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!