Rockwell Automation 1756-OF8H ControlLogix HART Analog I/O Modules - Manual (Page 48)

48 Rockwell Automation Publication 1756-UM533C-EN-P - February 2011
Chapter 3 ControlLogix Module Operation
Best Case Scenario - Requested Packet Interval
In the best case scenario, the controller sends the output data just before the
reserved network slot is available. In this case, the remotely located output
module receives the data almost immediately.
Worst Case Scenario - Requested Packet Interval
In the worst case scenario, the controller sends the data just after the reserved
network slot has passed. In this case, the module does not receive the data until
the next scheduled network slot.
Remote Output Modules Connected Via EtherNet/IP Network
When remote analog output modules are connected to the owner-controller via
an EtherNet/IP network, the controller multicasts data in the following way:
• At the RPI, the owner-controller multicasts data within its own chassis.
• The 1756-ENBT module in the local chassis immediately sends the data
over the network to the analog output module as long as it has not sent
data within a time frame that is 1/4 the value of the analog module’s
requested protocol interval.
IMPORTANT These best and worst case scenarios indicate the time required
for output data to transfer from the controller to the module once
the controller has produced it.
The scenarios do not take into account when the module will
receive new data (updated by the user program) from the
controller. That is a function of the length of the user program and
its asynchronous relationship with the requested protocol interval.