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Problem with update frequency in 28 bit mode on AD9833.

Question asked by Ilgiz on Aug 29, 2011
Latest reply on Aug 30, 2011 by LiamR



I am try use AD9833 for make FM modulation in 28 bit mode.


In first time I am send configuration 0x2000. After I am continuous send  frequency value: <LSB><MSB>,<LSB><MSB>.....<LSB><MSB>. But DDS each <LSB> and <MSB> transaction interprets how 14 MSB bits of FREQUENCY 28 bit register. But if I am change my bitstream: <LSB><MSB><configure(0x2000)>,<LSB><MSB><configure(0x2000)>.....<LSB><MSB><configure(0x2000)> DDS fine understand me. And it is strange for me. The AD9833 datasheet not have any description how it possible change frequency in 28 bit mode without put DDS in reset. Do I need send configuration before or after two consecutive send(lsb and msb ) frequency value? Can you give me more information how AD9833 update utput value in 28 bit mode and what command Sequence I am need send for update frequency in 28 bit mode without put DDS in reset?