Understand The Producer/Consumer Model; Specify The Requested Packet Interval (Rpi) - Allen-Bradley Rockwell Automation 1734-AENT User Manual

6 About the Adapter
Understand the
Producer/Consumer Model
Specify the Requested
Packet Interval (RPI)
Publication 1734-UM011D-EN-P - May 2011
• You maintain full control over the route taken by each message, which
enables you to select alternative paths for the same end device.
The CIP producer/consumer networking model replaces the old
source/destination (master/slave) model. The producer/consumer model
reduces network traffic and increases speed of transmission. In traditional I/O
systems, controllers poll input modules to obtain their input status. In the CIP
system, input modules are not polled by a controller. Instead, they produce
(multicast) their data either upon a change of state (COS) or periodically.
The frequency of update depends upon the options chosen during
configuration and where on the network the input module resides. The input
module, therefore, is a producer of input data, and the controller is a consumer
of the data.
The controller can also produce data for other controllers to consume. The
produced and consumed data is accessible by multiple controllers and other
devices over the EtherNet/IP network. This data exchange conforms to the
producer/consumer model.
The RPI is the update rate specified for a particular piece of data on the
network. The RPI can be specified for the adapter and include all of the I/O
modules communicating through it (using a rack-optimized connection) or
specified for a particular module (using direct connection).
When you add a module or an adapter to the I/O configuration of a
controller, you must enter the RPI as a parameter. This value specifies how
often to produce the data for that device. For example, if you specify an RPI of
50 ms, it means that every 50 ms the device should send its data to the
controller or the controller should send its data to the device.
Use RPIs only for devices that exchange data. For example, a ControlLogix
EtherNet/IP bridge module in the same chassis as the controller does not
require an RPI, because it is not a data-producing member of the system. Its
use is only as a bridge to remote racks.