What is Modbus protocol and what are its variants?

Modbus is a simple, open communication protocol originally developed by Modicon. Variants: Modbus RTU (Remote Terminal Unit) - binary encoding over RS-232/RS-485 serial lines, efficient and common; Modbus ASCII - ASCII encoding, human-readable but slower; Modbus TCP/IP - Modbus over Ethernet, modern installations. Communication model: master-slave with polling, one master queries devices by address. Data types: coils (discrete outputs), discrete inputs, holding registers (analog outputs), and input registers (analog inputs). Simple function codes (read/write coils and registers). Widely used for PLCs, VFDs, meters, and simple devices due to simplicity and open specification.