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Microprocessor

Addressing Mode of 8085 Microprocessor

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Introductions are commands to perform a task in the microprocessor. The instructions consist of opcode and data called an operand. The operand may be the source only, destination only or both of them. Similarly, the destination can be a register, a memory location, or an output port. The various format of specifying the operands are called Addressing mode. The 8085 has five addressing modes.they are given below:

  1. Direct Addressing Mode
  2. Register Direct Addressing Mode
  3. Register Indirect Addressing mode
  4. Immediate Addressing Mode
  5. Implied/Implicit Addressing mode

Direct Addressing Mode:

The instructions using this mode specifies an effective address as a part of the introduction. The instruction size either 2-bytes or 3-bytes with first-byte op-code followed by 1 or 2 bytes of address of data.

E.g: LDA 9500H

IN 80H

This type of addressing is called absolute addressing.

Register Direct Addressing Mode

This mode specifies the register or register pair that contains the data.

E.g MOV A, B

Here, register B contains data rather than the address of the data. Other examples are ADD, XCHG, etc.

Register Indirect Addressing mode


In this mode, the address part of the instruction specifies the memory whose contents are the address of the operand. So in this type of addressing mode, it is the address of the address rather than address itself. (One operand is register)

E.g MOV R, M MOV M, R STAX,LDAX etc.

Immediate Addressing Mode

In this mode, the operand position is the immediate data. For 8-bit data, instruction size is 2 bytes and for 16-bit data, instruction size is 3 bytes.

E.g. MVI A, 32H

LXI B,4567H

Implied/Implicit Addressing mode

The instructions of this mode do not have operands.

E.g. NOP: No operation

HLT: Halt

EI: Enable interrupt

DI: Disable interrupt

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