树莓派 驱动pca9685报错

我的报错 Traceback (most recent call last):
  File "simpletest.py", line 17, in <module>
    pwm = Adafruit_PCA9685.PCA9685()
  File "/usr/local/lib/python2.7/dist-packages/Adafruit_PCA9685/PCA9685.py", line 81, in __init__
    self._device.write8(MODE1, mode1)
  File "/usr/local/lib/python2.7/dist-packages/Adafruit_GPIO/I2C.py", line 114, in write8
    self._bus.write_byte_data(self._address, register, value)
  File "/usr/local/lib/python2.7/dist-packages/Adafruit_PureIO/smbus.py", line 256, in write_byte_data
    self._device.write(data)
IOError: [Errno 121] Remote I/O error
什么原因求解