Rockwell Automation 22-COMM-C ControlNet Adapter - Manual (Page 62)

6-2 Using Explicit Messaging
during message setup. These message connections are in
addition to the I/O connection. However, the tradeoff for
more message connections is decreased network
performance. If your application cannot tolerate this, do not
check the “Connected” box.
There are five basic events in the Explicit Messaging process. The details
of each step will vary depending on the type of controller being used.
Refer to the documentation for your controller.
Important: There must be a request message and a response message
for all Explicit Messages, whether you are reading or
writing data.
Figure 6.1 Explicit Message Process
Event
1. You format the required data and set up the ladder logic program to
send an Explicit Message request to the scanner or bridge module
(download).
2. The scanner or bridge module transmits the Explicit Message
Request to the slave device over the ControlNet network.
3. The slave device transmits the Explicit Message Response back to
the scanner or bridge. The data is stored in the scanner buffer.
4. The controller retrieves the Explicit Message Response from the
scanner’s buffer (upload).
5. The Explicit Message is complete. Note: When using a PLC-5
controller, delete the transaction ID so that it can be reused.
For information on the maximum number of Explicit Messages that can
be executed at a time, refer to the user manual for the bridge or scanner
and/or controller that is being used.
Performing Explicit Messages
➍
➎
➊
➋
Set up and send Explicit
Message Request
Complete Explicit
Message
Retrieve Explicit
Message Response ➌