how to get set able frequency at IOUT

Question

I&rsquo;m designing an LVDT excitation circuit using AD9838BCPZ DDS with a 16 MHz external MCLK , controlled by STM32F103C8T6 . The board generates a clean sine wave , but the frequency remains fixed even when new frequency values are written. I&rsquo;ve attached the schematic and would like help reviewing the design and understanding proper frequency generation and control

Antonius · Accepted Answer

What frequency is the desired output? 
 Setting the frequency register involves several transactions on the SPI bus. I recommend following the flow diagram in Figure 25. First set the RESET bit in the control register, followed by two transactions to write the frequency register. Finally, clear the RESET bit to get the DDS running. Each transaction is 16 bits in length. Note that data is captured on the falling edge of SCLK, not the rising edge.)

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how to get set able frequency at IOUT

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