Rockwell Automation 1770-KF2 Data Highway or Highway Plus Interface Module User Manual - Manual (Page 82)

Message Packet Formats
Chapter 5
5-3
The message bytes contain unsigned binary data from both the application
layer and the network layer. Figure 5.2 shows the general format of a
command message.
Figure 5.2
Command Message Packet Format
CMD STS FNC
ADDR
SIZE OR
DST SRC CMD STS TNS
From
Application
Layer
11329A
x
0 x
Network
Layer
Packet
Legend: x = low hex digit of CMD byte supplied by application layer
DATA 0
0 0
Command Block
(0)
Not all command messages have FNC, ADDR, SIZE, or DATA bytes.
Figure 5.3 shows the general format of a reply message. The definitions
of these bytes are the same as those for command messages. Not all reply
messages have DATA or EXT STS bytes.
Figure 5.3
Reply Message Packet Format
CMD STS DATA
DST SRC CMD STS TNS
Response Block
(From Application Layer)
From
Application
Layer
11330A
x
4 x
Network
Layer
Packet
Legend: x = low hex digit of CMD byte supplied by application layer
EXT
STS
Note that the bytes are shown from left to right in the order in which they
are transmitted across the link.
Message Packets