滑动变阻器控制直流电机转速（自己原来做的小实验） -

#include <at89x51.h>
#define uchar unsigned char
#define unit unsigned int
sbit eoc=P3^0;
sbit oe =P3^1;
sbit st =P3^3;
sbit s1=P2^5;
sbit s2=P2^6;
sbit s3=P2^7;
sbit P17=P1^7;
sbit pwm=P3^5;
uchar code tab[]={0x3F,0x06,0x5B,0x4F,0x66,0x6D,0x7D,0x07,0x7F,0x6F,0x0,0x0};//数码管共阳级显示0～9,不显示
uchar disp[4]={0,0,0,0};
unit ad_0809;
uchar out;
uchar scale=100;
uchar tt;
void delaynms(unit x);
void display();
void ad0809();
void key();
void InitTimer(void)
{
TMOD = 0x02;
TH0 = 0x00;
TL0 = 0x0FB;
EA = 1;
ET0 = 1;
TR0 = 1;
}
void main()
{
EA=1;
EX0=1;
IT0=1;//下降沿触发，cpu内存占用少，如果是低电平触发，cpu将耗大量内存在中断上，长时间的取ad转换数据
INTtimer();
while(1)
{ s1=s2=s3=0;//channel 0
P0=0xff;//input
oe=0;
st=0;
st=1;//清0
st=0;//启动
ad_0809=out;
display();
scale=disp[3]*200/5;
}
}
void EXINTO(void) interrupt 0
{ EA=0;
EX0=0;
oe=1;
out=P0;
oe=0;
EA=1;
EX0=1;
}
void delaynms(unit x)
{ while(x-->0)
{
unsigned char k;
for(k=10;k>0;k--);
}
}
void display()
{ unit i,scan;
disp[3]=(ad_0809*196)/10000; //the highest bit, 255*49/25＝4.99V
disp[2]=((ad_0809*196)/1000)%10;
disp[1]=((ad_0809*196)/100)%10;
disp[0]=((ad_0809*196)/10)%10;
scan=1;
for(i=0;i<4;i++)
{
P2=~scan;
P1=tab[disp[i]];
delaynms(10);
scan<<=1;
if(i==3)
{
P17=1;
}
}
}
void timer0_int () interrupt 1 using 2 // T0溢出中断，使用工作组2
{
tt++;
if(tt==200)
{
tt=0;
pwm=1;
}
if(scale==tt)
pwm=0;
}

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