I have AD9956 and I build a fractional divider PLL circuit as seen in Evaluation Board datasheet. I am using its crystal mounted on the evaluation board as a reference clock so that reference frequency is 25MHz. VCO frequency can be sweeped from 2.313 GHz to 2.4725 GHz. I can sweep frequency up and down using its program on the pc. Which register is responsible to program AD9956 to sweep frequency up and down in a loop so that I can write the register and do this action using your software?