8051 Program – signed to unsigned conversion 8bit

; subroutine Cr0

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

;

; input: r0 = signed byte

;

; output: r0 = magnitude

; Bit 21H = sign (21H is set if r0 is a negative number)

;

; alters: acc

Cr0:	mov a, r0	; read X into accumulator
	jb acc.7, Cr0a	; X is negative if bit 7 is 1
	clr 21H	; clear sign bit if 'positive'
	ret	; done
Cr0a:	cpl a	; X negative, find abs value
	inc a	; XA = complement(XT)+1
	mov r0, a	; save magnitude
	setb 21H	; set sign bit if 'negative'
	ret

; subroutine Cr1

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

;

; input: r1 = signed byte

;

; output: r1 = magnitude

; Bit 22H = sign (22H is set if r1 is a negative number)

;

; alters: acc

Cr1:	mov a, r1	; read X into accumulator
	jb acc.7, Cr1a	; X is negative if bit 7 is 1
	clr 22H	; clear sign bit if 'positive'
	ret	; done
Cr1a:	cpl a	; X negative, find abs value
	inc a	; XA = complement(XT)+1
	mov r1, a	; save magnitude
	setb 22H	; set sign bit if 'negative'
	ret

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

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Related topics:
8051 Program - signed to unsigned conversion 16bit   |   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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