I've just got my hands on an AD9910 Eval board and I am using the software to control it from a computer. Although my question is quite trivial, I just want to clarify why the GUI of the software says the maximum ref. clock frequency is 500MHz. You can see this if you let the cursor hover over the ref clk window. I'm anyway using a 1GHz input and it seems to work well. But I would still like to get this clarified. Thanks.