code 39
Code 39, Code 3 of 9, is an alphanumeric bar code with which the digits 0 to 9 and 26 letters can be represented. The designation Code 39 is better interpretable as 3 of 9. It refers to 9 information characters, five bars (S) and 4 spaces (L), of which three are wide and six are narrow.
The narrower information characters of code 39 are designated S0 and L0, the wider ones S1 and L1. The three wider information characters (S1 and L1) are used to determine the checksum. According to these specifications, a character in Code 39 format is represented as follows: S0-L0-S1-L0-S1-L0-S0-L1-S0. The number of characters is 9, three of which are wider.
Code 39 has only a limited range of information. The total character range was originally 39 characters and special characters, which was later increased to 43 characters. Each Code 39 character is limited by a start and a stop character. An asterisk (*) is used for this purpose. The error tolerance of Code 39 is relatively low. The error rate is relatively high and in the worst case is one miss character in 1.7 MB ofdata, in the best case it is one error in 4.5 MB of data.
A variant of Code 39 is Code 39 Full ASCII or Code 39e (extended), with which the complete ASCII character set with 128 characters can be represented. A control character is used to switch from Code 39 Full ASCII to Code 39.