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Absolute Addressing Mode in 8085 Microprocessor

In absolute addressing mode in the 8085 microprocessor, the effective address is provided directly in the address part of the instruction. The operand can be directly fetched by accessing the effective address. In this article, we will explore the absolute addressing mode and discuss the operations and examples of absolute addressing mode. We will also discuss the advantages, disadvantages and applications of absolute addressing mode in 8085 microprocessors.

Table of Content

Absolute Addressing Mode in 8085 Microprocessor

The absolute addressing mode is an addressing mode in which the operand is stored in the memory and the effective address is specified in the instruction itself. The effective address is specified directly in the instruction and contains the operand in which any operation is to be performed. The absolute addressing mode is also called the direct addressing mode.

Representation of Instructions in 8085 with Absolute Addressing Mode

The below format specifies the intrusion of 8085 microprocessors with absolute addressing mode.

Opcode

Memory Address

Operation of Absolute Addressing Mode

In absolute addressing mode, we require following operations to fetch the operand.

  • First identify the effective address from the address part of the instruction.
  • Then, go to the specified effective address.
  • The content present in the effective address gives the operand.
  • Then, fetch the operand and perform required operations.

Examples of Absolute Addressing Mode in 8085 Microprocessor

Some of the examples of absolute addressing mode in 8085 Microprocessor is given below.

Instruction of 8085microprocessor (Absolute mode used)

Description

LDA 2000H

Load content of memory address 2000H to the accumulator

LBCD 1005H

Load the content of memory address 1005H to the B-C register pair.

STA 3000H

Store the content of accumulator to memory address 3000H.

LDA Instruction

The LDA instruction is used to load content present in the specified memory address to the accumulator. Suppose we have an instruction LDA 5000H and opcode for LDA instruction is 3A. The address 5000H contains data 5AH and the accumulator contains data 4DH. Then after executing the LDA 3020H instruction the content in the memory address is copied to accumulator.

Content Training Table

The content training table for the above instruction is given below.

Location

Before Executing LDA 3020H instruction

After Executing LDA 3020H instruction

5000H

5AH

5AH

A

4DH

5AH

Address

Hexadecimal Code

Instruction

Description

1000

3A

LDA 5000H

A ← [5000H] content of 3020H address is copied to accumulator.

1001

00

It represents the lower byte of specified memory address.

1002

50

It represents the upper byte of specified memory address.

Timing Diagram for LDA Instruction

The timing diagram below shows the LDA instruction.

LDA Instructions

LDA Instructions

Advantages and Disadvantages of Absolute Addressing Mode

The advantages and disadvantages of absolute addressing mode are given below.

Advantages of Absolute Addressing Mode

The advantages of absolute addressing modes are given below.

  • It is simple addressing mode as it directly provides the effective address.
  • The operations in the operands can be performed easily as operand is available directly using effective address.

Disadvantages of Absolute Addressing Mode

The disadvantages of absolute addressing modes are given below.

  • The address is limited in the absolute addressing mode according to the address part of instruction.

Application of Absolute Addressing Mode

The absolute addressing mode can be used in interrupt handling to handle interrupt by directly jumping to the ISR address provided in the instruction itself.

Conclusion

From the above discussion we can conclude that the absolute addressing mode in 8085 microprocessors also called as direct mode directly specifies the effective address of the operand within the instruction. It is simple addressing mode in which operand can be fetched easily by accessing the memory only once.

Absolute Addressing Mode in 8085 Microprocessor – FAQs

What are Addressing Modes?

The addressing mode gives the information about where the operand is stored and how to get the effective address of the operand. In branch Instructions it gives the target address.

What are the Different Types of Addressing Mode in 8085 Microprocessor?

The different types of addressing mode in 8085 microprocessors are listed below.

  • Immediate Addressing Mode
  • Register Addressing Mode
  • Absolute Addressing Mode
  • Register Indirect Addressing Mode
  • Implied Addressing Mode
  • Relative Addressing Mode

What is Effective Address?

The address in which the operand is present is called effective address.


 


Reffered: https://www.geeksforgeeks.org

Electronics Engineering

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