- If the system is in the state a, a change of input from B = 0 to B = 1 sends the system to state c.
- Also, State c is a transient state, and thus the excitation variable X changes to 1.
- A short time later x changes to 1, moving the system to state d. This state is also a transient state changing X back to 0, followed by a change in x to 0.
- Moreover, The system now oscillates between states c and d.
- Of course, this type of situation can be used to advantage in a clock circuit by adding a delaying network to control the delay time Δt to create the desired oscillation frequency.
- In most systems, the oscillation is unacceptable, and the situation depicted by states c and d of the map must be avoided.
This situation can occur only when two or more feedback variables are present in the system.
This system has two external inputs, A and B, and two excitation variables, X and Y, that are fed back to the input of the circuit. Oscillation Problem
One critical race occurs if the system starts in state e and input B changes from 1 to 0.
The excitation variables begin to switch from XY = 00 toward XY = 11.
Due to unequal propagation delays, one of the excitation variables will reach a value of 1 while the other has not changed from a value of 0.
If the condition XY = 10 reached, the system moves to stable state d.
Also, If the condition XY = 01 reached rather than 10, the system moves to stable state b.
The final stable state reached from this input condition depends on the relative switching speeds of variables X and Y. This situation referred to as a critical race.