Modbus is a kind of serial communication protocol, which is an open standard to describe the communication and interactive information
At present, it has become the industry standard of automation communication protocol in the industrial field. At the same time, it is the common connection mode of most industrial electronic equipment, which can realize simple equipment communication between different manufacturers and products.
Modbus mainly includes MODBUS ASCII, Modbus RTU and Modbus TCP. The three communication protocols, technical models and function calls are the same. TCP is mainly used for network communication, while ASCII and RTU are mainly used for serial communication.
Take RTU protocol as an example: common function codes are 01, 02, 03, 04, 05, 06, 0f
01 is the state of reading the switch output, 05 is the state of writing a single switch output, 0f is the state of writing multiple switch outputs,
03 is read register value, 06 is write single register value, 10 is write multiple register values.
Modbus is connected with slave station. A single slave station can access 225 devices at most. It has high openness and communication stability, and is easy to deploy and maintain. It has become the most mainstream choice of global building automation and industrial automation.