Modbus Bus Protocol Based On Single-chip Technology Research

Fieldbus is one of the hotspot in automation development, and is regarded as a computer LAN in automation area. As a foundation of industrial communication network, fieldbus links up the field equipments of production process. There are nowadays many fieldbus standards, but MODBUS is the most important and popular one in industrial process areas. Many industrial equipments, such as PLC, DCS and intelligent instruments use MODBUS as their communication standards.Aiming at creating a platform for MCU being united into networks, implementing the communication between PC and MCU, achieving the goal of controlling MCU by PC, this paper constructs a master-slave appliance in which PC acts as master, MCU as slave and MODBUS Protocol as connecting carrier. The paper also designs a interface for RS232 serial conversing RS485, which achieves the voltage tolerance between PC serial and MCU serial. The applicance adopts cylic redundancy check to ensure the accuracy of communication data. The appliance consists of the bellowed units: common PC as master, AT89S52 MCU as the core unit, ADC0809 and DAC0832 as auxiliary units and Intel8155 MCU as the extensional interface.Based on the analysis on MODBUS Protocol and according to the characteristic of MODBUS information frame, to implement the communication between master serial and MCU, the master PC uses VC++6.0 as programming language, and the slave system achieves the function of capturing, analyzing and sending information data by the program compiled in C51 programming language. This paper realized MODBUS Protocol by MCU. It will have been a prospect of wide utility.