Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 51)

Data Highway Communication
Chapter 3
3Ć6
The whole purpose of Data Highway communication is to transfer data
from one station processor memory location to another. To accomplish
these data transfers, you can program the assignment command into the
1775–KA module.
Chapter 6 gives the details of the assignment command. For now, let’s just
look at the simple example in Figure 3.2. In this example, the assignment
command copies a word (16 bits) of data from the source to the
destination location. The source of the data is always specified on the
right of the equals sign (=), and the destination is always on the left.
Figure 3.2
Example Assignment Command
$B45:21 = $I12:33
Source Address
Address Delimiter
Asignment Command
Destination Address
Address Delimiter
10015-I
Note that an assignment command does not destroy the data at the source
location; rather, it just makes a copy of the source data at the destination
location. When the assignment is executed, both source and destination
will contain the same data.
There are two ways to use a data transfer command with the 1775–KA
module:
as a single command within a PLC–3 message instruction
as one of multiple commands within a message procedure
Figure 3.3 illustrates both of these methods for the same assignment
command. Note that a message instruction in the PLC–3 ladder diagram
program controls execution of the command in either case.
Data Transfers