User's Manual

Chapter 6 — Bar Code Symbologies
116 CK60 Series Handheld Computer User’s Manual
Bar code readers can respond to Uniform Symbology Specification symbols
in non-standard ways for particular applications. These methods are not for
general applications, because of the extra programming required. Code 39
Full ASCII is one example of a symbology feature or operating mode, and is
defined as part of the symbology specification. This mode can be used for
general applications or any open system applications.
Code 39 Full ASCII Mode
If the bar code reader is programmed for the task, the entire ASCII charac-
ter set (128 characters) could be coded using two character sequences: a
symbol (“$”,“.”,“%”,“/”) followed by a letter of the alphabet.
Concatenated Code 39
If the first data character of a symbol is a space, the reader may be pro-
grammed to append the information contained in the remainder of the
symbol to a storage buffer. This operation continues for all successive sym-
bols that contain a leading space, with messages being added to the end of
previously stored ones. When a message is read which does not contain a
leading space, the contents are appended to the buffer, the entire buffer is
transmitted, and the buffer is cleared.
Code 93
The introduction of Code 93 provided a higher density alphanumeric sym-
bology designed to supplement Code 39. The set of data characters in Code
93 is identical with that offered with Code 39. Each character consists of
nine modules arranged into three bars and three spaces.
Code 93 uses 48 of the 56 possible combinations. One of these characters,
represented by a square, is reserved for a start or stop character, four are
used for control characters, and the remaining 43 data characters coincide
with the Code 39 character set. An additional single module termination
bar after the stop character concludes the final space.
Code 93 is a variable length, continuous code that is not self-checking. Bar
and spaces widths may be one, two, three, or four modules wide. Its struc-
ture uses edge-to-similar-edge decoding. This makes the bar code immune
to uniform ink spread, which allows liberal bar width tolerances.
Code 93 uses two check characters. Its supporters believes this makes it the
highest density alphanumeric bar code. The dual check digit scheme pro-
vides for high data integrity. All substitution errors in a single character are
detected for any message length.
Code 128
Code 128 (C128) is one of the newest symbologies used by the retail and
manufacturing industries. It responds to the need for a compact alphanu-
meric bar code symbol that could encode complex product identification.