Rockwell Automation 1756-ENET/B ControlLogix Ethernet Communication Interface Module User Manual - Manual (Page 22)

Publication 1756-UM051B-EN-P - November 2000
1-4 About the 1756-ENET/B Module
Use of the Control and
Information Protocol (CIP) The Ethernet module uses the Control and Information Protocol (CIP).
CIP is the application layer protocol specified for Ethernet/IP, the
Ethernet Industrial Protocol, as well as for ControlNet and DeviceNet.
It is a message-based protocol that implements a relative path to send
a message from the “producing” device in a system to the
“consuming” devices. The producing device contains the path
information that steers the message along the proper route to reach its
consumers. Since the producing device holds this information, other
devices along the path simply pass this information; they do not need
to store it. This has two significant benefits:
•
You do not need to configure routing tables in the bridging
module, 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.
Understanding the
Producer/Consumer Model CIP uses the “producer/consumer” networking model, replacing 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 digital 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
over the ControlLogix backplane and over the Ethernet network. This
data exchange conforms to the producer/consumer model.
You configure the producer and consumer by creating controller
scoped tags using RSLogix 5000 software (see chapter 7).
Tag Type Description Specify Using RSLogix5000 Software
Produced
(1) Tags that the controller produced for other
nodes to consume. Enabled for producing
Number of consumers allowed
Consumed
(1) Tags whose values are produced by another
controller. Name of controller that owns the tag the local controller wants
to consume
Tag name or instance that the local controller wants to consume
Data type of the tag to consume
Update interval of how often the local controller consumes the tag
data
(1)
Produced and consumed tags must be controller-scoped tags of DINT or REAL data type, or in an array or structure.