Digital Logic and Design Flashcards

In two's complement representation using 8 bits, what is the decimal value of 1111 1111?

Answer: -1

In 8-bit two's complement, 11111111 represents -1 because inverting gives 00000000 and adding 1 gives 00000001=+1, confirming -1.

What is a race condition in a sequential circuit?

Answer: When the next state depends on the order in which multiple variables change simultaneously

A race condition occurs when multiple state variables change simultaneously and the final state depends on which variable changes first, potentially causing incorrect behavior.

Which Boolean expression represents the output of an SR NOR latch when S=1, R=0 (assuming it was previously reset)?

Answer: Q=1, Q'=0

With S=1 (Set) and R=0 in an SR NOR latch, the output is set: Q=1 and Q'=0.

What is the purpose of a priority encoder?

Answer: To generate a binary code corresponding to the highest-priority active input

A priority encoder accepts multiple inputs and outputs a binary code representing the highest-priority (typically highest-numbered) active input, resolving conflicts when multiple inputs are asserted.

How many product terms can a 4-variable K-map group of 4 adjacent cells eliminate?

Answer: 2 variables

A group of 4 cells (2²) in a K-map eliminates 2 variables from the product term, leaving a 2-literal expression.

Which of the following is NOT a valid state encoding for reducing glitches in sequential circuits?

Answer: Binary-weighted encoding

Binary-weighted encoding can cause multiple bits to change simultaneously during state transitions, increasing the risk of glitches; Gray, one-hot, and Johnson codes minimize simultaneous bit changes.

A 4-bit binary counter using JK flip-flops counts from 0000 to 1111. How many distinct states does it have?

Answer: 16

A 4-bit counter has 2⁴ = 16 distinct states, counting from 0 (0000) to 15 (1111) before recycling.