Modbus protocol conversion device and multiple on-line centralized control system

The invention discloses a Modbus protocol conversion device and a multiple on-line centralized control system. The Modbus protocol conversion device is used for being connected with one or more indoorunits and comprises one or more Modbus protocol converters, and each Modbus protocol converter is provided with a device address number and an on-line range corresponding to the device address number, wherein the on-line range corresponds to the maximum number of the indoor units to be connected to each Modbus protocol converter; according to the device address numbers, the on-line ranges, the total number of the indoor units and addresses of all the indoor units, each Modbus protocol converter is sequentially connected with the corresponding indoor unit till connection of all the indoor units is completed, wherein all the indoor units are sequenced according to the addresses. Through combination of the multiple Modbus protocol converters, the number of the indoor units is controlled, using is flexible, converter