Extension communication method based on Modbus communication protocol

The invention discloses an extended communication method based on a Modbus communication protocol, which comprises the following steps that: firstly, a host sends a first instruction, and a slave sets a change upper limit of each register according to the first instruction and returns a response; then, the host sends a full-amount data reading instruction, and the slave returns full-amount data; and finally, the host regularly sends a second instruction, the slave returns a change data response packet after receiving the second instruction, and the change data response packet comprises register data with the data change larger than the change upper limit between two adjacent instructions. 本发明公开一种基于Modbus通信协议的扩展通信方法，首先由主机发送第一指令，从机根据第一指令设置各寄存器的变化上限，并返回应答；然后主机发送读取全量数据指令，从机返回全量数据；以及最后，主机定期发送第二指令，从机接收到第二指令后，返回变化数据应答包，其中，变化数据应答包包括相邻两次指令间，数据变化大于变化上限的寄存器数据。