The Research And Development Of Foundation Fieldbus Communication Stack

Data link layer and partial application layer of foundation fieldbus communication layers are researched and developed in this thesis, which are based on foundation fieldbus protocols. Since fieldbus network is growing up in automation scopes, alse foundation fieldbus is one of those fieldbuses that have the best future, this research aimes to implement data link layer protocol and fieldbus access sublayer protocol of foundation fieldbus communication stack protocols.Firstly foundation communication arthitecture is briefly analyzed, it can indicate that foundation fieldbus definitions conform to the global definitions for the same portions, so foundation fieldbus is open and compatible.Secondly two layers are described in the thesis: the data link layer(DLL) and the fieldbus access sublayer(FAS). These descriptions include operations of virtual communication relationships which are provided by the FAS for communication, and FAS protocol state machines. Then this part focuses on presenting the researches of DLL activities, also communication models provided by the DLL are discussed in it. The DLL classifies field devices in terms of their functions. In this part, the link activity scheduler is introduced, it is a special sort of link master, that operates at the DLL as the bus arbiter for the link.Finally the design of the above layers is given. On one hand, the project of FAS is described as the design of its protocol state machines, which are some functions in this paper. On the other hand, for the DLL, the focus is the design of the lower level (media access) functions. A series of tasks are designed take advantage of Nucleus PLUS RTOS's abundant resources. Those tasks involve basic receiving messages task, responsing token tasks, competing link activity scheduler role tasks, scheduling communication tasks, and so on, which are developed to control accesses towards media. Simultaneously, a bandwidth allocation scheme for periodic communication adopted in the project is designated, it belongs to a sort of communication bandwidth allocation scheme,.