I would like to program an AD9913 to output two linear frequency ramps that are back-to-back. Each ramp has its own starting frequency, ending frequency, and time steps. I have tried this with a down ramp followed by an up ramp, and vice versa, and it works fine. However, if I try to do an up ramp followed by an up ramp (or a down ramp followed by a down ramp), the first ramp works fine, but then the output jumps immediately to the final frequency of the second ramp.
I am not doing any resets inbetween the two ramps. In the datasheet, it says that the delta tuning words and ramp rate words can be reprogrammed during a ramp, so for updating these values I am assuming that a reset is not needed. However, I am also changing the start and ending frequencies S0 and E0. Can these be reprogrammed while linear ramp mode is on? Or do I have to reset the ramp (presumably by setting CFR1[21:20] low)?