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B-2
ControlNet Overview
Exchange Information
on ControlNet
Publication CNET-UM001C-EN-P - November 2005
ControlNet communication modules use a message-based protocol that
implements a relative path to send a message from the producing module in a
system to the consuming modules. This protocol also allows you to
communicate between devices on ControlNet and DeviceNet or EtherNet/IP
without writing additional application code.
With unscheduled data the device where a message originates such as a
Logix5000 controller, contains the path information that steers the message
along the proper route to reach its consumers.
A full explanation of unscheduled and scheduled data is available on page B-4.
Since the producing module holds this information, other modules 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 module.
Scheduled data in Logix-based systems use the producer/consumer
networking model instead of a 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 a Logix 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
Logix backplane and over the ControlNet network. This data exchange
conforms to the producer/consumer model.
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