8051 Subtraction of 16-bit Numbers

This SUBB instruction along with carry flag is used for multi-byte numbers and will take care of the borrow of the lower operand. If CY = 1 prior to executing the SUBB instruction, it also subtracts 1 from the result.

Program to subtract 2762H – 1296H:

	ORG 0H
MAIN :
	CLR A
	CLR C
	MOV A, #62H
	SUBB A, #96H	; 62 – 96 = CCH, C = 1
	MOV R7, A
	MOV A, #27H
	SUBB A, #12H	; 27 – 12 – 1 = 14H
	MOV R6, A
	END	; end of asm source file

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Related topics:
8051 Addition of Unsigned Numbers   |   8051 Addition of 16-bit Numbers   |   8051 Subtraction of Unsigned Numbers   |   8051 Multiplication Unsigned 8-bit   |   8051 Division Unsigned 8-bit   |   8051 SUBB Instruction

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List of topics: 8051

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