User`s manual

A–20 Bar Codes
Postnet has the following characteristics:
• Ten digit character set (0 – 9)
• Illegal characters are not processed and are ignored.
• START and STOP codes
• No CENTER code
• Variable length characters per complete symbol
• A checksum is calculated automatically then embedded at the end of the
bar code.
• The human–readable data field is not printed.
Code 128 – USS
Code 128 includes three character subsets: A, B, and C. (Code 128–UCC
uses subset C only.) All contain the same bar patterns, except for the unique
start character that tells the bar code reader which subset is in use. Special
characters are available for switching between the subsets in order to
generate the shortest possible bar code. (Only subset C is used for 128–UCC,
so mode selection is not allowed.)
The Code 128 and 128–UCC structure is shown in Figure A–1 and described
on the following pages.
DATA FIELD
QUIETQUIET START STOP
LOWER GUARD BAND
CODE CODEZONE ZONE
OPTIONAL READABLE DATA FIELD
HEIGHT
UPPER GUARD BAND
STARTING
POSITION
CHECK DIGIT
FIELD
Figure A–1. Code 128 Structure
Start/Stop Codes
Code 128 contains special characters which use unique start/stop codes to
identify the leading and trailing end of the bar code. In the automatic mode,
start and stop codes are generated automatically. In the manual mode, you
must supply the start code, but the stop code is generated automatically.