GS1 EPC Tag Data Standard 1.6 - Indicod-Ecr

4584458545864587458845894590459145924593459445954596459745984599460046014602460346044605460646074608460946104611461246134614461546164617461846194620462146224623ASCII characters, or eight-bit data. The digit characters within this data are encodedseparately, at an average efficiency of 4.322 bits per digit or better, depending on thecharacter sequence. The non-digit characters are independently encoded at an averageefficiency that varies between 5.91 bits per character or better (all uppercase letters), to aworst-case limit of 9 bits per character (if the character mix requires Base 256 encodingof non-numeric characters).An Alphanumeric subsection consists of a series of A/N Header bits (see I.8.2.1),followed by from one to four Binary segments (each segment representing data encodedin a single numerical Base, such as Base 10 or Base 30, see I.8.2.4), padded if necessaryto complete the final byte (see I 8.2.5).I.8.2.1 A/N Header BitsThe A/N Header Bits are defined as follows: One or two Non-Numeric Base bits, as follows: ‘0’ indicates that Base 30 was chosen for the non-numeric Base; ‘10’ indicates that Base 74 was chosen for the non-numeric Base; ‘11’ indicates that Base 256 was chosen for the non-numeric Base Either a single ‘0’ bit (indicating that no Character Map Prefix is encoded), or a ‘1’bit followed by one or more “Runs” of six Prefix bits as defined in I.8.2.3. Either a single ‘0’ bit (indicating that no Character Map Suffix is encoded), or a ‘1’bit followed by one or more “Runs” of six Suffix bits as defined in I.8.2.3. A variable-length “Character Map” bit pattern (see I.8.2.2), representing the base ofeach of the data characters, if any, that were not accounted for by a Prefix or Suffix.I.8.2.2 Dual-base Character-map encodingCompaction of the ordered list of alphanumeric data strings (excluding those data stringsalready encoded in the Known-Length Numerics subsection) is achieved by firstconcatenating the data characters into a single data string (the individual string lengthshave already been recorded in the Aux Format section). Each of the data characters isclassified as either Base 10 (for numeric digits), Base 30 non-numerics (primarilyuppercase A-Z), Base 74 non-numerics (which includes both uppercase and lowercasealphas, and other ASCII characters), or Base 256 characters. These character sets arefully defined in Annex K. All characters from the Base 74 set are also accessible fromBase 30 via the use of an extra “shift” value (as are most of the lower 128 characters inthe Base 256 set). Depending on the relative percentage of “native” Base 30 values vs.other values in the data string, one of those bases is selected as the more efficient choicefor a non-numeric base.Next, the precise sequence of numeric and non-numeric characters is recorded andencoded, using a variable-length bit pattern, called a “character map,” where each ‘0’represents a Base 10 value (encoding a digit) and each ‘1’ represents a value for a nonnumericcharacter (in the selected base). Note that, (for example) if Base 30 encodingwas selected, each data character (other than uppercase letters and the space character)Copyright ©2005- 2011 GS1 AISBL, All Rights Reserved. Page 182 of 218