Digital Circuits Questions and Answers – Multiplexers (Data Selectors) – 1

This set of Digital Electronics/Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Multiplexers (Data Selectors) – 1”.

1. What is a multiplexer?
a) It is a type of decoder which decodes several inputs and gives one output
b) A multiplexer is a device which converts many signals into one
c) It takes one input and results into many output
d) It is a type of encoder which decodes several inputs and gives one output
View Answer

Answer: b
Explanation: A multiplexer (or MUX) is a device that selects one of several analog or digital input signals and forwards the selected input into a single line, depending on the active select lines.

2. Which combinational circuit is renowned for selecting a single input from multiple inputs & directing the binary information to output line?
a) Data Selector
b) Data distributor
c) Both data selector and data distributor
d) DeMultiplexer
View Answer

Answer: a
Explanation: Data Selector is another name of Multiplexer. A multiplexer (or MUX) is a device that selects one of several analog or digital input signals and forwards the selected input into a single line, depending on the active select lines.

3. It is possible for an enable or strobe input to undergo an expansion of two or more MUX ICs to the digital multiplexer with the proficiency of large number of ___________
a) Inputs
b) Outputs
c) Selection lines
d) Enable lines
View Answer

Answer: a
Explanation: It is possible for an enable or strobe input to undergo an expansion of two or more MUX ICs to the digital multiplexer with the proficiency of large number of inputs.
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4. 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) Encoding of binary information
View Answer

Answer: c
Explanation: The major functioning responsibility of the multiplexing combinational circuit is generation of selected path between multiple sources and a single destination because it makes the circuit too flexible. A multiplexer (or MUX) is a device that selects one of several analog or digital input signals and forwards the selected input into a single line, depending on the active select lines.

5. What is the function of an enable input on a multiplexer chip?
a) To apply Vcc
b) To connect ground
c) To active the entire chip
d) To active one half of the chip
View Answer

Answer: c
Explanation: Enable input is used to active the chip, when enable is high the chip works (ACTIVE), when enable is low the chip does not work (MEMORY). However, Enable can be Active-High or Active-Low, indicating it is active either when it is connected to VCC or GND respectively.
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6. One multiplexer can take the place of ___________
a) Several SSI logic gates
b) Combinational logic circuits
c) Several Ex-NOR gates
d) Several SSI logic gates or combinational logic circuits
View Answer

Answer: d
Explanation: A multiplexer (or MUX) is a device that selects one of several analog or digital input signals and forwards the selected input into a single line, depending on the active select lines. Since many operational behaviour can be performed by using a multiplexer. Whereas, a combinational circuit is a combination of many logic gates which makes the circuit more complex.

7. A digital multiplexer is a combinational circuit that selects ___________
a) One digital information from several sources and transmits the selected one
b) Many digital information and convert them into one
c) Many decimal inputs and transmits the selected information
d) Many decimal outputs and accepts the selected information
View Answer

Answer: a
Explanation: A digital multiplexer is a combinational circuit that selects one digital information from several sources and transmits the selected information on a single output line depending on the status of the select lines. That is why it is also known as a data selector.
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8. In a multiplexer, the selection of a particular input line is controlled by ___________
a) Data controller
b) Selected lines
c) Logic gates
d) Both data controller and selected lines
View Answer

Answer: b
Explanation: The selection of a particular input line is controlled by a set of selected lines in a multiplexer, which helps to select a particular input from several sources.

9. If the number of n selected input lines is equal to 2^m then it requires _____ select lines.
a) 2
b) m
c) n
d) 2n
View Answer

Answer: b
Explanation: If the number of n selected input lines is equal to 2^m then it requires m select lines to select one of m select lines.
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10. How many select lines would be required for an 8-line-to-1-line multiplexer?
a) 2
b) 4
c) 8
d) 3
View Answer

Answer: d
Explanation: 2n input lines, n control lines and 1 output line available for MUX. Here, 8 input lines mean 23 inputs. So, 3 control lines are possible. Depending on the status of the select lines, the input is selected and fed to the output.

11. A basic multiplexer principle can be demonstrated through the use of a ___________
a) Single-pole relay
b) DPDT switch
c) Rotary switch
d) Linear stepper
View Answer

Answer: c
Explanation: A basic multiplexer principle can be demonstrated through the use of a rotary switch. Since its behaviour is similar to the multiplexer. There are around 10 digits out of which one is selected one at a time and fed to the output.

12. How many NOT gates are required for the construction of a 4-to-1 multiplexer?
a) 3
b) 4
c) 2
d) 5
View Answer

Answer: c
Explanation: There are two NOT gates required for the construction of 4-to-1 multiplexer. x0, x1, x2 and x3 are the inputs and C1 and C0 are the select lines and M is the output.
The diagram of a 4-to-1 multiplexer is shown below: The output M is X1 in the given 4-to-1 multiplexer, if c1 = 0 & c0 = 1

13. In the given 4-to-1 multiplexer, if c1 = 0 and c0 = 1 then the output M is ___________
The output M is X1 in the given 4-to-1 multiplexer, if c1 = 0 & c0 = 1
a) X0
b) X1
c) X2
d) X3
View Answer

Answer: b
Explanation: The output will be X1, because c1 = 0 and c0 = 1 results into 1 which further results as X1. And rest of the AND gates gives output as 0.

14. The enable input is also known as ___________
a) Select input
b) Decoded input
c) Strobe
d) Sink
View Answer

Answer: c
Explanation: The enable input is also known as strobe which is used to cascade two or more multiplexer ICs to construct a multiplexer with a larger number of inputs. Enable input activates the multiplexer to operate.

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