:PROPERTIES: :ID: 29d52285-bccb-40dd-90f5-ac2e828c498b :mtime: 20231023031918 :ctime: 20231023031906 :END: #+title: finite state machine #+filetags: :public:project: * Definition Finite State Machine - *Finite State Machine* (FSM) – a deterministic machine (circuit) that produces outputs which depend on its internal state and external inputs - *States* – the set of internal memorised values, shown as circles on the state diagram - *Inputs* – External stimuli, labelled as arcs on the state diagram - *Outputs* – Results from the FSM * Types of FSM There are 2 main types of FSM: 1) [[id:a25405e3-fd5b-4d13-a0bd-730d0833e89c][moore machine]] 2) [[id:5b797b90-e399-4f96-a817-80a27556dd42][mealy machine]] * Problems with FSM Consider what could happen on power-up: - The state of the FFs could by chance be in one of the unused states - This could potentially cause the machine to become stuck in some unanticipated sequence of states which never goes back to a used state ** What can be done? – Check to see if the FSM can eventually enter a known state from any of the unused states – If not, add additional logic to do this, i.e., include unused states in the state transition table along with a valid next state – Alternatively use asynchronous Clear and Preset FF inputs to set a known (used) state at power up