.::Addressing Modes::.

The Pentium Uses 9 different Addressing Modes:

• Immediate Mode
• Register Operand Mode
• Displacement Mode
• Base Mode
• Base with Displacement Mode
• Scaled Index with Displacement Mode
• Base with Index and Displacement Mode
• Based Scaled Index with Displacement Mode
• Relative Addressing

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Immediate Mode

• The value in the operand is the data needed.

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Register Operand Mode

• The data is stored in a register.
• Can use any 32 or 16 bit general purpose register.

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Displacement Mode

• Address = Segment Register + Contents of Address Field
  • The displacement field of the instruction contains an address offset.
  • That address is combined with the segment register to get the true address in memory.
  • The data is located at that address in memory.

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Base Mode

• Address = segment Register + Contents of a Base Register
  • A base register contains the address offset of the segment.
  • That address is combined with the address of the segment from the segment register.
  • That is the actual address in memory where the data is stored.

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Base with Displacement Mode

• Address = SR + Base Register + Address from Instruction
  • The address from the base register is combined with the address from the instruction at the displacement field.
  • That Address is combined with the segment register to get the actual memory address.
  • The data is stored at that memory address.

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Scaled Index with Displacemnet Mode

• Address = SR + (Index Register * Scaling Factor + Address from Instruction)
  • The index register (which can be any general purpose register except SP) is multiplied with the scaling factor from the instruction (can be 1, 2, 4, or 8).
  • That is combined with the address from the instruction in the displacement field.
  • That address is combined with the segment register to get the actual memory address.
  • The memory address is where the data is stored.

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Base with Index and Displacement Mode

• Address = SR + Base Register + Index Register + Address from Instruction
  • The base register and the index register are combined (these can be any general purpose register but the index reister can not be the SP).
  • That address is combined with the address from the instruction in the displacement field.
  • That address is combined with the segment register to form the actual address in memory.
  • That memory address is where the data is stored.

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Based Scaled Index with Displacement Mode

• Address = SR + (Index Register * Scaling Factor + Base Register + Address from Ins.)
  • The index register is multiplied by the scaling factor which is found in the instrutction and the index register can be any general purpose register except for SP.
  • That is combined with the base register which can be any general purpose register.
  • That address is combined witht he address from the instruction in the displacement field.
  • That address is combined with the segment register to form the actual address in memory.
  • That memory address is where the data is stored.

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Relative Addressing

• Address = Program Counter + Address from Instruction
  • The Program Counter (which is the address of the next instruction) is combined with the address from the instruction which is in the displacement field.
  • This is the memory address where the data is stored.

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