Rockwell Automation 1756-IF4FXOF2F ControlLogix High-speed Analog I/O Module - Manual (Page 138)

138 Rockwell Automation Publication 1756-UM005B-EN-P - January 2013
Appendix E Module Operation in a Remote Chassis
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 16 - Owner-controller Receives Input Data from Remote Chassis
The reserved spot on the network and the module’s RTS are asynchronous to
each other. This means there are best and worst case scenarios as to when the
owner-controller receives updated channel data from the module in a remote
chassis.
Best Case RTS Scenario
In the best case scenario, the module performs an RTS multicast with updated
channel data just before the reserved network slot is made available. In this case,
the remotely located owner receives the data almost immediately.
Worst Case RTS Scenario
In the worst case scenario, the module performs an RTS multicast just after the
reserved network slot has passed. In this case, the owner-controller does not
receive data until the next scheduled network slot.
If the high-speed analog I/O module resides in a remote chassis, the role of the
RPI changes slightly with respect to getting data from the owner-controller.
40947 ControlNet Network
Input data at least as often as RPI.
I nput data in remote chassis
at the RTS and RPI rates.
High-speed Analog
I/O Module
ControlNet
Communication Module
Owner-controller
ControlNet
Communication Module
TIP Because it is the RPI and not the RTS that dictates when the module’s data is
sent over the network, we recommend the following:
• If you want to receive every sample, set the RPI < RTS.
• If you want fresh data each time the owner-controller receives a sample,
set the RTS < RPI.