ORG 0003H          ;ISR for /INT0
     LCALL INT0_ISR
     RETI

     ORG 0030H  
MAIN:                    ;main line code
     ;some code...
     ;still more code...
     ;still some more code...
HERE: MOV PCON,#02H      ;going to power down mode
      SJMP HERE

INT0_ISR:                 ;ISR for my interrupt
       ;do stuff
       ;do more stuff  
       RET