Code 128 A Generator

Code 128 subset A: uppercase letters and control characters, used in logistics and warehousing.

How Code 128 A is structured

Subset A is one of the three Code 128 code sets, opened by the start character whose value is 103. It carries uppercase A to Z, digits, punctuation and the 29 ASCII control characters 0x00 to 0x1F — which makes it the only subset that can hold a tab, a carriage return or a field separator inside a single symbol. Character geometry is unchanged: 11 modules per character, stop character 13.

Code 128 A check digit

The mod-103 check character is calculated exactly as for any Code 128 symbol; the only difference is the starting value of 103 that seeds the sum. Positions count per symbol character, so a control character counts once, not once per byte it represents.

Code 128 A compared with Code 128

Subset B prints the same printable characters plus lowercase, so B is the better general-purpose choice; A earns its keep only when control characters or a strict legacy mapping matter. For long digit strings, subset C packs two digits per character where A needs one character per digit. Compare the Code 128 generator page for the same breakdown of structure, check digit and use cases.

Common Code 128 A problems

Lowercase letters are rejected

Subset A has no lowercase. Convert the payload to uppercase, or move the data to a subset B or auto symbol — an encoder that silently upper-cases input is producing a symbol that scans back as different text than the label shows.

Tabs and carriage returns vanish from the input

Control characters are legal in subset A but a single-line text field usually strips them. Feed the payload through the batch input or a file instead of pasting it, then verify the returned string with a scanner that shows non-printing characters.

Readers return the data plus a stray character

Some readers configured for subset B or C read an A symbol with a substitute character where they cannot decode a control code. Reprogram the reader for the full Code 128 character set, or drop the control characters from the payload.

Where Code 128 A is used

Not sure this is the right symbology? The barcode format guide groups every supported 1D and 2D format by industry with its character set and limits.