Using GO in debug section

hi all i am new to keil.i wrote a timer program in C which is given in Mazidi's book.the proagram is compiling without any errors.the program will give 0x55 at port pin 1 and after some milliseconds it gives 0xAA.now when i use F5(GO)it is not working in loop(not showing 55 and AA,showing FF) whereas when i am using F10 then i can see the change in parellel port(for P1)window

kindly suggest what can be the problem

regards and thanks in advance

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