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AD9835 Documentation

Question asked by Spacerowa on Nov 27, 2010
Latest reply on Dec 16, 2010 by Spacerowa

I am able to successfully program the part, but achieving this stage was problematic because of inconsistencies and contradictions in the documentation which I had to work around. I refer to DATA SHEET ( 41503.pdf ), and APPLICATION NOTE AN-612.

  1. Data sheet p6 "...RESET (D12) = 1.... corresponds to an analogue output of fullscale". AN-621 p2 " D12=1 Reset bit.....output of DAC will be midscale".
  2. Data sheet p6 " When CLR(D11)=1, SYNC and SELSRC are set to zero". AN-621 p2 " D11=1, CLRBIT. When CLR=1 SYNC and SELSRC are set to 1"

Can anyone resolve these for me ?


And also the following to complete my understanding.

In the data sheet p6 there is a command for bit D11 to be used to select the FREQREG  when SELSRC=1. Bit D11 corresponds to bit A3 which is always zero. I have successfully programed with and without this command ( 5000 hex ). So what is its purpose ?

Does the RESET bit D12=1 overide the SLEEP bit D13=1 ? Otherwise how can the part be programed if powered off ?


I have also have comments on the functionality of the AD9835 online interactive design tool; but leave that for a separate discussion.


As I said, I have been successful but it was hard going. I would have found very useful some proven examples in the data sheet of instruction sequences for the important cases of FREQREG select using bits and pins; but there are none.


I have used many different instruction sequences which give an output on the desired frequency. My current preference is my own code i.e. D000, B000, ( Tuning word bytes 1-4 ), C000. It is a very logical, understandable sequence and it works ! But you won't find it in AN-621 and neither can you derive it from the interactive design tool.