Telecommunications Industry Forum (TCIF) Linked Code 39 (TLC 39) was invented in 2001 by Frederick Schuessler of Symbol Technologies, Inc. This symbology gave many companies the ability to continue to use their existing linear code scanners while transitioning to more sophisticated equipment that could also read the two-dimensional (2-D) components.
The symbol combines a Code 39 - Regular linear component that has an added linkage flag with a MicroPDF417 2-D stacked component that omits the leading data identifier (S). There is no separator pattern between the components and no required amount of space between them. The linkage flag appears as a set of five bars and four spaces (representing the letter T) to the right of the Code 39 symbol. Apart from this linkage flag and the omission of the data identifier, TLC 39 inherits its characteristics from Code 39 and MicroPDF417 and is decoded as these symbols would typically be.
Linear component; The required input string for the TLC39 begins with a regular linear Code 39. To link the Code 39 with the MicroPDF417 there is a 5 bar 'Code 39 link flag' printed right of the linear Code 39. The MicroPDF417 portion is placed on top of the linear Code 39.
The MicroPDF417 is not a regular MicroPDF417 and can not be read independently. TLC39 MicroPDF417 component can come in different formats and the format is identified by the data structure in the MicroPDF417, that just contains the raw data. The used 'envelope' number is the number that follows the first [RS]-character in the output. All the none printable characters, just as the AI's or DI's are added by the scanner based on the envelope. The most commonly used envelopes are 05 and 06. There are always four columns in the MicroPDF417 component used to encode supplementary data, such as the serial number, and other optional data elements
The TLC39 output is generally terminated with a [RS][EOT]. Linked is a Test sheet with sample TLC39's, a generic Composite Barcode Test Sheet (including a TLC39) with symbols for testing purposes, and another Telecommunications Industry Forum TLC39 sheet.