Question

What is the correct description of CIL instruction?

• A. Circulate left DR and D
• B. Circulate left AC and E
• C. Circulate left AR and D
• D. Circulate left AR and E

Hint:

CIL = Circulate Left AC and E CIR = Circulate Right AC and E These are common register-reference instructions in Mano's Basic Computer.

Answer 1

The Correct Option is B

Concept: In the basic computer organization proposed by Mano, several register-reference instructions perform shift and rotate operations. One such instruction is \[ \text{CIL} \] which stands for \[ \text{Circulate Left}. \] This instruction circulates the contents of the Accumulator (AC) together with the Extend bit (E).

Step 1: Recall the Accumulator and Extend bit.
The accumulator (AC) stores arithmetic and logical results. The Extend bit (E) acts as an additional carry bit.

Step 2: Understand the CIL operation.
In a circulate-left operation, the most significant bit of AC moves into E, and the previous value of E enters the least significant position of AC. Thus AC and E behave like a circular shift register.

Step 3: Identify the correct description.
Therefore, \[ \text{CIL}=\text{Circulate Left AC and E}. \]

Step 4: Write the final answer.
\[ \boxed{\text{Circulate Left AC and E}} \] Hence option (B) is correct.