8051 Program - unsigned to signed conversion 8bit

; subroutine Mr0

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

;

; input: r0 = magnitude

; Bits 21H & 22H = sign bits of operands X and Y

; (set if negative)

;

; output: r0 = signed byte

;

; alters: acc

Mr0:	jb 21H, Mr0b	;test X sign
	jb 22H, Mr0a	;test Y sign
	ret
Mr0b:	jnb 22H, Mr0a
	ret
Mr0a:	mov a, r0	;if r0 negative, get abs value
	cpl a	;complement magnitude of X
	inc a	;r0 = complement(r0)+1
	mov r0, a	;save in 2's complement
	ret	;done

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 16bit   |   8051 Program - signed to unsigned conversion 32bit   |   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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