High School Physics

Addressing modes in 8085 microprocessor

Last updated on May 26th, 2022 at 05:06 am

In this post, we will discuss different addressing modes in the 8085 microprocessor with examples.

Addressing modes in instructions

Each instruction indicates an operation to be performed on certain data. The process of specifying the data to be operated on (operand) by the instruction is known as ‘addressing’. The various formats for specifying operands are called addressing modes.

For example, the instructions MOV B, A, and MVI A, 82H are used to copy data from a source to a destination. In these instructions, the source can be a register or an 8-bit number (00H to FFH); the destination is a register. The source and destination are operands.

Different addressing modes in 8085

In the 8085 microprocessor, there are five addressing modes. These are:

  1. Immediate addressing
  2. Direct addressing
  3. Register addressing
  4. Register indirect addressing
  5. Implicit addressing.

The examples for each type of addressing mode are given below:

Direct Addressing

In this mode, the operand is specified within the instruction itself.

Examples of this type are:

LDA 4000H, STA 5513H, IN/OUT instructions (like IN PORT C, OUT PORT B, etc.) also fall under this category. The memory location address or input-output device address is given in the instruction.

Register Addressing

In this mode of addressing, the operand is in the general-purpose registers.

Examples are MOV A, B; ADD B, etc.

Register Indirect Addressing

In this mode of addressing, data transfer takes place between a register and a memory location.

MOV A, M; ADD M are examples of this mode of addressing.

Here, the data is in the memory location pointed to by the contents of the HL pair.

Immediate Addressing

MVI A, 07; ADI 0F are examples of Immediate Addressing mode.

The operand is specified in the instruction in this mode. Here, the operand address is not specified.

Implicit Addressing

In this mode of addressing, the operand is fully absent. Examples are RAR, RAL, CMA, etc.

The instruction CMA complements the contents of the accumulator. No specific data or operand is mentioned in the instruction.

Author of this post

This post is co-authored by Professor Saraswati Saha, who is an assistant professor at RCCIIT, a renowned degree engineering college in India. Professor Saha teaches subjects related to digital electronics & microprocessors.

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