Logic gate with truth table

Logic gate with truth table

Introduction

Boolean functions may be practically implemented by using electronic gates. The following points are important to understand.

• Electronic gates require a power supply.
• Gate INPUTS are driven by voltages having two nominal values, e.g. 0V and 5V representing logic 0 and logic 1 respectively.
• The OUTPUT of a gate provides two nominal values of voltage only, e.g. 0V and 5V representing logic 0 and logic 1 respectively. In general, there is only one output to a logic gate except in some special cases.
• There is always a time delay between an input being applied and the output responding .

Truth tables

 Truth tables are used to show logic gate functions. The NOT gate has only one input, but all the others have two inputs. When constructing a truth table, the binary values 1 and 0 are used. Every possible combination, depending on number of inputs, is produced. Basically, the number of possible combinations of 1s and 0s is 2n where n = number of inputs. For example, 2 inputs have 22 combinations (i.e. 4), 3 inputs have 23 combinations (i.e. 8) and so on. The next section shows how these truth tables are used.

Logic gates

Digital systems are said to be constructed by using logic gates. These gates are the AND, OR, NOT, NAND, NOR, EXOR and EXNOR gates. The basic operations are described below with the aid of truth table.Description of the six logic gates.

 Description of the  logic gates