The MCU system does not work properly, please check the following steps:
1. View the reset output of the dog. If possible, add an LED to the board and pull it down. This seems more convenient; if the watchdog reset signal is there, go down;
2. Check the MCU to see if there is any problem with the pin; the general programmer can write the program, indicating that the MCU is good; it is best to prepare a verified MCU on hand, there is a simple program inside, for example, in a certain A square wave with a duty cycle of 1 second is output on the port line, and can be measured with a multimeter.
Add one sentence: When designing the product, it should be in the key places: power supply, serial port, watchdog output and input, I/O port, etc. with different color LED indications for easy debugging; as a large batch product, some LEDs can be removed. On the one hand, it is to reduce costs, on the other hand, the process is confidential;
3. Check the magnetic capacitor, and some ceramic capacitors can’t be used. Simply change it. By the way, it is better to use the soldering strip to replace the tin in the solder pad and then pull out the device. Damage to the vias in the pad; when soldering new ceramic capacitors, it is good to re-weld with a multimeter;
4. Finally, only change the crystal oscillator; remember to buy a good crystal, some brands are better.
5. When the above steps are detected, the extraneous peripheral chips are removed; because some of the peripheral devices are faulty, the MCU minimum system does not work.