8051 Program - unsigned 16bit multiplication

; subroutine UMUL16

; 16-Bit x 16-Bit to 32-Bit Product Unsigned Multiply

;

; input: r1, r0 = multiplicand X

; r3, r2 = multiplier Y

;

; output: r3, r2, r1, r0 = product P = X x Y

;

; alters: acc, C

UMUL16:	push B
	push dpl
	mov a, r0
	mov b, r2
	mul ab	;multiply XL x YL
	push acc	;stack result low byte
	push b	;stack result high byte
	mov a, r0
	mov b, r3
	mul ab	;multiply XL x YH
	pop 00H
	add a, r0
	mov r0, a
	clr a
	addc a, b
	mov dpl, a
	mov a, r2
	mov b, r1
	mul ab	;multiply XH x YL
	add a, r0
	mov r0, a
	mov a, dpl
	addc a, b
	mov dpl, a
	clr a
	addc a, #0
	push acc	;save intermediate carry
	mov a, r3
	mov b, r1
	mul ab	;multiply XH x YH
	add a, dpl
	mov r2, a
	pop acc	;retrieve carry
	addc a, b
	mov r3, a
	mov r1, 00H
	pop 00H	;retrieve result low byte
	pop dpl
	pop B
	ret

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

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Related topics:
8051 Program - signed 8bit multiplication   |   8051 Program - unsigned 8bit multiplication   |   8051 Program - signed 8bit x 16bit multiplication   |   8051 Program - signed 16bit multiplication   |   8051 Program - signed 16bit multiply Accumulate   |   8051 Program - memory subroutines   |   8051 Program - math subroutines   |   8051 Program - conversion subroutines

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List of topics: 8051

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