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, low-level fieldbusses considered involve (1) ASI (Actuator-Sensor-Interface), which is an example of a lowest-level industrial interconnection; (2) NBIP (Nine-Bit Inter-processor 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 well-known 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.