ORG		00H
AJMP	START 
ORG		03H
AJMP	INT0SUB
ORG		0030H
START:
MOV	IE,#10000001B				
MOV	TCON, #00000001B			
MOV	SP,#20H
MOV	A,#0FEH
RTT:
RR		A
MOV	P0,A
ACALL	DELAY
AJMP	RTT
DELAY:
MOV	R3,#00H
DEL:
MOV	R4,#00H
DJNZ	R4,$
DJNZ	R3,DEL
RET
INT0SUB:								
PUSH	PSW
PUSH	A
SETB	RS0							
CLR		RS1
MOV	R1,#09H
LOOP:
MOV	A,#0H						
MOV	P0,A
ACALL	DELAY
MOV	A,#0FFH						
MOV	P0,A
DJNZ	R0,LOOP
POP		A
POP		PSW
RETI
END