I am using a AD9915 eval board to generate RF signals in order to drive an AOM. I want to modulate the phase of the RF output using the parallel port and the function pins. I would like to know if the base frequency for the phase modulation has to be set using the parallel frequency modulation or is it one of the profile modes. For instance, I want the DDS to generate a 80MHz signal and then modulate the phase of that signal. The phase word that I send to the DDS will be updated every two sync_clk cycles and therefore I will set the 'Parallel port streaming enable' bit high.
What I have tried so far is to set register 0x06 to 64 (enables parallel data port) and register 0x02 to 3 (enables parallel port streaming). Then I change the configuration pins F[3:0] to 0010 for setting the frequency, and then immediately change that to 0101 for phase modulation. I assume that io_update is not relevant since register 2 has been set to 3. Unfortunately, this protocol doesn't seem to be working. It's possible that there are other problems (hardware related ) that I have to look into but it would be great if someone could tell me whether the procedure I described is correct and if I need to change some other registers as well (or change the order in which I am doing things, e.g., set register 2 to 3 after setting frequency. Thanks!