SNN Formats
SNNs used by the system are 6-byte hexadecimal numbers. SNNs can be set and viewed in one of two formats:
- Time-based
- Manual
Time-based SNN Format and Assignment
When the time-based format is selected, the SNN represents a date and time based on the local clock of the computer that generated the SNN.
Time-based SNN Format
The assignment of time-based SNNs is automatic when you create a safety project or add
EtherNet/IP™
by changing the IP mode or controller type. Time-based SNNs generated by the software are always unique to the project, whether generated by project creation or IP mode change. Devices that are created directly under the controller port default to having the same SNN as that port on the controller.
IMPORTANT:
If you have a network diagram for your application, you must edit the SNNs of the controller to match your network diagram. We recommend that you edit the SNNs before you add devices to the I/O configuration in Controller Organizer.
When you add
CIP Safety™
I/O devices to ports under an adapter, as opposed to the controller, the following applies:- If no other device under the port uses an SNN, a time-based SNN is automatically assigned.
- If another device under the port uses an SNN, the device is assigned the same SNN as the first device in address order.
Manual SNN Format and Assignment
When the manual format is selected, the SNN represents a network type and must have a decimal value from 1…9999.
Manual SNN Format
Manual manipulation of an SNN is required for the following reasons:
- To make sure that each safety controller port on the same subnet has the same SNN in all projects
- To copy safety projects
ATTENTION:
If a safety project is copied into another project with different hardware or in another physical location, and the new project is within the same routable safety system, every SNN must be changed in the second system. SNN values cannot be repeated. For information about how to change the SNN, see the controller user manual.
IMPORTANT:
If you assign an SNN manually, make sure that system expansion does not result in a duplication of SNN and unique node reference combinations.
A warning appears if your project contains duplicate SNN and unique node reference combinations. You can still verify the project, but we recommend that you resolve the duplicate combinations.
However, there can be safety devices on the routable safety network that have the same SNN and node address and are not in the project. In this case, these safety devices are unknown to the
Studio 5000 Logix Designer®
application, and you may not see a warning. If there are duplicate unique node references, as the system user, you are responsible for proving that an unsafe condition cannot result.
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