Hello yangero,
Welcome to the NI forums! Before I answer your question, I am going to need some more information. Whether or not you need a resistor depends on what you are trying to do and what hardware you are using. Our various cards have many different features, several of which may require external resistors. If you could please let me know what your application is (e.g. voltage measurement, digital generation, etc), the device number you are using (e.g. PXI-6251), what settings you are using (screenshots could help), and where you see that you may need this resistor, I will be able to help you more effectively.
Neal M.
Applications Engineering National Instruments www.ni.com/support
