Bar Code SymbologiesAppendix —B
373TE 2000
5250 Terminal Emulation Programmer’s Guide
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 r epresent 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 mainly a numeric symbology (0–9) with six ex tra characters available for
assigning any symbol or letter desired.
Plessey codes are not self-checking and employ a variety of check charac-
ters. Plessey employs a polynomial-based Cyclic Redundancy Check
(CRC). For start and stop characters, Plessey employs a 1101 and pre-
viously used a 0101.
This symbology is very limited about what information can be encoded. It
is not consider ed for new applications.
MSI Co d e (V ariant of Plessey)
In addition to Plessey characteristics, the MSI Code employs a Modulus
10 Check. 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 weighting to 8-6-2-1.
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