# MCQs on Digital Electronics

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01․ In which code do the successive code characters differ in only one position?
Gray code
XS-3 code
8421 code
Hamming code

In Gray code successive numbers will differ by only one bit. It is also known as unit distance code or cyclic code or reflective code. It is an unweighted code.

02․ In which of the following codes do the successive characters differ in only 1-bit position?
8421 code
2421 code
cyclic code
binary code

In Gray code successive numbers will differ by only one bit. It is also known as unit distance code or cyclic code or reflective code. It is a unweighted code.

03․ Which of the following is a self-complementing code?
XS-3 code
Gray code
Hamming code
cyclic code

XS-3 code is obtained by adding '0011' to the BCD code. XS-3 code is a self complementing code and not a weighted code.

04․ The number of parity bits in a 12-bit Hamming code is
4
5
6
8

Hamming code is a set of error-correction codes that can be used to detect and correct bit errors that can occur when computer data is moved or stored. If you have m parity bits, it can cover bits from 1 up to 2m. If we subtract out the parity bits, we are left with 2m- m - 1 bits we can use for the data. As m varies, we get all the possible Hamming codes.

05․ A combinational circuit can be designed using only
AND gates
OR gates
OR and X-NOR gates
NOR gates

Combinational logic circuits are made up from basic NAND, NOR or NOT gates that are combined or connected together to produce more complicated switching circuits. These logic gates are the building blocks of combinational logic circuits.

06․ What is the logic which controls a stair case light associated with two switches A and B located at the bottom and top of the stair case respectively?
OR
AND
X-OR
X-NOR

Stair case switches are equivalent to X-OR or X-NOR gates. But For given condition, the gates used are X-OR gates only.

07․ The NAND gate can function as a NOT gate if
all inputs are connected together
inputs are left open
one input is set to 0
one input is set to 1

The output of NAND gate is high, when any one of the inputs is low, as well as output of NAND gate is low, when the all inputs are high.

08․ The NOR gate can function as a NOT gate if
all inputs are connected together
inputs are left open
one input is set to 0
one input is set to 1

The output of NOR gate is high, when all the inputs is low, as well as output of NOR gate is low, when any one of the inputs are high.

09․ An X-OR gate gives a high output
if there are odd number of 1s
if it has even number of 0s
if the decimal value of digital word is even
for odd decimal value.

X-OR and X-NOR gates are available with two inputs only. In X-OR gate output is ‘1’ when number of 1’s at the input is odd number. Hence it is known as odd number of 1’s detector.

10․ An exclusive NOR gate is logically equivalent to
inverter followed by an X-OR gate
X-OR gate followed by an inverter
NOT gate followed by a NOR gate
complement of a NOR gate

In X-OR gate output is ‘1’ when number of 1’s at the input is odd number. Hence it is known as odd number of 1’s detector. In X-NOR gate output is ‘1’ when number of 1’s at the input is even number. Hence it is known as even number of 1’s detector.

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