Code128

The Code128 (1981 ) is an alphanumeric bar code ( bar code) with high information density. The principle structure of a Code128 symbol consists of a start character, the payload, the checksum and the stop character. Before the start character and stop character behind a white area must be kept clear ( bright field or quiet zone) with a width of at least 10 modules.

The code 128 is fully described in the international standard ISO / IEC 15417.

The encoding consists of a multi- width code with eleven modules for each symbol. Three bars and three spaces of a maximum of four modules width forming the code pattern to a symbol. The mark structure is self-monitoring, since the number of modules shown in a bar always even, the number of space modules is odd.

Three different start symbols define the Code128 the valid character set, and thus the meaning of a particular bar code pattern. The change of character set within a read symbol is controlled by context-dependent special function codes. These control characters can best be understood as punctuation, structure the information.

There are permanent or temporary character set changes, which apply only to a single episode characters defined. Furthermore, there are special codes that control the caching of prefix codes or labeling of special applications. Moreover, there is the possibility of combining multiple, sequentially read reading symbols.

The alphabet from Code128 contains the allocation of 103 bytes to the dedicated barcode patterns. There are also three different start characters and 1 stop sign. The stop sign occupies a special position. It is composed of 13 modules with four strokes and is independent of a character set selection. Because the code is 128 ( as well as other barcodes ) his information about the line widths and line positions coded, a precise code printing is required in order to read the encoded information can reliably again. For barcode creation TrueType fonts, PDF files and bitmap graphics for bar code printing are ill-suited.

Fonts

There are three different fonts:

• Character set A contains numbers, uppercase letters, special characters and ASCII control characters.
• Character set B contains all numbers and upper and lower case letters, and special characters and escape characters.
• Especially for numerical requirements assigns character set C the barcode patterns 100 pairs of values ​​from "00" to "99" to (plus special FNC1 ).

Contains a barcode several contiguous numbers, it may be advantageous in between to switch to the character set C, so as to reduce the number of required symbols.

The test mark is calculated as the remainder modulo 103 from the weighted sum of the character weights ( table indexes ) and inserted directly into the barcode before the stop sign. The code is not context-free, in contrast to older codes, such as 2/5, the interpretation of a character is thus determined by preceding character.

The Code128 is based on the GS1 - 128, which makes use of the special properties of concatenation, character set changes and prefix explicit use. Previously, the GS1 -128 was referred to as EAN -128. Due to the name change of the underlying organization GS1 ( Global Standards ONE), the name was changed to GS1 -128. The specificity results from the structured code content for GS1 applications. The specifications for standardized data structures can be found in the international standard ISO / IEC 15418.