Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 150)

Network and Application Layer Protocols
Chapter 12
12Ć3
Network Packet Fields
As we discussed the communication protocol used on the data link, we
described control characters framing the network packet. Here at the
network level, you must generate the network packet. In this protocol the
network packet characters are generated directly from binary coded bytes
of data. This provides faster throughput on the link than if this data were
coded into ASCII characters.
Figure 12.2 shows the general format of the network packet for a
command message. Figure 12.3 shows the general format of the network
packet for a reply message. Note that bytes are shown from left to right in
the order in which they are transmitted on the link.
Note that the only difference between the network packet for a command
message and the network packet for a reply message is in the high nibble
of the CMD byte.
Figure 12.2
Command Message Packet Format
CMD STS FNC ADDR DATA
DST SRC CMD STS TNS
Data
(From Application Layer)
From
Application
Layer
10063–I
x
0 x
Network
Layer
Packet