Owner manual

Rockwell Automation Publication 1756-UM022A-EN-P - November 2012 45
Communicate over Networks Chapter 4
Assigning the Safety Network Number (SNN)
You can allow the Logix Designer application to automatically assign an SNN, or
you can assign the SNN manually.
Automatic Assignment
When a new controller or module is created, a time-based SNN is automatically
assigned. Subsequent new safety-module additions to the same CIP Safety
network are assigned the same SNN defined within the lowest address on that
CIP Safety network.
Manual Assignment
The manual option is intended for routable CIP Safety systems where the
number of network subnets and interconnecting networks is small, and where
users might like to manage and assign the SNN in a logical manner pertaining to
their specific application.
See Changing the Safety Network Number (SNN)
on page 45.
Automatic versus Manual
For typical users, the automatic assignment of an SNN is sufficient. However,
manual manipulation of the SNN is required if the following is true:
• Safety consumed tags are used.
• The project consumes safety input data from a module whose
configuration is owned by some other device.
• A safety project is copied to another hardware installation within the same
routable CIP Safety system.
Changing the Safety Network Number (SNN)
Before changing the SNN you must do the following:
• Unlock the project, if it is safety-locked.
See Safety-lock the Controller
on page 95.
• Delete the safety task signature, if one exists.
See Delete the Safety Task Signature
on page 98.
IMPORTANT
If you assign an SNN manually, make sure that system expansion does not
result in duplication of SNN and node address combinations.