Output feedback control of asynchronous sequential machines with disturbance inputs

This paper presents a control scheme for input/output asynchronous sequential machines with disturbance inputs. An unobservable and uncontrollable disturbance input can infiltrate into asynchronous machines and provoke unauthorized state transitions. We present the existence condition for a corrective controller that automatically counteracts the effects of disturbance inputs and restores desirable behavior to the controlled machine. Unlike input/state asynchronous machines, access to the machine's state is not available in the control procedure of input/output machines, so the control scheme requires state observation and fault detection modules. As a case study, the architecture of an asynchronous clock divider with the corrective controller is implemented and experimental verification on FPGA is provided for showing the applicability of the proposed controller.