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#include<reg52.h>


sbit led1 = P2 ^ 0;
sbit led2 = P2 ^ 1;
sbit led3 = P2 ^ 2;
sbit led4 = P2 ^ 3;


sbit key1 = P1 ^ 4;
sbit key2 = P1 ^ 5;
sbit key3 = P1 ^ 6;
sbit key4 = P1 ^ 7;


void delay (unsigned int t);
unsigned char key_scan(void);


void main()
{
unsigned char keyvalue;
bit run = 0;
unsigned char i = 0;
unsigned int speed = 10000;


while (1)
{
if (run)
{
P2 = ~(0x01<<i);
i++;
i &= ~0x08;
delay ( speed);
}
keyvalue = key_scan();
if (keyvalue !=0)
{
switch(keyvalue)
{
case 1:
run = 1;
break;
case 2:
run = 0;
break;
case 3:
speed /= 2;
break;
case 4:
speed *= 2;
break;

}

}
while(key1 == 0 ||key2 == 0 ||key3 == 0 ||key4 == 0 )
{
P2 = ~(0x01<<i);
i++;
i&= ~0x08;
delay (speed);

}


}
}
unsigned char key_scan(void)
{
unsigned char key =0;
if (key1 == 0)
key = 1;
else if (key2 == 0)
key = 2;
else if (key3 == 0)
key = 3;
else if (key4 == 0)
key = 4;
}




void delay (unsigned int t)
{
while (t--);
}