Modbs tcp protocol of smart 200, more than a dozen independent devices, each device is controlled by smart, each device is equipped with a data acquisition card, and PLC is used as modbus server. Then, the default port number is 502, and the port number of each device cannot be the same. Modbus is the industrial standard of communication protocol in industrial field, and now it is a common connection mode between industrial electronic devices. Profibus and profinet are also used in industrial environment. Because the protocols of profibus, profinet and Modbus are different, the master-slave station can't communicate, and the yt-pb-03 protocol converter is needed for protocol conversion to realize normal communication.