help on dds programong

hi

i have read ad9830 dds ic datasheet, but i have steel problem how i
should program it, for example i want to use pararel port for
interfacing , and for example want 3.1MHZ on out put, how i should
use D0 to D15 and A0,A1,A2? should i use both freq reg ( 0,1) and
all 4 phase reg ? or one is enouth?
any help would be most appreciated
thanks
payam