Research And Implementation Of MODBUS Protocol

The rapid development of computer technology, making the modern industrial production and control systems become more complex, while its reliability, real time, increasing accuracy requirements. Fieldbus control system performance to provide a new way to improve the development of field bus technology, mind control is to establish an open communications network. For historical reasons, different systems very different field bus protocols. Application of different bus protocols are also different..Modbus protocol defines the controller can identify and use the information structure. Widely used in industrial communication, the advantage of real-time, high reliability, suitable for small to medium-scale data transmission, such as the typical application of programmable logic controller (PLC). Agreement with the host polling mechanism, the master issued a query request from the device to perform an action; inquiry request received from the device, identify whether the implementation of the corresponding local data movement, organization response, the status of implementation or the data back to master device.In this paper, the rules of Modbus protocol, Modbus protocol detailed analysis of the principles of protocol software implementation, and then use the C language implementation of the completion of the agreement, which the software can be divided into application-level layer, protocol layer and port layer. Although the main, different from the station communication mode (the main station take the initiative to send a query task is passive from the station) but the main message from the station frame format is insignificant, so the main, from the station code sharing agreements are not affected.Finally, Frescale's latest MCF52259 (hereinafter referred to as "master") and MC9S08GB60 microcontroller (hereinafter referred to as "slave") for the hardware platform for the establishment of Modbus communication model, this model is applied to remote monitoring systems in hospital wards. Real-time operating system introduced ucosll MCF52259 hardware platform in the transplanting process, in real-time operating system uCOS-â…¡to complete communication tasks. Physical layer technology RS-485 bus master, from the docking station, complete information exchange between them. This system has completed an initial test results were very good, of course, be on-site inspection.