8051 Program - signed 16bit subtraction

; subroutine SUB16

; 16-Bit Signed (2's Complement) Subtraction

;

; input: r1, r0 = X

; r3, r2 = Y

;

; output: r1, r0 = signed difference D = X - Y

; Carry C is set if the result (D) is out of range.

;

; alters: acc, C, OV

SUB16:	anl PSW, #0E7H	;Register Bank 0
	mov a, r0	;load X low byte into acc
	clr C	;clear carry flag
	subb a, r2	;subract Y low byte
	mov r0, a	;put result in Z low byte
	mov a, r1	;load X high into accumulator
	subb a, r3	;subtract Y high with borrow
	mov r1, a	;save result in Z high byte
	mov C, OV
	ret

Source: Maths Subroutines for the 8051 microcontroller, W.G.Marshall 2002

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Related topics:
8051 Program - signed 16bit addition   |   8051 Program - signed 32bit addition   |   8051 Program - signed 32bit subtraction   |   8051 Program - signed 8bit multiplication   |   8051 Program - unsigned 8bit multiplication   |   8051 Program - memory subroutines   |   8051 Program - math subroutines   |   8051 Program - conversion subroutines

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List of topics: 8051

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