Addressing Modes
Addressing modes define how the operand of an instruction is accessed. They determine whether the operand is in a register, memory, or provided as an immediate value.
Types of Addressing Modes
1. Immediate Addressing
- Operand is specified directly in the instruction.
- Example:
MOV A, #5→ Load 5 into register A.
2. Register Addressing
- Operand is in a CPU register.
- Example:
MOV A, B→ Copy content of B into A.
3. Direct Addressing
- Operand’s memory address is given explicitly.
- Example:
MOV A, 2000H→ Load content of memory address 2000H into A.
4. Indirect Addressing
- Instruction specifies a register that contains the memory address of the operand.
- Example:
MOV A, (R1)→ Load content from memory location pointed by R1.
5. Register Indirect Addressing
- Similar to indirect but specifically through a register pointer.
6. Indexed Addressing
- Combines a base address from a register and an index to access operand in memory.
- Example: Arrays in memory
7. Relative Addressing
- Operand address is determined relative to the program counter (PC).
- Used for branch instructions.
Importance of Addressing Modes
- Provides flexibility in instruction execution
- Reduces instruction length
- Helps CPU efficiently access operands
- Essential for assembly programming and CPU design
Real-World Applications
- Assembly language programming
- Microprocessor instruction execution
- Compiler design
- Embedded systems programming
Conclusion
Addressing modes define how operands are accessed by the CPU. Understanding these modes is crucial for programming, CPU design, and optimizing memory usage in computer systems.