Kyocera ECOSYS FS-4100DN PRESCRIBE Commands Technical Reference Manual - Rev. - Page 94

Chapter 5 Barcodes Two-dimensional Barcodes PDF 417 is a two-dimensional stacked barcode symbology capable of encoding over a kilobyte of data per label. This is important for applications where a barcode must be more than merely an identifier, an index to reference a database. The portable data file approach is well suited to applications where it is impractical to store item information in a database or where the database is not accessible when and where the item's barcode is read. Because a PDF417 symbol can store so much data, item data such as the content of a shipping manifest or equipment maintenance history can be carried on the item, without requiring access to a remote database. Encoding data into a PDF417 barcode is a two-step process. First, data is converted into codeword values of 0-928, which represent the data. This is high-level encoding. Then the values are physically represented by particular bar/space patterns, which is low-level encoding. Decoding is the reverse process. In addition, PDF417 is an error-correcting symbology designed for real-world applications where portions of labels can get destroyed in handling. It performs error correction by making calculations, if necessary, to reconstruct undecoded or corrupted portions of the symbol. PDF417 Symbol Description At first glance, a PDF417 symbol looks like a set of stacked barcodes. When we look closer to analyze how the symbol is put together, there are several key elements. These are rows, start patterns, stop patterns, codewords, and modules, whose definitions are explained below. module The narrowest width of a bar or space in the barcode. All bars or spaces are multiples (up to six times) of this width. The nominal unit of measure. codeword A single group of bars and spaces (or elements) representing one or more numbers, letters, or other symbols (i.e., codeword values for the data to be encoded). Each PDF417 codeword contains four bars and four spaces, for a total of 17 module widths. Each codeword starts with a bar and ends with a space. See figure below. 1-module width 3-module wide bar 0 0 0 1 0 1 0 1 0 0 0 1 1 1 1 1 1 5-10