AD9912 I use spur killer, I need killed spur harmonic 2, It should write 0x01 or 0x02 to the register 0x0500 ?

I believe you are operating on the assumption the DAC harmonic spur is in phase with the fundamental signal. Not so. In fact, the phase of the DAC harmonic spur is not predictable as it depends on the non-linearity of the particular DAC being used. Because you do not know the phase of the DAC spur a priori, you can only guess at the required phase of the Spur Killer signal (which would be 180-degrees offset from the unknown phase of the DAC harmonic spur).

The AD9912 datasheet explains how to achieve spur reduction (see the Harmonic Spur Reduction section). Step 5 is the key (though it is subtle). You must ADJUST the phase of the "spur killer" signal to MINIMIZE the combined spur level (DAC spur plus Spur Killer spur). That is, you are faced with an adaptive process in which you are seeking the minimum of a function (i.e., final spur magnitude as a function Spur Killer gain and phase).

To attenuate the DAC spur you will need to try different Spur Killer phase values while observing the final output signal. The goal is to find the phase value that gives the most attenuation. Therefore, you will need to write an iterative loop that walks through the full range of Spur Killer phase values as you watch the output signal for maximum attenuation.

Then, once you have settled on the correct Spur Killer phase, you can fine tune the Spur Killer gain to get the maximum possible attenuation of the final output spur. Remember, complete spur reduction is a combination of both the correct Spur Killer level (gain) and the correct Spur Killer phase.

In summary, the procedure is as follows...

1. Observe the DAC output spectrum and estimate the magnitude of the spur you want to eliminate.
2. Set the Spur Killer frequency to the harmonic number associated with the spur you want to eliminate.
3. Set the Spur Killer gain to a value that is reasonably close to the level of the spur you want to eliminate (you do not need to be precise with the gain value at this point).
4. Try various Spur Killer phase values while observing the final output signal and use the phase value that results in the most spur attenuation (note that applying the correct phase at this point may not necessarily attenuate the spur completely as the gain setting might not be optimal).
5. Now that the correct phase value has been determined, make small adjustments to the Spur Killer gain while observing the final output signal. Again look for the gain value that results in the most spur attenuation.
6. At this point you have "dialed in" the Spur Killer parameters (harmonic number, gain, phase) yielding maximum spur attenuation.

Hope this proves helpful.

I believe you are operating on the assumption the DAC harmonic spur is in phase with the fundamental signal. Not so. In fact, the phase of the DAC harmonic spur is not predictable as it depends on the non-linearity of the particular DAC being used. Because you do not know the phase of the DAC spur a priori, you can only guess at the required phase of the Spur Killer signal (which would be 180-degrees offset from the unknown phase of the DAC harmonic spur).

The AD9912 datasheet explains how to achieve spur reduction (see the Harmonic Spur Reduction section). Step 5 is the key (though it is subtle). You must ADJUST the phase of the "spur killer" signal to MINIMIZE the combined spur level (DAC spur plus Spur Killer spur). That is, you are faced with an adaptive process in which you are seeking the minimum of a function (i.e., final spur magnitude as a function Spur Killer gain and phase).

To attenuate the DAC spur you will need to try different Spur Killer phase values while observing the final output signal. The goal is to find the phase value that gives the most attenuation. Therefore, you will need to write an iterative loop that walks through the full range of Spur Killer phase values as you watch the output signal for maximum attenuation.

Then, once you have settled on the correct Spur Killer phase, you can fine tune the Spur Killer gain to get the maximum possible attenuation of the final output spur. Remember, complete spur reduction is a combination of both the correct Spur Killer level (gain) and the correct Spur Killer phase.

In summary, the procedure is as follows...

1. Observe the DAC output spectrum and estimate the magnitude of the spur you want to eliminate.
2. Set the Spur Killer frequency to the harmonic number associated with the spur you want to eliminate.
3. Set the Spur Killer gain to a value that is reasonably close to the level of the spur you want to eliminate (you do not need to be precise with the gain value at this point).
4. Try various Spur Killer phase values while observing the final output signal and use the phase value that results in the most spur attenuation (note that applying the correct phase at this point may not necessarily attenuate the spur completely as the gain setting might not be optimal).
5. Now that the correct phase value has been determined, make small adjustments to the Spur Killer gain while observing the final output signal. Again look for the gain value that results in the most spur attenuation.
6. At this point you have "dialed in" the Spur Killer parameters (harmonic number, gain, phase) yielding maximum spur attenuation.

Hope this proves helpful.