*　　PWM 控制 DC电机转速：

*　　一定要对本实验的原理搞清楚，实验用了两个定时器中断

*　　在正向输出时T0中断输出低电平，T1输出高电平，T0的时间

*　　是定死的，也就是说输出的方波波长是不变的，T1定的时间

*　　是在T0中断程序里确定的，T1的时间永远小于或等于T0的

*　　时间，T0使每隔固定时间使输出低，T1则输出高。

*　　反向原理,类似

*　　fosc=6M

*　　利用定时器控制产生占空比可变的PWM波

*　　按K1，PWM值增加，则占空比增加,电机转快

*　　按K2，PWM值减小，则占空比减小,电机转慢。

*　　当PWM值增加到最大值(255)或减小到最小值(1)时，蜂鸣器报警。

*　　接线：P10:K1；P11:K2；P30:74LS02的5、6脚；74LS02的4脚接2、3脚；

*　　74LS02的1脚接DJ；直流电机:J4；喇叭:J5；P31:SIN

*-* PWM controlled DC motor speed:

* Be sure to find out the principles of the experiment, the experiment used two timer interrupts

* In the forward output T0 interrupt output low, T1 output high, T0 time

* Is scheduled to die, that is the output square wave length is constant, T1 given time

* T0 interrupt program is determined, T1 time is always less than or equal to T0

* Time, T0 so that the output low fixed time intervals, T1, the output is high.

* Reverse principle, similar

* Fosc = 6M

* Use a timer to control the duty cycle of the PWM wave variable

* Press K1, PWM value increases, the duty cycle increases, the motor rotates faster

* Press K2, PWM value decreases, the duty cycle decreases, the motor rotates slowly.

* When the PWM value to maximum (255), or reduced to a minimum (1), the buzzer alarm.

* Wiring: P10: K1　P11: K2　P30: 74LS02 5,6 feet　74LS02 4 feet to 3 feet　

* 74LS02 1 feet to DJ　DC: J4　Speaker: J5　P31: SIN

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