我编程的秒表，可是我不知道哪里错了没有显示出来

ORG 00H
LJMP MAIN
ORG 0BH
LJMP IT
ORG 30H
MAIN:MOV SP,#30H
MOV TMOD,#01H
MOV TH0,#3CH
MOV TL0,#0B0H
SETB EA
SETB ET0
SETB TR0
MOV 70H,#00H
MOV 71H,#00H
MOV 72H,#00H
MOV 73H,#00H
MOV R4,#0AH
D2:LCALL XS
LJMP D2
XS:MOV R1,#70H
MOV R2,#0FEH
D0:MOV A,@R1
MOV DPTR,#TABLE
MOVC A,@A+DPTR
MOV P1,A
MOV P3,R2
LCALL YS
INC R1
MOV A,R2
RL A
MOV R2,A
JNB ACC.4,D1
LJMP D0
D1:RET
ORG 500H
TABLE:DB 3FH,06H,5BH,4FH,66H,6DH,7DH,07H,7FH,6FH
IT:PUSH PSW
PUSH ACC
PUSH TH0
PUSH TL0
MOV TH0,#3CH
MOV TL0,#0B0H
DJNZ R4,PF
MOV R4,#0AH
INC 70H
MOV A,70H
CJNE A,#0AH,PF             0
MOV 70H,#00H

INC 71H
MOV A,71H
CJNE A,#06H,PF
MOV 71H,#00H

INC 72H
MOV A,72H
CJNE A,#0AH,PF
MOV 72H,#00H

INC 73H
MOV A,73H
CJNE A,#06H,PF
MOV 73H,#00H

PF:POP TL0
POP TH0
POP ACC
POP PSW
RETI
YS:MOV R7,#00H
DJNZ R7,$
RET

END