Reference Manual
748384-C
September 2003
Rosemount Analytical Inc. A Division of Emerson Process Management
Introduction 1-39
NGA2000 Reference
1-22 PC LON INTERFACE
It is possible to connect a PC to the LON. You
can monitor variables, and you can write values
into the configuration variables as desired.
It is possible to write software that uses Echelon
libraries to directly interface with the LON, how-
ever this is not an undertaking for the faint of
heart. If the performance limitations are ac-
ceptable, a better alternative is to use the DDE
function in Windows to enable high level appli-
cations such as Excel or Labview to communi-
cate with the analyzers.
Rosemount Analytical can supply a package of
software that allows this functionality. This con-
sists of a "DDE server" program, and some ex-
amples that show how to use it.
a. Performance
Windows allows a cycle time of about 65
micro seconds for the DDE protocol. This
means that it is possible to get about 10
variable updates per second through the
DDE server.
The DDE server is restricted to polling the
network - that is to say it has to request a
data update every time it wants one, rather
than simply listening to the network the way
the control module does. This also Emits
the performance and may interfere with the
operation of the control module menus (they
will get slower and unresponsive eventu-
ally).
All Windows programs tend to be somewhat
unstable, particularly if there are many en-
tries and exits of Microsoft applications, due
to the memory "leakage" problems afflicting
them. It is as well to have someone check
a PC for correct operation on a daily basis.
At this writing, Windows 95 operation has
not been tested.
NOTE
It is not possible to write data into a plat-
form control module from a PC, due to
the control module's acting as a network
manager.
It is also not possible to write configura-
tion data into an I/O module, since its
configuration variables are configured as
output variables.
b. Basic
Operation
A suitable LON hardware interface must be
installed and its driver installed into the
"CONFIG.SYS" file. For example, using the
Echelon SLTA serial device, the driver
LDVSLTA.SYS must be installed into CON-
FIG.SYS, with appropriate switch settings
(/p1 /d1 /a is typical). See the Echelon
documentation for details. Reboot the
computer so it takes effect. You may have
to use the memory management utilities un-
til the DOS memory is adequate for the ap-
plications.
Install the Rosemount Analytical DDE
server program by typing "SETUP" in the
Run... prompt of the Windows program
manager. It will be installed together with
the example files into a new directory called
NGASUITE.
Start the DDE server program. It will inter-
rogate the network, and once it is done it
will retire to an icon. You can open the icon
and select "File", and then the network in-
formation, and see what nodes are found.
The names and addresses of the nodes can
be directly edited by double clicking on the
appropriate field.
Verify that the TAG names do not contain
periods or arithmetical signs such as "-“ or
“/”. Edit them if they do.
Further help can be found in the accompa-
nying documentation and in the "Help"
screens built into the DDE server itself.
Open the desired Windows application and
use its DDE functionality to transfer data to
and from the DDE server.
