3 Digit Subtraction < or > - Electronic Circuits Projects Diagrams Free

Suraj143 · 18th August 2008, 03:01 AM

Hi I have a pair of 3 digit values. They are actual value & save value.

I need to subtract the save value from the actual value & need to decide is it greater than the save value.

I don’t need the exact result I need to know whether actual value > or < than the save value.

I wrote a small routine needs to check is it ok or not,

Code:

121	=actual value	(D3,D2,D1)
103	=save value	(SD3,SD2,SD1)


	movf	SD1,W
	subwf	D1,W		;substract digit1
	btfsc	STATUS,C
	goto	$+2
	decf	D2,F
	movf	SD2,W
	subwf	D2,W		;substract digit2
	btfsc	STATUS,C
	goto	$+2
	decf	D3,F
	movf	SD3,W
	subwf	D3,W		;substract digit3
	btfss	STATUS,C
	goto	$+3
	bsf	Result,1	;result	possitive
	return
	bcf	Result,1	;result	negative
	return

Pommie · 18th August 2008, 04:35 AM

You can do a much simpler comparison by just comparing the digits until you find a pair that are not equal. I'm assuming that D3 is the most significant byte.

Code:

		movfw	D3
		subwf	SD3,W
		btfss	STATUS,Z
		goto	GotResult
		movfw	D2
		subwf	SD2,W
		btfss	STATUS,Z
		goto	GotResult
		movfw	D1
		subwf	SD1,W
GotResult
		
;if zero flag set then numbers are equal
;if carry flag set then SD > D

Mike.

Suraj143 · 18th August 2008, 05:16 AM

Quote:

Originally Posted by Pommie

I'm assuming that D3 is the most significant byte.

Excellent it is correct.That is what I needed.I started from LSB, its better do the math part from MSB side like you did.

Thanks Mike

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18th August 2008, 03:01 AM	(permalink)
Suraj143	3 Digit Subtraction < or > Hi I have a pair of 3 digit values. They are actual value & save value. I need to subtract the save value from the actual value & need to decide is it greater than the save value. I don’t need the exact result I need to know whether actual value > or < than the save value. I wrote a small routine needs to check is it ok or not, Code: 121 =actual value (D3,D2,D1) 103 =save value (SD3,SD2,SD1) movf SD1,W subwf D1,W ;substract digit1 btfsc STATUS,C goto $+2 decf D2,F movf SD2,W subwf D2,W ;substract digit2 btfsc STATUS,C goto $+2 decf D3,F movf SD3,W subwf D3,W ;substract digit3 btfss STATUS,C goto $+3 bsf Result,1 ;result possitive return bcf Result,1 ;result negative return

18th August 2008, 04:35 AM	(permalink)
Pommie	You can do a much simpler comparison by just comparing the digits until you find a pair that are not equal. I'm assuming that D3 is the most significant byte. Code: movfw D3 subwf SD3,W btfss STATUS,Z goto GotResult movfw D2 subwf SD2,W btfss STATUS,Z goto GotResult movfw D1 subwf SD1,W GotResult ;if zero flag set then numbers are equal ;if carry flag set then SD > D Mike.