The possible causes and corresponding workarounds are as follows:
1) The oscillation setting is not done properly in the microcontroller (no oscillator, inappropriate oscillation frequency, etc.).
2) The supply voltage to the microcontroller is not appropriate.
3) The operating mode of the microcontroller is not set up properly (TEST pin, AM pin, etc.).
4) The microcontroller is not programmed properly.
1), 2) Use the correct oscillation setup and supply voltage as specified in the electrical characteristics section in the datasheet of each product.
3) Check the relevant settings on the printed circuit board.
4) Conduct verification tests on the programs written in the microcontroller.