Modbus is a widely used communication protocol in industrial automation and process control systems. Developed by Modicon (now Schneider Electric) in 1979, it has become a de facto standard for communication between programmable logic controllers (PLCs), sensors, actuators, and other industrial devices.

Key features of the Modbus protocol include:

1. Serial and Ethernet Versions:

   • Modbus can be implemented over serial communication interfaces such as RS-232, RS-485, and RS-422, as well as over Ethernet networks using TCP/IP.
   • The serial versions include Modbus RTU (Remote Terminal Unit) and Modbus ASCII (American Standard Code for Information Interchange), while the Ethernet version is known as Modbus TCP/IP.

2. Client-Server Architecture:

   • Modbus follows a client-server architecture, where one device (the Modbus master or client) initiates communication and requests data from one or more slave devices.
   • Slave devices respond to requests from the master and provide data or execute commands based on the master's instructions.

3. Simple and Lightweight Protocol:

   • Modbus is designed to be simple and lightweight, making it easy to implement and efficient in terms of communication overhead.
   • It uses a request-response model, where the master sends a request packet to a slave device, and the slave responds with a packet containing the requested data or status.

4. Addressing Scheme:

   • Modbus uses a simple addressing scheme to identify individual devices and data points on the network.
   • Each device on the network has a unique address, allowing the master to communicate with specific devices by addressing them directly.

5. Supported Data Types:

   • Modbus supports various data types, including binary (coils), discrete inputs, 16-bit integers (registers), and 32-bit floating-point numbers (holding registers).
   • Data can be read from or written to these data points using specific Modbus function codes.

6. Error Checking:

   • Modbus includes error checking mechanisms to ensure data integrity and reliability during communication.
   • Parity checking or CRC (Cyclic Redundancy Check) is often used to detect transmission errors and ensure the accuracy of data.

7. Open Standard:

   • Modbus is an open standard, allowing interoperability between devices from different manufacturers and facilitating integration into existing industrial systems.

Modbus is widely used in various industrial applications, including manufacturing, energy management, building automation, and remote monitoring. It offers a cost-effective and reliable communication solution for connecting industrial devices and systems in real-time control and monitoring applications.