# Documentation

## Model a Traffic Light Using Moore Semantics

The following chart uses Moore semantics to model a traffic light:

### Open the Model

To open the model of a Moore traffic light, click sf_moore_traffic_light or type `sf_moore_traffic_light` at the MATLAB® command prompt.

### Logic of the Moore Traffic Light

In this example, the traffic light model contains a Moore chart called Light_Controller, which operates in five traffic states. Each state represents the color of the traffic light in two opposite directions — North-South and East-West — and the duration of the current color. The name of each state represents the operation of the light viewed from the North-South direction.

This chart uses temporal logic to regulate state transitions. The `after` operator implements a countdown timer, which initializes when the source state is entered. By default, the timer provides a longer green light in the East-West direction than in the North-South direction because the volume of traffic is greater on the East-West road. The green light in the East-West direction stays on for at least 20 clock ticks, but it can remain green as long as no traffic arrives in the North-South direction. A sensor detects whether cars are waiting at the red light in the North-South direction. If so, the light turns green in the North-South direction to keep traffic moving.

The Light_Controller chart behaves like a Moore machine because it updates its outputs based on current state before transitioning to a new state, as follows:

When initial state Stop is active.  Traffic light is red for North-South, green for East-West.

• Sets output `y1` = RED (North-South) based on current state.

• Sets output `y2` = GREEN (East-West) based on current state.

• After 20 clock ticks, active state becomes `StopForTraffic`.

In active state StopForTraffic.  Traffic light has been red for North-South, green for East-West for at least 20 clock ticks.

• Sets output `y1` = RED (North-South) based on current state.

• Sets output `y2` = GREEN (East-West) based on current state.

• Checks sensor.

• If sensor indicates cars are waiting (`[sens]` is true) in the North-South direction, active state becomes `StopToGo`.

In active state StopToGo.  Traffic light must reverse traffic flow in response to sensor.

• Sets output `y1` = RED (North-South) based on current state.

• Sets output `y2` = YELLOW (East-West) based on current state.

• After 3 clock ticks, active state becomes `Go`.

In active state Go.  Traffic light has been red for North-South, yellow for East-West for 3 clock ticks.

• Sets output `y1` = GREEN (North-South) based on current state.

• Sets output `y2` = RED (East-West) based on current state.

• After 10 clock ticks, active state becomes `GoToStop`.

In active state GoToStop.  Traffic light has been green for North-South, red for East-West for 10 clock ticks.

• Sets output `y1` = YELLOW (North-South) based on current state.

• Sets output `y2` = RED (East-West) based on current state.

• After 3 clock ticks, active state becomes `Stop`.

### Design Rules in Moore Traffic Light

This example of a Moore traffic light illustrates the following Moore design rules:

• The chart computes outputs in state actions.

• The chart tests inputs in conditions on transitions.

• The chart uses temporal logic, but no asynchronous events.

• The chart defines chart inputs (`sens`) and outputs (`y1` and `y2`).