As I understnad you are the variables P2_6, P2_5, P2_7 are all bit variables of port 2 and you are assigning byte values to these variables. So in the simulation the code is working some how. That may be a bug in the Keil simulator. But when the code executes on the micro the value assignments are causing an unexpected behaviour.

Try doing this and I hope it will work.


#include <stdio.h>
#include <at89x52.h>

void nothing();
void main()
{
int i = 0;
P0 = 0x00;
P1 = 0x00;
P2 = 0x00;
P3 = 0x00;

for(i = 0; i < 200; i++){
P2_6 = 1;
nothing();
P2_6 = 0;
nothing();
}

for(i = 0; i < 200; i++){
P2_5 = 1;
nothing();
P2_5 = 0;
nothing();
}

while(1){
P2_7 = 1;
nothing();
P2_7 = 0;
nothing();
}
}

void nothing()
{
int i;
for(i = 0; i < 0x5000; i++);
}