MPU6050's Accelerometer of Z axis change from 9.8 to -9.8

Hi guys,

I'm currently using the MPU6050 to get the accelerometer and turn rate of my quadrotor, however, I found a very very strange problem with the data of z axis's accelerometer, It would change from 9.8 to -9.8 when the MPU6050 is a little tilted. If I put it upstand making the x axis down to the ground, the same thing happens!!! My controller is DSP28335, and I observe the raw data of MPU6050, finding that raw data is changing from 9.8 to -9.8, while the gyroscope is working very well.

But when I use an arduino to read the MPU6050, It's ok, so what's the problem?