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Friday, 1 November 2019

Addressing Modes of 8086 Microprocessor

Addressing Modes gives how the data is specified (operate) in a register. The different ways in which a source operand is denoted in an instruction is known as addressing modes. Basically there are 8 types of addressing modes.


1. Register addressing modes
2. Immediate addressing modes
3. Direct addressing modes
4. Register indirect addressing modes
5. Base plus index addressing modes
6. Register relative addressing modes
7. Base relative plus index addressing modes
8. Implied addressing modes


1. Register addressing modes:

Here, the data transfer operation will taken place between registers. Here source and destination is a register.

Example:

MOV AL, BL
Here, BL = Source
AL = Destination

2. Immediate addressing modes:

In immediate addressing modes, the data should be operated is directly specified in the instruction. It can be defined as the addressing mode in which the data operand is a part of the instruction itself.

Example:

MOV AX, 2222H
MOV AL, 0AH
Here the data 2222H will moves to register AX.

3. Direct addressing modes:

Direct addressing mode is the type of addressing mode in which the effective address of the memory location is written directly in the instruction. Here the address of the data to be operated is directly specified in the instruction itself.

Example:

MOV AX, [1000]
MOV [1000], AX

4. Register Indirect addressing modes:

In Register Indirect addressing modes, the address of the data to be operated is saved in a register. This type of addressing modes allows data to be addressed at any memory location through an offset address.

Example:

MOV AX, [BX]
MOV CX, [SP],
In MOV AX, [BX], the content of memory location saved in BX register is transferred to AX register.
In MOV CX, [SP] instruction, the content of memory location saved in SP is transferred to a register.

5. Base Plus index addressing modes

In Base Plus index addressing modes, the content of the base is added with DX register. The offset address of the operand is given by the sum of contents of the BX/BP registers and 8-bit/16-bit displacement in based addressing mode.


6. Base relative plus index addressing

The operands offset address is obtained by adding the contents of SI or DI register and 8-bit/16-bit displacements in indexed addressing mode.

Example: 

MOV AX, [BX + SI +CS]
MOV AX, [BX + SI +010]

7. Register Relative addressing modes:

In register relative addressing modes, the displacement is added with the content of the register.

8. Implied addressing modes:

Implied addressing modes, the instruction itself perform the operation and there is no operand part. The instruction itself performs the operation.

CLC àClear Carry, HLT

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