初学者求指导 汇编语言插入中断

计数程序中插入个中断，试了很多次，都没有成功，
计数程序：
ORG 0000H
MAIN:
MOV 30H,#0
MOV 31H,#0
OP:MOV A,30H
INC A
DA A
MOV 30H,A
MOV 50H,30H
ANL 50H,#0FH
MOV 70H,50H
SWAP A
MOV 55H,A
ANL 55H,#0FH
MOV 71H,55H
SWAP A
MOV A,31H
ADDC A,#0
DA A
MOV 31H,A
MOV 60H,31H
ANL 60H,#0FH
MOV 72H,60H
SWAP A
MOV 73H,A
ANL 73H,#0FH
SWAP A
LCALL QWE
LCALL QWER
JMP OP
QWE:
MOV R1,#70H
MOV R2,#01H
MOV A,R2
MOV P2,#80H
QW: MOV DPTR,#QQQQ
MOV A,@R1
MOVC A,@A+DPTR
MOV P0,A
LCALL QWERT
INC R1
MOV 37H,P2
MOV A,37H
RR A
MOV P2,A
MOV A,R2
JB ACC.3,U
RL A
MOV R2,A
SJMP QW
U:RET
QQQQ: DB 0C0H,0F9H,0A4H,0B0H,99H;
DB 92H,82H,0F8H,80H,90H;
QWERT: MOV R7,#10
Q1:MOV R6,#250
DJNZ R6,$
DJNZ R7,Q1
RET
QWER: MOV R5,#1
E1:MOV R4,#100
E2:MOV R0,#100
DJNZ R0,$
DJNZ R4,E2
DJNZ R5,E1
RET