GS1 EPC Tag Data Standard 1.6 - Indicod-Ecr

5665566656675668566956705671567256735674567556765677567856795680568156825683568456855686568756885689569056915692569356945695569656975698569957005701570257035704M.2 Decoding Alphanumeric dataWithin the Alphanumeric subsection of a Packed Object, the total number of datacharacters is not encoded, nor is the bit length of the character map, nor are the bitlengths of the succeeding Binary sections (representing the numeric and non-numericBinary values). As a result, the decoder must follow a specific procedure in order tocorrectly parse the AlphaNumeric section.When decoding the A/N subsection using this procedure, the decoder will first count thenumber of non-bitmapped values in each base (as indicated by the various Prefix andSuffix Runs), and (from that count) will determine the number of bits required to encodedthese numbers of values in these bases. The procedure can then calculate, from theremaining number of bits, the number of explicitly-encoded character map bits. Afterseparately decoding the various binary fields (one field for each base that was used), thedecoder “re-interleaves” the decoded ASCII characters in the correct order.The A/N subsection decoding procedure is as follows:Determine the total number of non-pad bits in the Packed Object, as described insection I.8.2Keep a count of the total number of bits parsed thus far, as each of the subsectionsprior to the Alphanumeric subsection is processedParse the initial Header bits of the Alphanumeric subsection, up to but not includingthe Character Map, and add this number to previous value of TotalBitsParsed.Initialize a DigitsCount to the total number of base-10 values indicated by the Prefixand Suffix (which may be zero)Initialize an ExtDigitsCount to the total number of base-13 values indicated by thePrefix and Suffix (which may be zero)Initialize a NonDigitsCount to the total number of base-30, base 74, or base-256values indicated by the Prefix and Suffix (which may be zero)Initialize an ExtNonDigitsCount to the total number of base-40 or base 84 valuesindicated by the Prefix and Suffix (which may be zero)Calculate Extended-base Bit Counts: Using the tables in Annex K, calculate twonumbers: ExtDigitBits, the number of bits required to encode the number of base-13 valuesindicated by ExtDigitsCount, and ExtNonDigitBits, the number of bits required to encode the number of base-40 (orbase-84) values indicated by ExtNonDigitsCount Add ExtDigitBits and ExtNonDigitBits to TotalBitsParsedCreate a PrefixCharacterMap bit string, a sequence of zero or more quad-basecharacter-map pairs, as indicated by the Prefix bits just parsed. Use quad-base bitpairs defined as follows: ‘00’ indicates a base 10 value; ‘01’ indicates a character encoded in Base 13;Copyright ©2005- 2011 GS1 AISBL, All Rights Reserved. Page 213 of 218