AnsweredAssumed Answered

AD9954 communication problem

Question asked by dmayer on Jun 19, 2013
Latest reply on Jul 3, 2013 by dmayer

Dear Community,


I just finished my DDS-Board which is driven by an LPC-Expresso microcontroller for communication via rs232 to the PC. The design of my board is strongly related to the AD-Eval-Board setup.

But unfortunately I experienced some problems setting up the DDS.


Here is what I am trying:

-communication via SPI with microcontroller

-set CFR1/CFR2 to desired values to get 400MHz clock from 25 MHz crystal

-get a single tone output for first result


But i did not get any output so far by following the example in the datasheet.


I then did some debugging research and it appears that communication does work: I am able to write CFR2<9> and issue an IO-Update to enable/disable the CRYSTAL_OUT pin.

But sadly thats everything that works so far. When trying to write any bit in CFR1 ,i.e. the CFR1<1> while monitoring the SYNC_CLK pin, it seems to have no impact at all. The SYNC_CLK appears as soon as CLKMODESELECT is pulled high and does not disappear when CFR1<1> is set.

I also tried to set a clock multiplicator in CFR2 to get the desired clock rate, but this did not work, too.


How could this strange behaviour of the part be explained? I hope i did just miss a stupid thing...

Thanks a lot!