AD9858 chip will take how long to respond the order it receive and begin to generate the wave? If I already use FPGA chip Cyclone_EP1C6T144C6 and AD9858 generate a single_tone mode wave , in there I use 80MHZ clock to deliver control word 、frequency word and phase word.when I want a 0.3us width wave ，my solution is counter 0.3us time ，then set the control register CFR and CFR to logic 1，and updata this control word to DDS core .But there don't generate the wave I expect. When I cut the deliver clock down to 20MHZ ,the same set will be generate the expect wave .But observe the wave on oscilloscope its quality is not good ! why cut down clock can generate? How to do this type wave?And how to improve the wave's quality?