What is the three letter instruction in the AVR assembly language that copies the value of one register into another?

Question

BlackTom AI · Accepted Answer

mov Rd, Rr directly implements a register-to-register copy in AVR assembly: it reads the 8-bit contents of source register Rr and writes the same 8-bit value into destination register Rd.

1) Relevant knowledge points and concepts
- AVR has 32 general-purpose 8-bit registers R0–R31.
- The mov instruction syntax is mov Rd, Rr and performs a simple copy (no arithmetic).
- mov does not affect the status register (SREG) flags.
- Other AVR instructions (ldi, lds, ld, st, movw, push/pop, cp, cpi) perform different operations (load immediate, load/store memory, word move, stack ops, compare) and are not simple register-to-register copies.

2) Step-by-step reasoning
- Identify the need: copy value from one register into another without changing the source.
- Choose the instruction whose documented effect is "Rd ← Rr".
- In AVR instruction set tables, mov is specified for exactly this behavior.

3) Example with intermediate steps
- Suppose r17 contains 0b10101010 and r16 contains 0b00000000.
- Execute: mov r16, r17
  - Step A: read bits from source register r17 → 0b10101010
  - Step B: write that value into destination register r16 → r16 becomes 0b10101010
- After execution: r16 = 0b10101010, r17 remains 0b10101010. SREG unchanged.

4) Why the correct answer is correct
- mov’s explicit semantic is to copy the content of one register into another, with the exact syntax and behavior required by the question. It is the canonical register-to-register copy instruction in AVR.

5) Why other options are incorrect (brief)
- ldi: loads an immediate constant into a register (not copying from another register).
- lds/ld/st: involve memory loads/stores, not direct register-to-register copy.
- movw: copies a 16-bit register pair (instruction name is four characters and different purpose).
- cp/cpi: compare instructions set flags and do not copy values.
- push/pop: use the stack, not a simple register copy.

6) Conclusion
The correct three-letter AVR instruction that copies one register into another is mov, which matches the provided answer: mov.

What is the three letter instruction in the AVR assembly language that copies the value of one register into another? Short answer

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