Rockwell Automation 1791DS-IBxxxx Guard I/O DeviceNet Safety Modules - Manual (Page 63)

Rockwell Automation Publication 1791DS-UM001J-EN-P - May 2013 63
Configure Modules with the Logix Designer Application Chapter 5
3. From the Module Properties dialog box, complete entries for the General
dialog box.
a. For Name, type a unique name.
b. For Node, choose the DeviceNet Node number, noting this number
and the switches on the actual modules must match.
c. For Description, if desired, type a description.
d. For Safety Network Number, use the default setting.
For a detailed explanation of the safety network number (SNN), see the
GuardLogix Controller Systems Safety Reference Manuals listed in the
Additional Resources on
page 10 .
The purpose of the Safety Network Number (SNN) is to make sure
that every module in a system can be uniquely identified.
For example, assume there are two identical GuardLogix control
systems—System A and System B—that are connected to a common
Ethernet network. System A and System B have three DeviceNet
networks with assorted standard and safety I/O modules. In systems
like this, modules can have the same node number, but if each
DeviceNet network has a unique SNN, each node will not have the
same SNN and node number combination.
Another example of the usage of SNNs is when 1756-DNB modules
are in the same chassis and the DeviceNet cables are inadvertently
disconnected. If the cables are reattached incorrectly, the connection in
the safety modules are broken because each 1756-DNB module is now
connected to devices with different SNNs.
We suggest that all safety modules on a network have the same SNN, to
make documentation easier. During configuration, the Logix Designer
application defaults a safety device’s SNN to match the SNN of the
lowest safety node on the network.