Hi,
This depends on what kind of transfer you are doing. For example if you want to do DMA, the ABUSN and BBUSN have to be deasserted to enable 16 bit DMA transfers. The Adress 0:4 need to be set to 11000 to make the transfer happen. There is a really good user manual that explains how to set things up and program the chip. Please refer to http://www.ni.com/pdf/manuals/320724.pdf for more information.
Hope this helps,
Aaron K.
Application Engineer
National Instruments