Addressing Modes in Instructions



The process of specifying the data to be operated by big instruction is called addressing. The various formats for specifying operands are called addressing modes. 


The 8085 has the following five types of addressing-

  1. Immediate addressing

  2. Memory Direct Addressing

  3. Register Direct Addressing

  4. Indirect addressing

  5. Implicit addressing


Immediate Addressing:

In this mode, the operand given in the instruction a byte or word- is transferred to the destination register or memory location.

Ex: MVI A, 9AH

The operand is a part of the instruction

The operand is stored in the register mentioned in the instruction.


Memory Direct Addressing

Memory Direct Addressing moves a byte or word by a memory location and register. The memory location address is given in the instruction.


LD805FH the instruction is used to load the content to the accumulator register.


Register Direct Addressing

Register Direct Addressing transfer a copy of a bit or b=word source register to destination register.

Example:

MOV B, C

It copies the content of register C to register B


Indirect Addressing

Indirect Addressing transfers a byte or word between a register and a memory location.

Example: MOV A, M

Here the data is in the memory location pointed to the contents of the HL pair. The data is moved to the accumulator.


Implicit Addressing

In this addressing mode, the data itself specifies the data to be operated upon.

Example: CMA

The instruction compliments the content of the accumulator. No specific data or operand is mentioned in the instruction.