Message Sets Available; Redundant Cabling - Allen-Bradley 1779-KFMR User Manual

Message Sets Available

Redundant Cabling

On a Data Highway II network, with a synchronous-device/DHII
interface, you can communicate with other nodes through messages of the
following message sets:
Data Highway
Time-Critical
Remote Command Control
Packet Assembler/Disassembler (PAD)
Station Management
In Chapter 7, we provide a comparison of these various message sets. In
the chapters that follow 7, we describe each message set in detail in its
own chapter.
If you install the redundant version of each node interface (see "Node
Interfaces") you can install a second complete cabling system for the Data
Highway II link (Figure 2.9).
In Figure 2.9, we show Cabling System A and Cabling System B for the
Data Highway II link. Each cabling system provides backup for the other.
Each node interface attempts to transmit each outgoing message across
both cabling systems. Each node interface continuously monitors the
quality of the signal it receives from each cabling system. As a node
interface receives a message, it always accepts the message from the
cabling system providing the better signal quality. If a cable in Cabling
System A becomes damaged, each node interface accepts its incoming
messages from Cabling System B. If Cabling System B becomes
damaged, each node interface accepts its incoming messages from
Cabling System A.
Although this redundant cabling configuration provides backup for the
cabling system, it does not provide any backup for the node interfaces. If
a node interface fails, the node has no way of communicating with other
nodes in the Data Highway II link.
Chapter 2
Introducing the 1779 KFM Interface
2 15