Đo tần số hiển thị led 7 thanh

Code:
#include <REGX52.H>
#include<stdio.h>
sbit led1= P1^0;
sbit led2= P1^1;
sbit led3= P1^2;
sbit led4= P1^3;
unsigned int ms,tan_so;

unsigned char m[10]= {0xC0,0xF9,0xA4,0xB0,0x99,0x92,0x82,0xF8,0x80,0x90};
int num,i,nghin,tram,chuc,donvi;
void delay(int time)
{
while(time--);
}
void sang(void)
{
int k;
nghin=num/1000;
tram=(num%1000)/100;
chuc=((num%1000)%100)/10;
donvi=((num%1000)%100)%10;
for(k=0;k<100;k++)
{
P2=m[nghin];
led1=1; led2=led3=led4=0;
delay(100);

P2=0xff;
delay(100);

P2=m[tram];
led2=1; led1=led3=led4=0;
delay(100);

P2=0xff;
delay(100);

P2=m[chuc];
led3=1; led1=led2=led4=0;
delay(100);

P2=0xff;
delay(100);

P2=m[donvi];
led4=1; led1=led3=led2=0;
delay(100);

P2=0xff;
delay(100);
}

}

void ngat0(void) interrupt 0
{
tan_so++;
}
void timer0(void) interrupt 1
{
TF0=0;
TH0=(65536-50000)>>8;
TL0=(65535-50000)%256;
ms++;
}
void main()
{

IE=0x81; //cho phep ngat toan cuc
TMOD = 0x01;
TR0=1;
TF0=1;
EA=1;
ET0=1;
IT0=1;

while(1)
{
if(ms>=20)
{
ms=0;
num=tan_so;
tan_so=0;
}
sang();

}
}