PHP programming ideas: Understand the principles and mechanisms of Modbus TCP communication

PHP Programming Ideas: Understand the principles and mechanisms of Modbus TCP communication

Modbus TCP is a common industrial communication protocol and is widely used in the field of industrial automation. In PHP programming, we can realize communication with Modbus devices by understanding the principles and mechanisms of Modbus TCP communication, thereby achieving control of the device and data acquisition.

1. Introduction to Modbus TCP communication principles and mechanisms
Modbus TCP is an application layer protocol based on the TCP/IP protocol, which defines the communication rules between the client and the server. Modbus TCP communication mainly includes the following key concepts:

1. Modbus server: Modbus server is a device that provides Modbus services. It receives and processes requests from clients and returns corresponding responses.
2. Modbus client: Modbus client is a device or program that sends a request to the Modbus server and receives the response returned by the server.
3. Modbus register: A set of consecutive internal addresses for storing data in a Modbus device. According to different data types, they can be divided into input registers (Read Input Registers), holding registers (Holding Registers), input status registers (Input Status Registers) and switch status registers (Coil Status Registers), etc.
4. Modbus frame: The basic data unit used in Modbus communication, including request frames and response frames. The request frame contains the request information sent by the client to the server, and the response frame contains the server's response information to the client's request.

2. PHP code example to implement Modbus TCP communication
The following is a simple demonstration of how to use PHP to communicate with the Modbus server and read the data in the input register.

First, we need to create a TCP connection using PHP's socket function and specify the IP address and port number of the Modbus server:

$serverIp = '192.168.1.100';
$serverPort = 502;

$socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
socket_connect($socket, $serverIp, $serverPort);

Next, we can build a Modbus read input register request frame and send it to the server:

$modbusRequest = "

";
socket_send($socket, $modbusRequest, strlen($modbusRequest), 0);

Then, we need to wait for the response frame returned by the server and parse and process it:

$modbusResponse = '';
$bufferSize = 1024;
socket_recv($socket, $modbusResponse, $bufferSize, MSG_WAITALL);

// 解析响应帧，读取输入寄存器的数据
$dataStartIndex = 9;  // 数据起始位置
$dataLength = ord($modbusResponse[8]);  // 数据长度
$data = substr($modbusResponse, $dataStartIndex, $dataLength);

// 将数据进行解析和处理
// ...

// 关闭连接
socket_close($socket);

The above code example is just a simple Modbus TCP communication implementation may involve more functions and data processing in practical applications. By understanding the principles and mechanisms of Modbus TCP communication, we can expand and optimize according to specific needs.

3. Summary
In PHP programming, understanding and mastering common communication protocols such as Modbus TCP is crucial for communicating and controlling industrial equipment. This article introduces the principles and mechanisms of Modbus TCP communication and provides PHP code examples. I hope it can provide readers with some help and ideas when implementing Modbus TCP communication-related functions. Through careful study and practice, I believe you can use Modbus TCP to achieve more powerful functions in PHP programming.

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