Omron OMNUC W R88A-NCW152-DRT, Руководство пользователя

Страница: 162 / 292

6.8 Communications Using Explicit Messages
6-65
6
6.8 Communications Using Explicit Messages
This section explains Explicit Message communications frames, how to send Explicit Messages
using the CMND instruction, and Explicit Message command and response blocks.
6.8.1 Explicit Messages Overview
Explicit Messages are sent and received as described below.
Explicit Message communications are basically executed in one-byte units (eight bits).
Communications frames for Explicit Messages are as follows:
Table 6.25 Explicit Message Communications Frames
Header Node
address
Service
code
Class Instance Attribute Data Footer
Table 6.26 Explicit Message Communications Frames
Item Explanation
Header Indicates the beginning of an Explicit Message, and whether the frame is an Explicit Message request
or response.
The header is automatically set by DeviceNet, so the user need not pay attention.
Node address Request: Specifies the node address of the slave or master being requested.
Response: Specifies the node address of the master or slave sending the response.
Service code Request: Specifies the code for the service being requested (read, write, etc.).
Response: The highest bit (bit 15) of the requested service code is changed to 1 and returned.
Class Function classification (major item) Indicates the classification for each function speci-
fied by DeviceNet. When a function is specified, it is
specified by these three codes.
Instance Item classification (minor item)
Attribute Attribute (The set value for each function is
allocated.)
Data Request: The data to be written.
Response: The requested data to be read or an error message is attached.
Footer Indicates the end of the Explicit Message and the section of data for which a CRC check is to be exe-
cuted.
The footer is automatically set by DeviceNet, so the user need not pay attention.