Rockwell Automation 1775-S5_SR5,D17756.5.5 User Manual PLC-3 FAMILY I/0 - Manual (Page 82)

Addressing DH and DH+ Data Transfers
Chapter 5
5-8
The logical ASCII addressing method allows you to communicate with
another device by specifying an address based on the internal memory
structure of the target device. The scanner sends the address as a string of
ASCII characters to the remote station. Upon receiving the string of
ASCII characters, the remote station converts the data into a usable logical
address.
The scanner offers two types of logical ASCII addressing; data type and
word range. In both methods, the scanner transmits the address as an
ASCII string, but the packet of data transmitted by the scanner on the
DH/DH+ link differs.
Data Type
You can use Logical ASCII Data Type addressing to transfer data table
sections without counting the actual words per data table structure. With a
data type packet, the receiving station is notified of the type of data
being sent.
Each station has a common understanding of how the different data types
will be received. It is the responsibility of the sending station to translate
the way it stores a particular data type into this common structure before
transmitting. The receiving station then translates the structure into it’s
method of storage for that particular data type.
To format a logical ASCII data type address, you enclose the address
parameters in double quotes (”):
Format: Example:
$” address”,size $”N55:0”,20
Figure 5.6
Example of Logical ASCII Address that Accesses the First Word in File 1
$ ”
LogicalĆASCII data type delimiter
Word address in memory
LogicalĆASCII data type delimiter
Address delimiter
I1:0 ”
Symbols are allowed inside the double quotes if they are defined in the
remote station.
Using Logical ASCII
Addressing