Question

What is the number of clock pulses required to completely load and then unload a 4-bit register?

• A. 4
• B. 7
• C. 16
• D. 32

Hint:

General formula for SISO register: Time to load is $n$ cycles. Time to unload (starting after load) is $n-1$ cycles. Total $2n-1$.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
For a Serial-In Serial-Out (SISO) register, bits are shifted in one by one and shifted out one by one.
Step 2: Key Formula or Approach:
For an $n$-bit SISO register:
- To Load: $n$ clock pulses.
- To Unload: $n-1$ additional clock pulses.
- Total = $2n - 1$.
Step 3: Detailed Explanation:
Given $n = 4$ bits:
1. Pulse 1-4: The 4 bits are shifted into the register. After the 4th pulse, the first bit that was entered is already present at the output pin.
2. Pulse 5: The 2nd bit reaches the output.
3. Pulse 6: The 3rd bit reaches the output.
4. Pulse 7: The 4th bit reaches the output.
Total pulses = $4 + 3 = 7$.
Step 4: Final Answer:
Total pulses required = 7.