GS1 EPC Tag Data Standard 1.6 - Indicod-Ecr

25022503250425052506250725082509251025112512251325142515251625172518251925202521252225232524252525262527252825292530253125322533253425352536253725382539254025412542single character, the corresponding 6-bit string is specified in Table 48 (Appendix G).For an Escape sequence, the corresponding 6-bit string is specified in Table 48(Appendix G) by finding the escape sequence in the “URI Form” column. Concatenatethose 6-bit strings in the order corresponding to the input, then append six zero bits(000000).The resulting bit string is of variable length, but is always at least 6 bits and is always amultiple of 6 bits.14.4Decoding ProcedureThis procedure decodes a bit string as found beginning at bit 20 h in the EPC memorybank of a Gen 2 Tag into an EPC Tag URI. This procedure only decodes the EPC andfilter value (if applicable). Section 15.2.2 gives the complete procedure for decoding theentire contents of the EPC memory bank, including control information that is storedoutside of the encoded EPC. The procedure in Section 15.2.2 should be used by mostapplications. (The procedure in Section 15.2.2 uses the procedure below as a subroutine.)Given: A bit string consisting of N bits b N-1 b N-2 …b 0Yields: An EPC Tag URI beginning with urn:epc:tag:, which does not contain controlinformation fields (other than the filter value if the EPC scheme includes a filtervalue); OR An exception indicating that the bit string cannot be decoded into an EPC Tag URI.Procedure:1. Extract the most significant eight bits, the EPC header: b N-1 b N-2 …b N-8 . Referring toTable 16 in Section 14.2, use the header to identify the coding table for this binaryencoding and the encoding bit length B. If no coding table exists for this header, stop:this binary encoding cannot be decoded.2. Confirm that the total number of bits N is greater than or equal to the total number ofbits B specified for this header in Table 16. If not, stop: this binary encoding cannotbe decoded.3. If necessary, truncate the least significant bits of the input to match the number of bitsspecified in Table 16. That is, if Table 16 specifies B bits, retain bits b N-1 b N-2 …b N-B .For the remainder of this procedure, consider the remaining bits to be numberedb B-1 b B-2 …b 0 . (The purpose of this step is to remove any trailing zero padding bits thatmay have been read due to word-oriented data transfer.)For a variable-length coding scheme, there is no B specified in Table 16 and so thisstep must be omitted. There may be trailing zero padding bits remaining after allsegments are decoded in Step 4, below; if so, ignore them.4. Separate the bits of the binary encoding into segments according to the “bit position”row of the coding table. For each segment, decode the bits to obtain a character stringthat will be used as a portion of the final URI. The method for decoding each columndepends on the “coding method” row of the table. If the “coding method” rowCopyright ©2005- 2011 GS1 AISBL, All Rights Reserved. Page 89 of 218