Accessing To Cip Objects; Explicit Messaging; Implicit Messaging - Leuze electronic MSI 400 Series Manual

8.6

Accessing to CIP objects

8.6.1

Explicit Messaging

Explicit message transmission uses the TCP/IP protocol as well as an EtherNet/IP-specific encapsulation
layer. Explicit message transmission can be connection-free (UCMM) and connected, e.g. session-based.
The latter is termed Class 3 Messaging. Both UCMM and Class 3 use an EPATH to address the required
data. An EPATH is made up of the service, class, instance and attribute ID.
With explicit message transmission, each attribute of the following objects can be accessed:
• Identity class (0x01) [chapter 8.4.1]
• Assembly class (0x04) [chapter 8.4.2]
• Discrete input point object (0x08) [chapter 8.4.3]
• Discrete output point object [chapter 8.4.4]
• Discrete einput group object (0x1D) [chapter 8.4.5]
• Discrete output group object (0x1D) [chapter 8.4.6]
• Vendor-specific object (0x78) [chapter 8.4.8.7]
Each request must possess a valid EPATH referring to the required object/attribute. The appropriate attrib-
ute can be read using the GetAttributeSingle service, if it is labeled as Read in these tables. The appropri-
ate attribute can be written using the SetAttributeSingle service, if it is labeled as Write in these tables.
8.6.2

Implicit Messaging

Implicit message transmission uses EtherNet/IP, the UDP/IP protocol as well as an EtherNet/IP-specific en-
capsulation layer. Implicit message transmission is also termed Transport Class 1. The PLC can set up a
Class 1 connection with the MSI 430 module, by placing the service request Forward_Open with it. This
configures connection information for the exchange of input/output data, e.g. the RPI unicast or multicast
connections, amongst other things. Class 1 connections only support assemblies for the exchange of input/
output data or "wild cards" to signal data-free heartbeat connections. Configuration assemblies are accep-
ted as part of the Forward_Open-Service, with the exception of TCP/IP objects (Class 0xF5), although are
not processed by the MSI 430 module.
As the configuration details of the connection are only sent once in the Forward_Open-Frame, implicit mes-
sage transmission is aligned to performance and has a lower telegram overhead than explicit message
transmission. Assembly instances possess predefined attributes in a specific order. Nonetheless, the
sender, i.e. the PLC; specifies the data size in Forward_Open during the setup of the Class 1 connection.
This means that only data byte from the beginning of the instance up to the specified size are exchanged.
The MSI 430 module supports seven static assembly instances. These are listed in the table Overview of
the assembly class (0x04) supported by the MSI 430 module [chapter 8.4.2]. All data members of the in-
stance has fixed coding. Dynamic assembly instances are not currently supported by the MSI 430 module.
An I/O assembly contains either input or output data, but not both at the same time. The following figure
shows the data flow when multiple assembly instances are used. Predefined assemblies are interconnec-
ted by blue lines, vendor-specific assemblies by black lines. The controller module is shown as a hatched
rectangle.
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EtherNet/IP gateway
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