User`s guide

BAR CODE INFORMATION
Copyright © 2006, Cognitive. 257
by the allowable pattern of bars and spaces in each codeword. The
printer converts the raw data to a series of numeric values following
rules that provide optimum data compression. PDF417 provides several
different rule sets, or modes, for optimum data compression.
PDF417 provides error detection and correction within the bar code
block. The thoroughness of the automatic error checking is called the
security level of the code. There are eight security levels, numbered 0-8,
as shown below.
Security
Level
Error
Limit
0 0
1 2
2 6
3 14
4 30
5 62
6 126
7 254
8 510
As long as the number of unreadable or missing code words in the bar
code block is less than the number indicated for the applicable security
level, the code may be read without error.
A high security level provides very reliable data encoding. However, the
bar code block gets bigger with increasing security, since more
codewords are needed to provide the necessary error checking data.
Processing speed also increases significantly with increasing security,
since more error checking calculations are performed.
Cognitive printers automatically handle most of the decisions and tasks
associated with printing PDF417 bar codes. They select the best mode
for the data, encode it, and do all calculations associated with start and
stop characters and error-checking.
POSTNET
POSTNET is designed for use with the nine digit ZIP + 4 postal code.
Each character to be encoded is represented by five bar code elements,
with each element being either a short or tall bar followed by a space.
The bar and space widths are constant.