Rockwell Automation Publication 1756-UM542A-EN-P - September 2014 47
Glossary
The following terms and abbreviations are used throughout this manual. For
definitions of terms not listed here, refer to the Allen-Bradley Industrial
Automation Glossary, publication
AG-7.1.
Add-On Instructions Add-on instructions are custom RSLogix 5000 software and the Logix Designer
app
lication instructions that you design and create. With add-on instructions,
you can create new instructions for sets of commonly-used logic, provide a
common interface to this logic, and provide documentation for the instruction.
Best Master Clock Algorithm The algorithm performed by each node to determine the clock that will become
t
he master clock on a subnet and the Grandmaster clock for the domain. The
algorithm primarily compares priority1, clock quality, priority2, and source
identity to determine the best master among available candidates.
Boundary Clock A boundary clock has more than one port, for example, a managed Ethernet
sw
itch, and perform the duties as a master or slave clock.
Common Industrial Protocol (CIP) The common industrial protocol (CIP) is an open industrial protocol for
in
dustrial automation applications.
CIP Sync CIP sync is the Open DeviceNet Vendors Association (ODVA) implementation
of t
he Institute of Electrical and Electronics Engineers (IEEE) 1588-2008
standard. The protocol provides a mechanism to synchronize clocks between
controllers, I/O devices, and other automation products.
Clock A node participating in the PTP protocol that is capable of providing a
mea
surement of the passage of time since a defined epoch. There are three types
of clocks in IEEE 1588-2008: boundary, transparent, and ordinary clocks.
Coordinated System Time (CST) In its simplest form, CST is a backplane clock propagated between all modules
o
n the ControlLogix backplane. Its presence is necessary whenever time
coordination between modules in the chassis is required.
Device Level Ring (DLR) A DLR network is a single-fault tolerant ring network intended for the
in
terconnection of automation devices. This topology is also implemented at the
device level. No additional switches are required.
Domain A logical grouping of clocks that synchronize to each other by using the PTP
p
rotocol, but that are not necessarily synchronized to clocks in another domain.
Greenwich Mean Time (GMT) GMT is the mean solar time of the longitude (0°) of the former Royal
O
bservatory at Greenwich, England, or Greenwich meridian. UTC replaced
GMT as the basis for the main reference time scale or civil time in various regions
on 1 January 1970.
Global Positioning System (GPS) GPS is a satellite-based navigation system made up of a network of 24 satellites
pl
aced into orbit by the U.S. Department of Defense. GPS provides reliable
timing services (as well as positioning and navigation) on a continuous basis in all
weather, day and night, anywhere on or near the Earth that has an unobstructed
view of four or more GPS satellites.
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