Codes

7 September 2022
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Code Group
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A unique string of binary digits.
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Weighted Code
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A code in which corresponding decimal digits are easily determined by adding the weights associated with the 1's in the group's code.
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8421 Code
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A weighted code where the respective bits have decimal weights corresponding with 8421.
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Self-Complementing Codes
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The complement of the code group corresponds to the 9's complement. Example: 2421
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Nonweighted Decimal Codes
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Ecess-3, 2-out-of-5
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Ecess-3 Code
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0011 + (8421 code#)
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2-out-of-5 Code
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Two of the five bits must be 1's; is error-detecting. Used in USPS bar code.
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Unit-Distance Codes
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Only one bit changes between two successive integers being coded. Example: Grey code.
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Grey Code
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0: 0000 1: 0001 2: 0011 3: 0010 4: 0110 5: 0111 6: 0101 7: 0100 8: 1100 9: 1101 10: 1111 11: 1110 12: 1010 13: 1011 14: 1001 15: 1000
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Characters
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Alphabetic symbols, numeric symbols, special symols, certain control operations.
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Alphanumeric Codes
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Codes that are used to represent characters.
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ASCII
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(7 Bits) American Standard Code for Information Interchange
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Unicode
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(16 Bits) Unicode Standard provides encoding for English characters, foreign characters, punctuation, math symbols, technical symbols, geometric shapes, and dingbats.
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Error Detection
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Methods used to detect errors in transmission of binary information.
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Error Detecting Codes
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Codes that provide some level of error detection; do not necessarily detect all errors.
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Parity Bit
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An additional bit appended to a transmission so that the number of 1's in a code group is even or odd, depending on the parity rule in use (Even Parity, Odd Parity). Single and Triple Errors are detectable, because an odd number of incorrect bits will alter the code group's parity. Double errors are non-detectable, because an even number of incorrect bits will not alter the code group's parity.
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Error Detecting Capability
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1 less than the *minimum* number of errors that a code cannot always detect. Parity Bit would be single error detecting, because the minimum error it cannot detect would be 2 bits; 2-1 = 1 = Single Error Detecting.
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Distance (between Code Groups)
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Given the code groups for two characters in some coding scheme, it is the number of bits that must be changed in the first code group and the second code group. Basically the number of bits that need to be changed to get from one code group to the next.
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Error Detecting Capability (D)
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D = (minimum distance) - 1
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Error Correction (C)
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The relationship between the minimum distance of a code and its error-detecting and correcting capabilities. C + D = M-1, where Cโ‰คD
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Hamming Code
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Single error-correcting code; code group contains coded bits and parity bits. 7654321=bโ‚„bโ‚ƒbโ‚‚pโ‚ƒbโ‚pโ‚‚pโ‚ pโ‚: even over 1,3,5,7 pโ‚‚: even over 2,3,6,7 pโ‚ƒ: even over 4,5,6,7