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Addressing Modes of 8086 – An overview…

Published on Oct 20 2009 // 8086 Details

Definition: An instruction acts on any number of operands.The way an instruction accesses its operands is called its Addressing modes.

Operands may be of three types :

    • Implicit
    • Explicit
    • Both Implicit and Explicit.

Implicit operands mean that the instruction by definition has some specific operands. The programmers do NOT select these operands.

Example: Implicit operands

XLAT ; automatically takes AL and BX as operands
AAM ; it operates on the contents of AX.

 
Explicit operands mean the instruction operates on the operands specified by the programmer.
 
Example: Explicit operands

MOV AX, BX; it takes AX and BX as operands
XCHG SI, DI; it takes SI and DI as operands

Implicit and explicit operands

Example: Implicit/Explicit operands

MUL BX; automatically multiply BX explicitly times AX 

The location of an operand value in memory space is called the Effective Address (EA)

We can classify the addressing modes of 8086 into four groups:

  • Immediate addressing
  • Register addressing
  • Memory addressing
  • I/O port addressing

The first three Addresssing modes are clearly explained.