Modbus TCP/IP is a variant of the Modbus protocol that uses the Transmission Control Protocol/Internet Protocol (TCP/IP) as the underlying communication technology. It enables communication between devices over Ethernet networks, making it suitable for industrial automation systems and applications that rely on TCP/IP networking infrastructure.
Working of Modbus TCP IP protocol is as below:
- Network Setup: Modbus TCP/IP operates over Ethernet networks, so devices participating in the communication must be connected to the same Ethernet network. This can be a local area network (LAN) or a wide area network (WAN) depending on the deployment scenario.
- IP Addressing: Each device in a Modbus TCP/IP network is assigned a unique IP address. The IP address allows devices to be identified and locate one another on the network. Devices can use either static IP addresses or obtain dynamic IP addresses through protocols like Dynamic Host Configuration Protocol (DHCP).
- TCP/IP Communication: Modbus TCP/IP uses the TCP/IP suite of protocols to establish reliable and connection-oriented communication between devices. The TCP protocol ensures that data packets are delivered in the correct order and without error. It provides acknowledgments, retransmissions, and flow control mechanisms to ensure reliable data transmission.
- Modbus Application Protocol: At the application layer, Modbus TCP/IP uses the Modbus Application Protocol (MBAP). The MBAP encapsulates Modbus commands and data into TCP/IP packets, allowing devices to exchange Modbus-specific requests and responses.
- Function Codes: Modbus TCP/IP uses the same set of function codes as other Modbus variants (such as Modbus RTU or Modbus ASCII). These function codes define the type of operation to be performed, such as reading or writing data registers, coils, or discrete inputs.
- Request-Response Model: In Modbus TCP/IP, the master device (initiating device) sends Modbus requests to the slave device (responding device) using TCP/IP packets. The request contains the necessary information, such as the slave device’s IP address, function code, and any additional parameters required for the operation. The slave device processes the request and sends a response packet back to the master, containing the requested data or an error code, if applicable.
- Port Number: Modbus TCP/IP uses port 502 as the default port for communication. Devices participating in Modbus TCP/IP communication need to listen on this port to receive Modbus requests.
Modbus TCP/IP offers several advantages, including the ability to leverage existing Ethernet infrastructure, support for larger network sizes, and compatibility with a wide range of devices. It allows for real-time monitoring and control of remote devices over Ethernet networks, making it a popular choice in modern industrial automation systems.