pwm原程序利用定时器，在P2_5上输出PWM波。为了演示，使占空比从1％~99％再从99％~1％连续变化。频 率约为200Hz。可以用于用于直流电机的驱动等方面-pwm timer using the original procedure, in P2_5 output PWM wave. For demonstration, so that the duty cycle from 1 ~ 99 ~ 99 from 1 for the changes. Frequency of about