Rockwell Automation 1756-OF8H ControlLogix HART Analog I/O Modules - Manual (Page 47)

Rockwell Automation Publication 1756-UM533C-EN-P - February 2011 47
ControlLogix Module Operation Chapter 3
Output Modules in a
Remote Chassis If an output module resides in a remote chassis, the role of the requested packet
interval changes slightly with respect to getting data from the owner-controller,
depending on what network type you are using to connect to the modules.
Remote Output Modules Connected Via ControlNet Network
When remote analog output modules are connected to the owner-controller via a
scheduled ControlNet network, in addition to instructing the controller to
multicast the output data within its own chassis, the requested packet interval
also reserves a spot in the stream of data flowing across the ControlNet network.
The timing of this reserved spot does or does not coincide with the exact value of
the requested packet interval, but the control system will guarantee that the
output module will receive data at least as often as the specified requested packet
interval.
The reserved spot on the network and when the controller sends the output data
are asynchronous to each other. This means there are best and worst case
scenarios as to when the module receives the output data from the controller in a
networked chassis.
ControlNet Network
Output data at least as
often as RPI
Immediate backplane
transfers to module
Data sent from
owner at module’s
RPI rate
Owner-controller ControlNet Bridge Module ControlNet Bridge Module Output Module
41360
Output Module in Remote Chassis with Requested Protocol Interval Reserving a Spot in Flow of Data