org 0000h
                jmp main

main:           mov p1,#00h
                clr p3.7
                call delay1sec
                mov p1,#ffh
                setb p3.7
                call delay1sec
                jmp main

delay1sec       mov 40h,#10
del2sec2        mov 41h,#200
del2sec1        mov 42h,#250
                djnz 42h,$
                djnz 41h,del2sec1
                djnz 40h,del2sec2
                ret