hi kamala,
first of all, why aren't u a registered user?
i strongly advise u to resgister and become a
member.
any how! u're obviously not familiar with the
8051 mcu.
if ur prgram works on the simulator that
doesn't necessarily mean that it would work
in the system.in fact there are numerous flaws
in ur program.
1- u didn't initialize ur stack.
do initialize the stack to 2fh or 30h : mov sp,#30h
2- initialize loop to an address like 0100h
to make sure ur main program doesn't overlap
with interrupt addresses:
org 0100h
loop:
.....


which assembler r u using?
keep in touch and let me know how u progress.

happy programming!
mourad