User's Manual

Bar Code SymbologiesAppendix —B
409700 Series Color Mobile Computer User’s Manual
of data into several PDF417 symbols which are logically linked. There is
no theoretical limit on the amount of data that can store in a group of
PDF417 symbols.
The capacity of PDF417 can be helpful in applications where the data
must travel with the labeled item, where a host database is not always avail-
able for quick look-up. PDF417 is used for hazardous materials labeling;
storing technical specifications, and calibration data on electronic instru-
ments; encoding fingerprints and photographs on the backs of drivers’ li-
censes.
The maximum data density is determined by the smallest elements which
can be reliably printed and scanned. Using the smallest recommended ele-
ment size of 0.0075 inch wide and 0.010 inch high, the maximum data
density i n the binary mode is 686 bytes per square inch (106.2 bytes per
square centimeter). In the printable ASCII mode the density is 1144 char -
acters per squ are inch (177.2 characters per squ ar e centimeter).
Micro PDF417
Micro PDF417 is deriv ed from PDF417. The code has a limited set of
symbol sizes and a fixed level of error correction for each symbol size.
Module dimensions are user-specified so that the symbol may be printed
with a variety of printers. The symbology allows up to 150 bytes, 250 al-
phanumeric characters, or 366 numeric digits to be stored. This is done by
specifying one of three compaction modes: data, text or numeric. Text
Compaction mode permits all printable ASCII characters to be encoded
(values 32 to 126 inclusiv e) as well as selected control characters. Byte
Compaction mode permits all 256 possible 8-bit byte values to be en-
coded. This includes all ASCII characters value 0 to 127 inclusive and pro-
vides for international character set support
Micro PDF417 is designed for applications where the symbol must be
smaller than PDF417 will allow.
Plessey
Plessey finds its origin in the pulse width modulated (PWM) code devel-
oped in England. It is widely used for shelf markings in grocery stores.
Pulse width modu lated codes represent e ach bit of information by a bar
and space pair. A zero bit consists of a narrow bar followed by a wide
space, while a one bit consists of a wide bar followed by a narrow space. It
is mainly a numeric symbology (0-9) with six extra characters available for
assigning any symbol or letter desired.
Plessey codes employ a variety of check characters and a polynomial-based
Cyclic Redundancy Check (CRC). For start and stop characters, Plessey
employs a 1101 and previously used a 0101.
This symbology is very limited about what information can be encoded. It
is not considered for new applications.