AD2S1210 Encoder signal

Hello Dear All,

 

I am trying to implement AD2S1210 resolver digital converter chip to motor position reading with using TI 28379 DSP.  I have developed control board for  AD2S1210 circuit, and I am getting position data with SPI communication it works perfect. I have not changed configuration register and only I am configuring  RES0 and RES1 in reading moode either 12 or 16 bit resolution, it works. 

However, in my application I want to use also encoder (A, B, NM) signal to DSP and I want to read position data in parallel to SPI interface. I did not changed to configuration register, I just set RES0 and RES1 to 16 bit resolution in reading mode. I have flowing problems: 

- In stationary resolver position(there is no movement in rotor), A and B signals has variable frequency pulse, after some time it goes fixed period signals close to 10 MhZ, it is like oscillator signal.

- In constant speed resolver mode ( rotor in constant speed mode), A and B signal has not regular frequency signal, A and B has non-uniform periodic signal.   

 

Instead of using my inverter control board which includes AD2s1210 chip,  I tried my DSP codes with my DSP,    I have integrated my DSP to AD2S1210 Evaluation Board . My code works perfect both SPI and encoder works great. In encoder signals A and B have

- constant signal at stationary rotor position. 

- uniform frequency at constant speed of rotor.  

as it is expected. 

 

Please, could you help me to find out the root cause of the problem. Is it in my inverter control board regarding to ad2s1210 circuitry peripheral, misconnection, or oscillator signal? 

Or is the problem related to configuration, I am missing something