PreCAT - Section C – Digital Electronics
Combinational Logic Circuits
Question 1: A combinational circuit is one in which the output depends on the
A. input combination at the time
B. input combination and the previous output
C. input combination at that time and the previous input combination
D. present output and the previous output
Question 2: Which one of the following set of gates are best suited for 'parity' checking and
'parity' generation.
A. NOR gate
B. AND, OR, NOT gates
C. EX-NOR or EX-OR gates
D. NAND gate
Question 3: Which is the major functioning responsibility of the multiplexing combinational
circuit?
A. Decoding the binary information
B. Generation of all minterms in an output function with OR-gate
C. Generation of selected path between multiple sources and a single destination
D. All of the above
Question 4: The number of control lines for an 8 – to – 1 multiplexer is
A. 2
B. 3
C. 4
D. 5
Question 5: The Gray code for decimal number 6 is equivalent to
A. 1100
B. 1001
C. 0101
D. 0110
Question 6: The gates required to build a half adder are
A. The gates required to build a half adder are
B. EX-OR gate and AND gate
C. EX-OR gate and OR gate
D. Four NAND gates.
Sunbeam Institute of Information Technology, Pune
PreCAT - Section C – Digital Electronics
Question 7: A device which converts BCD to seven segment is called
A. Encoder
B. Decoder
C. Multiplexer
D. Demultiplexer
Question 8: The logic circuit given below (Fig.1) converts a gray code y1y2 y3 into
A. Excess-3 code.
B. Binary code.
C. BCD code.
D. Hamming code
Question 9: The excess 3 code of decimal number 26 is
A. 0100 1001
B. 1000 1001
C. 01011001
D. 01001101
(Add 011 to each BCD)
Question 10: The number of control lines for 32 to 1 multiplexer is
A. 4
B. 5
C. 16
D. 6
Sunbeam Institute of Information Technology, Pune
PreCAT - Section C – Digital Electronics
Question 11: The result of adding hexadecimal number A6 to 3A is
A. DD
B. EF
C. F0
D. E0
Question 12: A full adder logic circuit will have
A. Two inputs and one output.
B. Three inputs and three outputs.
C. Two inputs and two outputs.
D. Three inputs and two outputs.
Question 13: The 2’s complement of the number 1101110 is
A. 0010001
B. 0010001
C. 0010010
D. None
Question 14: For a binary half adder having two inputs A and B the correct set of logical
expressions for the output (=𝐴 𝑝𝑙𝑢𝑠 𝐵) 𝑎𝑛𝑑 𝐶(=𝑐𝑎𝑟𝑟𝑦) are
A. 𝑆=𝐴𝐵+𝐴𝐵 & 𝐶=𝐴𝐵
B. 𝑆=𝐴𝐵+𝐴𝐵 & 𝐶=𝐴𝐵
C. 𝑆=𝐴𝐵+𝐴𝐵 & 𝐶=𝐴𝐵
D. 𝑆=𝐴𝐵+𝐴𝐵 & 𝐶=𝐴𝐵
Question 15: The logic function implemented by the circuit below is (ground implies a logic “0”)
Sunbeam Institute of Information Technology, Pune
PreCAT - Section C – Digital Electronics
A. F = AND (P,Q)
B. F = OR (P,Q)
C. F = XNOR (P,Q)
D. F = XOR (P,Q)
Question 16: The Boolean function realized by the logic circuit shown is
A. F = Ʃm (0,1,3,5,9,10.14)
B. F = Ʃm (2,3,5,7,8,12.13)
C. F = Ʃm (1,2,4,5,11,14.15)
D. F = Ʃm (2,3,5,7,8,9.12)
(𝑭 = 𝑨 𝑩 𝑪(𝑫 +𝑫 ) +𝑨 𝑩𝑫(𝑪 +𝑪 ) + 𝑨𝑩 𝑪 (𝑫 +𝑫 ) + 𝑨𝑩𝑪 𝑫)
Question 17: The Boolean function f implemented in the figure using two input multiplexers is
A. 𝐴𝐵 𝐶 + 𝐴𝐵𝐶
B. 𝐴𝐵𝐶 + 𝐴𝐵 𝐶
C. 𝐴𝐵𝐶 + 𝐴𝐵 𝐶
D. 𝐴𝐵𝐶 + 𝐴𝐵𝐶
Question 18: The minimum number of 2-to-1 multiplexers required to realize a 4-to-1 multiplexer is
A. 1
B. 2
Sunbeam Institute of Information Technology, Pune
PreCAT - Section C – Digital Electronics
C. 3
D. 4
Question 19: Full adder can be implemented using -----------.
A. 3 half adders
B. 2 half adders
C. 2 subtractors
D. None of the above
Question 20: Design a combinational circuit with three inputs which produces output 1 when
more than 1 input are 1.
A. AC + BC + AB
B. AC + BC + A
C. AC + B + AB
D. C + BC + AB
Question 21: how many 2 line to 4 line decoders are required to form 4 line to 16 line
A. 2
B. 3
C. 4
D. 5
Question 22: An encoder has 2^n inputs and n outputs.
A. True
B. False
Question 23: Octal to binary encoder has
A. 3 inputs, 8 outputs
B. 8 inputs, 3 outputs
C. 9 inputs, 3 outputs
D. None of the above
Question 24: To design 16:1 multiplexer by using 4:1 multiplexer requires how many flip
flop?
A.3
B.4
C.5
D.6
Sunbeam Institute of Information Technology, Pune
PreCAT - Section C – Digital Electronics
Question 25: In a 7 segment display the segments b and c are lit up. The decimal number
displayed will be
A. 9
B. 7
C. 3
D. 1
Question 26: x = 1, y = 1, z = 1, choose correct from the following
A. sum = 1, carry = 0
B. sum = 0, carry = 1
C. sum = 1, carry = 1
D. None of the above
Question 27: Divide 1011.11 by 11
A. 11.01
B. 11.11
C. 11.00
D. None of the above
Question 28: Divide 100100.11 by 111
A. 101.11
B. 101.10
C. 101.01
D. 101.00
Question 29:
Inputs = Encoder: ___ :: Decoder : ____
Outputs = Encoder: ____ :: Decoder: ______
A. 3,3,8,8
B. 3,8,8,3
C. 8,3,3,8
D. 8,8,3,3
Question 30: Which of the following is not output of comparator?
A. A=B
B. A-B
C.A<B
D.A>B
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