Rockwell Automation RECOMM-IBUS Interbus Communications Module - Manual (Page 65)

Using Explicit Messaging (PCP Communications) 7-5
7.3.1 PCP Read Message Format
PCP Reads require the following Command and Reply message
formats:
Command
Reply
Table 7.3 – Command Message Format
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)
Table 7.4 – Reply Message Format
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