16 Rockwell Automation Publication CNET-UM001F-EN-P - February 2018
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 lets you communicate
between devices on a ControlNet, DeviceNet, or EtherNet/IP network
without writing additional application code.
With unscheduled data, the device from which a message originates, such as
a Logix 5000 controller, contains the path information that makes sure the
message reaches its consumers.
For a full explanation of unscheduled and scheduled data, see
Network
Update Time (NUT) on page 16 on page 17.
Because the producing module holds this information, other modules along
the path simply pass the information along and do not need to store it. The
significant benefits include the following:
• 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 transmission
speed.
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 the ControlNet network. This data exchange conforms
to the producer/consumer model.
A ControlNet network link’s most important function is to transport time-
critical control information, such as I/O data and control interlocking. Other
information that is not time-critical, such as program uploads and downloads,
is also transported but does not interfere with time-critical messages because
a ControlNet network can transmit scheduled and unscheduled data.
On a ControlNet network link, nodes transfer information by establishing
connections. Each message sent by a producer contains a Connection ID
(CID). Nodes that have been configured to recognize the CID consume the
message, becoming consumers themselves.
Information on a
ControlNet Network
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