In TesStand development screen, if you look at the toolbox just under the File - Edit- View - etc. menu bar, you will see a drop down box, usually located directly under the Help menu item. Usually this box has Labview selected. This is the function prototype adapter that is used for calling test steps. If you want to call a Labview vi, you must select Labview in this box. To call a DLL, click on arrow beside the box and select C/C++ DLL. Then in your sequence window, if you add a test step or action step, you will notice that the icon next to the step type has changed to the C icon. If you select a step type like Numeric Limit Test, then click Specify Module button, you will get a window somewhat similar to the one Labview gives you when using the Call Library f
unction. The window allows you to enter the DLL file name, the DLL function name, and all parameters and their data type. Once you see this window, the rest should be clear. Don't forget to change the proptype adapter back to Labview to insert a Labview step.