Rockwell Automation RECOMM-PBUS PROFIBUS Communications Module - Manual (Page 77)

Using Explicit Messaging (Parameter Protocol) 7-3
7.3 Parameter Protocol
This protocol uses four 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).
Refer to sections 7.3.1 and 7.3.2 for a description of the data that is
required in each word.
Figure 7.2 – Parameter Message Format
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