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Unformatted text preview: CMPT 250 Final Exam April 15, 2002 • You have 180 minutes to complete this exam. • Answer all questions in an answer booklet. Do not hand in your question sheet. • There is a total of 75 points on this exam; points for each question are indicated. • Read through the entire exam before you begin. • There are 8 pages ( not counting this page); make sure you have them all. • No books, calculators or any other aids are allowed. • Where appropriate, clarity and simplicity of your solutions count, as well as correctness. • All “Figures” are at the back of the exam. CMPT 250 Final Exam, Apr. 15, 2002 1. [10 points] Suppose we want to create a control circuit to control a garage door opener. The circuit will have the following control inputs. These signals will be 1 when the given condition is true and 0 when it is false: • b up : A button has been pushed to raise the door. • b down : A button has been pushed to lower the door. • sensor : A sensor has detected something under the door—if it’s currently going down, it should go back up. • end : The door is all the way up or down—the door should stop. The circuit will have two output signals: • motor up : When set, the motor will raise the door. • motor down : When set, the motor will lower the door. These signals should never both be set to one; it will burn out the motor. When both are zero, the door will be held in its current position. Draw an ASM diagram that describes this circuit. 2. [10 points] We want to create a VHDL entity to implement this combinatorial circuit: Y X A B C Figure 1 contains a VHDL implementation of an AND gate; you can use it for reference....
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