# Combinational Logic Circuits in Digital Logic Design MCQs

Q1. How many 3-line-to-8-line decoders are required for a 1-of-32 decoder?.

A. 1.

B. 2.

C. 4.

D. 8.

Q2. Convert BCD 0001 0010 0110 to binary..

A. 1111110.

B. 1111101.

C. 1111000.

D. 1111111.

Q3. Convert BCD 0001 0111 to binary..

A. 10101.

B. 10010.

C. 10001.

D. 11000.

Q4. How many data select lines are required for selecting eight inputs?.

A. 1.

B. 2.

C. 3.

D. 4.

Q5. How many 1-of-16 decoders are required for decoding a 7-bit binary number?.

A. 5.

B. 6.

C. 7.

D. 8.

Q6. The implementation of simplified sum-of-products expressions may be easily implemented into actual logic circuits using all universal ________ gates with little or no increase in circuit complexity. (Select the response for the blank space that will BEST make the statement true.).

A. AND/OR.

B. NAND.

C. NOR.

D. OR/AND.

Q7. Which of the following statements accurately represents the two BEST methods of logic circuit simplification?.

A. Boolean algebra and Karnaugh mapping.

B. Karnaugh mapping and circuit waveform analysis.

C. Actual circuit trial and error evaluation and waveform analysis.

D. Boolean algebra and actual circuit trial and error evaluation.

Answer= Boolean algebra and Karnaugh mapping

Q8. Which of the following combinations cannot be combined into K-map groups?.

A. Corners in the same row.

B. Corners in the same column.

C. Diagonal corners.

D. Overlapping combinations.

Q9. As a technician you are confronted with a TTL circuit board containing dozens of IC chips. You have taken several readings at numerous IC chips, but the readings are inconclusive because of their erratic nature. Of the possible faults listed, select the one that most probably is causing the problem..

A. A defective IC chip that is drawing excessive current from the power supply.

B. A solar bridge between the inputs on the first IC chip on the board.

C. An open input on the first IC chip on the board.

D. A defective output IC chip that has an internal open to�Vcc.

Answer= An open input on the first IC chip on the board

Q10. Which gate is best used as a basic comparator?.

A. NOR.

B. OR.

C. Exclusive-OR.

D. AND.

Q11. In VHDL, macrofunctions is/are:.

A. digital circuits..

B. analog circuits..

C. a set of bit vectors..

D. preprogrammed TTL devices..

Q12. Which of the following is an important feature of the sum-of-products form of expressions?.

A. All logic circuits are reduced to nothing more than simple AND and OR operations..

B. The delay times are greatly reduced over other forms..

C. No signal must pass through more than two gates, not including inverters..

D. The maximum number of gates that any signal must pass through is reduced by a factor of two..

Answer= All logic circuits are reduced to nothing more than simple AND and OR operations.

Q13. An output gate is connected to four input gates; the circuit does not function. Preliminary tests with the DMM indicate that the power is applied; scope tests show that the primary input gate has a pulsing signal, while the interconnecting node has no signal. The four load gates are all on different ICs. Which instrument will best help isolate the problem?.

A. Current tracer.

B. Logic probe.

C. Oscilloscope.

D. Logic analyzer.

Q14. The binary numbers A = 1100 and B = 1001 are applied to the inputs of a comparator. What are the output levels?.

A. A > B = 1, A < B = 0, A < B = 1.

B. A > B = 0, A < B = 1, A = B = 0.

C. A > B = 1, A < B = 0, A = B = 0.

D. A > B = 0, A < B = 1, A = B = 1.

Answer= A > B = 1, A < B = 0, A = B = 0

Q15. A logic probe is placed on the output of a gate and the display indicator is dim. A pulser is used on each of the input terminals, but the output indication does not change. What is wrong?.

A. The output of the gate appears to be open..

B. The dim indication on the logic probe indicates that the supply voltage is probably low..

C. The dim indication is a result of a bad ground connection on the logic probe..

D. The gate may be a tristate device..

Answer= The output of the gate appears to be open.

Q16. Each "1" entry in a K-map square represents:.

A. a HIGH for each input truth table condition that produces a HIGH output..

B. a HIGH output on the truth table for all LOW input combinations..

C. a LOW output for all possible HIGH input conditions..

D. a DON'T CARE condition for all possible input truth table combinations..

Answer= a HIGH for each input truth table condition that produces a HIGH output.

Q17. Looping on a K-map always results in the elimination of:.

A. variables within the loop that appear only in their complemented form..

B. variables that remain unchanged within the loop..

C. variables within the loop that appear in both complemented and uncomplemented form..

D. variables within the loop that appear only in their uncomplemented form..

Answer= variables within the loop that appear in both complemented and uncomplemented form.

Q18. What will a design engineer do after he/she is satisfied that the design will work?.

A. Put it in a flow chart.

B. Program a chip and test it.

C. Give the design to a technician to verify the design.

D. Perform a vector test.

Answer= Program a chip and test it

Q19. What is the indication of a short on the input of a load gate?.

A. Only the output of the defective gate is affected..

B. There is a signal loss to all gates on the node..

C. The affected node will be stuck in the LOW state..

D. There is a signal loss to all gates on the node, and the affected node will be stuck in the LOW state..

Answer= There is a signal loss to all gates on the node, and the affected node will be stuck in the LOW state.

Q20. In HDL, LITERALS is/are:.

A. digital systems..

B. scalars..

C. binary coded decimals..

D. a numbering system..

Q21. A decoder can be used as a demultiplexer by ________..

A. tying all enable pins LOW.

B. tying all data-select lines LOW.

C. tying all data-select lines HIGH.

D. using the input lines for data selection and an enable line for data input.

Answer= using the input lines for data selection and an enable line for data input

Q22. How many 4-bit parallel adders would be required to add two binary numbers each representing decimal numbers up through 300(10)?.

A. 1.

B. 2.

C. 3.

D. 4.

Q23. Which statement below best describes a Karnaugh map?.

A. A Karnaugh map can be used to replace Boolean rules..

B. The Karnaugh map eliminates the need for using NAND and NOR gates..

C. Variable complements can be eliminated by using Karnaugh maps..

D. Karnaugh maps provide a visual approach to simplifying Boolean expressions..

Answer= Karnaugh maps provide a visual approach to simplifying Boolean expressions.

Q24. A certain BCD-to-decimal decoder has active-HIGH inputs and active-LOW outputs. Which output goes LOW when the inputs are 1001?.

A. 0.

B. 3.

C. 9.

D. None. All outputs are HIGH..

Q25. The design concept of using building blocks of circuits in a PLD program is called a(n):.

A. hierarchical design..

B. architectural design..

C. digital design..

D. verilog..

Q26. When adding an even parity bit to the code 110010, the result is ________..

A. 1110010.

B. 1111001.

C. 110010.

D. 00 1101.

Q27. Which of the following combinations of logic gates can decode binary 1101?.

A. One 4-input AND gate.

B. One 4-input AND gate, one OR gate.

C. One 4-input NAND gate, one inverter.

D. One 4-input AND gate, one inverter.

Answer= One 4-input AND gate, one inverter

Q28. What is the indication of a short to ground in the output of a driving gate?.

A. Only the output of the defective gate is affected..

B. There is a signal loss to all load gates..

C. The node may be stuck in either the HIGH or the LOW state..

D. The affected node will be stuck in the HIGH state..