Understand The Producer/Consumer Model; Specify The Requested Packet Interval (Rpi); Support Of Rack Optimized And Direct Connections - Allen-Bradley Rockwell Automation 1734-AENT User Manua

1-6 About the 1734-AENT Adapter
Understand the
Producer/Consumer Model
Specify the Requested
Packet Interval (RPI)
Support of Rack Optimized
and Direct Connections
Publication 1734-UM011A-EN-P - February 2004
This has two significant benefits:
• You do not need to configure routing tables in the bridging modules,
which greatly simplifies maintenance and module replacement.
• 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
50ms the device should send its data to the controller or the controller should
send its data to the device.
RPIs are only used 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; it is used only as a bridge to remote racks.
The 1734-AENT adapter supports both direct and rack optimized
connections. A direct connection is a real-time data transfer link between the
controller and whatever module occupies the slot that the configuration data
references. Direct connection messaging occurs at a cyclic rate specified by the
RPI during configuration. A rack optimized connection is a grouping of data