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.
  4. Record the system design in your lab notebook.
  5. Use buttons for the inputs, LEDs for the outputs, and for the clock use either the 555 or a function generator. You might want to use the wiring boards in the lab instead of your own proto-boards, since the lab boards have buttons and a clock built-in.

Group Implementation: The morning lab section should implement one working system. The afternoon lab section should implement two working systems. You should design the system as a group, and then split up the wiring for implementation.

** Each person should be sure that they understand the design procedure. **

Thank you and have fun.