Specifications

44 RSLinx – Training Guide
Data Format: AdvanceDDE, XL_Table and CF_Text
A brief discussion of available Data Formats for DDE communications follows.
It is intended to provide you with a general understanding of Data Format from a user
standpoint.
Normally no user intervention or control of data formats is possible, and for the most
part, the use of different data formats is transparent to the user. There is one major
exception - you will certainly notice a vast improvement of the speed at which your data
is transferred if one of the “higher” levels of the available data formats is used.
Microsoft has implemented two Data Formats that are available for DDE conversations:
CF_Text and XL_Table.
CF_Text is the simplest and easiest to implement. All DDE compliant
applications should be able to understand this data format. It is the basic level of
compliance to Microsoft’s DDE specification. Microsoft has also defined a faster
data format called XL_Table. Microsoft has only implemented this data format in
Excel.
FastDDE is a proprietary format used by Wonderware that is faster than
XL_Table, but does not incorporate error checking.
From a data throughput standpoint, CF_Text is slow and XL_Table is fast. In a general
way, you can think of CF_Text as an ASCII transfer with each data item being a single
message, while XL_Table blocks the data into a table, so many items may be a single
message.
RSLinx can communicate using any of these data formats
. When a DDE channel is
established, a form of handshaking takes place that automatically establishes the data
format to be used (the fastest format both the client and server can understand).