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EECS 318

Electronics Lab

Laboratory #6

Introduction to Digital Logic

Objective:

The objective for this lab is to understand the fundamentals of logic gates and its use in implementing basic Boolean functions.

Equipment:

1 - Digital Probe Kit 1 - Breadboard 1 - DC Power Supply

Components:

1 - 74HC08 (AND) 1 - 74HC04 (NOT) 1 - 74HC32 (OR) 1 - 240Ω Resistors

1 - LED 3 - 1kΩ Resistors

1 - DIP Switch

Background: In this lab, the input to the logic gates will be applied from DIP Switches. A bright LED

and a current limiting resistor will be connected to the output of each logic gate. The LED will indicate the functional behavior of a Boolean expression. A diagram for connecting digital inputs and outputs is shown below.

Digital Inputs and Outputs Connections

When the switch is closed or in other words if the switch is in the ON position, the

input is low (0V). This is because when the switch is closed, a direct path exists

between +5 V and GND thus shorting the circuit. When the switch is open, the above

path is open circuited making current flow through the IC chip. When a digital output is

low (0V), the LED is off. When the digital output is high (5V), the LED is on and the

current is limited by the 240Ω resistor. The digital circuit will break without a current

limiting input resistor. The LED will break without a current limiting output resistor.

Two digital outputs should never be connected to the same node. This will break the

digital circuit. However, a digital output can be connected to multiple digital inputs.

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The internal connections for each of the integrate circuits are shown below. The power

connections for each of the integrated circuits are also shown below.

Integrated Circuit Connections

In this experiment, you will verify the truth tables of the basic AND, OR, and NOT logic

gates. You will also construct a circuit to represent an arbitrary Boolean expression.

Procedure:

1. Place the integrated circuits with AND, OR, and NOT gates on a breadboard properly. Also place the DIP switch. All of these components should be placed across the gap in the center of the breadboard.

2. Design and sketch three circuit schematics for verifying the AND, OR, and NOT

logic functions. The first circuit schematic for the AND logic function has been

provided.

+5V +5V +5V

14 1K 1K 1

3 7408

2 240 Ω

7 +

-

3

A

A A’

0

1

OR

A B A+B

0 0

0 1

1 0

1 1

3. Construct the circuits, one at a time, on a breadboard with switches and an LED.

Experimentally verify the truth tables for NOT, AND, and OR gates. A and B are

switches. The output for each logic gate will be on an LED. (LED Off = 0, LED

On = 1)

AND

A B AB

0 0

0 1

1 0

1 1

4. Complete the truth tables for two-input NAND, NOR, and EXOR. You need not experimentally verify these logic gates.

NAND NOR

A B AB (AB)’ A B A+B (A+B)’

0 0 0 0

0 1 0 1

1 0 1 0

1 1 1 1

EXOR

A B A’ B’ AB’ A’B AB’+A’B

0 0

0 1

1 0

1 1

5. Complete the truth table for the Boolean function F = AB + B’C + AC’.

F

A B C B’ C’ AB B’C AC’ AB+B’C AB+B’C+AC’

0 0 0

0 0 1

0 1 0

0 1 1

1 0 0

1 0 1

1 1 0

1 1 1

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6. Finish designing and sketching the circuit schematic for the Boolean function F =

AB + B’C + AC’. Remember, multiple outputs cannot be connected to the same

input, but an output can be connected to multiple inputs. Verify output with

instructor to receive full credit for this lab.

+5V +5V

14 1

7408

3 A 2

7

+5V

+5V +5V +5V

14 14 14

4 1

7404 1 2

7408 6

7432 3

B 5 2 + 7 7 7 F

-

+5V

+5V +5V +5V

14 14 14

9 4

7404

3 4 C

7

7408

8 10

7

7432

6 5

7

7. Construct the circuit on a breadboard with switches and an LED. Experimentally

verify the truth table. A and B are switches. The output for each logic gate will be

on an LED. (LED Off = 0, LED On = 1)

F

A B C AB+B’C+AC’

0 0 0

0 0 1

0 1 0

0 1 1

1 0 0

1 0 1

1 1 0

1 1 1