Rockwell Automation Publication 1734-UM018D-EN-E - September 2017 9
Overview of the 1734 POINT I/O EtherNet/IP Adapter Chapter 1
Understand the Producer/
Consumer Model
The CIP producer and consumer networking model replaces the old source and
destination (master and slave) model. The producer and 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 or
unicast) their data either upon a change of state (COS) or periodically.
Multicast is the default mode for version 17 Logix and earlier controllers and
unicast is the default for version 18 with multicast as a selectable option.
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 also produces 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 and consumer model.
Specify the
Requested
Packet Interval (RPI)
The Requested Packet Interval or 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 in the I/O system (using a rack-optimization or
enhanced rack-optimization 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 and the controller
should send the consumed (output) 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.
Support for Rack-
optimization, Enhanced
Rack-optimization, and
Direct Connections
The I/O adapters supports direct, rack-optimization, and enhanced rack-
optimization connections. A direct connection is a real-time data transfer link
between the controller and the module occupying the slot that the configuration
data references.
Direct I/O connections occur at a cyclic rate specified by the RPI during
configuration. A rack-optimization connection is a grouping of data from one or
more digital I/O modules into a single block of data sent over a single connection
at the same data rate.
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