Lab 3: Exclusive OR and Exclusive NOR Circuits

Introduction

Two Boolean expressions occur quite frequently in designing combinational circuits:

x = A\B + AB\

and

y = AB + A\B\

x defines the Exclusive OR function to be one that yields an output that is HIGH whenever its inputs are different. Similarly, y defines the Exclusive NOR function, which yields an output that is HIGH whenever its inputs are the same. While these circuits are combinational circuits, they have been given their own symbols, and both have been implemented with integrated circuits.

Equipment Needed

Microprocessor power supply

Solderless breadboard

2 – 7400

1 – 7486

Procedure

Part A.

1. Draw the Sum of Products circuit for the XOR and its associated truth table.

2. Implement the circuit using all NAND gates and verify the circuits function by creating a function table.

3. Add an inverter to the output and verify that the new output performs an XNOR function by creating a function table.

4. Mount a 7486 on the circuit board. Connect toggle switches to one of the XOR circuits of the IC, and connect an LED monitor to its output.

5. Draw the truth table to verify that the circuit performs an XOR function.

6. Disconnect the LED monitor from the output of the 7486 circuit and insert an inverter between the monitor and the circuit.

7. Verify that the new circuit performs the XNOR function by creating a truth table.

8. Remove the inverter you added in step 6 and insert it between the toggle switch and the A input.

9. Draw a truth table for this circuit. What function is being performed?

Part B. Binary Complementer

1. Construct the circuit shown in figure 1. The inputs are connected to the data switches and the output will be observed on the LED indicators. SW4 and LED4 are considered the LSB.

2. Set all the input switches to binary 0 state, including logic switch A. (IN = 0000, A = 0). Record the output in a truth table.

3. Keep all the input switches at 0 and set logic switch A. IN = 0000, A = 1). Record the output in the truth table.

4. For each of the input states in the truth table, record the output state with logic switch A at LO and HI.

5. From the truth table and figure 1, determine the function of this circuit.

Part C. Parity Generator application.

Design a four-bit even parity generator that uses Exclusive OR circuits. This circuit should have four inputs and an output that is HIGH only when an odd number of inputs are HIGH. Make a truth table of the circuit. Implement the circuit and verify the output using the truth table and the 7486 IC.