RSLinx & DDE links

Danocane

Member
Join Date
Aug 2002
Location
Topeka, Kansas
Posts
79
I have a question for those using Rockwell RSLogix and RSLinx Pro or RSLinx Gateway. I have set up DDE links from RSLinx Gateway to an Excel spread sheet. Using Excel's VBasic I have images of the the equipment controlled through 12 different PLC5 PLCs on a DH+ network that change colors or change captions as the PLC controls change equipment functions. This makes a very good mimic of the various operations occuring through out the plant. Where the problem comes in is that members of supervision have seen this operate and want to have more PCs setup with this function in other areas of the plant. The company is willing to pay the expense of more PCs and more copies of RSLinx Pro (this is the lowest version of RSLinx that allows DDE links). So All I have to do is setup the PCs and the software to communicate with my PC which has the PKTX comm card through our existing intranet. I can copy the Excel programs to the new PCs, But I cannot seem to locate the DDE Topic Confiquration Files in any of the RSLinx folders. OK so here is my question: Where do I find the DDE Topic Configuration Files that RSLinx has stored on my PC so I can copy them to the other machines? Or do I have to rewrite these files to each of the new PCs?
 
Last edited:
I think the DDE topics are actually stored in the Windows Registry, so they're not easy to transport between PC's manually.

There is a "Backup / Restore" utility that comes with RSLinx and lets you transports whole RSLinx configurations between PC's (or to have them survive reinstalls). It backs up configured drivers, and DDE configurations, shortcuts.. that kind of thing.

It's an executable in the RSLinx program folder (Backup.exe) and you can run it from the Start->Programs->Rockwell Software->RSLinx path or from the command line.

You might not need RSLinx Professional at each remote station if you can set up NetDDE to have data served by the RSLinx installation that is on the machine with the PKTX card (hopefully it's running NT or 2000!). I'm not a NetDDE expert, so I'll bow out at this point and leave this for guys with more experience.
 
DDE/netDDE/OPC Servers

One server should be enough.

With DDE or OPC protocol drivers, two methods are usually provided to access datas :

1) you choose to define data tags in the driver software
2) you choose to not define data tags

In this second case (assuming your software is configured as a DDE server), datas are accessed from the clients (Excel's cells or VB code here). The server is directly asked for values like this :

Cell 3,B =application|topic!item

where "topic" and "item" refer to your addressing mode in PLCs (PLC name/address/alias + data address), and "application" contains path and name of your server (DDE example, OPC is a little bit different)

BTW, there are several advantages... :
- lighter configuration : there is no database in your server.
- each client can access and show different datas
- datas can be reached from any DDE compliant application on the network (Excel, SCADA, DataBase....) if your server allows to share datas with netDDE.
...But drawbacks and risks too :
- any technical user can read/write datas in PLCs
- be sure that someone won't appreciate such an unsecured data sharing method...

So, you may add to such a solution another intermediate level, with security management and data filtering. An easy way consists in using EXCEL's capabilities (since Excel can be a server too !):

- Disable netDDE in your protocol server, and only access datas from a "front" local Excel spreadsheet
- Build for each network user/category some sheets, readable as data containers.
- Manage security in your front sheet (public / private datas, system datas, restricted access, and so on)
- You could create only one application for all users, by showing datas on your intranet, with restricted user's access through Internet Explorer. Try some combinations with Excel w or w/o Frontpage.

DDE / netDDE examples, downloadable softwares (running DDE/netDDE/OPC servers) at : http://www.kepware.com/

I hope this can help someone
 
Thanx Guys for the response's

Thanx Ken for the registry information I'll start drilling down through the registry today To see if I can locate the info I need.

Thanx Laurent for your input also....I basically chose not to define tags in this spreadsheet function. For a basic security I have disabled writes to the PLC's. This function can only read the data available to the DDE link and the Excel sheets are all protected from user intervention. This should prevent anyone from altering the PLC programs.

Thanx Dan
 
RSLINX START AS WINDOWS SERVICE

Hi, i'm Elias Castañeda from Mexico.

I have a problem, I configure RSLinx to start as windows service on Windows NT service pack 6 and set mode to Automatic. Also I configured a NetDDE Service as Automatic.

I develop a Visual Basic Application that try to get some values over the network via NetDDE Protocol, It's work fine while the user is currently logged in, but when the user is not logged in and the CTRL ALT SUPR Screen is activated, the application fails with the following error: Timeout while waiting for DDE response

This machine are in a lock room outside the city and is so dificult that each time when the electrical supply have interruptions we must go to login into windows.

What can i do?
 

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