Live State Machine

UML statechart

A traffic-signal controller drawn as a genuine UML state machine — initial pseudostate, three states, four guarded transitions. Firing an event (or letting the timer run) moves a live token: the active state glows, the taken transition pulses, and an event-trace log records the run. The diagram is not a picture of the machine; it is the machine.

live circuit · mode=full state RED

Live State Machine

Run the machine or fire events by hand. Click a state or transition to read it.

causal signal trace paused

Enter the machine Power-on follows the initial transition into Red.

t_{\mathrm{stage}}=\htmlData{math-slot=value}{\mathtt{0.00}}\,\mathrm{s}

step 1 / 4 Enter the machine

Notebook · 4 parts · 4 wires · event-driven finite-state executor

recommended lab 7 of 18

Predict guarded state transitions and identify a liveness failure.

Builds on: 8-Bit Digital Adder

predict · then test

An event arrives with no enabled transition from the current state. What must a deterministic machine do?

Commit before the explanation appears. This is a prediction, not a quiz score.

governing model

\delta : S \times \Sigma \rightarrow S \;\cdot\; (s, e) \mapsto s_{\text{next}} \text{ if guard}(e)

structural inventory

initial pseudostate
Red / Green / Yellow states
4 guarded transitions
event queue + trace log

boundaries

deterministic $\delta$
one active state
guarded, timed transitions

diagnosis challenge Fault identity withheld: infer it from the changed outputs first.