Problem using SPI interface to work with 9250

We are planning to use the MPU9250 chip in our product, and we bought the MPU9250 break out board for evaluation. We connected our MCU board to the MPU9250 break out board via SPI interface. We have already removed resisters R2 and R4 on the MPU9250 board as mentioned in the data sheet. In our software, we tried sending out one byte address (register address) first and then read back data by sending a dummy data (we put zero).
First we tried to read the WHO_AM_I register value, then tried the address from zero to 0xff, however the data we read back is either 0 or 0xff. We monitor the timing sequence of nCS, SCLK and SDI and it looked perfect. However the SDO shows analog signal, that meant it go up to VDD and then discharge to 0 gradually, which I think is not right.


Is there anything I need to do on the MPU9250 break out board other than removing R2 and R4 if I want to access the board via SPI? I would be appreciated if you could provide any hint.