FILTER7:
CLR 	A
MOV 	R2,A
MOV 	R3,A
MOV 	R6,A 
MOV 	R7,A
MOV 	R4,#3FH
MOV 	R5,#OFFH
MOV 	R0,#4					
DAVI:
;輸人采樣值到寄存器B,A中
MOV 	Rl,A						
ADD 	A, R7					
MOV 	R7,A
MOV 	A, B
ADDC 	A,R6
MOV 	R6,A
CLR 	C						
MOV 	A,R3
SUBB 	A,R1
MOV 	A,R2
SUBB 	A,B
JNC 		DAV2
MOV 	A,R1						
MOV 	R3,A
MOV 	R2 ,B
DAV2:
CLR 	C						
MOV 	A, R1
SUBB 	A,R5
MOV 	A,B
SUBB 	A,R4
JNC 	DAV3
MOV 	A,R1						
MOV 	RS,A
MOV 	R4,B
DAV3:
DJNZ 	R0,DAVI
CLR 	C
MOV 	A,R7						
SUBB 	A,R3
XCH 	A, R6
SUBB 	A,R2
XCH 	A,R6						
SUBB 	A,RS
XCH 	A,R6
SUBB 	A,R4
CLR 	C						
RRC 	A
XCH 	A,R6
RRC 	A
MOV 	R7,A						
RET