Omron SYSMAC CJ1W-EIP21, Operation Manuals

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8 Message Communications
8-10
CJ-series EtherNet/IP Units Operation Manual for NJ-series CPU Unit (W495)
In the CIP world, each device is modeled as a collection of objects. An Object abstractly represents the
specific configuration elements of a device.
In the CIP Common Specification, “Object,” “Class,” “Instance,” “Attribute,” and “Service” are defined as
follows: (Source: CIP Common Specification)
You use the Class ID, Instance ID, and Attribute ID to access an object.
You specify these three IDs to designate an object in a device. When you make a request from an
external device for a service, you must specify the Class ID, Instance ID, and Attribute ID. (The
Instance ID and Attribute ID are not required for some services.)
These are called Internal Object Identifiers (IOI) because they identify the Class ID, Instance ID, and
Attribute ID within the device. Refer to 8-3 CIP Objects Sent to the EtherNet/IP Unit for the class ID,
instance ID, attribute ID, and service code for each object.
Request Path (IOI)
Term Definition
Object An abstract representation of a particular component within a device.
Class A set of objects that all represent the same kind of system component.
Instance A specific and real (physical) occurrence of an object.
Attribute A description of an externally visible characteristic or feature of an object.
Service A request from an external object (e.g., to read data).
Object Instance
Data
Data
Data
Data
Processing
Attributes
Service
External request
(example: read)
Device
Object
Object
Object
.....
Example: Reading the Name of a Device
(Identity
Object Class ID = 01)
Service Request
Get_Attribute_
Single
Destination
Class: 1
Instance: 1
Attribute: 7
Response
Product Name
Instance ID = 1
Attribute = 7
Device
Class ID = 1
Instance ID = 1
Attribute 7
Attribute 6
Attribute 1
Class ID = 2