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]