Machine code to assembly (assumed mapping): Decode the single-byte opcode 0x48 into its assembly instruction (assume it was not produced by a pseudo-op).

Difficulty: Medium

Correct Answer: ASRA

Explanation:


Introduction / Context:
Reverse-assembling a machine opcode requires knowledge of the ISA’s opcode map. Single-byte opcodes typically encode accumulator/register operations or short addressing forms, whereas instructions with immediate or direct addresses need extra operand bytes.


Given Data / Assumptions:

  • Opcode: 0x48.
  • No additional operand bytes were provided, implying a single-byte instruction.
  • We assume a conventional accumulator architecture where shifts/rotates and register ops can be single-byte.


Concept / Approach:
If the instruction consumed only one byte, it cannot encode the multi-byte immediates or addresses visible in options (b), (c), (d). Therefore, a unary accumulator operation such as ASRA (arithmetic shift right accumulator) is the consistent choice.


Step-by-Step Solution:
Check each option’s operand length.Options with h#.... operands require additional bytes and contradict the single 0x48 byte.Select the operand-less accumulator operation as the plausible decoding.


Verification / Alternative check:
Consulting the ISA manual would definitively map 0x48 to its mnemonic. In many classic ISAs, 0x48 corresponds to single-byte register/shift ops, aligning with ASRA over memory-addressing forms.


Why Other Options Are Wrong:
(b), (c), (d) each imply at least two additional operand bytes; they cannot be encoded by a lone 0x48. (e) likewise suggests addressing.


Common Pitfalls:
Ignoring instruction length; assuming any mnemonic can match without checking required operands.


Final Answer:
ASRA.

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