Tuesday, March 22, 2016

8051 Addition

The ADD instruction has the following format:

ADD A, source ; ADD the source operand to the accumulator

The ADD instruction tells the CPU to add the source byte to register A and put the result in register A. To add two numbers such as 25H and 34H, each can be moved to a register and then added together:

MOV A, #25H; load 25H into A
MOV R2, #34H; load 34H into R2
ADD A, R2; add R2 to accumulator (A = A + R2)

Add – ADD A, src-byte
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.


ADD A,direct address
Encoding:00100101 direct address


ADD A, #immediate data
Encoding:00100100 immediate data

MOV A, #0H
MOV R0, #55H; load 55H in to R0
MOV R1, #90H; load 90H in to R1
MOV 20H, #33H; load 33H in to memory location 20h
ADD A, 20h
ADD A, @R1
ADD A, #03h
END; end of asm source file

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

List of topics: 8051

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