PIC單片機的BCD碼加法程序

;*******************? Unsigned BCD Addition?? ***************
;
;?????? This routine performs a 2 Digit Unsigned BCD Addition
; It is assumed that the two BCD numbers to be added are in
; locations Num_1 & Num_2. The result is the sum of Num_1+Num_2
; and is stored in location Num_2 and the overflow carry is returned
; in location Num_1
;
;?? Performance :
;?????????????? Program Memory? :?????? 25
;?????????????? Clock Cycles??? :?????? 17?? ( worst case )
;
;*******************************************************************;
;
Num_1?? equ???? 8?????? ; Overflow flow carry overwrites Num_1
result? equ???? 8
;
Num_2?? equ???? 9?????? ; Num_2 + Num_1 overwrites Num_2
O_flow? equ???? 9
;
;
?include???????? "picreg.h"
;
BCDAdd? movf??? Num_1,W
?clrf??? Num_1?????????? ;clear num_1
?addwf?? Num_2,1???????? ; do binary addition
?btfsc?? STATUS,C??????? ;< 256 then skip
?goto??? inc_n1n2??????? ;else inc all
?movlw?? 66????????????? ;add 66
?addwf?? Num_2,1???????? ;/
?btfss?? STATUS,DC?????? ;half carry?
?goto??? sub_06????????? ;no then subtract
?btfss?? STATUS,C??????? ;full carry?
?goto??? sub_60????????? ;yes then subtract
inc_n1? incf??? Num_1,1???????? ;inc it
?retlw?? 0?????????????? ;clr w
sub_06? btfss?? STATUS,C??????? ;full carry
?goto??? sub_66????????? ;yes subtract 66
?movlw?? 6?????????????? ;else subtract 6
?goto??? sub_com???????? ;do common
sub_66? movlw?? 66?????????????
sub_com subwf?? Num_2,1??????????????????
?retlw?? 0
sub_60? movlw?? 60
?goto??? sub_com
inc_n1n2
?movlw?? 66
?addwf?? Num_2,1
?goto??? inc_n1
;
;********************************************************************
;?????????????? Test Program
;*********************************************************************
main??? movlw?? 99
?movwf?? Num_1????? ; Set Num_1 = 99 ( max BCD digit )
?movlw?? 99
?movwf?? Num_2????? ; Set Num_2 = 99
;
?call??? BCDAdd???? ; After addition, Num_2 = 98
;????????????????????????? ;? and Num_1 = 01 ( 99+99 = 198 -> max number )
;
self??? goto??? self
;
;
?org???? 1FF
?goto??? main
;
?END