ADDRESSING MODES OF 8085


ADDRESSING MODES OF 8085
To perform any operation, we have to give the corresponding instructions to the microprocessor. In each instruction, programmer has to specify 3 things:
Ø  Operation to be performed.
Ø  Address of source of data.
Ø  Address of destination of result.
The method by which the address of source of data or the address of destination of result is given in the instruction is called Addressing Modes.  The term addressing mode refers to the way in which the operand of the instruction is specified. Intel 8085 uses the following addressing modes:
1.     Direct Addressing Mode
2.     Register Addressing Mode
3.     Register Indirect Addressing Mode
4.     Immediate Addressing Mode
5.     Implicit Addressing Mode or Implied Addressing
1. Direct Addressing Mode:-
In this mode, the address of the operand is given in the instruction itself.
Ex: - LDA 2500 H Load the contents of memory location 2500 H in accumulator.
  •          LDA is the operation.
  •         2500 H is the address of source.
  •         Accumulator is the destination.
2. Register Addressing Mode:-
In this mode, the operand is in general purpose register.
Ex: - MOV A, B Move the contents of register B to A.
  •       MOV is the operation.
  •       B is the source of data.
  •       A is the destination.
3. Register Indirect Addressing Mode:-
In this mode, the address of operand is specified by a register pair.
Ex: - . LDAX B  Move data from memory location specified by B-C pair to accumulator.
  •         LDAX is the operation.
  •         B is the memory location specified by B-C register pair.
  •         A is the destination.
4. Immediate Addressing Mode:-
In this mode, the operand is specified within the instruction itself.
Ex :-  MVI A, 05 H Move 05 H in accumulator.
  •         MVI is the operation.
  •         05 H is the immediate data (source).
  •         A is the destination.
5. Implicit Addressing Mode or Implied Addressing:-
If address of source of data as well as address of destination of result is fixed, then there is no need to give any operand along with the instruction.
Ex: - CMA Complement accumulator.
  •       CMA is the operation.
  •        A is the source.
  •         A is the destination.

REFERENCES
  1. R. S. Gaonkar, Microprocessor Architecture, Programming, and Applications with the 8085, Fifth Edition, Penram International Publishing (India) Private Limited.
  2. S Ghoshal, Microprocessor Based System Design, Macmillan India Limited, 1996
  3. M. Mano, Digital Logic and Computer Design, Prentice – Hall India
  4. B. Ram - Fundamentals of Microprocessor and Microcontrollers
  5. “Microprocessors: Principles and Applications” by A Pal
  6. “Microprocessors and Microcontrollers : Architecture, Programming and Interfacing Using 8085, 8086 and 8051” by Soumitra Kumar Mandal
  7. “Introduction to Microprocessors and Microcontrollers” by Crisp John Crisp
  8. “Microprocessors And Microcontrollers” by A Nagoor Kani
  9. “Microprocessors And Microcontrollers : Architecture, Programming and System Design 8085, 8086, 8051, 8096” by KRISHNA KANT
  10. “8 - Bit Microprocessor” by Vibhute

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