Addressing Modes (Cambridge (CIE) A Level Computer Science) : Revision Note

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