Rockwell Automation 1336-GM6 Enhanced DeviceNet Communications Module - Manual (Page 74)

7-4 Using DeviceNet Explicit Messaging
Messaging for the 1747-SDN
Scanner The SLC copies an Explicit Message into the scanner’s M0-file.
When the copy is completed the scanner moves the message into a
queue for processing. Up to 10 Explicit Messages can be in this
queue.
When the scanner receives a response message it is placed into a
queue. The first response in the queue is available from the M1-file.
When the message delete command is copied into the scanner the
message is complete and the next available response will appear in
the M1-file.
The format of Request and Response messages is in Figure 7.2Figure
7.2.
Figure 7.2 Format of DeviceNet Messages
For information on M-File locations, refer to the 1747-SDN
DeviceNet Scanner Module Manual, Publication 1747-5.8.
The message buffer is composed of two sections:
• Transaction header — three words that contain information
identifying the message transaction.
• Transaction body — in a request, this contains the DeviceNet
Class, Instance, Attribute and Service Data portions of the
transaction. In a response, this contains the Service Data only.
Format of 32-word M0-file
Write of Explicit Message Request
Format of 32-word M1-file
Read of Explicit Message Response
15 0 15 0
Transaction
Header (3 words) TXID COMMAND TXID STATUS word 0
PORT SIZE PORT SIZE
SERVICE MAC ID SERVICE MAC ID
CLASS SERVICE RESPONSE DATA
Transaction Data
(up to 29 words) INSTANCE "
ATTRIBUTE "
SERVICE DATA "
" " word 31