30-10-2012, 04:01 PM
Addressing modes
Addressing modes.docx (Size: 97.28 KB / Downloads: 23)
The addressing modes indicate a rule to identify the operands location.
Addressing modes are techniques for the purpose of accommodating the following provisions.
• To give programming versatility to the user.
• To reduce the number of bits in the address field of the instruction.
To provide flexibility for writing programs.
The various addressing modes available are :
1. Implied mode.
2. Immediate mode.
3. Register mode.
4. Register indirect mode.
5. Auto increment or auto decrement mode.
6. Direct address mode.
7. Indirect address mode.
8. Relative address mode.
9. Indexed addressing mode.
10. Base register addressing mode.
Implied Mode:
In this mode the operands are specified implicitly in the definition of the instruction.
All register reference instructions that use an accumulator are implied mode instruction.
Example: CMA compliment accumulator.
advantage
it results in shorter instruction formats.
Shorter instructions take up lesser space in memory.
Zero address instructions in a stack organized computer are implied mode.
Immediate Mode:
The purpose of an address is to identify an operand value to be used in executing the instruction.
Some times the operand values is contained in the instruction itself, this mode of operand specification is called immediate addressing mode.
Example: MVI A, 45.
Indirect Address Mode:
In this mode the address field of the instruction gives the address where the effective address is stored in memory.
The instruction is obtained from memory and it uses its address part to access memory again to read the effective address.
Effective Address = Address part of instruction + content of CPU register.
The CPU register may be the program counter, an index register or a base register
Addressing modes.docx (Size: 97.28 KB / Downloads: 23)
The addressing modes indicate a rule to identify the operands location.
Addressing modes are techniques for the purpose of accommodating the following provisions.
• To give programming versatility to the user.
• To reduce the number of bits in the address field of the instruction.
To provide flexibility for writing programs.
The various addressing modes available are :
1. Implied mode.
2. Immediate mode.
3. Register mode.
4. Register indirect mode.
5. Auto increment or auto decrement mode.
6. Direct address mode.
7. Indirect address mode.
8. Relative address mode.
9. Indexed addressing mode.
10. Base register addressing mode.
Implied Mode:
In this mode the operands are specified implicitly in the definition of the instruction.
All register reference instructions that use an accumulator are implied mode instruction.
Example: CMA compliment accumulator.
advantage
it results in shorter instruction formats.
Shorter instructions take up lesser space in memory.
Zero address instructions in a stack organized computer are implied mode.
Immediate Mode:
The purpose of an address is to identify an operand value to be used in executing the instruction.
Some times the operand values is contained in the instruction itself, this mode of operand specification is called immediate addressing mode.
Example: MVI A, 45.
Indirect Address Mode:
In this mode the address field of the instruction gives the address where the effective address is stored in memory.
The instruction is obtained from memory and it uses its address part to access memory again to read the effective address.
Effective Address = Address part of instruction + content of CPU register.
The CPU register may be the program counter, an index register or a base register