Ca l8 addr modes, Slides of Computer Architecture and Organization

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Addressing Modes

Addressing Modes

• (^) address field of a typical instruction is relatively small
• (^) aim is to reference a large number of memory locations in main memory or virtual memory

Addressing Modes

• (^) Immediate addressing
• (^) Direct addressing
• (^) Indirect addressing
• (^) Register addressing
• (^) Register Indirect addressing
• (^) Displacement addressing
• (^) Stack addressing

Notations

• (^) A – contents of address field in the instruction
• (^) R – Contents of address field that refer to a register
• (^) EA – Effective address of the memory location containing the referenced operand
• (^) (X) – Contents of location X
• (^) one or more bits in the instruction format can be used as the mode field

Direct addressing

• (^) the address field contains the effective address of the operand.
• (^) EA = A A Instruction Operan d Memory

Indirect addressing

• (^) address field refers to address in memory, which in turn contains the address of the operand: EA = [A] A Instruction Operan d Memory

Register Indirect addressing

• (^) Similar to indirect addressing but address field refers to a register rather than a memory location: EA = [R] R Instruction Registers Operand Memory

Displacement addressing

• (^) Combines capabilities of direct addressing and register indirect addressing.
• (^) EA = A + [R]

Displacement addressing

R A Instruction Registers Operand Memory

Stack addressing

• (^) Similar to register indirect addressing. Stack Pointer maintained in a register
• (^) EA = [R] Instruction Top of Stack Implicit