8051 Program – subtraction 16bit

;16bit subtraction
; R6 R7
; - R4 R5
; = R2 R3
; Subtract the low bytes R5 from R7, leave the answer in R3
; Subtract the high byte R4 from R6, less any borrow, and leave the answer in R2.
	ORG 0H
MAIN:
	MOV R6,#22H	;Load the first value into R6 and R7
	MOV R7,#0DBH
	MOV R4,#1AH	;Load the second value into R4 and R5
	MOV R5,#0F9H
	LCALL SUB_16
	SJMP MAIN
SUB_16:
		; step 1
	MOV A,R7	;Move the low-byte into the accumulator
	CLR C	;Always clear carry before first subtraction
	SUBB A,R5	;Subtract the second low-byte from the accumulator
	MOV R3,A	;Move the answer to the low-byte of the result
		; step 2
	MOV A,R6	;Move the high-byte into the accumulator
	SUBB A,R4	;Subtract the second high-byte from the accumulator
	MOV R2,A	;Move the answer to the high-byte of the result
	RET
	END

; subtract 2 byte number from another 2 byte number
; register operation
	ORG 0H
	MOV R1,#56
	MOV R2,#78
	MOV R3,#12
	MOV R4,#34	;7856-3412 = 4444
	CLR C
	MOV A,R1
	SUBB A,R3
	MOV R5,A
	MOV A,R2
	SUBB A,R4
	MOV R6,A
	SJMP $
	END

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Related topics:
8051 Program - arithmetic operation 8bit   |   8051 Program - addition 8bit   |   8051 Program - subtraction 8bit   |   8051 Program - multiplication 8bit   |   8051 Program - division 8bit   |   8051 Program - addition 16bit   |   8051 Program - multiplication 16bit   |   8051 Program - division 16bit   |   8051 Program - addition multibyte   |   8051 Program - multiplication 16bit by 8bit   |   8051 Program - addition 8bit 2digit bcd   |   8051 Program - memory subroutines   |   8051 Program - math subroutines   |   8051 Program - conversion subroutines

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List of topics: 8051

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