Node Interfaces; Data Highway Ii Network - Allen-Bradley 1779-KFMR User Manual

Chapter 2
Introducing the 1779 KFM Interface

Node Interfaces

Data Highway II Network

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The following node interfaces can be used in a Data Highway II link:
Asynchronous-Device/DHII Interface (Cat. No. 1779-KFL)
Redundant Asynchronous-Device/DHII Interface
(Cat. No. 1779-KFLR)
Synchronous-Device/DHII Interface (Cat. No. 1779-KFM)
Redundant Synchronous-Device/DHII Interface
(Cat. No. 1779-KFMR)
PLC-2/DHII Interface (Cat. No. 1779-KP2)
Redundant PLC-2/DHII Interface (Cat. No. 1779-KP2R)
PLC-3/DHII Interface (Cat. No. 1779-KP3)
Redundant PLC-3/DHII Interface (Cat. No. 1779-KP3R)
The Data Highway II network is an industrial area network which
provides peer-to-peer communication between nodes. A Data
Highway II network is illustrated in Figure 2.5.
Stations/Nodes
At each node interface, you must assign a unique link address to each
node of the link. A host (computer or PLC processor) and its interface to
the Data Highway II link make up a station. A station is an input/output
point in the communication system. A node is the point at which each
station accesses the medium. Because each station communicates through
a node on the Data Highway II link, it may appear that we use the terms
node and station interchangeably at times. However, we will show later
that there is not always a one-to-one relationship between stations and
nodes.
Within a station that contains a synchronous-device or
asynchronous-device interface, a local host/interface link is required for
access to the Data Highway II link. Two such stations are shown in
Figure 2.5.
One node is comprised of a 1779-KFM interface to a computer through
an RS-422/449 link limited to 4,000 cable-feet.
Another node is comprised of a 1779-KFL interface to two host
devices. Each 1779-KFL interface has two channels for connection to
two standard-link devices at the same time. Through either channel it
can interface either an RS-232-C compatible device or an RS-422
compatible device to the Data Highway II link.
Although the host/interface links are not Data Highway II links, they are a
part of the Data Highway II network.