#include
#define uchar unsigned char
uchar cnt,pos;
uchar led[4]={0xfe,0xfd,0xfb,0xf7};
bit flag;
void t0isr() interrupt 1
{
TH0=(65536-50000)/256;
TL0=(65536-50000)%256;
cnt++;
if(cnt>=20)
{
cnt=0;
flag=~flag;
if(flag)
{
P1=led[pos];
pos++;
pos%=4;
}
else P1=0xff;
}
}
main()
{
TH0=(65536-50000)/256;
TL0=(65536-50000)%256;
TR0=1;
ET0=1;
EA=1;
while(1);
}