What is addressing mode?

The different ways in which a source operand is denoted in an instruction is known as addressing modes. There are 8 different addressing modes in 8086 programming -

(i) Immediate address mode: The addressing mode in which the data operand is a part of the instruction itself is known as immediate addressing mode.

Example: MOV CX, 4929 H, ADD AX, 2387 H, MOV AL, FFH

(ii) Register address mode: It means that the register is the source of an operand for an instruction.

Example: MOV CX, AX ;copies the contents of the 16-bit AX register into ;the 16-bit CX register),

ADD BX, AX

(iii) Direct addressing mode: The addressing mode in which the effective address of the memory location is written directly in the instruction.

Example: MOV AX, [1592H], MOV AL, [0300H]

(iv) Register indirect mode: This addressing mode allows data to be addressed at any memory location through an offset address held 1n any of the following registers: BP, BX, DI & SI.

Example: MOV AX, [BX], Suppose the register BX contains 4895 H, then the contents ;4895H are moved to AX

ADD CX, [BX]

(v) Based addressing mode: In this addressing mode, the offset address of the operand is given by the sum of contents of the BX/BP registers and 8-bit/16-bit displacement.

Example: MOV DX, [BX + 04], ADD CL, [BX + 08]

(vi) Index addressing mode: In this addressing mode, the operands offset address is found by adding the contents of SI or DI register and 8-bit/16-bit displacements.

Example: MOV BX, [SI + 16] ADD AL, [DI + 16]

(vii) Based index addressing mode: In this addressing mode, the offset address of the operand is computed by summing the base register to the contents of an index register.

Example: ADD CX, [AX + SI], MOV AX, [AX + DI]

(viii) Based indexed with displacement mode: In this addressing mode, the operands offset is computed by adding the base register contents. An Index registers contents and 8 or 16-bit displacement.

Example: MOV AX, [BX + 1), ADD CX, [BX + SI + 16]