Rockwell Automation 20-COMM-I Interbus Adapter - Manual (Page 72)

6-10 Using Explicit Messaging (PCP Communications)
PCP Write Message Format
PCP Writes require the following Command and Reply message
formats:
Command
Reply
Word Name Description
0 CR The Communication Reference (CR #) to write to
1 Index The index of the variable to write
2 Sub Index The sub-index of the variable to write (not used)
3 Data Length The # of bytes of data following (1, 2, or 4 bytes)
4 Data Word 1
Contains 8-bit (1 byte) write data (stored in the high byte),
16-bit, (2 byte) write data, and the most significant word for
32-bit (4 byte) write data
5 Data Word 2 Least significant word for 32-bit (4 byte) write data
Word Name Description
0
Command
Word Echo Echo of the Command Word (0008h)
1
Message
Length Number of words following
2 CR The Communication Reference (CR #) the Reply is from
3 Result
Result Code:
0=Success
FFFFh = Timeout
FFFEh = Out of buffers to store the reply
FFFDh = Invalid CR
FFFCh = Could not connect to device with CR
FFFBh = Reply of Command bigger than buffer
20COMM-UM007A-EN-P.book Page 10 Tuesday, January 22, 2002 10:52 AM