PIC Microcontoller Math Method

Increment / Decrement

packed BCD

From Regulus Berdin

;Increment/Decrement routines for packed BCD 
; 
;6 digit bcd in bcd1:bcd2:bcd3:...(lsb:msb) 
; 
; 
 cblock 0x0c 
 tmp 
 bcd1:3 
 endc 
inc_bcd: 
 movlw bcd1 
 movwf FSR 
 movlw 3 ;adjust for number of digits 
 movwf tmp 
iloop movlw 0x67 
 addwf INDF 
 movlw 0x60 
 skpdc 
 movlw 0x66 
 skpc 
 subwf INDF 
 skpz 
 goto iquit 
 incf FSR 
 decfsz tmp 
 goto iloop 
iquit retlw 0 
 
 
dec_bcd: 
 movlw bcd1 
 movwf FSR 
 movlw 3 ;adjust for number of digits 
 movwf tmp 
dloop movlw 1 
 subwf INDF 
 addwf INDF,w 
 movlw 0x6 
 skpnc 
 movlw 0x66 
 skpndc 
 subwf INDF 
 xorlw 0x66 
 skpz 
 goto dquit 
 incf FSR 
 decfsz tmp 
 goto dloop 
dquit retlw 0 
The routines can accomodate to any number of BCD digits, just change the movlw 3. 
 

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