ASCII: American Standard Code for Information Interchange

• 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?

William Anderson (Schoolworkhelper Editorial Team)

William completed his Bachelor of Science and Master of Arts in 2013. He current serves as a lecturer, tutor and freelance writer. In his spare time, he enjoys reading, walking his dog and parasailing. Article last reviewed: 2022 | St. Rosemary Institution © 2010-2024 | Creative Commons 4.0

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