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Chapter 5— Linear Bar Codes
Step 5: The checksum is the smallest number that when added to the
number in Step 4 equals a multiple of ten. In our example, 85 + 5 = 90,
which is a multiple of 10. Therefore, the checksum digit is 5. It is called a
modulo checksum because you take the modulo, or remainder, of the sum.
For the programmers, it is:
10 - (85 mod 10) = the checksum.
You can create UPC-A and EAN13 bar codes with and without a
checksum supplied. If the programmer supplies a checksum digit, the
printer creates the bar code with that checksum digit, even if it is incorrect.
Most laser scanning devices are not able to decode the bar code if the
checksum digit is incorrect.
UPC-E bar codes, useful for small items like candy and gum, are created
through the method of "zero suppression." For example, if you were to
encode 01000000567, the resulting bar code would be a compressed bar
code that only contains the data, the compression scheme, and the
checksum without all the extra zeros. For our example, the bar code would
decode to 1056707. Please refer to the UPC Symbol Specification Manual
from the Uniform Code Council for more information on zero
suppression.
UPC-E and EAN8 bar codes have a few restrictions. First, the number
system character must be set to 0. Number systems 1 through 9 do not
support UPC-E and EAN8 bar codes and may not be decoded by a laser
scanning device. In case your application requires it, the number system
may be set to something other than 0. Second, if the programmer supplies
a checksum digit, the printer creates the bar code with that checksum
digit, even if it is incorrect. If the checksum digit is incorrect, most laser
scanning devices are not able to decode the bar code. Therefore, the
programmer may send six digits (no number system, no checksum), seven
digits (number system, no checksum), or eight digits (number system and
checksum) and create a bar code.
You only use plus 2 and plus 5 bar code extensions for periodicals and
paperback books. Specifically, the bar code specification states that the
plus 2 extension should only be used for a periodical issue number. The
plus 2 and plus 5 extensions do not contain any checksum according to
the bar code specification.
To create an extended bar code, place a space between the data that should
go into the UPC/EAN bar code and the data that should go into the
extension. You can also use the PLUS2 and PLUS5 bar code types to
create the extension separately. Remember to leave ample space (about
nine times the ratio) between the UPC/EAN bar code and the extension.
EasyCoder PL-Series Printer Programmer's Reference Manual
37
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