Rockwell Automation 1756-IH16ISOE ControlLogix Sequence of Events Module - Manual (Page 24)

Publication 1756-UM528A-EN-P - April 2004
2-8 How Does the Sequence of Events Module Operate in a ControlLogix System?
Sequence of Events Module
in a Remote Chassis If your Sequence of Events module physically resides in a chassis
other than where the owner-controller is (e.g. a remote chassis
connected via ControlNet), the role of the RPI and the module’s
Enable CST Capture behavior changes slightly with respect to getting
data to the owner-controller.
The RPI and Enable CST Capture behavior still define when the
module multicasts data within its own chassis (as described in the
previous section), but only the value of the RPI determines when the
owner-controller receives it over the network.
Remote Input Module Connected Via ControlNet
When a Sequence of Events module resides in a remote chassis
connected by a scheduled ControlNet network, the RPI:
• instructs the module to multicast data in its own chassis at a
specific interval.
• reserves a “spot” in the stream of data flowing across the
ControlNet network.
The timing of this “reserved” spot may or may not coincide with the
exact value of the RPI, but the control system guarantees that the
owner-controller receives data at least as often as the specified RPI.
Figure 2.2 Sequence of Events Module in Remote Chassis with Data Coming At
Least as Often as RPI
40947 ControlNet
Input data multicast in
module’s chassis at RPI
Input data at least as often as RPI
Owner-controller ControlNet Bridge module Sequence of Events module ControlNet Bridge module