What is the correct sequence of steps to execute the below given instruction?
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What is the correct sequence of steps to execute the below given instruction?**
add R1, R2
- I) Internally decode the instruct- II) Get the instruction from memory into the processor
- III) Store the result into another register
- IV) Take the values from registers and add them
Show answer & explanation
The CPU execution cycle follows the fetch-decode-execute-store sequence. First, the instruction must be fetched from memory (II), then decoded to understand what operation to perform (I), then the operands are retrieved and the arithmetic operation is executed (IV), and finally the result is stored in the destination register (III). Option D correctly represents this fundamental processor pipeline order.
Step-by-step Derivation:
The instruction execution follows the standard CPU cycle phases:
Fetch (II): Get the instruction from memory into the processor — this must happen first to obtain the instruction bytes.
Decode (I): Internally decode the instruction — the processor must interpret the opcode and operands to understand it's an ADD operation on R1 and R2.
Execute (IV): Take the values from registers and add them — retrieve R1 and R2 values from the register file and perform the addition.
Store/Write-back (III): Store the result into another register — write the sum back to the destination register (typically R1 or a specified result register).
The correct sequence is: (II) → (I) → (IV) → (III), which matches option D.