How to write Modbus TCP communication code using PHP

How to use PHP to write Modbus TCP communication code

Modbus is a communication protocol used in the field of industrial automation and is widely used for data transmission between PLC (programmable logic controller) and other automation equipment . Modbus TCP is a variant of the Modbus protocol that uses the TCP/IP protocol stack as the transport layer to allow remote communication over the network.

This article will introduce how to use PHP to write Modbus TCP communication code and provide some code examples.

1. Install the PHP extension that supports Modbus TCP
   First, you need to install the PHP Modbus extension, which provides functions and methods for operating the Modbus protocol. You can find various extensions such as phpmodbus and phpmodbuscli on the PECL (PHP Extension Community Library) website. Depending on your operating system and PHP version, select and install the appropriate extension.
2. Create Modbus TCP connection
   In PHP, you can use the modbus_new function to create a Modbus TCP connection. The following is the sample code:

<?php
// 创建Modbus TCP连接
$modbus = modbus_new_tcp("192.168.1.1", 502);
if(!$modbus) {
    die("无法创建Modbus TCP连接");
}
?>

In the above code, we use the modbus_new_tcp function to create a Modbus TCP connection, and the parameters include the IP address and port number of the remote device. If the connection creation fails, we use the die function to output an error message and terminate the program.

3. Read Modbus Registers
   Once the Modbus TCP connection is created, we can use the modbus_read_registers function to read the specified registers. The following is the sample code:

<?php
// 读取Modbus寄存器
$address = 0; // 起始寄存器的地址
$count = 10; // 要读取的寄存器数量
$data = modbus_read_registers($modbus, $address, $count);
if(!$data) {
    die("无法读取Modbus寄存器");
}
?>

In the above code, we use the modbus_read_registers function to read the specified number of registers starting from the specified address. If the read fails, we use the die function to output an error message and terminate the program.

4. Write Modbus register
   In addition to reading the register, we can also use the modbus_write_register function to write to the specified register. The following is the sample code:

<?php
// 写入Modbus寄存器
$address = 0; // 要写入寄存器的地址
$value = 100; // 要写入的值
$result = modbus_write_register($modbus, $address, $value);
if(!$result) {
    die("无法写入Modbus寄存器");
}
?>

In the above code, we use the modbus_write_register function to write the specified value to the specified register. If the write fails, we use the die function to output an error message and terminate the program.

5. Close Modbus TCP connection
   After completing Modbus communication, we should use the modbus_close function to close the Modbus TCP connection to release resources. The following is the sample code:

<?php
// 关闭Modbus TCP连接
modbus_close($modbus);
?>

In the above code, we use the modbus_close function to close the Modbus TCP connection created earlier.

Summary
This article introduces how to use PHP to write Modbus TCP communication code. First, we need to install the PHP extension that supports Modbus TCP. We then create a Modbus TCP connection and perform data transfer by reading and writing registers. Finally, we close the Modbus TCP connection to release resources. I hope these code examples can help you implement Modbus TCP communication in PHP and find application in the field of industrial automation.

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