag comprises detailed information of all the operated data points, wherein the detailed information comprises a specific address of the data point, a specific type of the data point, an ordinal number of the data point and a specific meaning of the data point.

3. The batch reading and transmitting method for PLCs based on MQTT and S7 protocol according to claim 1, wherein the step 3) specifically comprises:

and opening a new thread through the analysis result of the XML file, calling the method for reading bytes provided by the S7 protocol by the thread, reading data in the PLC at a start address, and calling the method of the S7 protocol for a plurality of times when the number of bytes to be read is larger than N bytes until all the bytes are read.

4. The batch reading and transmitting method for PLCs based on MQTT and S7 protocol according to claim 1, wherein the step 4) specifically comprises:

4.1 Converting the specific address into the offset of a byte list, and completely extracting bytes of the data according to the number of bytes occupied by each data type;

4.2 The bytes are rearranged and then the reordered byte sequence is de-serialized into the original data in the PLC.

5. The batch reading and transmitting method for PLCs based on MQTT and S7 protocol according to claim 1, wherein the step 5) specifically comprises:

and packaging the original data into a Key-Value format through a function, wherein the Key Value represents the IP address of the PLC, the Value is the data in the PLC, and triggers the corresponding theme of the MQTT to transmit the data to the remote client.

6. The PLC batch writing method based on the MQTT and the S7 protocol is characterized by comprising the following steps of:

1) Constructing an XML file structure when writing PLC data, and writing the parameter information of the PLC and the data to be written into the XML file;

2) Analyzing the XML file, judging the integrity of the analysis result, if the analysis result is complete, performing the step 3), otherwise returning to the step 1);

3) And distributing a new thread for the analysis result of the XML file, and writing data into the PLC bit by bit in the new thread by utilizing the analysis result of the XML file.

7. The method for batch writing of PLCs based on MQTT and S7 protocols as claimed in claim 6, wherein the nested structure of the XML file is specifically:

an XML file is provided with only one root node, all primary child nodes of the root node are used as dividing basis of data blocks, the XML file is divided into a plurality of data blocks, each data block corresponds to one PLC, each data block is divided into three layers of nested structures, the first layer of nested structures is an equipment label, the attribute of the equipment label contains necessary information required by connection of the PLCs, and the necessary information comprises: the IP address of the PLC, the CPU type of the PLC, the name of the PLC and fixed parameters when the PLC is connected; the second layer of nested structure is a data block label, and the attribute of the data block label comprises an address block of a target address to be monitored of the PLC; the nested structure of the third layer is a data point label, and the attribute of the data point label comprises detailed information of all the operated data points, wherein the detailed information comprises a specific address of the data point, a specific type of the data point, an ordinal number of the data point, data to be written of the data point and a specific meaning of the data point.

8. The batch writing method for PLCs based on MQTT and S7 protocol according to claim 6, wherein the step 3) specifically comprises:

and opening a new thread through the analysis result of the XML file, calling the bit-by-bit writing method provided by the S7 protocol by the thread, and writing the data bit by bit according to the specific address of the data point.