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Add, Configure, Monitor, and Replace CIP Safety I/O Devices
Set the Safety Network
Number (SNN)
Chapter 5
The assignment of a time-based SNN is automatic when adding new safety I/O
devices. Subsequent safety device additions to the same network are assigned the
same SNN defined within the lowest address on that CIP safety network.
For most applications, the automatic, time-based SNN is sufficient. However,
there are cases when the manipulation of an SNN is required.
See Assign the Safety Network Number (SNN) on page 51.
Use Unicast Connections on
EtherNet/IP Networks
Unicast connections are point-to-point connections between a source and a
destination node. You do not have to enter a minimum or maximum RPI range or
default value for this type of connection.
To configure unicast connections, choose the Connection tab and check Use
Unicast Connection over EtherNet/IP.
Set the Connection Reaction
Time Limit
The Connection Reaction Time Limit is the maximum age of safety packets on
the associated connection. If the age of the data used by the consuming device
exceeds the Connection Reaction Time Limit, a connection fault occurs. The
Connection Reaction Time Limit is determined by the following equations:
Input Connection Reaction Time Limit = 
Input RPI x [Timeout Multiplier + Network Delay Multiplier]
Output Connection Reaction Time Limit = 
Safety Task Period x [Timeout Multiplier + Network Delay Multiplier - 1]
The Connection Reaction Time Limit is shown on the Safety tab of the Module
Properties dialog box.
Figure 18 - Connection Reaction Time Limit
Specify the Requested Packet Interval (RPI)
The RPI specifies the period that data updates over a connection. For example, an
input module produces data at the RPI that you assign.
For safety input connections, you can set the RPI on the Safety tab of the Module
Properties dialog box. The RPI is entered in 1 ms increments, with a range of
1…100 ms. The default is 10 ms.
Rockwell Automation Publication 1756-UM022C-EN-P - May 2015
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