BEE BEE Bachelor of Electrical Engineering Digital Logic and Design Questions and Answers 3

Question 1

What is the propagation delay disadvantage of a ripple carry adder compared to a carry lookahead adder?

Accepted Answer

Its delay grows linearly with bit width

Answer

In a ripple carry adder, each full adder must wait for the carry from the previous stage, causing linear delay growth.

Question 2

Which state encoding technique assigns adjacent states codes that differ by only one bit?

Accepted Answer

Gray encoding

Answer

Gray encoding ensures adjacent states differ by exactly one bit, reducing transition glitches.

Question 3

In a Moore finite state machine, when does the output change?

Accepted Answer

Only on clock edges when state changes

Answer

In a Moore machine, outputs depend only on the current state, so they change synchronously with state transitions on clock edges.

Question 4

What is the purpose of a don't-care condition in a truth table?

Accepted Answer

To allow flexibility in minimization for unused input combinations

Answer

Don't-care conditions represent input combinations that cannot occur or whose output is irrelevant, allowing greater simplification.

Question 5

How many select lines are needed for an 8-to-1 multiplexer?

Accepted Answer

3

Answer

An 8-to-1 multiplexer requires 3 select lines since 2^3 = 8 input channels.

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