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:
A serial-in serial-out (SISO) shift register loads bits one by one. To "completely load" means filling all $n$ flip-flops. To "unload" means shifting all stored bits out through the output terminal.
Step 2: Detailed Explanation:
1. To load $n$ bits into an $n$-bit register, it takes $n$ clock pulses. For a 4-bit register, loading takes 4 pulses.
2. After the 4th pulse, the first bit is already at the output.
3. To shift out the remaining $(n-1)$ bits, we need $(n-1)$ more pulses.
4. Total pulses = $n + (n-1) = 4 + 3 = 7$.
Step 3: Final Answer:
The total clock pulses required is 7.