FREE LESSON · Digital logic · 4 OF 4
Finite State Machines Explained
Logic mastery: design a state machine — Make control explicit and test every transition
A finite-state machine is a small executable specification.
Name the states, inputs, transition function, and outputs. Moore-style outputs depend on state; Mealy-style outputs may also depend directly on inputs. Reachability analysis exposes dead or unsafe states, while temporal properties state what must always or eventually happen.
Control logic becomes debuggable when hidden history is promoted into explicit state.
Traffic light with a remembered request
States can encode vehicle green, yellow, all-red, and pedestrian crossing. A button sets a pending-request bit so a brief press is not lost. Transitions respect minimum timing and the invariant that conflicting directions are never green together. The model cleanly separates request memory from phase control.
If a real requirement depends on history, that history must exist somewhere in the state.