Question

Consider the following instruction. \[ \texttt{ADD R1, R2, R3} \] What is the meaning of the above instruction?

• A. Add the contents of registers R1 and R2 and place the sum in R3
• B. Add the contents of registers R1, R2 and R3 and place the sum in another register
• C. Add the contents of registers R2 and R3 and place the sum in R1
• D. Instruction is invalid

Hint:

In most three-address instruction formats, remember: Destination Register $\leftarrow$ Source Register 1 + Source Register 2.

Answer 1

The Correct Option is C

Concept: Many assembly language architectures use a three-operand instruction format in which the first operand represents the destination register and the remaining operands represent source registers. Step-by-Step Analysis:
• Identify the opcode: The opcode is ADD, which performs arithmetic addition.
• Identify the destination register: The first register listed is R1. This is where the result will be stored.
• Identify the source registers: The second and third registers are R2 and R3. Their contents are used as operands.
• Perform the operation: The instruction can be represented as: \[ R1 \leftarrow R2 + R3 \] Thus, the contents of R2 and R3 are added and the result is stored in R1. Conclusion: The instruction adds the contents of registers R2 and R3 and places the result in R1. Therefore, option (C) is correct.