Configuring a DDE Client connection to a DDE Server

The DDE Client task/worksheet is used to configure a DDE Client connection to a DDE Server application such as Microsoft Excel (or any other Windows program supporting this interface).

Dynamic Data Exchange (DDE) is a protocol for dynamic data exchange between Windows applications, such as Excel. A DDE conversation is an interaction between server and client programs. IWS provides interfaces that run as clients or as servers. See DDE Client Runtime and DDE Server in the Runtime Tasks (Tasks on the Home tab of the ribbon).

To run as a server, start the DDE or NetDDE server task as described in Runtime Tasks.
To run as a client, configure the DDE interface worksheet on the Comm tab.

Network Dynamic Data Exchange (NetDDE) is an extension of DDE that works across computers on a network.

To run IWS as a server to a NetDDE connection, you must start the DDE Server application.
To run IWS as a client to a NetDDE connection, use the same DDE interface worksheets with the proper configuration to address a IWS project.

Note: When running NetDDE, IWS accepts the WRITE triggers only. To read data, you must configure a write command on the server computer.

To open a new DDE worksheet, right-click on the DDE folder and click the prompt screen.

A new DDE worksheet displays, as in the following figure.

Figure 1. DDE Worksheet

The DDE worksheet dialog is divided into two areas:

Header area (top section), contains information for the whole group and defines the tags to start the reading and writing and to receive connection status
Body area (bottom section), where you define tags in the project and items related to the DDE server application

Every DDE interface is based on addressing an application using the following three structures:

Application Name
Topic
Item

The first task is to find these identifiers in the DDE Server application.

Use the parameters in the DDE client worksheet Header area as follows:

Description field: Type a description of the DDE worksheet for documentation purposes.
Application Name field: Type the DDE server application name.
Topic field: Specify a topic in the server application.
Connect field: Type a tag to control the connection of the IWS DDE client and DDE server application. When this tag is set to 1, it requests a connection to the server. If the connection is not possible or if it fails, IWS sets the tag to zero again. If the connection is OK, this value remains set to 1.
Read Trigger field: Type a tag to command a reading of the table. When this tag changes value, IWS generates polling to the DDE server. You can use this parameter with local DDE only; you cannot use it with NetDDE servers.
Enable Read when Idle field: Type a tag value higher than zero to enable a reading of the equipment.
Read Status field: Contains the status of the reading command.
Write Trigger field: Type a tag enabling IWS to generate poke commands to the server.
Enable Write on Tag Change field: Type a tag value higher than zero to enable the communication driver to check continuously for changes in a tag value in the worksheet. When the driver detects a change occurs, it writes the changed tag on the equipment, along with the tag's address.
Write Status field: Contains the status of the writing command.

Use the DDE client Body area parameters as follows:

Tag Name field: Type a tag to read or write the IWS database from the DDE server application.
Item field: Type the ITEM part of the DDE address on the server. Refer to your server software documentation for information about the proper syntax for APP, TOPIC, and ITEM.
You can configure the Topic and Item fields with tags on the address using the syntax: text{tag}. IWS evaluates the value of {tag} to a string and uses it on the address. For example:
- Topic: topic_{tag_topic_name}_example
- Item: {tag_item_name} or A{tag_number}

Configuring a NetDDE connection is similar to configuring a DDE connection, except for the Header Application name and topic. Before starting your tests, verify that you enable the DDE Server on the station with which you want to exchange data.

Note: When connecting to servers other than IWS, please refer to the server documentation for information about the proper syntax of APP, TOPIC, and ITEM.

Use the NetDDE Client worksheet Header parameters to define the tags that start reading and writing, and tags that receive the connection status, as follows:

Application Name field: Type computer name\NDDE$, where computer name must be a valid network computer name.
Topic field: Type the UNISOFT$ topic name to connect to another IWS station.

Use the DDE client worksheet Body parameters to relate each tag to each ITEM part of the DDE server address, as follows:

Tag Name field: Specify the IWS local database tag name that is related to some remote tag name.
Item field: Specify the remote tag name that is related to the local tag name.

Note: By default, the DDE Client module supports DDE Servers that handle string data in the UNICODE format. If the DDE Server handles string data in the ASCII ANSI format, the following setting must be configured manually in the project_name.app file (you can use Notepad to edit this file):

[Options]
DDEANSI=1