Lesson 2.1 Evaluating Logic Gates PDF

**Lesson 2.1** **Lesson Objective:** - **Discusses the action of each logic gate using Boolean expressions** **and truth tables.** **EVALUATING LOGIC GATES** Nowadays, computers have become an integral part of life as they perform many tasks and operations in quite a short span of time. O...

**Lesson 2.1** **Lesson Objective:** - **Discusses the action of each logic gate using Boolean expressions** **and truth tables.** **EVALUATING LOGIC GATES** Nowadays, computers have become an integral part of life as they perform many tasks and operations in quite a short span of time. One of the most important functions of the CPU in a computer is to perform logical operations by utilizing hardware like **Integrated Circuits** software technologies & **electronic circuits**. But, how this hardware and software perform such operations is a mysterious puzzle. In order to have a better understanding of such a complex issue, we must have to acquaint ourselves with the term **Boolean Logic**, developed by **George Boole**. For a simple operation, computers utilize binary digits rather than digital digits. All the operations are carried out by the Basic Logic gates. **What are Basic Logic Gates?** A **logic gate** is a basic building block of a digital circuit that has two inputs and one output. The relationship between the i/p and the o/p is based on a certain logic. These gates are implemented using electronic switches like transistors, diodes. Logic gates are used in **microprocessors**, **microcontrollers**, **embedded system applications**, and in **electronic and electrical project circuits**. The basic logic gates are categorized into seven: **AND**, **OR**, **XOR**, **NAND**, **NOR**, **XNOR**, and **NOT**. These logic gates with their logic gate symbols and truth tables are explained below. - **AND GATES** The **AND** gate is named so because, if 0 is false and 1 is 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 on the left, and the output terminal is on the right.) The output is \"true\" when both inputs are \"true.\" Otherwise, the output is \"false.\" In other words, the output is 1 only when both inputs are 1.  - **OR GATES** The **OR gate** gets its name from behaving like the logical inclusive \"or.\" The output is true if one or both of the inputs are true. If both inputs are false, then the output is false. In other words, for the output to be 1, at least one input must be 1. - **XOR GATES** The **XOR (exclusive-OR) gate** acts in the same way as the logical \"either/or.\" The output is true if either, but not both, of the inputs are true. The output is false if both inputs are \"false\" or if both inputs are true. Similarly, the output is 1 if the inputs are different but 0 if the inputs are the same. - **NAND GATES** The **NAND (Negated AND) 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. Another way to visualize it is that a NAND gate inverts the output of an AND gate. The NAND gate symbol is an AND gate with the circle of a NOT gate at the output. - **NOR GATES** The **NOR (NOT OR) gate** is a combination OR gate followed by an inverter. Its output is true if both inputs are false. Otherwise, the output is false. - **XNOR GATES** The **XNOR (exclusive-NOR) gate** is a combination of an XOR gate followed by an inverter. Its output is true if the inputs are the same and false if the inputs are different. - **NOT GATES** A logical inverter, sometimes called a **NOT gate** to differentiate it from other types of electronic inverter devices, has only one input. A NOT gate reverses the logic state. If the input is 1, then the output is 0. If the input is 0, then the output is 1. The truth table is used to show the logic gate function. All the logic gates have two inputs except the **NOT** gate, which has only one input. This table includes all the input logic state combinations either high (1) or low (0) for every input terminal of the logic gate through the equivalent output logic level like high or low. The NOT logic gate circuit is shown above and its truth table is extremely easy indeed When drawing a truth table, the binary values 0 and 1 are used. Every possible combination depends on the number of inputs. If you don't know about the logic gates and their truth tables and need guidance on them, please go through the following infographic that gives an overview of logic gates with their symbols and truth tables. **What is the Easiest Way to Learn Logic Gates?** The easiest way to learn the function of basic logic gates is explained below. - For **AND** Gate -- If both the inputs are high then the output is also high - For **OR** Gate -- If a minimum of one input is high then the output is High - For **XOR** Gate -- If the minimum one input is high then only the output is high - **NAND** Gate -- If the minimum one input is low then the output is high - **NOR** Gate -- If both the inputs are low then the output is high. - **XNOR** Gate -- If both inputs are the same then the output is high. - **NOT** Gate -- If an input is high then the output is low. **ACTIVITY NO. 2.1** **Name: [ ] Grade & Level: [ ] Date:\_\_\_\_\_\_\_\_\_\_\ ** **I. Draw a line between each symbol and the correct name.** **II. Complete the truth table for the following gates.**