#include <reg51.h>
void main(void)
  {
    unsigned char mydata[] = {0x25,0x62,0x3F,0x52};
    unsigned char sum=0;
    unsigned char x;
    unsigned char chksumbyte;
    for(x=0;x<4;x++)
      {
        P2=mydata[x];    		
        sum=sum+mydata[x];		
        P1=sum;        		
      }
    chksumbyte=~sum+1;  		
    P1=chksumbyte;     		
  }