Rockwell Automation 1756-IH16ISOE ControlLogix Sequence of Events Module - Manual (Page 12)

Publication 1756-UM528A-EN-P - April 2004
1-2 What is the ControlLogix Sequence of Events Module?
CST cannot easily translate to real-time but serves as a relative time
reference. Each module in a chassis has access to this reference. The
Sequence of Events module grabs the current CST value at the time of
the input state change to timestamp the input data.
You can propagate the same CST value across multiple chassis,
effectively making sure that modules in separate chassis use the same
time reference in all their operations, if necessary.
You can extend a single CST value across multiple chassis that are
physically connected via 1756-SYNCH modules. Additionally, multiple
ControlLogix systems–even those that are geographically separated–
can use the 1756HP-GPS module to share a common real-time
reference. For more information on extending a single CST value
across multiple chassis, see Appendix C.
On-Board Data Storage
Once a CST timestamp is captured for an input transition, the
module’s operational mode impacts how the module functions with
respect to:
• what data is stored on-board
• how much data is stored for each input point
• how the data is sent to the controller
The next section briefly describes the two modes of operation
available with the Sequence of Events module and how they impact
the module’s behavior.