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Digital Codes
12 questions By Tony R. Kuphaldt
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Question 7 of 12
A nearly universal standard for representing text data in digital form is the ASCII code. What does the acronym “ASCII” stand for, and what is the format of this code?
Reveal answer“ASCII” = American Standard Code for Information Interchange. Basic ASCII is a seven-bit binary code capable of representing all alphabetical characters used in the English language (upper-case as well as lower), as well as Arabic numerals, English punctuation marks, and some miscellaneous control codes for teletype machines.
Challenge question: although ASCII technically requires only 7 bits, a full 8 bits (1 byte) is usually reserved for each ASCII character in computer systems. Explain why.
Notes:ASCII is arguably the lingua franca of the digital world. Despite its humble beginnings and Anglo-centric format, it is used worldwide in digital computer and telecommunication systems. Let your students know that every plain-text computer file is nothing more than a collection of ASCII codes, one code for each text character (including spaces).
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Question 8 of 12
Decode this set of ASCII characters, to reveal a secret message (all codes given in hexadecimal format):
49 20 4C 6F 76 65 20 45 6C 65 63 74 72 6F 6E 69 63 73 21
Reveal answerI’ll let you decode this message on your own!
Notes:This question provides students with practice using an ASCII reference table.
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Question 9 of 12
Explain why Binary Coded Decimal (BCD) is sometimes referred to as the “8421” code. Why is this code used at all?
Reveal answerBCD uses groups of four binary bits to represent each digit of a decimal number. The LSD place weights are 8-4-2-1, while the next significant digit’s place weightings are 80-40-20-10, and so on.
Follow-up question: the four bits used for each BCD character could be called half of a byte (8 bits). There is a special word for a four-bit grouping. What is that word?
Notes:Discuss with your students the purpose of using BCD to represent decimal quantities. While not an efficient usage of bits, BCD certainly is convenient for representing decimal figures with discrete (0 or 1) logic states.
