EtherNet/IP 6-2
© 2005 HMS Industrial Networks.
AB7607 User manual
CIP Messaging
Two types of messaging are used. The regular or repeated transport of a specific
set of data items is known as Implicit Messaging. Both parties agree in advance
and allocate resources for the data being transported. The connection ID within
the Implicit message defines the meaning of the data and establishes the transport
rate and transport class. The term Implicit Messaging can be interchangeable with
the term I/O Messaging.
A one time transport of a data item where both parties do not know in advance of
what’s being transferred is known as Explicit Messaging. Explicit messaging is
used for point to point type messaging. The protocol of the message data describes
(addresses) the data to be transferred. In object modeling the address is in terms of
class number, instance number, and attribute number.
Messages can be sent as Connected or Unconnected. With Connected Messaging
device resources are reserved in advance of data transfer and are dedicated and
always available. Unconnected messaging provides a means for a device to send a
request without establishing a connection prior to data transfer. This is accom-
plished through the UCMM or UnConnected Message Manager of the EtherNet/
IP protocol. With UCMM all objects are accessible.
The Anybus-X will handle up to 64 concurrent unconnected transactions. Up to
16 class 3 (messaging) connections are supported.
All Explicit Messages have message data defined in a format called the Message
Router Protocol Data Unit (MR_PDU). There are Requests and Responses.
The MR_PDU Request format includes a Service code, Path Size, Path, and data,
if any for the Service. The Path is an encoded series of bytes or Segments describ-
ing the location of the data item involved in the transfer. The Logical Segment is
most often used. It describes the Class, Instance, and Attribute of the data. The
Path may also include a Port Segment. The Port segment describes a path or way