Introduction
Code 128 is a high-density alphanumeric symbology. Since it was
introduced in early 1980s, it has been widely adopted by many industry
applications. UCC/EAN derives its retail carton tracking standard UCC/EAN-128 based on Code 128 symbology.
Code 128 is a variable
length, continuous symbology with multiple element widths. Every Code 128
symbol has a check character. Each character is encoded with three bars and
spaces, in total 11 modules.
Code 128 is designed to encode 128 full ASCII characters.
Code 128 has 106 different printed character patterns. Each printed
character can have one of three different meanings, depending on the
context selector. Three different start characters tell the reader the
character set used in the following encoding, and three shift codes permits
changing character set inside the symbol. From the table below, we can see that character set A and B
is used to encode alpha-numeric
information while character set C offers double density when being used to
encode
numeric data. The special character Shift, changes the character set of the
immediately followed character. The shift work only with Code A or
Code B characters. Four FNC characters are listed, FNC2 is used to tell
barcode reader to store the data and transmit with next symbol; FNC1,
FNC3 and FNC4 are reserved for future applications.
In an open system, the minimum value of X dimension is 7.5 mils. the
minimum bar height is 15 percent of the symbol length or 0.25
inches, whichever is greater. The starting and trailing quiet
zones should be at least 0.25 inch wide.
Structure of a code 128 barcode
A typical code 128 barcode has the following structure:
- A start character
- Message encoded
- Check character
- Stop Character
- Termination bar (bar+space+bar)
Check Digit Calculation
Every Code 128 symbol requires a check character being placed between
encoded data and stop character. The check
character is derived from a modulo 103 calculation of the weighted sum of all
characters. Here is the procedure to calculate the check character:
- Take the value (0 through 102)
of each character in the message. This includes the
start character, shift character, but excluding the stop character.
-
Start with the first character of the data, assign the weight for each
character. The first character has a weight of 1, the second character
has a weight of 2.. and increment by 1. Note that the start character also has a
weight of 1. stop character is excluded in the calculation.
- Multiply the character value with weight. Sum all the results.
- Divide the result by 103 and get the remainder. Look up the
remainder in the table to get the check character.
- The stop character, and
termination bar is appended after the check character.
Web Tool
At barcode knowledge library we provide free web-based utilities for
readers to calculate check digits, performing character mapping. To
calculate code 128 check digit, refer to this page. If you have
purchased Morovia Code128 Font, you may consider checking out this
page for additional utilities for character mapping.
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