ELEC 101
Prof. Rich Kozick
April 30, 1998

## Laboratory 13 Sequential Logic Circuit Design: Game Show Detector

Problem: Design and implement the two-button game show detector circuit formulated in class. A summary of the circuit operation is as follows.

Inputs: Boolean X1, X2 for the contestants' buttons
Outputs: Boolean Q1, Q2 to indicate which contestant pressed the button first
Initially, Q1 = Q2 = 0
If X1 = X2 = 0 and no button was pressed, then remain at Q1 = Q2 = 0
If X1 = 1 first, then Q1 = 1 and Q2 = 0
If X2 = 1 first, then Q1 = 0 and Q2 = 1
Also need a CLEAR input to reset the state to Q1 = Q2 = 0

Question: Can you design this circuit using combinational logic only? Please explain.

Suggested Procedure:

1. Develop a state diagram and a transition table.
2. Decide whether to use D flip-flops (7474 IC) or JK flip-flops (7476 IC). The 7476 should be in your lab kit, and the 7474 will be available in lab.
3. An IC containing 4-input NAND gates will also be available in lab. Remember that you have ICs with inverters and 2-input NAND gates in your lab kit.