The system has 6 inputs and 5 outputs:
Inputs
First floor -button located inside the elevator or on the first floor,which may be used to take the elevator to the first floor, from any floor.
Second floor -button located inside the elevator or on the second floor, which may be used to take the elevator to the second floor, from any floor.
Third floor - button located inside the elevator or on the third floor,which may be used to take the elevator to the third floor, from any floor.
Fourth floor - button located inside the elevator or on the fourth floor, which may be used to take the elevator to the fourth floor, from any floor.

Outputs
4 leds used to indicate the elevator's location. - These outputs are used to indicate what floor the elevator is at. Use 4 LEDs and each will indicate a floor. When the LED is turned on the elevator is at that location. Use LED0, LED1, LED2, and LED3.
Door - When this output is equal to logic 1, it indicates the elevator door is open. Use LED7.

1. The system several states and I will describe some of them: 1st floor open door, 1st floor closed door, 2nd floor open door, 2nd floor closed door.

2. The elevator should remain at rest until someone presses a button. The rest states are defined to be the states where the door is closed.

3. If someone presses the 1 or First floor button, the elevator should go to the 1st floor, open the door and remain in this state for a small amount of time, then close the door. Assume the elevator takes one clock cycle to travel from from one floor to an adjacent one and that the door stays open for four clock cycles.

4. The same behavior will apply to the other floors input buttons.

5. The elevator has a safety feature associated with the doors. If the doors are closing and it is detected that an object is in the doors way, the doors remain in the open position.