Rockwell Automation 5730 DriveLogix5730 Controller for PowerFlex 700S Drives with Phase II Control - Manual (Page 155)

Communicating with Devices on a ControlNet Link 7-15
Maximum Number of Produced and Consumed Tags
The maximum number of produced/consumed tags that you can configure
depends on the connection limits of the communication device that transfers
the produced/consumed data.
Each produced tag uses one connection for the tag and the first configured
consumer of the tag. Each consumer thereafter uses an additional
connection.
Size Limit of a Produced or Consumed Tag
A produced or consumed tag can be as large as 488 bytes, but it must also fit
within the bandwidth of the ControlNet network:
• As the number of connections over a ControlNet network increases,
several connections, including produced or consumed tags, may need to
share a network update.
• Since a ControlNet network can only pass 500 bytes in one update, the
data of each connection must be less than 488 bytes to fit into the update.
If a produced or consumed tag is too large for your ControlNet network,
make one or more of the following adjustments:
• Reduce the Network Update Time (NUT). At a faster NUT, less
connections have to share an update slot.
• Increase the Requested Packet Interval (RPI) of all connections. At a
higher RPI, connections can take turns sending data during an update
slot.
• For a ControlNet bridge module (CNB) in a remote chassis, select the
most efficient communication format for that chassis:
The Rack Optimization format uses an additional 8 bytes for each slot in its
chassis. Analog modules or modules that are sending or getting diagnostic,
fuse, or timestamp data require direct connections and cannot take
advantage of the rack optimized form. Selecting “None” frees up the 8 bytes
per slot for other uses, such as produced or consumed tags.
• Separate the tag into two or more smaller tags:
– Group the data according to similar update rates. For example, you
could create one tag for data that is critical and another tag for data
that is not as critical.
– Assign a different RPI to each tag.
• Create logic to transfer the data in smaller sections (packets).
Are most of the modules in the chassis
non-diagnostic, digital I/O modules? Then select this communication format for
the remote communication module:
yes rack optimization
no none