I am now using W7200 MCU to develop a communication system with PC using an internal timer(TIM3). I found out that the system is always totally down, the LEDs were off and even no reponse when I pressed reset button. The only thing I can do is plug out the power supply and connect it again. In my code, I use PA2, PA3, PA8, PA11, PA12, PB2, PB5, PB6, PB7, PB10, PB11 and PB12 as the output pins, and use PA13, PA14, PA15, PB13, PB14, PB15, PC14 and PC15 as the inputs. Would you please give me some suggestion about where the problem should be?