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The 8051 Instruction Set

Atmel 8051 Microcontrollers Hardware Manual 1-24

4316E–8051–01/07

1.14.2 ADD A,<src-byte>

Function: Add

Description: ADD adds the byte variable indicated to the Accumulator, 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 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.

Example: The Accumulator holds 0C3H (1100001lB), and register 0 holds 0AAH (10101010B). The following instruction,

ADD A,R0

leaves 6DH (01101101B) in the Accumulator with the AC flag cleared and both the carry flag and OV set to 1.

ADD A,R

Bytes: 1

Cycles: 1

Encoding: 0 0 1 0 1 r r r

Operation: ADD

(A) ← (A) + (R

)

ADD A,direct

Bytes: 2

Cycles: 1

Encoding: 0 0 1 0 0 1 0 1 direct address

Operation: ADD

(A) ← (A) + (direct)

ADD A,@R

Bytes: 1

Cycles: 1

Encoding: 0 0 1 0 0 1 1 i

Operation: ADD

(A) ← (A) + ((R

))

ADD A,#data

Bytes: 2

Cycles: 1

Encoding: 0 0 1 0 0 1 0 0 immediate data

Operation: ADD

(A) ← (A) + #data

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Atmel C51 Handbuch Seite 26