用stc89c52实现固定频率的占空比的方波的产生。主要用到的模块有定时器和串口发送。用串口发送来控制方波产生的占空比，用于控制电机和开关电源-With stc89c52 duty cycle to achieve a fixed frequency square wave generation. The main module used in timers and serial port. Sent to control the use of serial production of the