Omron 3G3MV-PDRT2 - Overview of Explicit Messages; Explicit Message Communications Frame

Chapter 6
6-3
Message Communications
■ Overview of Explicit Messages
Explicit messages are sent and received as described below. Basically explicit message communi-
cations are executed in 1-byte (8-bit) units.
Explicit Message Communications Frame
Header Node
address
Service
code
Class Instance Attribute Data Footer
Item Content
Header The header indicates the beginning of an explicit message and that the frame is an
explicit message request/response. It is set automatically for DeviceNet, so there is no
particular need to be concerned with it.
Node address Request: Set the node address of the Slave/Master to be requested.
Response: The node address of the responding Slave/Master is set.
Service code Request: Set the code of the requested service (read/write, etc.).
Response: The MSB (most significant bit) of the requested service code is changed to
“1” and returned.
Class Function classification (major
classification)
Indicates the classification of a function defined by
DeviceNet. To specify a function, specify these three
codes.
Instance Instance classification (minor
classification)
Attribute Attribute (Set values are
assigned for each function.)
Data Request: Set the data to be written.
Response: Read-requested data or fault message are attached.
Footer This is the part that indicates the end of the explicit message and executes the CRC
check. It is set automatically for DeviceNet, so there is no particular need to be con-
cerned with it.