课 4, 主题 4

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addressing-modes

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Addressing methods

What is an addressing method?

An addressing method is a way in which an instruction in assembly language or machine code can access data stored in memory
There are five main addressing methods:
- Immediate
- Direct
- Indirect
- Indexed
- Relative

Addressing mode	Description	Example instruction	Explanation
Immediate	The operand is a constant value included directly in the instruction	`MOV AX, 1234h`	Moves the immediate value `1234h` into the `AX` register
Direct	The exact memory address of the operand is given in the instruction	`MOV AX, [1234h]`	Moves the value stored at memory location `1234h` into the `AX` register
Indirect	A register contains the memory address of the operand	`MOV AX, [BX]`	If `BX = 2000h`, this moves the value at memory location `2000h` into `AX`
Indexed	Uses a base register and an index to calculate the memory address	`MOV AX, [BX + SI]`	If `BX = 0050h` and `SI = 1000h`, this moves the value at `1050h` into the `AX` register
Relative	The operand is an offset relative to the current instruction address	`JMP +5`	Tells the program to jump forward 5 instructions from the current line Used in branching

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