ORG 0000H
AJMP MAIN
ORG 0030H
MAIN:
MOV 77H,#0FH
MOV 78H,#42H
MOV 79H,#40H
MOV 7AH,#00H
MOV 7BH,#03H
MOV 7CH,#0E8H
LCALL DIV_MB
SJMP MAIN
;=================================================
; DIVISION FOR THREE-BYTE DATA
; DIVIDEND FROM 77H&78H&79H
; DIVISOR FROM 7AH&7BH&7CH
; QUOTIENT TO
;ARITHMETICAL COMPLIMENT TO 7DH&7EH&7FH
; 2008_05_08 BY SZCKIC
;=================================================
DIV_MB: MOV 7DH,#00H
MOV 7EH,#00H
MOV 7FH,#00H
MOV R7,#18H
NEXTBIT:
CLR C
MOV A,79H
RLC A
MOV 79H,A
MOV A,78H
RLC A
MOV 78H,A
MOV A,77H
RLC A
MOV 77H,A
;Arithmetical compliment
MOV A,7FH
RLC A
MOV 7FH,A
MOV A,7EH
RLC A
MOV 7EH,A
MOV A,7DH
RLC A
MOV 7DH,A
MOV 5AH,7DH
MOV 5BH,7EH
MOV 5CH,7FH
MOV 5DH,7AH
MOV 5EH,7BH
MOV 5FH,7CH
LCALL TDEC
JNC UPDATE
DJNZ R7,NEXTBITTMP
RET
UPDATE: INC 79H
MOV 7FH,5CH
MOV 7EH,5BH
MOV 7DH,5AH
DJNZ R7,NEXTBITTMP
RET
NEXTBITTMP:LJMP NEXTBIT
;=================================================
; Subtracter for three-byte data
;=================================================
TDEC: CLR C
MOV A,5CH
SUBB A,5FH
MOV 5CH,A
MOV A,5BH
SUBB A,5EH
MOV 5BH,A
MOV A,5AH
SUBB A,5DH
MOV 5AH,A
RET
除法程序写成了子程序方式,很便利调用,除法中要频频用到三字节数据巨细的比较,所以也写成了一个小子程序。
思路很简略,抛开咱们习惯了的乘法口诀,以一个小学二年级学生的思路去做就简略了,一步一步的比较、移位,只不过这里是二进制而不是习惯了的十进制,当然二进制也有一个长处那就是:
假定A,B是两个相同位数的二进制数据(首位不为0),且A>B,则A必定小于2倍的B,所以关于每次移位只用比较一次。