Gray code (Reflected Binary Code) is designed such that successive values differ by only one bit. This is useful in error detection and mechanical encoders.
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Q.6Easy
A multiplexer with 8 inputs requires how many select lines?
Answer: B
For n select lines, 2^n inputs are possible. For 8 inputs: 2^n = 8, so n = 3. An 8:1 multiplexer needs 3 select lines (A, B, C).
Q.7Easy
The BCD equivalent of decimal 47 is:
Answer: A
In BCD, each decimal digit is converted separately to 4-bit binary. 4 = 0100, 7 = 0111. So 47 in BCD = 0100 0111.
Q.8Easy
A full adder has how many inputs and outputs?
Answer: B
Full adder has 3 inputs (A, B, Cin) and 2 outputs (Sum, Cout). It differs from half adder which has 2 inputs and 2 outputs.
Q.9Easy
A JK flip-flop with J=1, K=1 performs:
Answer: D
JK flip-flop truth table: J=0,K=0 (No change), J=1,K=0 (Set), J=0,K=1 (Reset), J=1,K=1 (Toggle). When both are 1, output toggles.
Q.10Easy
In a 4-bit ripple counter using negative edge-triggered flip-flops, if the input frequency is 16 MHz, what is the frequency at the output of the third flip-flop?
Answer: A
In a ripple counter, each flip-flop divides the frequency by 2. The third flip-flop output frequency = 16 MHz / 2³ = 816 = 2 MHz
Q.11Easy
Which logic gate produces HIGH output only when both inputs are different?
Answer: B
XOR (Exclusive OR) gate produces HIGH output when inputs are different (01 or 10). When inputs are same (00 or 11), output is LOW
Q.12Easy
A SR flip-flop with S=0, R=0 results in:
Answer: C
When S=0 and R=0, the SR flip-flop holds its previous state. No change occurs because neither set nor reset is activated
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.15Easy
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.16Easy
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
Q.17Easy
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.18Easy
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.19Easy
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.20Easy
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).
