User's Manual

Chapter 6 — Bar Code Symbologies
120 CK60 Series Handheld Computer User’s Manual
international character set support. Micro PDF417 is designed for applica-
tions where the symbol must be smaller than PDF417 will allow.
MSI Code (Variant of Plessey)
The MSI Plessey bar code is a variant of the Plessey bar code. It is a pulse-
width modulated non-self checking code, and is used primarily in store
shelf labeling. Each character consists of eight elements, four bars and four
spaces. The character set includes the digits 0 through 9. A Modulo 10
checksum is appended to the end of the code. For start and stop checks,
MSI employs a single bit pair of 1 as a start symbol and a single bit pair of 0
as a stop symbol. MSI reverses the 1-2-4-8 BCD pattern for bit pair weight-
ing to 8-6-2-1.
PDF417
The PDF417 symbology is a stacked 2D symbology that allows you to scan
across rows of code. Each row consists of start/stop characters, row identifi-
ers, and symbol characters, which consist of four bars and four spaces each
and contain the actual data. This symbology uses error correction symbol
characters appended at the end to recover loss of data.
PDF417 stores up to 1800 printable ASCII characters or 1100 binary char-
acters per symbol. The symbol is rectangular; the shape of the symbol is
adjusted to some extent by setting the width and allowing the height to
grow with the data. It is also possible to break large amounts 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 available
for quick look-up. PDF417 is used for hazardous materials labeling; storing
technical specifications, and calibration data on electronic instruments;
encoding fingerprints and photographs on drivers’ licenses.
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 in 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 square inch (177.2 characters per square centimeter).
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 modulated codes represent each 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