ISR:

RETURN:       
MOV SP,#9     ;maybe stack is anything first you load 9 on it
POP 7         ;with 2 pop you provide changing return addr
POP 7         
MOV R7,#01H   ;change upper address in pc <b>-- But <i>to what??</i></b>
PUSH 7
MOV R7,#00H   ;change lower address in pc <b>-- But <i>to what??</i></b>
PUSH 7
RETI