Which of the following do not represent memory-reference instructions? A. mode = 1, opcode = 010 B. mode = 0, opcode = 111 C. mode = 1, opcode = 111 D. mode = 1, opcode = 110 E. mode = 1, opcode = 001

1. AB & C only
2. BB & D only
3. CA & D only
4. DA & E only

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Correct answer: A. B & C only

Explanation

In Mano's basic computer, opcodes 000–110 are memory-reference instructions (mode bit chooses direct or indirect). Opcode 111 is a register-reference instruction when I = 0 and an I/O instruction when I = 1. So B and C are not memory-reference.