SW API Porting Guide

Unmanaged C++ TE_USB_FX2_Open()
of TE_USB_FX2_CyAPI.dll

You can use this function to select the desired module without the need to call TE_USB_FX2_Close() before. Though doing so would not cause any problems.
Close is automatically realized by the TE_USB_FX2_Open() function, if a handle to the driver is already open (i.e. TE_USB_FX2_Open() has been successfully called before).

Managed C# TE_USB_FX2_Open()
of TE_USB_FX2_CyUSB.dll

You can use this function to select the desired module without the need to call TE_USB_FX2_Close() before. This function is not necessary.

Unmanaged C++ TE_USB_FX2_Close()
of TE_USB_FX2_CyAPI.dll

It can be freely called but it is rare that you would ever need to call TE_USB_FX2_Close() explicitly (though doing so would not cause any problems).

Managed C# TE_USB_FX2_Close()
of TE_USB_FX2_CyUSB.dll

It cannot be freely called and it is rare that you would ever need to call TE_USB_FX2_Close() explicitly. Furthermore, if it is used in the wrong way, the program can raise exceptions.