Safety Network Number (SNN) Assignment
When you create controller projects, the programming software generates an SNN value automatically whenever it recognizes a new subnet that contains
CIP Safety™
devices:- EachCIP Safety™-capable port on the controller is assigned an SNN. The safety controllers have up to three safety network numbers: a separate SNN for each Ethernet port, and one SNN for the backplane.
- If a bridge or adapter device is in the I/O tree and a childCIP Safety™device is added, the subnet that is created by the bridge or adapter is assigned an SNN.
For typical users, the automatic assignment of a time-based SNN is sufficient. However, manual assignment of the SNN is required if the following is true:
- One or more controller ports are on a CIP Safety subnet that already has an established SNN.
- A safety project is copied to another hardware installation within the same routableCIP Safety™system.
Rockwell Automation®
recommends changing each SNN to the SNN already established for that subnet, if one exists. That way, devices created later in the project are automatically assigned the correct SNN. Each safety network must have a unique safety network number. You must be sure that a unique SNN is assigned to each
CIP Safety™
network that contains safety devices.
TIP:
Multiple safety network numbers can be assigned to a
CIP Safety™
subnet or a ControlBus™ chassis that contains multiple safety devices. However, for simplicity, we recommend that each CIP Safety™
subnet has only one unique SNN.The SNN can be software-assigned (time-based) or user-assigned (manual).
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