Fbise Notes-Computer

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Computer Logic and Gates CH# 06

Short Questions and Answers

i. What is Logical gate?

Ans: Logical Gates:

A Logical gates are the basic building blocks of digital computer. Logical gates operate on two voltage levels and process digital signals which represents binary digits 0 and 1.

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ii. Define truth table.

Ans: Truth Table:

A truth table represents a digital logic circuit in table form. it shows how a logic circuit's output responds to all the possible combinations of the inputs using logic '1' for true and logic '0' for false.

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iii. Define Boolean Function?

Ans: Boolean Function:

A Boolean function is an expression formed with binary variables, the logical operators i.e; OR, AND, and NOT, parenthesis and equal sign.

A Boolean function can be transformed from an algebric expression into a logical circuit composed of AND, OR and NOT gates. A binary variable can take the value of 0 or 1.

Example:

F = x+y

The function F is equal to 0, if x = 0 and y = 0. For all the other combinations the function will be equal to 1.

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iv. What is Karnaugh Map?

Ans: Karnaugh Map:

K-map is a pictorial form of a truth table. It consists of square boxes called cells. All the possible combinations of variables involved in a Boolean function are written inside the cells. A two variable K-map contains 2²= 4 cells, three variables 2³= 8 and so on.

Use of K-map:

K-map is used for logic simplification. it provides a pictorial method of grouping together expressions with common factors and therefore eliminating unwanted variables.

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v. Draw three variable Karnaugh map for variables X,Y and Z.

Ans: Simplification of three variable k-map for X,Y and Z

It consists of eight cells having two rows and four columns. Rows are labled with the complement and normal form of the variable X. Each column is labbled with two variables Y and Z in normal or complimented form. Each cell contains a product term of variables X,Y and Z in its respected cell.

Example :

The term X compliment, Y normal and Z compliment is placed in cell that is in row X compliment and column Y normal and Z compliment.