Guidelines For Connecting The 1771 Krf; Chapter Objectives; Data Highway And Data Highway Plus Networks; Network Guidelines 2 - Allen-Bradley 1771-KRF/B User Manual

Chapter Objectives

Data Highway and Data Highway
Plus Networks

Guidelines for Connecting the 1771 KRF

This chapter contains the following:
what DH/DH+ networks are
what a remote I/O network is
network guidelines
typical applications using the KRF
Data Highway and Data Highway Plus are local area networks that allow
peer-to-peer communication between PLCs, computers, and other
intelligent devices:
Data Highway
DH connects up to 64 nodes and has a communication rate of 57.6K baud.
It implements peer-to-peer communication through a modified
token-passing scheme called floating master. In this arrangement, each
node has equal access to be master. The nodes bid for temporary
mastership based on their need to send information. Fault recovery
timeouts are used if mastership token is lost.
Data Highway Plus
DH+ connects up to 64 nodes and has a communication rate of 57.6 or
115.2K baud. It implements peer-to-peer communication with a
token-passing scheme to rotate link mastership among its nodes. DH+
also uses timeouts to recover from a fault that disables the node that has
the token. Use a DH+ link when you want to connect a small number of
nodes that communicate frequently on a common link. For example, you
would use DH+ to connect a small group of PLC-5s (usually 10 or less)
involved in a single integrated process.
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