Fieldbus Networks: Real-Time from the Application Software Perspective

Fieldbus communication networks aim to interconnect sensors, actuators and controllers within distributed computer-controlled systems. Therefore, they constitute the foundation upon which real-time applications are to be implemented. The problem of engineering real-time distributed applications is a complex one. A potential leap towards the use of fieldbus in such time-critical applications lies in the evaluation of its temporal behaviour. In the past few years several research works have been performed on a number of fieldbuses. However, these have mostly focusing on the message passing mechanisms, without taking to account the real implementations of those communication protocols, and emphatically without taking into account the application development tools for those distributed systems. The main contribution of this paper is to provide an application software perspective for engineering real-time with fieldbus networks and to show how this perspective influences a purely communication-based perspective. We address the case of P-NET fieldbus networks and the Process-Pascal tool to develop P-NET based distributed applications. 1