A 3-to-8 decoder has how many output lines, and what is the number of active outputs for any single input combination?
Answer: A
A 3-to-8 decoder has 2³ = 8 output lines. For any valid input combination, exactly 1 output line is activated (HIGH), while others remain LOW
Q.44Easy
In VHDL, what does the 'rising_edge' function detect?
Answer: B
'rising_edge' detects a transition from LOW (0) to HIGH (1) on a signal, commonly used in synchronous designs to trigger actions on positive clock edges
Q.45Easy
Which of the following is NOT a characteristic of ROM (Read-Only Memory)?
Answer: B
Standard ROM is programmed during manufacturing and cannot be reprogrammed by users. PROM, EPROM, and EEPROM allow user programming, but basic ROM does not
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Q.46Easy
In a 16×4 RAM, what do the numbers 16 and 4 represent respectively?
Answer: D
16×4 RAM means 16 memory words (locations), each storing 4 bits of data. This requires log₂(16)=4 address lines. Total capacity = 16 words × 4 bits = 64 bits
Q.47Easy
What is the fundamental difference between combinational and sequential circuits?
Answer: B
Combinational circuits: output = f(present inputs only). Sequential circuits: output depends on present inputs AND past states (memory elements like flip-flops store history)
Q.48Easy
Which of the following is a characteristic of asynchronous counters?
Answer: B
Asynchronous (ripple) counters work by cascading flip-flops where the output of one flip-flop triggers the next, creating a ripple effect.
Q.49Easy
A BCD counter counts from 0 to 9 and then resets. How many flip-flops are minimum required?
Answer: C
BCD (Binary Coded Decimal) requires 4 bits to represent decimal digits 0-9 (2^4 = 16 combinations, but only 10 are used).
Q.50Easy
In a multiplexer (MUX) with 3 select lines, how many input lines can it handle?
Answer: C
A multiplexer with n select lines can handle 2^n input lines. For 3 select lines: 2^3 = 8 input lines.
Q.51Easy
A demultiplexer (DEMUX) with 4 select lines has how many output lines?
Answer: C
A demultiplexer with n select lines has 2^n output lines. For 4 select lines: 2^4 = 16 output lines.
Q.52Easy
Which type of flip-flop has the simplest truth table and is used for frequency division?
Answer: B
A T flip-flop toggles its output when T=1 and holds when T=0, making it ideal for frequency division and counter design.
Q.53Easy
Which of the following is a volatile memory?
Answer: C
RAM (Random Access Memory) is volatile and loses all data when power is removed. ROM, EPROM, and Flash memory are non-volatile.
Q.54Easy
Which of the following is a sequential circuit?
Answer: C
Sequential circuits have memory elements (flip-flops) and their output depends on past inputs. Flip-flops are the basic sequential elements; multiplexers, encoders, and decoders are combinational circuits.
Q.55Easy
In state machine design, if a machine has 15 different states, the minimum number of flip-flops needed is?
Answer: B
To represent 15 states, we need n flip-flops such that 2^n ≥ 15. Since 2^4 = 16 ≥ 15, minimum 4 flip-flops are required.
Q.56Easy
In a 3-to-8 decoder, if the binary input is 101, which output line will be activated?
Answer: A
Binary 101 = 5 in decimal, so output line 5 is activated in a decoder.
Q.57Easy
Which of the following logic gates has an output of 1 only when both inputs are different?
Answer: A
XOR (Exclusive OR) produces 1 when inputs are different and 0 when they are same.
Q.58Easy
What is the Boolean expression for a 2-input NAND gate?
Answer: B
NAND gate is the complement of AND, so Y = (A.B)' where . represents AND operation.
Q.59Easy
In a Multiplexer (MUX), how many select lines are required for an 8:1 MUX?
Answer: B
For 2^n inputs, n select lines are needed. For 8 inputs, log₂(8) = 3 select lines.
Q.60Easy
What is the primary purpose of using parity bits in error detection?
Answer: B
Parity bits are used for error detection by tracking whether the number of 1s in data is even or odd.
