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Bar code is a printed label with different bar and space to represent different
characters. The bars and spaces in each symbol are grouped in such a way to represent
a specific ASCII character. The interpretation of these groups is based on a particular
set of rules called symbologies. Various
symbologies have been developed for particular applications. Some are
alphanumeric, while others contain the full ASCII set, or only numeric data. It
is important to choose a right bar code symbology for
your products.
Choosing the
Right Bar Code
There are many types of bar code symbologies each having
their own special characteristics and features. Most symbologies
were designed to meet the needs of a specific application or a specific industry.
For example the UPC symbology was designed for identifying
retail and grocery items and PostNET was designed to
encode Zip Codes for the US Postal Service. You should choose a universal
symbology that is supported by most manufacturers.
Bar Code Densities
The density or resolution of a bar
code is dependent upon the narrowest element of a bar code (X dimension), and can
vary from high resolution: nominally less than 0.009 inches (0.23 mm); medium resolution:
between 0.009 inches (0.23 mm) and 0.020 inches (0.50 mm); and low resolution: greater
than 0.020 inches (0.50 mm).
For the most effective and reliable
scanning with any input device, use the lowest bar code density possible that will
print on a given area on the label or page. This will make it easier to print and
allow a higher depth of field for scanning. When space is available, Code 39 and
Code 128 are the best possible choices when implementing most bar codes solutions.
Symbologies
Several of the most commonly supported
symbologies are outlined below. The list below
compares some of the important features between the symbologies.
The Bar Code specifications for each of the symbologies
can be requested from the trade organizations listed in the Bar Code Links
CODE 39
Code 39 is variable length and is
the most frequently used symbology in industrial bar
code systems today. The principal feature is to encode messages using the full alphanumeric
character set. Three of the nine elements (bars) are wide and six elements are narrow.
The Code 39 bar code uses four special characters "$", "/", "+". "%" which can be
paired with alphanumeric characters to extend to the full ASCII character set.
CODE 128
Code 128 is variable length and encodes
the full 128 ASCII character set. Each character is represented by 11 modules that
can be one of four bar widths. Code 128 is the most easily read code with the highest
message integrity due to several separate message check routines.
Of all the common linear symbologies, Code 128 is the most flexible. It supports both
alpha and numeric characters easily, has the highest number of characters per inch,
and is variable length. Code 128 is usually the best choice when implementing a
new symbology.
It is sometimes advantageous to break
up long messages into multiple, shorter symbols. If the first character of a Code
128 symbol is a Function Code 2 (FNC2), then the scanned symbol is appended to a
storage buffer. This operation continues for all successive Code 128 symbols with
a FNC2 being added to previously stored ones. When a Code 128 symbol is scanned
which does not include a FNC2, it is appended to the buffer, the entire buffer is
transmitted, and the buffer is cleared.
UPC
UPC-A (Universal Product Code-A) is
fixed length, is the most common bar code for retail product labeling and is seen
in most grocery stores across the United States. The symbology
encodes a 12 digit numeric only number. The first six digits are assigned from the
Uniform Code Council (UCC) in Dayton, Ohio, the next five digits are assigned by
the manufacturer, and the final digit is a modulo 10 check digit. The nominal height
for the UPC-A bar code is one inch. The reduced size is 80% of the nominal size.
UPC-E (Universal Product Code-E) is also
fixed length and is a compressed six digit code used for marking small packages
including magazines and paperback books. The printed value of the UPC-E code is
a twelve digit code. UPC-E symbols are UPC-A symbols that have been zero suppressed
(i.e. consecutive zeros are not included in the symbol). The nominal height for
the UPC-E bar code is one inch. The reduced size is 80% of the nominal size.
EAN/JAN
The EAN/JAN-13 is fixed length and
is similar to the UPC-A symbology, but encodes a 13th
digit. Also, the "12th and 13th" digits of an EAN-13,
may represent a country code in its entirety or just the beginning of the country
code, which may vary from 2 to 3 digits. The nominal height for the EAN/JAN-13 bar
code is one inch. The reduced size is 80% of the nominal size.
The EAN/JAN-8 is fixed length and
is similar to the UPC-E code, but includes two more digits for the country code.
The nominal height for the EAN/JAN-8 bar code is one inch. The reduced size is 80%
of the nominal size.
Interleaved
2 of 5
Interleaved 2 of 5 is a variable length,
even numbered, numeric bar code symbol. It is typically used in industrial and master
carton labeling. The symbology uses bars to represent
the first character and the interleaved (white) spaces to represent the second character.
Each character has two wide elements and three narrow elements.
A modulo 10 check character can be
used to enhance data security for Interleaved 2 of 5 symbols. When this option is
selected, the last digit of the symbol is assumed to be the check digit, and it
is compared to a calculated check digit to verify the symbol.
Check Digit
A modulo 10 check character can be
used to enhance data security for Interleaved 2 of 5 symbols. When this option is
selected, the last digit of the symbol is assumed to be the check digit, and it
is compared to a calculated check digit to verify the symbol.
CODE 93
Code 93 encodes the full 128 ASCII
character set using 9 modules arranged into 3 bars with adjacent spaces. Two of
the characters are check characters. Code 93 is similar to Code 39 but encodes more
characters per inch. Code 93 encodes the full 128 ASCII character set and is encoded
similarly to the extended Code 39.
It is sometimes advantageous to break
up long messages into multiple, shorter symbols. If the first character of a Code
93 symbol is a space (ASCII 32), then the scanned symbol is appended to a storage
buffer. This operation continues for all successive Code 93 symbols with a leading
space being added to previously stored ones. When a Code 93 symbol is scanned which
does not include a leading space, it is appended to the buffer, the entire buffer
is transmitted, and the buffer is cleared.
Codabar
Codabar is a variable length
symbology capable of encoding 16 characters within any length message.
Codabar can encode six special alphanumeric characters,
capital letters A through D, and all numeric digits. Codabar
symbology for any new applications today should not
be considered except under unusual circumstances because it is limited and out-dated.
Listed below are the options for the Codabar
symbology.
References:
http://www.dataid.com/bcsymbology.htm
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