Rockwell Automation 1775-S5_SR5,D17756.5.5 User Manual PLC-3 FAMILY I/0 - Manual (Page 68)

DH and DH+ Communication
Chapter 4
4-8
The purpose of DH/DH+ 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 scanner.
Figure 4.3 is an example of an assignment command line. For details, see
chapter 5. Since the following example does not specify a remote station,
this transfer occurs within the local systems memory.
Figure 4.3
Example Assignment Command Line
$B45:21 = $I12:33
11233
Assignment Command
Destination Address
Address Delimiter
Address Delimiter
Source Address
In the above example (Figure 4.3), 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 equal sign (=), and the
destination is always on the left.
An assignment command does not destroy the data at the source location; it
copies the source data at the destination location. When the assignment
executes, both the source and destination contain the same data.
You can use a data transfer command with the scanner:
as a single command within a message instruction
as one of multiple commands within a message procedure
Figure 4.4 illustrates both of these methods for the same assignment
command. A message instruction in the ladder program controls execution
of the command in either case.
Data Transfers