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:**

- Develop a state diagram and a transition table.
- 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.
- 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.
- Record the system design in your lab notebook.
- 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.