Hierarchical finite-state machines and their use for digital control

This paper discusses the behavioral description, logic synthesis, and practical use of control units modeled as hierarchical finite-state machines with virtual states. The technique considered here provides a natural mechanism for top-down decomposition and enables us to develop any complex control algorithm step-by-step, where, at each stage, we are only dealing with a particular level of abstraction. Within any level, the specification encapsulates the control data and functions and allows recursive calls. Finally, the approach enables control units to be designed such that they incorporate new properties such as flexibility and extensibility. The primary functional components of a control algorithm can be reused in future applications.