Coupling Architectures for Low- Level Fieldbusses

This paper deals with hierarchical, multiple fieldbus-based architectures using four case studies that present some concepts reusable in developing the interconnections of intelligent sensors and actuators. The single-master, lowlevel fieldbusses considered involve (1) ASI (ActuatorSensor-Interface), which is an example of a lowest-level industrial interconnection; (2) NBIP (Nine-Bit Interprocessor Protocol), which is an example of a special purpose link-layer protocol for microcontrollers; and (3) Bitbus, which is an example of well-established fieldbus utilized for almost 20 years in various applications. The paper begins with classification issues; particularly, coupling architectures are treated both from the viewpoint of more classical interconnections of wide-area and local-area networks, and from the viewpoint of fieldbus domain. Next part introduces the ASI and NBIP protocols while the wellknown Bitbus is reviewed in applications. To offer more complex insight, implementation tools -developed particularly to support low-level fieldbus interconnecting experiments -are also mentioned. Four case studies demonstrating consequently NBIP-ASI, ASI-ASI, and two different Bitbus-NBIP hierarchical coupling structures create the kernel of the paper. Finally, brief notes about origins, results, and current targets of the project conclude the contribution.