A proposal to improve flexibility in real-time fieldbus networks

摘要

A typical approach to real-time fieldbus arbitration is the use of an off-line scheduler that generates a cyclic static table containing the allocation of bus-time-slots to the transaction of process control variables. This approach, e.g. used in the FIP fieldbus (Factory Instrumentation Protocol), is highly inflexible in the sense that any system changes, such as adding a sensor, requires the interruption of the fieldbus operation. In this article the use of a planning scheduler is proposed to overcome such inflexibility. This scheduler compromises between the advantages and disadvantages of typical dynamic and static scheduling. The possible use of the planning scheduler within the FIP context is also described resulting in a compatible FIP-like fieldbus.