1
Bangladesh Army University of
Engineering & Technology (BAUET)
          Dept. of CSE
    Course Code: CSE- 2101
Course Title: Digital Logic Design
Mirza A.F.M.Rashidul Hasan,   D.Engg &
               Ph.D
                 Lecture-1
     Fundamentals of Digital
         Logic System
Digital electronics is the foundation of modern computers
and digital communications.
Massively complex digital logic circuits with millions of
gates can now be built onto a single integrated circuit (IC)
such as a microprocessor.
These IC circuits can perform millions of operations per
second.
Number System
Common Number Systems
                                        Number Systems
• Each number system is associated with a base or radix
  -The decimal number system is said to be of base or radix 10
• A number in base r contains r digits 0,1,2,...,r-1
  -Decimal (Base 10): 0,1,2,3,4,5,6,7,8,9
• Numbers are usually expressed in positional notation
     –   MSD: most significant digit
                                                                 7
     –   LSD: least significant digit
Common Number Systems
                             Used by Used in
System    Base Symbols       humans? computers?
Decimal    10   0, 1, … 9      Yes       No
Binary     2    0, 1           No        Yes
Octal      8    0, 1, … 7      No        No
Hexa-      16   0, 1, … 9,     No        No
decimal         A, B, … F
Conversion Among Bases
 Decimal           Octal
 Binary         Hexadecimal
        Decimal Number
                    Weight
• 12510 => 5 x 100 =   5
               2 x 101 = 20
               1 x 102 = 100
                         125
             Base
                    Binary to Decimal
                   Binary                                      Decimal
Technique
  • Multiply each bit by 2n, where n is the “weight” of the bit
  • The weight is the position of the bit, starting from 0 on the right
  • Add the results
                             Bit “0”
                 1010112 =>            1   x   20   =    1
                                       1   x   21   =    2
                                       0   x   22   =    0
                                       1   x   23   =    8
                                       0   x   24   =    0
                                       1   x   25   =   32
                                                        4310
                      Decimal to Binary
    12510 = ?2                    2 125
                                  2   62     1
                                  2   31     0
                                                            12510 = 11111012
                                 2    15     1
                                  2    7     1
                                  2    3     1
                                  2    1     1
                                       0     1
Technique
  • Divide by two, keep track of the remainder
  • First remainder is bit 0 (LSB, least-significant bit)
  • Second remainder is bit 1
  • Etc.
     Decimal to Octal
Decimal              Octal
Binary            Hexadecimal
              Decimal to Octal
• Technique
  – Divide by 8
  – Keep track of the remainder
                  Example
123410 = ?8
              8   1234
              8    154   2
              8     19   2
              8      2   3
                     0   2
                             123410 = 23228