# OPC vs DDE

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#### Mark Riche

I wonder if anyone knows of a good website to explain / recommend the differences between OPC and DDE for plc data manipulation.

Thanks,

Mark Riche, P. Eng.
Electrical Design Engineer
Northwest Territories Power Corporation
4 Capital Drive
Hay River, Northwest Territories
X0E 1G2
ph (867) 874-5266
Fax (867) 874-5264

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#### Christopher Di Biase

well I don't know of a good web site, though http://www.opcfoundation.org might have some information. The long and short of the argument is this:

DDE = old technology. DDE is a hold over for Windows 3.0 and was originally intended for program to program communications. Microsoft
developed this technology and is attempting to phase it out.

OPC = new technology. OPC is based on Microsoft's COM/DCOM technology which is the replacement for DDE/NetDDE. COM is much faster and more robust that DDE, as such OPC is also faster and more robust. OPC also allows for additional functionality specific to the automation industry that DDE did not support (things like data quality, time stamps, etc) Also
Microsoft is still nurturing and developing COM (and the newer COM+) so the technology is likely to have M$'s backing for a long time. basically if you're developing a custom application / HMI, you should use OPC is at all possible. Doing so gives you the ability to talk to just about any PLC on any current or future Windows platform. Also it might (I stress might) be possible (help me out Linux gurus) to port the same code to a Linux platform, and use one of the Linux COM implementations. Christopher Di Biase [email protected] G #### Gord Ellis Hello Bart, I think that should be www.opcfoundation.org Gord... ============================================== Gord Ellis, P.Eng. Northern Dynamic Inc. J103-155 Frobisher Drive Waterloo, Ontario Canada N2V 2E1 Tel/Fax: (519) 725-2071/2072 web: www.nordyn.com B #### Brook Bolton R #### Roy Smith Have you had any experience with the documented failures with DCOM? It seems as though it can just fail without any reason and their are no ways to recover untill DCOM is ready to start working > well I don't know of a good web site, though http://www.opcfoundation.org might have some information. The long and short of the argument is this: > > DDE = old technology. DDE is a hold over for Windows 3.0 and was originally intended for program to program communications. Microsoft > developed this technology and is attempting to phase it out. > > OPC = new technology. OPC is based on Microsoft's COM/DCOM technology which is the replacement for DDE/NetDDE. COM is much faster and more robust that DDE, as such OPC is also faster and more robust. OPC also allows for additional functionality specific to the automation industry that DDE did not support (things like data quality, time stamps, etc) Also > Microsoft is still nurturing and developing COM (and the newer COM+) so the technology is likely to have M$'s backing for a long time.

>

> basically if you're developing a custom application / HMI, you should use OPC is at all possible. Doing so gives you the ability to talk to just about any PLC on any current or future Windows platform. Also it might (I stress might) be possible (help me out Linux gurus) to port the same code to a Linux platform, and use one of the Linux COM implementations.

>

> Christopher Di Biase

> [email protected]