Code 128 - Printronix L7032 Programmer's Reference Manual

Code 128

Code 128 includes three subsets: A, B, and C. All contain the same bar
patterns, except for the unique start character instructing the bar code reader
which subset is being used. Special characters are available for switching
between the subsets in order to generate the shortest possible bar code. The
Code 128 structure is shown in Figure 9 and described on the following
pages.
STARTING
POSITION
QUIET START
ZONE CODE
LOWER GUARD BAND
OPTIONAL READABLE DATA FIELD
Quiet Zone
Both ends of the bar code structure require blank quiet zones. The quiet
zones should be at least 0.25 inches wide and completely blank to ensure
accurate reading of the start/stop codes and to prevent adjacent bar codes
from overlapping. You are responsible for providing sufficient space on the
form for the quiet zones.
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.
CHECK DIGIT
FIELD
STOP QUIET
DATA FIELD
CODE ZONE
Figure 9. Code 128 Structure
QUIET
ZONE
STARTING
POSITION
START
CODE
OPTIONAL
READABLE
DATA DATA
FIELD
FIELD
STOP
LOWER
GUARD CODE
BAND
HEIGHT
QUIET
ZONE
HEIGHT
Code 128
CHECK
DIGIT
FIELD
195