Computer Studies - Junior Secondary 2 - Logic gates
Logic gates
Logic gates
Term: 2nd Term
Week: 9
Class: Junior Secondary School 2
Age: 13 years
Duration: 40 minutes of 2 periods each
Date:
Subject: Computer studies
Topic:- Logic gates
SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to
INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source
INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures
INSTRUCTIONAL PROCEDURES
PERIOD 1-2
|
PRESENTATION |
TEACHER’S ACTIVITY |
STUDENT’S ACTIVITY |
|
STEP 1 INTRODUCTION |
The teacher revises the previous lesson on BASIC |
Students pay attention |
|
STEP 2 EXPLANATION |
She defines truth table and logic gates |
Students pay attention and participates |
|
STEP 3 DEMONSTRATION |
She lists and explains the types of logic gates |
Students pay attention and participate |
|
STEP 4 NOTE TAKING |
The teacher writes a summarized note on the board |
The students copy the note in their books |
NOTE
LOGIC GATES
A logic gate is a device that acts as a building block for digital circuits. They perform basic logical functions that are fundamental to digital circuits. Most electronic devices we use today will have some form of logic gates in them.
A truth table is a means for describing how logic circuit’s output depends on the logic level present at the circuit’s input.
Types of Logic Gates
The OR gate gets its name from the fact that it behaves after the fashion of the logical inclusive ‘or.’ The output is “true” if either or both of the inputs are “true.” If both inputs are “false,” then the output is “false.”
Logic gates – NOT logic gateOR gate symbol
Truth Table of ‘OR’ Gate
|
INPUT ( a ) |
INPUT ( b ) |
OUTPUT (a + b)
|
|
0 |
0 |
0 |
|
0 |
1 |
1 |
|
1 |
0 |
1 |
|
1 |
1 |
1 |
The AND gate is so named because, if 0 is called “false” and 1 is called “true”, the gate acts in the same way as the logical “and” operator. The following illustration and table show the circuit symbol and logic combinations for an AND gate. (In the symbol, the input terminals are at left and the output terminal is at right.) The output is “true” when both inputs are “true”. Otherwise, the output is “false”.
Logic gates – AND logic gateAND gate symbol
Truth Table of ‘AND’ Gate
|
INPUT ( a ) |
INPUT ( b ) |
OUTPUT (a * b)
|
|
0 |
0 |
0 |
|
0 |
1 |
0 |
|
1 |
0 |
0 |
|
1 |
1 |
1 |
A logical inverter sometimes called a NOT gate to differentiate it from other types of electronic inverter devices, has only one input. It reverses the logic state.
Logic gates – NOT logic gateNOT gate symbol
Truth Table for ‘NOT’ Gate
|
INPUT (a) |
OUTPUT (a¯)
|
|
0 |
1 |
|
1 |
0 |
The NOR gate is a combination of OR gate followed by an inverter. Its output is “true” if both inputs are “false”. Otherwise, the output is “false”.
Logic gates – NOR logic gateNOR gate symbol
Truth Table for ‘NOR’ Gate
|
INPUT X |
INPUT Y |
OUTPUT (OR) X+Y |
OUTPUT (NOR) (X+Y¯¯¯¯¯¯¯¯¯¯¯¯¯¯) |
|
0 |
0 |
0 |
1 |
|
0 |
1 |
1 |
0 |
|
1 |
0 |
1 |
0 |
|
1 |
1 |
1 |
0 |
The NAND gate operates as an AND gate followed by a NOT gate. It acts in the manner of the logical operation “and” followed by negation. The output is “false” if both inputs are “true”. Otherwise, the output is “true”.
Logic gates – NAND logic gateNAND gate symbol
Truth Table for ‘NAND’ Gate
|
INPUT X |
INPUT Y |
OUTPUT (AND) X.Y |
OUTPUT (NAND) (X.Y¯¯¯¯¯¯¯¯¯¯) |
|
0 |
0 |
0 |
1 |
|
0 |
1 |
0 |
1 |
|
1 |
0 |
0 |
1 |
|
1 |
1 |
1 |
0 |
EVALUATION: 1. Define
2. List and explain three types of logic gates
CLASSWORK: As in evaluation
CONCLUSION: The teacher commends the students positively