Rockwell Automation 1756-IH16ISOE ControlLogix Sequence of Events Module - Manual (Page 129)

1 Publication 1756-UM528A-EN-P - April 2004
Appendix
C
Synchronizing CSTs Across Multiple
Chassis
Overview While each ControlLogix chassis uses the CST on its backplane to
serve as the single time reference for all modules in the chassis, the
CSTs between separate chassis are different from each other by
default. You can synchronize CSTs between chassis;
synchronization is especially useful when Sequence of Events
modules reside in a remote chassis (with respect to the location of
the controller).
Some applications must be designed in such a way that a Sequence
of Events module cannot reside in the controller’s local chassis. Yet,
the controller still needs the timestamp from when transitions occur
on the remote module in terms it understands. For the timestamp with
the input data to make any sense to the controller, the CSTs in the
separate chassis must be synchronized. In other words, in this case,
any chassis that contain Sequence of Events module must
synchronized via SynchLink.
Using a Time Master
Each ControlLogix chassis can house a time master (ControlLogix
controller or 1756-SYNCH module), a device that establishes the
CST for a ControlLogix chassis. In a single chassis scenario, the
ControlLogix controller typically serves as the time master. When
you require CST synchronization across multiple chassis, you need
a time master in each chassis and those masters must receive a
single CST from a common source.
You can use ControlLogix SynchLink modules (1756-SYNCH) to
synchronize CSTs between ControlLogix chassis. In the most basic
terms, the following occurs to synchronize time between chassis:
• You must use RSLogix 5000, v13 or greater. (You can
synchronize CSTs between chassis with previous versions of
RSLogix 5000 but those versions require a ControlLogix
controller be located in each chassis. This section describes
synchronizing CSTs with v13 or greater.)
• A 1756-SYNCH module is located in each chassis, local
and remote.