DOS pin of AD2S1210 are always low on my board. The resolver on my system is TNS2640N321E64 from Tamagawa in Japan. The waveform of exciting and feedback is shown in attachment of figure 2, where the exciting wave is blue, sine feedback is yellow, cosine is purple. I changed the exciting frequency register and the frequency can vary with my setting. In figure 1, the DOS is yellow with a narrow positive pulse about 250ns, LOT is purple, and sample signal is blue. Two sample pulses will follow a normal position sampling cycle of 5 ms to clear fault register. The schematic gram of resolver is attached as well, and the resolver reset signal comes from system reset during 512us after power on.
I have been troubled by this problem more than a week. I am looking forward to your reply as soon as possible.