Prerequisite – Addressing Modes
1. Register Mode :
In register addressing mode, the operand is placed in one of 8 bit or 16 bit general purpose register. The data is in the register that is specified by the instruction.
Example:
MOV R1, R2
Instruction has register R2 and R2 has operand.
2. Register Indirect Mode :
In register indirect addressing mode, the address of operand is placed in any one of the registers. The instruction specifies a register that contains the address of the operand.
Example:
ADD R1, (R2)
Instruction has register R2 and R2 has memory address of operand.
Difference between Register Mode and Register Indirect Mode :
| REGISTER MODE | REGISTER INDIRECT MODE |
|---|---|
| Operand is placed in general purpose register. | Operand’s offset is placed in one of the resgiters. |
| In register mode, address field contains the effective address of operand. | In register indirect mode, address field contains reference of effective address. |
| It requires only one register reference to access data. | It requires two register references to access data. |
| No further calculation is required to perform the operation. | Require further calculation to find the effective address. |
| Register addressing mode is fast. | register indirect addressing mode is slow. |
| It is easier to access the data in register mode. | It is a bit complex to access the data in register indirect mode. |
| It uses temporary variables. | It uses pointers. |
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