How does the 1999 AIM International Symbology Specification for Code 128 differ from previous versions?

Code 128 Symbology Overview

Code 128 Introduction

Code 128 is a linear bar code symbology capable of encoding the full 128-character ASCII character set and extended character sets.

Code 128 Characteristics

The characteristics of Code 128 are:
a) Encodable Character Set:

b) Code type: Continuous

c) Elements per symbol character: 6, comprising 3 bars and 3 spaces, each of 1, 2, 3 or 4 modules in width (STOP character: 7 elements comprising 4 bars and 3 spaces)

d) Character Self-checking: Yes

e) Symbol Length: Variable

f) Bidirectionally Decodable: Yes

g) Symbol Check Character: One, mandatory

h) Data Character Density: 11 modules per symbol character (5,5 modules per data character in Code Set C)

i) Non-data Overhead: Equivalent to 35 modules

Code 128 Code Sets

a. Code Set A includes all of the standard upper case U.S. alphanumeric keyboard characters and punctuation characters together with the control characters, (i.e. characters with ASCII values from 00 to 95 inclusive), and seven special characters.

b. Code Set B includes all of the standard upper case alphanumeric keyboard characters and punctuation characters together with the lower case alphabetic characters (i.e. characters with ASCII values from 32 to 127 inclusive), and seven special characters.

c. Code Set C includes the set of 100 digit pairs from 00 to 99 inclusive, as well as three special characters. This allows numeric data to be encoded as two data digits per symbol character, at effectively twice the density of standard data.

Code 128 Special characters

The last seven characters of Code Sets A and B (character values 96 - 102) and the last three characters of Code Set C (character values 100 - 102) are special non-data characters with no ASCII character equivalents, which have particular significance to the bar code reading device.