How to use PHP and MODBUS TCP protocol to communicate with industrial control systems

How to use PHP and MODBUS TCP protocol to communicate with industrial control systems

Abstract: This article will introduce how to use PHP programming language combined with MODBUS TCP protocol to achieve industrial control system communication. We will discuss the fundamentals of the MODBUS TCP protocol and provide code examples for MODBUS TCP communication using PHP.

1. Introduction to MODBUS TCP protocol
MODBUS TCP protocol is a communication protocol based on TCP/IP, which is widely used in communication between devices in the field of industrial automation. It realizes remote communication between devices through Ethernet, and supports functions such as transmitting data, reading registers, and writing registers.

The main roles of MODBUS TCP protocol communication include: Master and Slave. The master station is responsible for sending commands to the slave station and receiving responses, while the slave station is responsible for responding to the master station's commands.

2. Use PHP to implement MODBUS TCP communication
The following is a code example of MODBUS TCP communication written in PHP:

<?php
class ModbusTCP {
    private $socket;
    
    public function __construct($ip, $port) {
        $this->socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
        socket_connect($this->socket, $ip, $port);
    }
    
    public function readRegisters($slaveId, $registerAddress, $registerCount) {
        $buffer = pack("nnnn", $slaveId, 0x03, $registerAddress, $registerCount);
        socket_send($this->socket, $buffer, strlen($buffer), 0);
        
        $response = '';
        $bytes = socket_recv($this->socket, $response, 2048, MSG_WAITALL);
        
        $registers = unpack("n*", substr($response, 9));
        
        return $registers;
    }
    
    public function writeRegister($slaveId, $registerAddress, $registerValue) {
        $buffer = pack("nnn", $slaveId, 0x06, $registerAddress, $registerValue);
        socket_send($this->socket, $buffer, strlen($buffer), 0);
    }
    
    public function __destruct() {
        socket_close($this->socket);
    }
}

// 使用示例
$modbus = new ModbusTCP('192.168.0.1', 502);
$registers = $modbus->readRegisters(1, 0, 10);

foreach ($registers as $address => $value) {
    echo "Register $address: $value
";
}

$modbus->writeRegister(1, 0, 100);

The above code implements the key functions of MODBUS TCP communication. The ModbusTCP class encapsulates related methods of MODBUS TCP communication, including creating and closing socket connections, reading registers, and writing registers.

In the usage example, we created a ModbusTCP instance and connected to the IP address 192.168.0.1 and the port 502 MODBUS TCP slave. Then, we read the values ​​of the first 10 registers of the slave and print them out. Finally, we write the data with the value 100 to the first register of the slave.

3. Summary
This article introduces the basic principles and code examples of how to use PHP programming language combined with MODBUS TCP protocol to realize industrial control system communication. Developers can refer to the code examples provided in this article to use PHP and MODBUS TCP protocol to communicate with industrial control systems in actual projects. By deeply understanding the basic principles of the MODBUS TCP protocol, we can better master the communication methods of industrial control systems and provide stable and reliable support for equipment communication in the field of industrial automation.

Reference materials:
[1] MODBUS Application Protocol Specification v1.1b3. https://modbus.org/docs/Modbus_Application_Protocol_V1_1b3.pdf

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