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DCN Next Generation Video Display en | 6
Bosch Security Systems B.V. | 2005 January | 9922 141 70451
3 DDE links
3.1 Introduction
The DCN Next Generation Video Display application LBB 4184 provides DDE (Dynamic Data Exchange)
links. Through these links external programs that have DDE client capability can access information regarding
the congress. The DDE server implemented in the Video Display application is a so-called “hot” DDE server.
This means that the server refreshes the DDE links whenever there is new data available. The DDE client
does not need to ask for an update. The DDE links are also made available as NETDDE links so other PCs
connected to the DCN Next Generation PC through a MS-Windows compatible network can access the
information too. Some DCN Next Generation DDE links can transmit large amounts of data. A DDE client
that wants to access DCN Next Generation DDE links must be able to deal with DDE datablocks up to 64
kilobyte in size. The VD application must be started by the user before the DDE links can be used.
3.1.1 DDE link naming conventions
A DDE link name consists of 3 parts:
1. The service name: This is the name used to address the DDE server. For DCN Next Generation
this name will always be “DCNNG”.
2. The topic name: This name identifies the class of data that must be transported across the DDE
link. For DCN Next Generation links the topic indicates which DCN Next Generation application
shall provide the data.
3. The data-item name: Topics may have more than one data-item at their disposal. This name
identifies which data-item must be sent through the link.
Example: To query the voting number
Service: “DCNNG”
Topic: “VOTING”
Data-item: “NUM”
DDE link: “DCNNG|VOTING!NUM”
3.1.2 NETDDE link naming conventions
NETDDE link names are derived from the normal DDE link name in the following manner:
1. The service name is replaced by “\\<servername>\NDDE$”. <Servername> is the network name
of the PC on which the Video application is running. (This name is determined by the Network
applet in the Windows Control Panel.)
2. The topic name is replaced by “DCNNG_<topic>$”. <Topic> is the same topic name for the link
as used for regular DDE.
3. The data-item name is the same as for regular DDE.
Example: The same link is described as in the example above, this time provided by a PC that has
the network name “VIDEO_SERVER”.
Service: “\\VIDEO_SERVER\NDDE$”
Topic: “DCNNG_VOTING$”
Data-item: “NUM”
NETDDE link: “\\’VIDEO_SERVER\NDDE$’|’DCNNG_VOTING$’!NUM”
The NETDDE part in the previous example is given in MS-Excel syntax. Other DDE client applications
might require a slightly different syntax especially for the | and ! characters and the quotes that separate the
different parts of the link-name. Refer to the documentation of your DDE client application for the exact
syntax required by your application.
i Note
The NETDDE is not supported in Windows XP Service Pack 2. Therefore DDE should be converted
locally and then send over the network.