Question

Question: We wish to add a yellow light to our traffic light example on page B-68. We will do this by changing the clock to run at 0.25 Hz (a 4-second clock cycle time), which is the duration of a yellow light. To prevent the green and red lights from cycling too fast, we add a 30-second timer. The timer has a single input, called TimerReset, which restarts the timer, and a single output, called TimerSignal, which indicates that the 30-second period has expired. Also, we must redefine the traffic signals to include yellow. We do this by defining two output signals for each light: green and yellow. If the output NSgreen is asserted, the green light is on; if the output NSyellow is asserted, the yellow light is on. If both signals are off, the red light is on. Do not assert both the green and yellow signals at the same time, since American drivers will certainly be confused, even if European drivers understand what this means! Draw the graphical representation for the finite-state machine for this improved controller. Choose names for the states that are different from the names of the outputs.

Short answer

Answer

The following is the graphical representation of the traffic system:

Step-by-step solution

Definition of finite-state machine 

The finite-state machine consists of states and edges. The edges are used to show the transition from state to another. A new state for yellow light is added to the traffic system. The duration for yellow light is 0.25 Hz or 4 seconds. According to the problem, the light is operated from red to yellow on passing the signal. If the signal is not sent then the light stays at the same stage.

Design finite-state machine for traffic system 

The following is the graphical representation of the traffic system: