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MCQOPTIONS
This section includes 105 Mcqs, each offering curated multiple-choice questions to sharpen your Digital Electronics knowledge and support exam preparation. Choose a topic below to get started.
| 51. |
ADHL does not offer a multiplication operator. |
| A. | 1 |
| B. | |
| Answer» B. | |
| 52. |
Modern computers transfer data between different devices over a common set of connecting lines called a data bus. |
| A. | 1 |
| B. | |
| Answer» B. | |
| 53. |
The normal outputs of a magnitude comparator are ________. |
| A. | A < B, A = B, and A > B |
| B. | Sum, difference, and carry |
| C. | Cin, Cout, and Sum |
| D. | A = B, A + B, and carry |
| Answer» B. Sum, difference, and carry | |
| 54. |
A(n) ________ is a logic circuit that accepts a set of inputs that represents a binary number, and activates only the output that corresponds to that input number. |
| A. | decoder |
| B. | LED |
| C. | encoder |
| D. | demultiplexer |
| Answer» B. LED | |
| 55. |
The outputs of a 7485 four-bit magnitude comparator when the inputs are A = 0110 and B = 1010 are: A < B is 1 A = B is 0 A > B is 1 |
| A. | 1 |
| B. | |
| Answer» C. | |
| 56. |
Output 6 of a 74138 octal decoder is selected when it is enabled by a data input of: A0 = 1 A1 = 1 A2 = 0 |
| A. | 1 |
| B. | |
| Answer» C. | |
| 57. |
What is the HDL key issue in the design of the MUX and DEMUX? |
| A. | Having the MUX and DEMUX part of the library |
| B. | Using the case statement in the process |
| C. | Describing the functions |
| D. | Assigning signals under certain conditions |
| Answer» E. | |
| 58. |
The data transmission system shown in below has a problem; the parity error output is always high. A logic analyzer is used to examine the system and shows that the DATA IN on the left matches the DATA OUT on right. What might be causing the problem? |
| A. | The error gate could be defective. |
| B. | The storage circuit could be defective. |
| C. | The parity checker could be bad. |
| D. | Any of the above. |
| Answer» E. | |
| 59. |
Output 3 of a 74138 octal decoder is selected when it is enabled by a data input of: A0 = 1 A1 = 1 A2 = 0 |
| A. | 1 |
| B. | |
| Answer» B. | |
| 60. |
A four-line multiplexer must have as inputs four data inputs and two select inputs. |
| A. | 1 |
| B. | |
| C. | 1 |
| D. | |
| Answer» B. | |
| 61. |
When data input I5 of a 74148 octal-to-binary encoder is active, the data output is: A0 = 1 A1 = 0 A2 = 0 |
| A. | 1 |
| B. | |
| C. | 1 |
| D. | |
| Answer» C. 1 | |
| 62. |
The device that generates a coded output from a single active numeric input line is ________. |
| A. | a decoder |
| B. | a multiplexer |
| C. | a comparator |
| D. | an encoder |
| Answer» E. | |
| 63. |
A VARIABLE can be thought of as a piece of scrap paper used to write down some numbers that can be used later. |
| A. | 1 |
| B. | |
| Answer» B. | |
| 64. |
In most modern computers, the transfer of data takes place over a common set of connecting lines called a ________. |
| A. | data bus |
| B. | bus line |
| C. | bus cable |
| D. | data line |
| Answer» B. bus line | |
| 65. |
What must be done in the given figure in order to use two 7485 4-bit comparators to compare two 8-bit numbers? |
| A. | The P < Q, P = Q, and P > Q outputs of COMP A must be connected to the same outputs of COMP B. |
| B. | The P < Q, P = Q, and P > Q outputs of COMP A must be connected to the <, =, and > inputs of COMP B. |
| C. | The = input of COMP A must be connected to Vcc, and the < and > inputs must be connected to ground. |
| D. | The P < Q, P = Q, and P > Q outputs of COMP A must be connected to the <, =, and > inputs of COMP B, the = input of COMP A must be connected to Vcc, and the < and > inputs must be connected to ground. |
| Answer» E. | |
| 66. |
Which is the decimal number for the BCD number, 10110110? |
| A. | 182 |
| B. | 36 |
| C. | 116 |
| D. | 10110110 is not a valid BCD number. |
| Answer» E. | |
| 67. |
What is an important attribute of the conditional signal assignment statement? |
| A. | Its tristate outputs |
| B. | Its sequential evaluation |
| C. | Its use of library components |
| D. | Its fast activation times |
| Answer» C. Its use of library components | |
| 68. |
A breadboard-circuit design using a BCD-to-decimal decoder has a problem wherein the operation of the system is erratic. The technician uses his scope to examine the waveforms throughout the system and doesn't really see any problems. While he's scratching his head, what helpful advice can you offer him as to what might be wrong and what to do to correct the problem? |
| A. | The decoder is thermally intermittent; replace it. |
| B. | There is probably a bad connection on the wire wrap protoboard; recheck the wiring. |
| C. | Glitches are probably the culprit; strobe the decoder. |
| D. | The decoder is thermally intermittent and must be replaced; or there is probably a bad connection on the wire wrap protoboard, and the wiring must be rechecked. |
| Answer» D. The decoder is thermally intermittent and must be replaced; or there is probably a bad connection on the wire wrap protoboard, and the wiring must be rechecked. | |
| 69. |
Multiplexing of digital signals is usually required when: |
| A. | moving data internally within a microprocessor. |
| B. | moving data between memory and storage registers in a microprocessor. |
| C. | moving data over long distance transmission lines. |
| D. | moving data internally within a microprocessor or between memory and storage registers. |
| Answer» D. moving data internally within a microprocessor or between memory and storage registers. | |
| 70. |
In order to select data input I1 of a 74151 eight-line multiplexer, the select inputs must be: |
| A. | 1 |
| B. | |
| C. | 1 |
| D. | |
| Answer» B. | |
| 71. |
If by chance more than one of the inputs in an HDL encoder is activated at the same time, the priority encoder ________. |
| A. | enters a fault mode |
| B. | ignores the least significant input |
| C. | resamples the data |
| D. | finds some other input |
| Answer» C. resamples the data | |
| 72. |
An everyday illustration of a multiplexer is ________. |
| A. | the volume control in a stereo receiver |
| B. | the function switch on a stereo receiver |
| C. | the balance control on a stereo receiver |
| D. | the treble-bass control on a stereo receiver |
| Answer» C. the balance control on a stereo receiver | |
| 73. |
What is the purpose of a decoder's inputs? |
| A. | To allow the decoder to respond to the inputs to activate the correct output gate. |
| B. | To disable the decoder outputs so that all outputs will be inactive. |
| C. | To disable the inputs and activate all outputs. |
| D. | To allow the decoder to respond to the inputs to activate the correct output gate, and to disable the inputs and activate all outputs. |
| Answer» E. | |
| 74. |
The circuit shown below is a(n) ________. |
| A. | 4-bit magnitude comparator |
| B. | 4-bit half adder |
| C. | 8-bit comparator |
| D. | 8-bit binary adder |
| Answer» B. 4-bit half adder | |
| 75. |
Which statement best describes the given figure, and what is the function of the terminal labeled EN? |
| A. | Quad two-input multiplexer. EN is the enable input, which requires an active LOW for the device to work. |
| B. | Quad two-bit multiplier, EN is the active HIGH trigger. |
| C. | Dual quad-input multiplexer, which requires an active LOW on the EN terminal for the device to work. |
| D. | Quad two-input AND gate, which requires an active LOW on the EN input to enable all the gates. |
| Answer» B. Quad two-bit multiplier, EN is the active HIGH trigger. | |
| 76. |
What VHDL techniques are used to describe a priority encoder? |
| A. | Integer outputs and priority coding |
| B. | Signal outputs and priority coding |
| C. | Tristate outputs and priority coding |
| D. | Variables and priority coding |
| Answer» D. Variables and priority coding | |
| 77. |
Refer to the display multiplexer given below. The MSD display is blank, while the LSD seems to be OK. The input and output lines to the 74157 and 7449 are checked with a scope and can be seen changing levels. The A input on the 74139 also changes; however, the 0 output on the 74139 is always LOW and the 1 output is always HIGH. The B and EN inputs on the 74139 are always LOW. What could cause the problem and what should be done to correct it? |
| A. | The 74139 is defective; replace it. |
| B. | The EN pin on the 74139 could have a bad connection; check the connection. |
| C. | The 74139 is defective and must be replaced; or the EN pin on the 74139 could have a bad connection, which should be checked. |
| D. | The MSD display is bad; replace it. |
| Answer» D. The MSD display is bad; replace it. | |
| 78. |
When data input I1 of a 74148 octal-to-binary encoder is active, the data output is: A0 = 0 A1 = 0 A2 = 1 |
| A. | 1 |
| B. | |
| Answer» C. | |
| 79. |
Determine the correct output for the multiplexer and its associated timing diagram given below. |
| A. | Ya |
| B. | Yb |
| C. | Yc |
| D. | Yd |
| Answer» E. | |
| 80. |
The IEEE/ANSI symbol for a decoder has the internal designation bcd/dec. This means the decoder is a: |
| A. | decimal-to-BCD decoder with ten inputs and four outputs. |
| B. | BCD-to-decimal decoder with ten inputs and four outputs. |
| C. | decimal-to-BCD decoder with four inputs and ten outputs. |
| D. | BCD-to-decimal decoder with four inputs and ten outputs. |
| Answer» E. | |
| 81. |
In order to select data input I3 of a 74151 eight-line multiplexer, the select inputs must be: |
| A. | 1 |
| B. | |
| C. | 1 |
| D. | |
| Answer» B. | |
| 82. |
What are the outputs of a 7485 four-bit magnitude comparator when the inputs are A = 1001 and B = 1010? |
| A. | A < B is 1 A = B is 0 A > B is 1 |
| B. | A < B is 0 A = B is 1 A > B is 0 |
| C. | A < B is 0 A = B is 0 A > B is 1 |
| D. | A < B is 1 A = B is 0 A > B is 0 |
| Answer» E. | |
| 83. |
The 74139 dual four-line demultiplexer functions as a decoder if ________. |
| A. | the line is grounded |
| B. | data input is on the line |
| C. | data input is on the A0 line |
| D. | the A0 line is grounded |
| Answer» B. data input is on the line | |
| 84. |
A(n) ________ has a number of input lines, only one of which is activated at a given time, and produces on N-bit output code, depending on which input is activated. |
| A. | encoder |
| B. | code converter |
| C. | demultiplexer |
| D. | decoder |
| Answer» B. code converter | |
| 85. |
What type of device is shown in the given figure, and what inputs (A3,A2,A1,A0) are required to produce the output levels as shown? |
| A. | A binary-to-decimal encoder; 0,1,1,1 |
| B. | A decimal-to-binary decoder; 1,1,1,0 |
| C. | A BCD-to-decimal decoder; 0,1,1,1 |
| D. | A decimal-to-BCD encoder; 1,1,1,0 |
| Answer» D. A decimal-to-BCD encoder; 1,1,1,0 | |
| 86. |
A logic circuit that determines if one input is equal to another is called a comparator. |
| A. | 1 |
| B. | |
| Answer» B. | |
| 87. |
How is the number one (1) indicated on the outputs of a 7447 BCD-to-seven-segment code converter? |
| A. | Segment a is active. |
| B. | Segment b is active. |
| C. | Segments a and b are active. |
| D. | Segments b and c are active. |
| Answer» E. | |
| 88. |
Why are control inputs included in an HDL magnitude comparator? |
| A. | For cascading the chips |
| B. | For control signal input |
| C. | For signal control |
| D. | For internal interconnections |
| Answer» B. For control signal input | |
| 89. |
The circuit in Figure 9-8 is defective; data is not appearing on the output lines. A check with the scope shows data pulses on the serial data line and multiplex control lines, S0–S2; no parity error is indicated. A further check with a logic probe indicates that Vcc and ground appear to be present. What might be wrong with the circuit? |
| A. | The demultiplexer may be bad. |
| B. | The parity checker is defective. |
| C. | The parity generator may be bad. |
| D. | The parity checker is defective, or the parity generator may be bad. |
| Answer» B. The parity checker is defective. | |
| 90. |
All outputs of the 74138 octal decoder are disabled (HIGH) when the enable inputs are: |
| A. | 1 |
| B. | |
| C. | 1 |
| D. | |
| Answer» B. | |
| 91. |
For the input values (A0–A3, B0–B3, Data Select = 1) given for the circuit given below, what will be indicated on the displays? |
| A. | A = 0, B = 5 |
| B. | A = 5, B = 0 |
| C. | A = 6, B = 0 |
| D. | A = 0, B = 6 |
| Answer» E. | |
| 92. |
The diagram given below shows a ________, and in order for the decimal number 3 to be displayed, terminals ________ must be ________. |
| A. | common-cathode seven-segment display, ef, LOW |
| B. | common-anode seven-segment display, abcdg, HIGH |
| C. | common-anode seven-segment display, abcdg, LOW |
| D. | common-cathode seven-segment display, abcdg, HIGH |
| Answer» D. common-cathode seven-segment display, abcdg, HIGH | |
| 93. |
For the inputs shown in the given figure, the outputs for P > Q, P = Q, and P < Q are ____, ____, and ____, respectively. |
| A. | 1,1,1 |
| B. | 1,0,1 |
| C. | 1,0,0 |
| D. | 0,1,0 |
| Answer» D. 0,1,0 | |
| 94. |
Referring to the figure given below, what output code will appear on the output (A3,A2,A1,A0) when the 5 key is pressed? |
| A. | 1010 |
| B. | 101 |
| C. | 1101 |
| D. | 1011 |
| Answer» B. 101 | |
| 95. |
One can safely state that the output lines for a demultiplexer are under the direct control of the: |
| A. | input data select lines. |
| B. | the internal AND gates. |
| C. | the internal OR gate. |
| D. | Input data line. |
| Answer» B. the internal AND gates. | |
| 96. |
The BCD/DEC decoder shown in figure (a) is examined with a logic analyzer and the results are shown in the waveforms in figure (b). What, if anything, is wrong with the circuit? |
| A. | The "2" output is shorted to Vcc. |
| B. | The A1 input is internally open. |
| C. | The A1 input node is internally stuck LOW. |
| D. | Nothing is wrong with the circuit. |
| Answer» D. Nothing is wrong with the circuit. | |
| 97. |
It is suspected that the comparator in the figure given below has a problem. The inputs are activated in the table shown below and the corresponding outputs noted. What is most likely wrong with the circuit? For P0 – P3 = 1 and Q0 – Q3 = 0, P > Q = 1, P = Q = 1, P < Q = 0 For P0 – P3 = 0 and Q0 – Q3 = 1, P > Q = 0, P = Q = 1, P < Q = 1 For P0 – P3 = 1 and Q0 – Q3 = 1, P > Q = 0, P = Q = 1, P < Q = 0 |
| A. | The P0–P3 inputs are defective. |
| B. | One or more of the Q inputs is bad. |
| C. | The P = Q output is shorted to Vcc. |
| D. | Nothing is wrong; the circuit is functioning properly. |
| Answer» D. Nothing is wrong; the circuit is functioning properly. | |
| 98. |
A device that selects one of several inputs to be placed on the output is a multiplexer. |
| A. | 1 |
| B. | |
| C. | 1 |
| D. | |
| Answer» B. | |
| 99. |
Refer to the figure given below. The logic function generator being implemented with the multiplexer in this circuit produces a constant LOW on the output. The ABC inputs are checked and appear to be pulsing; also, the 0–7 and EN inputs are checked with the scope and all appear to be at 0 V. A check with the DMM confirms that power is on. What is the problem, and what should be done to correct it? |
| A. | The output is shorted to Vcc; replace the IC. |
| B. | The scope's vertical input is in the AC mode and the common connection for the 0,2,3 and 5 inputs is bad. Set the scope's vertical input mode to DC, and repair the bad solder connection. |
| C. | Power has not been applied to the circuit; apply power. |
| D. | The output is shorted to ground; replace the IC. |
| Answer» C. Power has not been applied to the circuit; apply power. | |
| 100. |
A 16-input multiplexer is to be used to perform parallel-to-serial data conversion. Which of the following counters would be required to provide the data select inputs? |
| A. | MOD 8 |
| B. | MOD 16 |
| C. | MOD 4 |
| D. | MOD 2 |
| Answer» C. MOD 4 | |