multibyte_bcd_sub.asm

PIC单片机精简BCD加法减法汇编程序

;---------------------------------------------多字节十进制减法

入口：运算字节长度 B_COUNT ,TEMP2 :被减数低字节地址 ,TEMP3 :减数低字节地址
出口：被减数区为结果



MULTIBYTE_BCD_SUB;###############################

		MOVF	TEMP3,W
		MOVWF	FSR
		MOVF	INDF,W
		MOVWF	TEMP1

		MOVF	TEMP2,W
		MOVWF	FSR
		MOVF	INDF,W
		MOVWF	TEMP	

		CALL	BCD_SUB
		MOVF	TEMP,W
		MOVWF	INDF		

		BTFSS	TEMP1,0x00
		GOTO	NO_CARRY_HAPPEN			;无借位产生
		
		MOVLW	0x01
		SUBWF	B_COUNT,W
		BTFSC	STATUS,Z
		GOTO	NO_CARRY_HAPPEN			;最高字节运算

		MOVWF	COUNT
		MOVF	TEMP2,W
		MOVWF	FSR
		DECF	FSR,F
SUB_CARRY_BIT
	
		MOVF	INDF,W
		MOVWF	TEMP
		CALL	BCD_SUB
		MOVF	TEMP,W
		MOVWF	INDF
		DECF	FSR,F
		DECFSZ	COUNT,F
		GOTO	SUB_CARRY_BIT

		BTFSC	TEMP1,0x00
		GOTO	MULTIBYTE_BCD_SUB_END		;最高位产生借位，运算失败
		
NO_CARRY_HAPPEN
		DECF	TEMP2,F
		DECF	TEMP3,F
		DECFSZ	B_COUNT,F
		GOTO	MULTIBYTE_BCD_SUB
MULTIBYTE_BCD_SUB_END
		
		RETURN
;---------------------------------------------十进制减法子程序
BCD_SUB;######################################
;入口：被减数TEMP,减数TEMP1; 出口：结果TEMP,借位位TEMP1
;---------------------------------------------
		MOVF	TEMP1,W
		SUBWF	TEMP,F
		CLRF	TEMP1
		RLF	TEMP1,F				;借位送入
		BTFSS	STATUS,DC
		GOTO	SUBJUST				;DC=1

		BTFSS	TEMP,0x03			;LSD>9?
		GOTO	BCD_SUB_END1	
		BTFSC	TEMP,0x02				
		GOTO	SUBJUST	
		BTFSS	TEMP,0x01			
		GOTO	BCD_SUB_END1	
SUBJUST	
		MOVLW	0x06
		SUBWF	TEMP,F		
BCD_SUB_END1
		BTFSS	TEMP1,0x00
		GOTO	BCD_SUB_END2
		CLRF	TEMP1
		BTFSS	TEMP,0x07			;MSD>9?
		GOTO	BCD_SUB_END	
		BTFSC	TEMP,0x06				
		GOTO	BCD_SUB_END2	
		BTFSS	TEMP,0x05			
		GOTO	BCD_SUB_END
		
BCD_SUB_END2	
		MOVLW	0x60
		SUBWF	TEMP,F				;假设MSD>9

		CLRF	TEMP1
		BTFSS	STATUS,C
		RETURN	

		MOVLW	0x01
		MOVWF	TEMP1
BCD_SUB_END	
		RETURN