Hello,
These two links should help out in calling dll functions.
[Configuring the Call Library Function Node]: https://zone.ni.com/reference/en-XX/help/371361M-01/lvexcodeconcepts/configuring_the_clf_node/
[Tutorial: Configuring the Call Library Function Node to call a Simple DLL]: http://forums.ni.com/t5/Developer-Center-Resources/Tutorial-Configuring-the-Call-Library-Function-No...
Thank you