Difference between Register Mode and Register Indirect Mode
Prerequisite – Addressing Modes
1. Register Mode: In register addressing mode, the operand is placed in one of the 8-bit or 16-bit general-purpose registers. 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 ode: In register indirect addressing mode, the address of the 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 the memory address of operand.
Difference between Register Mode and Register Indirect Mode are as follows:time-consumingregisteredregistered
| Parameters | REGISTER MODE | REGISTER INDIRECT MODE |
|---|---|---|
| Operand | The operand is placed in the general-purpose register. | The operand’s offset is placed in one of the registers. |
| Address Field | In register mode, the address field contains the effective address of the operand. | In register indirect mode, the address field contains a reference of the effective address. |
| Register References | It requires only one register reference to access data. | It requires two register references to access data. |
| Calculations | No further calculation is required to perform the operation. | Requires further calculation to find the effective address. |
| Processing Speed | Register addressing mode is fast. | Register indirect addressing mode is slow. |
| Accessing of data | It is easier to access the data in register mode. | It is a bit complex to access the data in register indirect mode. |
| Uses | It uses temporary variables. | It uses pointers. |
| Advantage | Requirement of a small address field and no time consuming memory accesses. | There is no such constraint imposed on the address range by the address field. |
| Disadvantage | Constrained Address Space | To retrieve the operand, there is need for two memory references for the execution of instruction: one to get its address and another to get its value. |
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