Code 128 is an alphanumeric, very high-density, compact, variable length bar code scheme that can encode the full 128 ASCII character set. Each character is represented by three bars and three spaces totaling 11 modules. Each bar or space is one, two, three, or four modules wide with the total number of modules representing bars an even number and the total number of modules representing a space an odd number. Three different start characters are used to select one of three character sets.

Code 128 supports 107 unique characters, including:

• Four function characters

• Four code set selection characters

• Three start characters

A Code 128 bar code consists of the following elements:

• Leading quiet zone

• Start character

• Data characters

• Mandatory check character

• Stop character

• Termination bar

• Trailing quiet zone

An example of a Code 128 bar code is shown below: