Addressing Modes of 8086

Posted By on September 15, 2014


Download PDF
Programmamer`s model of 8086
Segment Override prefix

Various addressing modes of 8086/8088

1)      Register Addressing mode

2)      Immediate Addressing mode

3)      Register Indirect Addressing mode

4)      Direct Addressing mode

5)      Indexed Addressing mode

6)      Base Relative Addressing mode

7)      Base Indexed Addressing mode

Register Addressing Mode

Data transfer using registers is called register addressing mode. Here operand value is present in register. For example

MOV AL,BL;

MOV AX,BX;

Immediate Addressing mode

When data is stored in code segment instead of data segment immediate addressing mode is used. Here operand value is present in the instruction. For example

MOV AX, 12345;

Direct Addressing mode

When direct memory address is supplied as part of the instruction is called direct addressing mode. Operand offset value with respect to data segment is given in instruction. For example

MOV AX, [1234];

ADD AX, [1234];

Register Indirect Addressing mode

Here operand offset is given in a cpu register. Register used are BX, SI(source index), DI(destination index), or BP(base pointer). BP holds offset w.r.t Stack segment, but SI,DI and BX refer to data segment. For example

MOV [BX],AX;

ADD AX, [SI];

Indexed Addressing mode

Here operand offset is given by a sum of a value held in either SI, or DI register and a constant displacement specified as an operand. For example

Lets take arrays as an example. This is very efficient way of accessing arrays.

My_array DB ‘1’, ‘2’, ‘3’,’4,’5’;

MOV SI, 3;

MOV AL, My_array[3];

So AL holds value 4.

Base Relative Addressing mode

Operand offset given by a sum of a value held either in BP, or BX and a constant offset sepecified as an operand. For example

MOV AX,[BP+1];

JMP [BX+1];

Base Indexed

Here operand offset is given by sum of either BX or BP with either SI or DI. For example

MOV AX, [BX+SI]

JMP [BP+DI]

Programmamer`s model of 8086
Segment Override prefix

Download PDF

Posted by Akash Kurup

Founder and C.E.O, World4Engineers Educationist and Entrepreneur by passion. Orator and blogger by hobby

Website: http://world4engineers.com