Chapter
5
51
Programming the Local Host
In this chapter you will read about how to generate a ladder-diagram
program for a PLC-2 family processor (local host) to communicate
through the KP2 interface to the host of a remote node.
The generation of commands is discussed as if transmitted to the PLC-2
family processor at a remote node. If another type of PLC processor is at
the remote node, refer to the manual for the node interface of that PLC
processor for information on that processor’s addressing conventions. For
a computer (and some processors) at a remote node to accept commands
from this local node, it must have a file at the remote node host to
simulate a PLC-2 family data table.
A Data Highway II network allows access to the memory of each remote
node. This means that data table information at any operating PLC
processor can be transmitted to another PLC processor, or to a computer,
and used by the other node to control its own part of an operation.
The communication zone is a set of rungs with a well-defined beginning
(header) rung and a well-defined ending (delimiter) rung that you enter
into your control program. The rungs between the header and delimiter
tell your highway interface what messages to generate and what messages
to accept while this process is running. Figure 5.1 shows a simple
communication zone including each function type. The following
sections explain the communication zone rungs in detail.
Actual communication zone rungs for any host processor may vary. If,
for instance, a PLC-2 will not generate any messages and will accept all
messages from other nodes, you need not enter a communication zone at
all. The length of this zone is a function of the number of remote nodes
with which the local host processor communicates and the number of
types of commands to be sent to these remote nodes.
Chapter Objectives
Communication Zone
