The Implementation Of Modbus Protocol Using ARM7and μC/OS-Ⅱ

Fieldbus is one of the hotspots of today’s field of industrial automation, and is known asthe computer local area network in the field of automation. Nowadays,they are manystandards of the fieldbus.However,Modbus protocol is one of the important criteria and it isone of the most popular protocol of the global industry, a lot of industrial equipment, such asPLC, DCS, intelligent instruments and so on using the Modbus protocol as they contact thecommunications standard. At present, almost8or16-bit microcontroller is the hardwareplatform of the Modbus communication protocol. However, with the development of moderntechnology,production automation continuously improving, the microcontroller due to its ownresources and performance, has been increasingly unable to meet the increasingly complexapplications. Embedded system with its powerful features, more rapid processing speed, willreplace the MCU gradually and become a research hotspot.The Modbus communication platform is built using ARM processor based on the theoryof Modbus protocol and UART to realize the communication and the remote control betweenPC and IO devices.This system consists of three parts: the host, the slave and IO devices. ThePC is as a host and the ARM processor as the slave. In order to achieve the control of the hostto the slave, Modbus protocol is used between PC and ARM processor,which is also utilizedto connect the slave and IO devices. The whole system includes hardware design and softwaredesign. The hardware design comprise the selection of ARM processor,the design ofperipheral circuit and serial communication interface circuit and the design of PCB. Thesoftware design comprise the initialization procedures of serial communication interface,interrupt handlers of serial receive ports and serial transmit ports, the CRC checkingprocedures, the Modbus communication protocol frame processing program,etc. we chooseARM cortex-M3LM3S1138as the ARM processor, DI/DO and AI/AO as the IO devices.In view of the requirements of current product performance which is continuouslyimproved and upgraded fast, μC/OS-Ⅱis transplanted that can be cut and deprived of the linemulti-tasking real-time kernel. The use of the kernel of these mechanisms designed to achievethe Modbus protocol, can greatly improve the real-time and stability of the system.The test result show that the system has a good stability and the real-time property.It can work in severe conditions like mine, and monitor the environment or terminal equipment, canalso connect with other company’s products.