I used 50MHz's crystal oscillator and enabled the PLL, but the SYNC_CLK pin only outputs a high level. What's the matter?
When you say its a crystal oscillator - does the reference source drive an output all by itself or does it need to be hooked up to a resonant circuit? The AD9914 REFCLK inputs require an ac-coupled driven signal. I suspect this is the problem. Check to make sure the reference inputs have a time varying signal on them as a first step.
If there is a signal present on those inputs which meets the specs outlined in the REFCLK input section of the spec table, then one explanation could be that there has not been a valid I/O Update signal provided. You could check this by reading back the contents of the registers.
Thanks for your reply. I use an active crystal oscillator and when the power is on, 50MHz clock signal is generated.
and I select single-ended source,single ended input,I can find the signal in the REF_CLK pin.I think I also write a valid I/O Update signal.So I wonder if the chip is broken？
A damaged device is always a possibility. If there is a valid signal on the reference inputs, you should get some signal out of the SYNC_OUT pin
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