Hi Pranav,

naturally any function, which interrupts another must save p2_shadow:

p2_shadow equ 30h

mov_p2 macro new_val
mov p2_shadow, new_val
mov p2, new_val
endm


Any_main_level_function: ;no other interrupting, but interuptable
mov_p2 #80h
; do something
mov_p2 #20h
; do something
ret

Any_interrupt_function: ;others interrupting and interruptable
push p2_shadow
mov_p2 #80h
; do something
mov_p2 #20h
; do something
pop p2_shadow
mov p2, p2_shadow
reti

Any_highest_level_interrupt_function: ;others interrupting but no interruptable
mov p2, #80h
; do something
mov p2, #20h
; do something
mov p2, p2_shadow
reti


Peter