8051 Addition with Carry

Add with Carry – ADDC A, src-byte

ADDC simultaneously adds the byte variable indicated, the carry flag and the Accumulator contents, leaving the result in the Accumulator. The carry and auxiliary-carry flags are set respectively, if there is a carry-out from bit 7 or bit 3, and cleared otherwise. When adding unsigned integers, the carry flag indicates an overflow occurred. OV is set if there is a carry-out of bit 6 but not out of bit 7, or a carry-out of bit 7 but not out of bit 6; otherwise OV is cleared. When adding signed integers, OV indicates a negative number produced as the sum of two positive operands or a positive sum from two negative operands. Four source operand addressing modes are allowed: register, direct, register-indirect, or immediate.

ADDC A,Rn
Encoding:00111nnn

ADDC A, direct address
Encoding:00110101 direct address

ADDC A,@Ri
Encoding:0011011i

ADDC A,#immediate data
Encoding:00110100 immediate data

Example:
The Accumulator holds 0C3H (11000011B) and register 0 holds 0AAH (10101010B) with the carry flag set. The following instruction,

ADDC A,R0

leaves 6EH (01101110B) in the Accumulator with AC cleared and both the Carry flag and OV set to 1.

Example:

	ORG 0H
MAIN :
	MOV A, #0H
	MOV A, #9CH
	ADD A, #64H	; A= 9C+ 64, C= 1
	MOV A, #0C3H
	MOV R0, #0AAH
	ADD A, R0	; A = C3 + AA + 1= 6EH
	END	; end of asm source file

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Related topics:
8051 Addition   |   8051 Addition of Unsigned Numbers   |   8051 Addition of 16-bit Numbers   |   8051 Binary Coded Decimal   |   8051 ADDC Instruction   |   8051 ADD Instruction

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List of topics: 8051

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