EtherNet/IP gateway
Wieland Electric GmbH | BA000970 | 11/2016 (Rev. F)
Accessing to CIP objects
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Explicit Messaging
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Explicit message transmission uses the TCP/IP protocol as well as an EtherNet/IP-specific en-
capsulation layer. Explicit message transmission can be connection-free (UCMM) and connec-
ted, e.g. session-based. The latter is termed
. 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) [ch. 8.4.1, p. 84]
•
Assembly class (0x04) [ch. 8.4.2, p. 85]
•
Discrete input point object (0x08) [ch. 8.4.3, p. 86]
•
Discrete output point object [ch. 8.4.4, p. 88]
•
Discrete einput group object (0x1D) [ch. 8.4.5, p. 89]
•
Discrete output group object (0x1D) [ch. 8.4.6, p. 90]
•
Vendor-specific object (0x78) [ch. 8.4.8.7, p. 98]
Each request must possess a valid EPATH referring to the required object/attribute. The ap-
propriate attribute can be read using the GetAttributeSingle service, if it is labeled as
in
these tables. The appropriate attribute can be written using the SetAttributeSingle service, if it
is labeled as
in these tables.
Implicit Messaging
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Implicit message transmission uses EtherNet/IP, the UDP/IP protocol as well as an EtherNet/IP-
specific encapsulation layer. Implicit message transmission is also termed
.
The PLC can set up a Class 1 connection with the SP-COP2-ENI module, by placing the service
request
with it. This configures connection information for the exchange of in-
put/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 accepted as part of the
Forward_Open-Service, with the exception of TCP/IP objects (Class 0xF5), although are not
processed by the SP-COP2-ENI module.
As the configuration details of the connection are only sent once in the Forward_Open-Frame,
implicit message 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 SP-COP2-ENI module supports seven static assembly instances. These are listed in the
table
Overview of the assembly class (0x04) supported by the SP-COP2-ENI module [ch. 8.4.2,
p. 85]
. All data members of the instance has fixed coding. Dynamic assembly instances are not
currently supported by the SP-COP2-ENI module.
An I/O assembly contains either input or output data, but not both at the same time. The follo-
wing figure shows the data flow when multiple assembly instances are used. Predefined as-
semblies are interconnected by blue lines, vendor-specific assemblies by black lines. The con-
troller module is shown as a hatched rectangle.
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