Introduction. Allen-Bradley Rockwell Automation 1734-AENT

Chapter

4

CIP Safety and the Safety Network Number

Introduction

To understand the safety requirements of a CIP Safety control system, including the safety network number (SNN), you must first understand how communication is routable in CIP control systems.

Topic

The Routable CIP Safety Control System

Considerations for Assigning the Safety Network Number (SNN)

Page

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The Routable CIP Safety

Control System

The CIP Safety control system represents a set of interconnected CIP

Safety devices. The routable system represents the extent of potential mis-routing of packets from an originator to a target within the CIP

Safety control system. The system is isolated such that there are no other connections into the system. For example, because the system below cannot be interconnected to another CIP Safety system through a larger, plant-wide Ethernet backbone, it illustrates the extent of a routable CIP Safety system.

CIP Safety System Example

Router/

Firewall

(1)

Switch Switch

SmartGuard

CIP Safety I/O

CIP Safety I/O CIP Safety I/O

CIP Safety I/O

CIP Safety I/O

CIP Safety I/O

(1) The router or firewall is set up to limit traffic.

CIP Safety I/O

CIP Safety I/O

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Chapter 4 CIP Safety and the Safety Network Number

Unique Node Reference

The CIP Safety protocol is an end-node to end-node safety protocol.

The CIP Safety protocol allows the routing of CIP Safety messages to and from CIP Safety devices through non-certified bridges, switches, and routers.

To prevent errors in non-certified bridges, switches, or routers from becoming dangerous, each end node within a routable CIP Safety control system must have a unique node reference. The unique node reference is a combination of a safety network number (SNN) and the node address of the node.

Router/

Firewall

Switch

Safety Network Number

The safety network number (SNN) is assigned by software or by the user. Each CIP Safety network that contains Safety I/O nodes must have at least one unique SNN. Each ControlBus chassis that contains one or more safety devices must have at least one unique SNN. Safety network numbers assigned to each safety network or network sub-net must be unique.

TIP

More than one SNN can be assigned to a CIP Safety subnet or a

ControlBus chassis that contains more than one safety device.

However, for simplicity, we recommend that each CIP Safety subnet have one and only one unique SNN. This is also the case for each ControlBus chassis.

CIP Safety Example with More Than One SNN

Switch

36

CIP Safety I/O

CIP Safety I/O

SNN_2

SNN_1

CIP Safety I/O

CIP Safety I/O

SNN_4

SNN_3

CIP Safety I/O

CIP Safety I/O

SNN_6

SNN_5

SmartGuard

CIP Safety I/O

CIP Safety I/O

SNN_7

Publication 1756-RM093F-EN-P - January 2010

CIP Safety and the Safety Network Number Chapter 4

Each CIP Safety device must be configured with an SNN. Any device that originates a safety connection to another safety device must be configured with the SNN of the target device. If the CIP Safety system is in the start-up process prior to the functional safety testing of the system, the originating device may be used to set the unique node reference into the device.

The SNN used by the system is a 6-byte hexadecimal number. The

SNN can be set and viewed in one of two formats: time-based or manual. When the time-based format is selected, the SNN represents a localized date and time. When the manual format is selected, the SNN represents a network type and a decimal value from 1…9999.

SNN Formats

Publication 1756-RM093F-EN-P - January 2010

The assignment of a time-based SNN is automatic when creating a new GuardLogix safety controller project and adding new Safety I/O modules.

Manual manipulation of an SNN is required in the following situations:

•

If safety consumed tags are used.

•

If the project will consume safety input data from a module whose configuration is owned by some other safety device.

•

If a safety project is copied to a different hardware installation within the same routable CIP Safety system.

IMPORTANT

If you assign an SNN manually, take care to ensure that system expansion does not result in duplication of SNN and node address combinations.

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