Allen-Bradley 1756 ControlLogix User Manual

Chapter 5
Produce and Consume Tags (interlock controllers)
80 Rockwell Automation Publication CNET-UM001F-EN-P - February 2018
Depending on system size, your ControlNet network may lack the bandwidth
for large tags. If a tag is too large for your ControlNet network, make one or
more of these adjustments.
Table 20 - Tag Adjustments
Adjustment Description
Increase the requested packet interval
(RPI) of your connections. This is the
recommended method.
At higher RPIs, connections can take turns sending data during an update period.
Reduce your network update time (NUT). At a faster NUT, fewer connections have to share an update period.
For a ControlNet 1756-CN2, 1756-CN2R,
1756-CNB, or 1756-
CNBR bridge module
in a remote chassis, choose the most
efficient communication format for that
chassis.
Are most of the modules in the
chassis non-diagnostic, digital I/O
modules?
Then choose this communication
format for the remote 1756-CN2 or
1756-CNB module
Yes Rack optimization
No None
The rack optimization format uses an additional eight bytes for each slot in its
chassis. Analog modules or modules that are sending or receiving diagnostic,
fuse, timestamp, or schedule data require direct connections and cannot take
advantage of the rack-optimized form. Selecting None frees up the eight bytes
per slot for other uses, such as produced or consumed tags.
Separate the tag
into two or more smaller
tags.
1. 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.
2. Assign a different RPI to each tag.
Create logic to transfer the data in
smaller sections (packets).
For information on how to do this, see the Logix 5000 Controllers Common
Procedures Programming Manual, publication 1756-PM001.
A Logix 5000 controller can produce only controller-scoped, user-created
tags in the local controller’s tag structure. Logix 5000 controllers cannot
produce I/O tags or tags aliased to I/O tags.
To produce a tag, perform this procedure.
1. Open the Logix Designer project containing the tag you want to
produce.
Produce a Tag

Allen-Bradley 1756 ControlLogix Specifications

General

Brand	Allen-Bradley
Model	1756 ControlLogix
Category	Controller
Language	English