How to parse Modbus TCP command and response data using PHP

How to use PHP to parse the command and response data of Modbus TCP

Overview:
Modbus is a common communication protocol that is widely used in the field of industrial automation. Modbus TCP is a variant of the Modbus protocol based on TCP/IP networks. Using Modbus TCP protocol for communication in PHP can realize data interaction with Modbus devices. This article will introduce how to use PHP to parse Modbus TCP command and response data, and provide relevant code examples.

The basic process of Modbus TCP communication is as follows:

1. Establish a TCP connection: Use PHP's socket function to establish a TCP connection with the Modbus device.
2. Assemble Modbus commands: Use PHP to assemble commands to read/write registers into binary data according to the Modbus protocol format.
3. Send command: Send the assembled command to the Modbus device through the TCP connection.
4. Receive response: Use PHP's socket function to receive the data returned by the Modbus device.
5. Parse response: Parse the binary data into a readable data format according to the Modbus protocol format.

The following is a sample code that uses PHP to parse Modbus TCP commands and response data:

<?php
// Modbus设备信息
$host = '192.168.1.1';  // Modbus设备的IP地址
$port = 502;  // Modbus设备的端口号

// Modbus命令
$readCommand = pack('nnnn', 0x0001, 0x0004, 0x0000, 0x0008);  // 读取0x0000 ~ 0x0008的寄存器
$writeCommand = pack('nnnC*', 0x0001, 0x0006, 0x0000, 0x01, 0x00, 0x0A);  // 向0x0000的寄存器写入值0x0A

// 建立TCP连接
$socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
$result = socket_connect($socket, $host, $port);
if (!$result) {
    die("连接Modbus设备失败！");
}

// 发送读取命令
socket_write($socket, $readCommand, strlen($readCommand));

// 接收响应数据
$response = socket_read($socket, 1024);
$registers = unpack('n*', substr($response, 9));  // 解析寄存器数据

// 打印读取到的寄存器值
echo "读取到的寄存器值：";
foreach ($registers as $register) {
    echo $register . " ";
}

// 发送写入命令
socket_write($socket, $writeCommand, strlen($writeCommand));

// 接收响应数据
$response = socket_read($socket, 1024);

// 解析响应数据
// TODO: 根据Modbus协议解析响应数据

// 关闭TCP连接
socket_close($socket);
?>

In the above sample code, first establish TCP based on the IP address and port number of the Modbus device connect. Then, use the pack() function to convert the command data read/written to the register into binary format and send it to the Modbus device through the TCP connection. After receiving the data returned by the device, use the unpack() function to parse the register data. The read register value can be processed using the corresponding method, while the write operation needs to be parsed and processed according to the Modbus protocol.

Summary:
By using PHP to parse the commands and response data of Modbus TCP, data interaction with Modbus devices can be achieved. This article provides basic code examples and introduces the basic communication flow. Readers can expand and optimize according to their own needs to achieve more complex functions. Hope this article can be helpful to readers!

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