sry, i forgot to mention that the sensor was working before. I read the datasheet again. i noticed that the absolute max rating for Vin (input voltage for all control pins) is from -0.3v to VDD_IO+0.3 v. I hooked up VDD-IO to 3v. so based on the max rating, the input voltage should be no more than 3.3v. But the output high voltage from PIC is ard 4.5v. Could this be the reason that the sensor stops working?