code 128
Code 128 is a universal, variable-length alphanumeric bar code that can represent the ASCII character set of 128 characters. It is a very compact bar code that is used extensively around the world. There are three Code 128 variants, 128A, 128B and 128C, which are used for specific applications.
Code 128 is a multi-width code whose bar code consists of three bars (S) and three gaps (L) each with different widths. The sum of all bar and gap widths is always eleven. For error correction, the checksum of the bar widths always results in an even number. According to the mentioned specifications, an encoding of a character according to the code 128 looks like this: S2- L2-S1-L2-S1- L3. The sum of bar and gap widths is 11, the sum of bar widths - in the example: 4 - is even.
For Code 128, the total length of the bar code information is variable and depends only on the scan width.
Code 128 can encode three different codes: Code 128A, Code 128B, and Code128 C. Code 128A only partially represents the ASCII character set and does not support lowercase letters, but does support the ASCII control characters. Code 128B supports the full ASCII character set but no control characters and Code 128C is a very compact numeric code that supports only digits. Which code is used is determined by the start character. In Code 128A, the start character has the value 103, in 128B 104, and in 128C 105. The stop character that follows the checksum consists of 4 dashes and 3 gaps in all three Code 128 variants and has the value 106. Code A and Code B differ in that Code A contains all control characters such as Acknowledgement( ACK), Bell( BEL), Backspace ( BS), Form Feed( FF), etc., Code B, on the other hand, contains upper and lower case letters, and Code C contains the digits 0 to 99.