PHP development practice: building flexible and reliable Modbus TCP communication applications

PHP Development Practice: Build Flexible and Reliable Modbus TCP Communication Applications

As a popular communication protocol, Modbus TCP is widely used in industrial control systems, realizing communication and data between devices through Ethernet Interaction. As a powerful server-side programming language, PHP can be used to build flexible and reliable Modbus TCP communication applications. This article will introduce how to use PHP to develop Modbus TCP communication applications and give corresponding code examples.

1. Introduction to Modbus TCP protocol
Modbus TCP is an application form of Modbus protocol. It is based on the TCP/IP protocol stack and is used for communication and data exchange between devices in the network. Modbus TCP uses the standard Modbus protocol format to encapsulate Modbus RTU/ASCII data in TCP/IP messages and transmit them through the network. Modbus TCP adopts a connection-oriented communication method and is simple, efficient, and reliable.

2. Communication method between PHP and Modbus TCP
PHP can communicate with Modbus TCP through the Socket extension module. First, you need to use the socket_create() function to create a Socket socket, and then use the socket_connect() function to establish a connection with the Modbus TCP device. After the connection is established, you can use the socket_write() function to send a request message to the Modbus TCP device, and then use the socket_read() function to receive the response message returned by the device. Finally, use the socket_close() function to close the connection.

3. PHP code example
The following is a simple PHP code example that implements the function of reading holding register data from a Modbus TCP device.

<?php
// Modbus TCP设备地址
$host = "192.168.1.1";
// Modbus TCP端口号
$port = 502;

// 创建Socket套接字
$socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
if ($socket === false) {
    echo "创建Socket套接字失败！";
    exit();
}

// 建立与Modbus TCP设备的连接
$result = socket_connect($socket, $host, $port);
if ($result === false) {
    echo "连接Modbus TCP设备失败！";
    exit();
}

// 读取保持寄存器数据的请求报文
$request = hex2bin("0001000000060113000002");

// 发送请求报文到Modbus TCP设备
$result = socket_write($socket, $request, strlen($request));
if ($result === false) {
    echo "发送请求失败！";
    exit();
}

// 接收Modbus TCP设备返回的响应报文
$response = socket_read($socket, 1024);
if ($response === false) {
    echo "接收响应失败！";
    exit();
}

// 处理Modbus TCP设备返回的响应数据
$data = substr($response, 9);
$registers = unpack("n*", $data);
print_r($registers);

// 关闭与Modbus TCP设备的连接
socket_close($socket);
?>

In the above code, a Socket socket is first created using the socket_create() function, and then the socket_connect() function is used to establish a connection with the Modbus TCP device. Then, use the hex2bin() function to convert the request message to be sent into binary format, and then use the socket_write() function to send the request message to the device.

After receiving the response message returned by the device, use the socket_read() function to read the response message and parse out the holding register data. Finally, use the socket_close() function to close the connection to the device.

4. Summary
This article introduces how to use PHP to develop Modbus TCP communication applications and gives corresponding code examples. Through the communication between PHP and Modbus TCP, data exchange and control between devices can be realized. Developers can modify and extend the code according to actual needs to meet their own application requirements. I hope this article can help readers understand the principles of Modbus TCP communication and successfully apply it to actual projects.

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