8051 Program - signed to unsigned conversion 16bit

; subroutine Cr0r1

; 16-Bit 2's Complement -> magnitude / Sign Bit Conversion

;

; input: r1, r0 = signed word

;

; output: r1, r0 = magnitude

; Bit 21H = sign (21H is set if negative number)

;

; alters: acc, C

Cr0r1:	mov a, r1	; high byte into accumulator
	jb acc.7, c0a	; negative if bit 7 is 1
	clr 21H	; clear sign bit if 'positive'
	ret	; done
c0a:	setb 21H	; set sign flag
	mov a, r0	; number is negative
	cpl a	; complement
	add a, #1	; and add +1
	mov r0, a
	mov a, r1	; get next byte
	cpl a	; complement
	addc a, #0
	mov r1, a
	ret

; subroutine Cr2r3

; 16-Bit 2's Complement -> magnitude / Sign Bit Conversion

;

; input: r3, r2 = signed word

;

; output: r3, r2 = magnitude

; Bit 22H = sign (22H is set if negative number)

;

; alters: acc, C

Cr2r3:	mov a, r3	; read high into accumulator
	jb acc.7, c1a	; negative if bit 7 is 1
	clr 22H	; clear sign bit if 'positive'
	ret	; done
c1a:	setb 22H	; set sign flag
	mov a, r2	; number is negative
	cpl a	; complement
	add a, #1	; and add +1
	mov r2, a
	mov a, r3	; get next byte
	cpl a	; complement
	addc a, #0
	mov r3, a
	ret

; subroutine Cr4r5

; 16-Bit 2's Complement -> magnitude / Sign Bit Conversion

;

; input: r5, r4 = signed word

;

; output: r5, r4 = magnitude

; Bit 22H = sign (22H is set if negative number)

;

; alters: acc, C

Cr4r5:	mov a, r5	; read high into accumulator
	jb acc.7, c3a	; negative if bit 7 is 1
	clr 22H	; clear sign bit if 'positive'
	ret	; done
c3a:	setb 22H	; set sign flag
	mov a, r4	; number is negative
	cpl a	; complement
	add a, #1	; and add +1
	mov r4, a
	mov a, r5	; get next byte
	cpl a	; complement
	addc a, #0
	mov r5, a
	ret

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

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

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List of topics: 8051

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