Rockwell Automation 1779-KP3R DATA HIGHWAY II - Manual (Page 10)

Overview
Chapter 1
1-4
You also have the option of running redundant cabling. You can order
Allen–Bradley Data Highway II interface modules with dual ports, which
allows you to install a back–up cable system. Thus providing more
security for your system if a failure occurs. See Chapter 2 for information
on redundant cabling.
A device and its communication interface make up a node on the Data
Highway II network (figure 1.4). The node sending a message is the
source node; the node receiving a message is the destination node.
Figure 1.4
Sample Data Highway II Nodes
Data Highway II
sends the message.
The source node
receives the message.
The destination node
PLC-3
1779-KP3
Computer
1779-KFM
10994-I
Allen–Bradley Data Highway II has its own Data Highway II proprietary
communication protocol between the network communication interfaces.
All communication interface modules connected to this network ‘‘talk” to
each other using this protocol. For more information on Data Highway II
protocol, refer to Data Highway II Asynchronous–device Interface User’s
Manual (Publication 1779–6.5.1) or the Data Highway II
Synchronous–device Interface User’s Manual (Publication 1779–6.5.2).
In a Data Highway II configuration, the nodes are situated along a
physical bus (figure 1.5). Communication is sent across the entire length
of the cable to the end nodes. Each node waits and ‘‘listens” for any
message addressed to it, accepts the message, and signals the original
sender that it has received the message.
Data Highway II Communication