Rockwell Automation 20-COMM-I Interbus Adapter - Manual (Page 67)

Using Explicit Messaging (PCP Communications) 6-5
The ladder example used in this manual performs PCP Reads and PCP
Writes.
PCP Read Message Format
PCP Reads require the following Command and Reply message formats:
Command
Reply
Word Name Description
0 CR The Communication Reference (CR #) to read from
1 Index The index of the variable to read
2 Sub Index The sub-index of the variable to read (not used)
Word Name Description
0
Command
Word Echo Echo of the Command Word (0004h)
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
4 Data Length The # of bytes of data following (1, 2 or 4 bytes)
5 Data Word 1
Contains 8-bit (1 byte) data reads (stored in the high byte),
16-bit (2 byte) data reads, and the most significant word for
32-bit (4 byte) data reads
6 Data Word 2 Least significant word for 32-bit (4 byte) data reads
20COMM-UM007A-EN-P.book Page 5 Tuesday, January 22, 2002 10:52 AM