• Recall: Computers communicate using binary
  • Therefore, computers do NOT process information using characters (e.g. letters).
  • Each letter or character has a number representation that the computer uses to refer to the character.
  • ASCII: American Standard Code for Information Interchange
  • ASCII is a code for representing English characters as numbers.
  • The ASCII numbers range from 0 to 255, each representing a character.
  • Numbers 0-32 are set aside for communications and printer control
  • Numbers 33-127  are standard characters
  • Numbers 128-255 are extended characters, or those not found on the keyboard.
  • Humans process information in decimal and ASCII
  • Therefore, when communicating with a computer, the computer will translate the information from ASCII to binary for us! (and also binary to ASCII)
  • Recall
  • When converting binary to decimal, binary numbers have a place value of base 2.
  • That is
  • · 27 26 25 24 23 22 21 20

  • o or

  • · 128                  64                    32                    16                    8                     4                     2                     1

  • Recall:
  • Convert the following binary numbers to decimal numbers
  • 00000101
  • 00001000
  • 01110101
  • 01010001
  • Notice: All the binary numbers are 8 digits long.
  • Each byte in memory can hold an ASCII character.
  • Each byte holds 8 bits
  • Each bit can be represented by a 1 or 0
  • Therefore, each byte can hold an ASCII character that is composed of 8 bits.
  • Recall: Memory can be thought of an array of boxes that holds a single byte of information.
  • Solve:
  • Convert the following binary numbers to ASCII characters
  • 0111010101010001
  • Solution:
  • Step 1:
    • Break apart the sequence into 8 bit (1 byte) sections to decode
    • 111010101010001=1110101 and 0101000
  • Note: because 1110101 is seven digits and eight is needed, simply add a 0 to the front: 01110101
  • Step 2:
    • Convert each 8 bit sections to decimal numbers
      • 01110101 =  117
      • 01010001 =   81
  • Step 3:
    • Convert decimals to ASCII characters (by looking it up to the table)
      • 117 = u
      • 81 = Q
  • Therefore, 0111010101010001 = uQ

Recall:

  • The ASCII representation for the letter ‘w’ is 11910. What is the ASCII representation for the letter ‘w’ in binary form?

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