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Computer Code
Introduction
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The Language of electronic component is binary
All numeric and non-numeric data must be
converted into binary language so that computer can
understand it
Representation of all numeric and non-numeric data
in binary digits is known as computer code
Computer code is represented in different coding
schemes
Coding Schemes
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BCD Code
ASCII Code
EBCDIC Code
Unicode
BCD Code
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Stands for Binary Coded Decimal
Used to represent decimal digits in binary
4-bit code
Each decimal digit is represented by 4 binary digits
Used by early computers
BCD Code
http://electronicsarea.com/bcd-code/
Example
http://electronicsarea.com/bcd-code/
Example
http://electronicsarea.com/bcd-code/
ASCII Code
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American Standard Code for Information Interchange
Most widely used coding scheme for personal
computers
7-bit code can represent 128 characters
Not enough to represent some graphical characters
displayed on computer screens
An 8 bit code can represent 256 characters
Extended 128 unique codes represent graphic
symbols
ASCII Code
http://www.gjszlin.cz/ivt/esf/ostatni-sin/kodovani-textu.php?lang=1
Example
Character
B
i
n
a
r
y
Decimal Code
66
105
110
97
114
121
Binary Code
01000010
01101001
01101110
01100001
01110010
01111001
EBCDIC Code
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Extended Binary Coded Decimal Interchange Code
8-bit code
Divided into two group of 4 bits
Each group cam represent one hexadecimal digit
Normally used in mainframe computers
Can represent 256 characters
EBCDIC Code
http://www.rtty.com/CODECARD/codecrd1.htm
Unicode
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16 bit code
Represent 65536 characters
Started to replace ASCII code
Can represent the characters of all languages in the
world
Boolean Algebra
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Algebra of logic
Also called logical algebra or switching algebra
Uses symbols to represent logical statements instead
of words
Consists of different rules to manipulate rules
Similar to calculus
Boolean Algebra
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Used in the designing of logic circuits in computer
Computer chips consists of transistors that are
arranged in logical gates
Each gate performs a single logical operation
Computer performs logical operation by processing
electrical pulses
Design of a particular circuit is based on a set of
logical statements
Results of boolean algebra can be true or false
The digit 1 indicates true and 0 indicates false result
Elements of Boolean Algebra
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An expression in Boolean Algebra can be formed
using different elements of Boolean algebra
Different elements of Boolean algebra are as follows:
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Boolean Variables
Boolean Constants
Logical Operators
Parentheses
Logical Operators in Boolean Algebra
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Symbols used to perform logical operations are called
logical operators
Different logical operators are:
◦ AND
◦ OR
◦ NOT
Basic Logic Gates
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Many basic functions of the arithmetic and control
units are carried out by logic gates
Each gate accepts input and produces an output
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NOT Gate
AND Gate
OR Gate
NAND Gate
NOR Gate
XOR Gate
XNOR Gate
Boolean Expression
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Logical statement that is either true or false
Consists of different elements of Boolean Algebra
Logic Diagrams and Expressions
Logic Equation
Truth Table
XY Z
F = X + YZ
000
0
001
1
010
0
011
0
100
1
101
1
110
1
111
1
F = X +Y Z
Logic Diagram
X
Y
F
Z
Boolean equations, truth tables and logic diagrams describe the
same function!
 Truth tables are unique, but expressions and logic diagrams are
not. This gives flexibility in implementing functions.
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Boolean Algebra
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Invented by George Boole in 1854
An algebraic structure defined by a set B = {0, 1}, together with two binary
operators (+ and ·) and a unary operator ( )
Identity element
1.
X +0= X
2.
X .1=X
3.
X+ 1=1
4.
X .0=0
5.
X+X=X
6.
X .X = X
Idempotence
7.
X+X=1
8.
X .X = 0
Complement
9.
X=X
Involution
10.
X +Y = Y + X
11.
12.
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(XY) Z = X(Y Z)
Associative
14.
(X + Y) + Z = X + (Y + Z)
X(Y + Z) = XY + XZ
15.
X + YZ = (X + Y) (X + Z)
Distributive
16.
X +Y =X .Y
17.
X .Y = X +Y
DeMorgan ’s
XY = YX
Commutative
References
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Slides Taken From:
www.cse.yorku.ca/~mack/1011/01.NumberSystems.p
pt
Introduction to Information Technology by Riaz
Shahid, CM Aslam and Safia Iftikhar
The Concepts of Information Technology by Imran
Saeed, Ahsan Raza, Tariq Mehmood and Zafar
Hussain