hello, in RsLinx if I go to DDE/OPC - then to Update ControlLogix Tag Info and click on Update all what will this do? Please explain the function of this button and also if you click on it what will happen? thanks

Update ControlLogix Tag Information
The predefined item @CLTagUpdateAddressSpace for a ControlLogix topic allows the merging of new tags added to the controller into the current list of tags that the OPC Server keeps without taking the existing tags off scan. If the topic server is active and of type CLx when this item is read, RSLinx re-reads the tag information from the controller and merges the changes with the current tag information.

This functionality is required for client applications such as RSView or other third party products to view updated tag information while RSLinx already has an active topic running.

The global address space and the program address space are uploaded at once, therefore, you can not select which address space(s) to upload.

To use the predefined item:

Put this item on scan to activate this feature.

Add the item and mark it as inactive.

To do a read, use the Async2->Read menu item in the OPC Test Client. The syntax for adding the item is:
[name of topic for CLx processor]@CLTagUpdateAddressSpace
There are no parameters for this predefined item.