Code 128 Barcode Specification

Following a few days of generally musing on the Bardecode blog it is probably time for a more technical post again. This time we are back to barcode specification, as was done a week or so ago with Code 39 barcodes. This time though we are moving boldy into the world of Code 128 barcode specifications.

Code 128 Barcodes are among the most complicated linear barcodes which is great for stuffing them with information but less great for their production. Firstly it is worth remembering that they require a better quality to get a successful read than either Code 25 or 39. However this concern is pointless unless the barcode itself is correct. Below is a list of some of the basic principles which make a Code what it is.

  • 4 different width of bar/space.
  • 3 symbol sets (A, B and C).
  • Symbol set C encodes pairs of digits and is one of the best ways to store large numbers in a linear barcode.
  • Ability to switch between symbol sets.
  • Barcodes include start and stop character plus a built in checksum.
  • Each character is made up of 3 bars and 3 spaces – except for the stop character which has 4 bars and 3 spaces.
  • The number of black bars should leave remainder 1 when divided by 3.

For more information please view our knowledge base which covers the issue of checksums (vital to code 128 barcodes) and many other common issues.


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