Rockwell Automation 20-COMM-P Profibus Adapter - Manual (Page 73)

Using Explicit Messaging (Parameter Protocol) 6-3
Event
1. You format the required data and set up the ladder logic program to
send an Explicit Message request to the scanner module (download).
2. The scanner module transmits the Explicit Message Request to the
slave device over the PROFIBUS network.
3. The slave device transmits the Explicit Message Response back to
the master.
4. The controller retrieves the Explicit Message Response.
5. The Explicit Message is complete.
This protocol uses 4 words in the Profibus I/O area. Requests and
responses are a handshake procedure and cannot be batched, meaning
that if the master sends a request, it has to wait for the response before
sending a new request.
With this protocol you can:
• Read 8-bit, 16-bit, or 32-bit parameters from any DPI port
• Write 8-bit, 16-bit, or 32-bit parameters to any DPI port
• Read the Host Fault object
To enable this protocol set Parameter 23 - [Parameter Mode] to “Par
Prot” (default).
Figure 6.2 Parameter Message Format
Parameter Protocol
Bit 15-12 11 10-0 15-12 11 10-0
Parameter Access
Word 1 (PCA)
RC SPM PNU RC SPM PNU
Parameter Access
Word 2 (IND)
Subindex Subindex
Parameter Access
Word 3 (PVA)
Parameter value
(32 bit high word)
Parameter value
(32 bit high word)
Parameter Access
Word 4 (PVA)
Parameter value
(32-bit low word/8-bit & 16-bit
value)
Parameter value
(32-bit low word/8-bit & 16-bit
value)
Request
Response
20COMM-UM006A-EN-P.book Page 3 Friday, September 28, 2001 10:43 AM