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 :
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- 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 |
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XLAT ; automatically takes AL and BX as operands
AAM ; it operates on the contents of AX.
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Explicit operands mean the instruction operates on the operands specified by the programmer.
| Example: Explicit operands |
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MOV AX, BX; it takes AX and BX as operands
XCHG SI, DI; it takes SI and DI as operands
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Implicit and explicit operands
| Example: Implicit/Explicit operands |
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MUL BX; automatically multiply BX explicitly times AX
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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.