# Top 250 Digital Circuits Objective Questions and Answers

In this article, we published the top 250 digital electronic circuits objective and answers for electrical and instrumentation engineers.

## Digital Circuits Objective Questions

The below list provides all the multiple-choice questions (MCQ) related to digital circuits.

Answers are available at the bottom of the article.

1. Circuits made up of combinations of logic gates, with no feedback from outputs to inputs.

2. What digits are used in the binary number system?

3. Which of the following is a non-volatile device?

4. Which of the following does not form DACs?

5. It is needed to translate a high-level program into a sequence of machine instructions that performs the desired task.

6. Low-speed modems method of modulation is usually

7. The number of input combinations will equal ​_____ for an N-input truth table.

8. Quad 2-input XOR gates in the 7400 Family of TTL devices have a device number equivalent to

9. CMOS means

10. The maximum deviation of DAC output from its ideal value, is expressed as a percentage of full scale.

11. A counter that counts from a maximum count downward to zero

12. How many different ways can we implement the inversion operation in a logic circuit?

13. It is said to be a universal gate because any digital system can be implemented with it.

14. A system of coordinating I/O between the transmitting and receiving devices.

15. Use the expression for x = D + [(A+B)C]’ · E to determine the output of the circuit for the conditions A = B = E = 1, C = D = 0.

16. What is the normal resting state of the SET and CLEAR inputs in a flip-flop

17. A digital circuit that takes a 4-bit BCD input and activates the required outputs to display the equivalent decimal digit on a 7-segment display.

18. A technique often used to eliminate decoding spikes.

19. The system program used to translate directly an assembly language to machine language is called

20. The Boolean expression for a six-input OR gate

21. A program which can be executed on several different computers to compare their speed and performance.

22. An electrical connection common to all segments of an LCD.

23. The most widely used 7-bit alphanumeric code is the

24. A computer programming language in which groups of 1s and 0s are used to represent instructions.​

It is also the only language a computer actually understood.

25. What does a computer do with the data it receives from an ADC?

26. A circuit made up of combinations of logic gates, with no feedback from output to input.

27. An unconnected input is termed as ​ ​ ​ ​ ​ ​ ​ ​ ​ .

28. An RS flip-flop will not change in state when

29. An IC that transforms parallel data to serial in the asynchronous format and vice versa.

30. From a 3-bit binary counter design using T flip-flops, determine the number of T flip- flops needed in its circuit implementation.

31. Another name for a decade counter

32. Meaning of checksum in ROM’s

34. A binary counter that counts from 0000 to 1001 before it recycles.

35. A translated program in machine language is called

36. A single bit comparator is usually implemented using

37. A state causing the flip-flop to change or reverse its state.

38. The processor or central processing unit is

39. A digital circuit is also referred to as a/an _______ circuit.

40. TTL, DTL, and ECL which are frequently used to refer to certain “families” of digital integrated circuits, are actually names of

41. A type of computer bus which is bidirectional.

42. A monostable multivibrator has

43. An astable multivibrator has

44. An instruction that causes data in the accumulator to be moved to the memory or a peripheral register.

45. Which of the following is the language used in making an internet web page?

46. A logic circuit that is triggered by a clock signal is

47. What is the normal resting state of the SET and CLEAR inputs in a NAND gate latch?

48. An acceptable voltage range of logic 1 for TTL.

49. A result which is obtained when one is added to the least significant bit position of a binary number in the 1’s complement.

50. The time difference which results when a clock may not arrive at all flip-flops at precisely the same time.

51. A momentary, narrow, spurious, and sharply defined change in volume.

52. In a computer system, it is a unit of hardware where the control keys are located.

53. That part of a computer instruction that defines what type of operation the computer is to execute on specified data.

54. What is the condition of the flip-flop when Q = 0 and Q = 1?

55. A preproduction model of a system built for testing and debugging,

56. Equivalent of decimal value of 178 in straight binary code is _____ and in BCD is ​ ​ ​ ​ ​ ​ ​ ​ ​ .

57. The data manipulated by a program is called ​ ​_______ depending on its nature and extent.

58. Which of the following involves digital quantities?

59. With OR operation, 1 + 1 = ​ ​ ​ ​ ​ ​ ​ ​ ​

60. What is the function of the comparator in the ADC?

61. A flip-flop which follows its input in the next state.

62. Typical propagation delay range for modern digital integrated circuits is

63. It is the required interval immediately following the active edge held of clocks during which the control inputs must be held.

64. All arithmetic operations take place in the _______ of a computer

65. What is the smallest type of computer in terms of their physical size?

66. An input that disables multiplexers or demultiplexers when it is HIGH.

67. What graphical device is used to convert a truth table to its corresponding logic circuit in a simple and orderly process?

68. In Boolean algebra, X + 1 =

69. Which of the following is not a dynamic test instrument?

70. A circuit that produces an output pulse for a fixed period of time in response to a trigger and then returns to its quiescent state.

71. What is the major advantage of serial transfer over parallel transfer?

72. Application of excessive current to a fuse in order to open it.

73. What capital letter corresponds to 1000101 in the ASCII code?

74. A type of multivibrator circuit which generates a square wave of its own is the

75. The flip-flop can change only when the appropriate clock transition occurs.​

It is a condition called

76. How many AND gates and 4-bit binary adders are needed to implement a 2-bit to 3-bit binary multiplier?

77. Which of the following is a form of De Morgan’s theorem?

78. A circuit with no memory characteristic and whose output depends only on the current value of its inputs.

79. Class of programmable logic devices wherein both its AND and its OR arrays are programmable.

80. Simplify the expression y = AB’D + AB’D’.

81. The ​_____ belongs to a class of codes called the minimum-change codes, in which only one bit in the code group changes when going from one step to the next.

82. What is the principal register of an arithmetic logic unit?

83. It represents machine instructions by mnemonic names and allows memory addresses and other ​ constants to be represented by symbols rather than bit strings.

84. There are ​ ​_____ flip-flops for a 3-bit binary counter.

85. Data retrieval from a memory is called

86. A command to an ADC to start conversion

87. If a certain circuit acts as AND gate when used with positive logic (H = 1, L = 0), what function will it perform when used with negative logic (H = 0, L = 1).

88. How many flip-flops are required for a counter that will count 0 to 255?

89. A T flip-flop can be derived by

90. A circuit that operates in such a way that its output is high when all its inputs are high.

91. It is the required interval immediately following the active edge of the clock signal during which the control inputs must be held stable.

92. One of the standard levels of complexity of integrated circuits which contains 100,000 and more number of gates.

93. Duty cycle for repetitive waveform is defined as the

94. Processors with more than two registers for arithmetic and logical operations are classified as

95. How many bits are in a byte?

96. In clock circuits, SWG means

97. An acceptable voltage range of a logic 0 for CMOS operating at VDD = 5 V.

98. Refer to the debugging method in which the program is executed one instruction at a time and the register contents can be examined after each step?

99. A digital circuit that produces an output code depending on which of its inputs is activated.

100. The state of a flip-flop when Q = 0 and Q’ = 1

101. This bus carries lines that control the operation of the memory from the microprocessor to the memory.

102. High-speed modems transmit between

103. A magnitude comparator has 22n entries in the truth table where n =

104. An acceptable voltage range of a logic 1 for CMOS operating at VDD = 5 V.

105. How many inputs does a full adder have?

106. Convert 1000 1001 0111 (BCD) to its decimal equivalent.

107. The output of an inverter is connected to the input of a second inverter. Determine the output level of the second inverter.

108. Perform binary subtraction to 6 ¼ and 4 ½ would result to

109. An acceptable voltage range of a logic 0 for TTL.

110. An n-bit binary parallel adder requires ​______ in its least design.

111. A sequential logic circuit where the storage elements commonly used are time-delay devices (usually gates).

112. What is the output of an EX-OR gate when a logic signal and its exact inverse are connected to its input?

113. A small change made in resistance or capacitance to time a circuit precisely.

114. An equivalent Boolean equation for an exclusive NOR is

115. When a flip-flop is set, what are the states of Q and Q’?

116. Asynchronous flip-flop input used to clear Q immediately to 0.

117. This occurs when the result of an arithmetic operation is a larger number than the output register can accommodate.

118. In designing a 16 x 1 multiplexer, how many selection lines are needed?

119. What type of gate is equivalent to a NAND gate followed by an inverter?

120. A situation in a system where it can never leave or progress to another state.

121. “Limbo” state of a flip-flop occurs when

122. How many logic gates are in a VLSI chip?

123. Noise margin, which is one indication of how likely it is that information communicated between digital building blocks will be incorrect due to noise, depends on

124. The most commonly used IC package for digital integrated circuits is the

125. This type of bus carries the memory address from the computer to the memory.

126. Why are voltage DAC’s generally slower than current DAC’s?

127. If F = XY + X’Y’ Boolean expression is to be implemented using decoders and OR gates, the connection involves

128. The triangle inside the rectangle which is part of the IEEE/ANSI symbol at clock input

129. What is the hex equivalent of an ASCII code which means “HELP”?

130. A table used by a PLD language such as PALASM, to calculate the expected outputs for a set of inputs.

131. An input signal that can activate or disable a gate.

132. When power is first applied to any flip-flop circuit, it is impossible to predict the initial state of Q and Q’.​

What could be done to ensure that NAND latch always started off in the Q = 1 state?

133. Arrival of a clock signal at the clock inputs of different flip-flops at different times as a result of propagation delays.

134. Which of the following does not describe a flip-flop?

135. An area of memory that holds the ASCII characters that are being displayed on a monitor.

136. Which of the following does not describe a flip-flop circuit?

137. Text editors and formatters belong to the area of computing known as ​ ​ ​ ​ ​ ​ ​ ​ ​ .

138. The decimal system is composed of ​_____ numerals or symbols.

139. A term synonymous with CLEAR in computer systems.

140. A property whereby the output of a digital-to-analog converter either increases or stays the same as the input is increased.

141. A decoder with four inputs can have a maximum of how many outputs?

142. A programmable block of logic within a gate array, that contains a flip-flop for storage and also allows the user to specify logic functions on its inputs.

143. What binary number follows 1110?

144. Which type of flip-flop is best suited for synchronous transfer because it requires the fewest interconnections from one flip-flop to the other?

145. An analog memory output circuit used to eliminate aperture error is called a

146. What will be the state of Q and Q’ after a flip-flop has been reset?

147. If each digit of a decimal number is represented by its binary equivalent, the result is a code called

148. The portion of an instruction cycle where the instruction is sent from memory to the instruction register

149. The state of the flip-flop after the occurrence of a clock pulse is called as its

150. The fastest method for transferring data from one register to another is the

151. An actuator in the DAC

152. Which of the items below is not one of the three major sections of an MPU?

153. Speeds of modems are generally classified by the number of ​_____ they can transmit.

154. Add the hex numbers 58 and 24.

155. What are the three basic parts of a BCD adder circuit?

156. A JK flip-flop will operate in the toggle mode when

157. Determine the sum-of-product expression for a circuit with four inputs and an output that is HIGH only when A is low at the same time that exactly two inputs are low.

158. What is meant by interfacing in a computer system?

159. It consists of the instructions and data that the computer hardware manipulates to perform useful work.

160. What is the binary ASCII code for a question mark?

161. What is the only input combination that will produce a high at the output of a five-input AND gate?

162. A register which holds the data being written into or read out of the addressed memory location.

163. The most important memory element which is made of an assembly of logic gates is called

164. Instruction mnemonic means

165. A term used to describe the logic function created when open-collector outputs are tied together.

166. What happens when the input to a digital IC is left unconnected for TTL ICs?

167. How does the operation of asynchronous input differ from that of a synchronous input?

168. A counter that counts sequentially but does not step through all possible states, it returns to zero after a particular state.

169. A representation of numbers when negative numbers are obtained by complementing their positive equivalent and adding 1.

171. How many inputs does a half adder have?

172. Low-speed modems generally handle data rates between

173. An instruction that alters the normal course of a program by causing it to jump to another instruction.

174. A digital circuit test equipment which is a troubleshooting tool that generates a short- duration pulse when activated manually, usually by pressing the button is the ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ .

175. What device puts data on the data bus during a write operation?

176. What is the largest number that can be represented using 8 bits?

177. A square wave oscillator or clock generator

178. Convert (614)8 to decimal.

179. How many bits are required to represent an eight digit decimal number in BCD?

180. What JK input condition will always set Q upon the occurrence of the active clock transition?

181. In BCD, the code 1111 is

182. Class of programmable logic devices wherein its AND array is programmable while its OR array is hard-wired.

183. What is the decimal equivalent of (1101011)2?

184. Which of the following is NOT an advantage of state tables in sequential logic circuit design?

185. Convert (B2F)16 to octal.

186. This occurs when the result of an arithmetic operation is a more negative number than the output register can accommodate.

187. A computer language that enables Programmable Array Logic (PAL) users to generate a file that can be used to blow a PAL.

188. Data storage in a memory is termed as

189. A digital circuit that oscillates between two unstable output states.

190. A shift register in which the output of the last flip-flop is connected to the input of the first flip-flop.

191. The one-input RS flip-flop is the ​______ flip-flop.

192. A circuit designed to produce a clean output in response to a switch closure.

193. How many flip-flops should be used to realize 32-count capacity?

194. An outstanding advantage of LCDs from LEDs.

195. The time it takes for the DAC output to settle to within ½ step size of its full scale value when the digital input changes from zero to full scale.

196. An IC that contains a large number of interconnected logic functions wherein the user can program the IC for a specific function by selectively breaking the appropriate interconnections.

197. What is an operand address?

198. The ______ operation result will be 1 if any one or more variables is a 1.

199. What is the next binary number following (10111)2 in the counting sequence?

200. A diagram consisting of a set of circles, where each circle contains a number of states within it.

201. The fan out capability of a digital building block depends on the current capability of its output and the current requirement of each input driven by that output, and maybe defined as the

202. A ring counter where the output is inverted and tied back to the input

203. A ​______ takes the complete decimal number and represents it in binary.

204. A situation when a circuit’s output level for a given set of input conditions can be assigned as either

205. Correcting the faults in a circuit or a system.

206. A one-input JK flip-flop is the ______ flip-flop.

207. A 20 KHz clock signal is applied to a JK flip-flop when J = 1, K = 1.​

What is the frequency of the flip flop output waveform?

208. A block added to the combinational logic circuit to form a sequential logic circuit is the

209. Given: x = A’BC (A+D)’.​

Determine the output of the circuit x if A = 0, B = 1, C = 1 and D = 0.

210. A multiwire connection between digital circuits is usually called a

211. How does a CMOS integrated circuit respond to a floating input?

212. A register which holds the address of the word currently being accessed.

213. Class of mass memory devices that use a laser beam to write and read onto a specified coated disk.

214. An instruction that causes data to be brought from memory into an accumulator register.

215. This type of fault has the same effect as an internal short between IC pins.

216. How many logic gates are in an MSI chip?

217. A ______ condition that exists if a circuit output depends on which of two nearly simultaneous inputs arrive at a point in the circuit first.

218. The state of the flip-flop before the occurrence of a clock pulse is called as its

219. The state of a flip=flop when Q = 1 and Q’ = 0.

220. An included input terminals in a magnitude comparator IC which is significant when both inputs compared are equal is called as its

221. It converts a non-electrical physical quantity to an electrical quantity.

222. How many logic gates are in an SSI chip?

223. A multiplexer is described by its size through ​_______, where n = number of bits.

224. Which of the items below can perform parallel-to-serial data conversion?

225. In Boolean algebra, G + GF =

226. In the 7400 Family of TTL Devices, Quad 2-input NAND gates has a device number equivalent to

227. In Boolean algebra, B · B’ =

228. How many outputs does a full adder have?

229. What is the largest decimal value that can be represented using 12 bits?

230. What will be the states of Q and Q’ after a flip-flop has been cleared?

231. A bistable multivibrator has

232. Which of the following items below is NOT one of the three basic operations of Boolean algebra?

233. The number of digits used by a number system.

234. Which of the following is NOT an internal digital IC fault?

235. The most primitive instructions that can be given to a computer are those interpreted directly by the hardware in ______ form.

236. Another name for a digital multiplexer is

237. A single word memory location used to temporarily hold data during program execution.

238. With a ________, a processor can store data at ay address and read back the stored information at any time.

239. What is the most common type of digital IC package?

240. In the data sheet of a digital building block, operating speed is typically expressed in terms of

241. A JK flip-flop can be made to function like a T flip-flop by simply

242. Change in state is

243. Small circles on the input or output lines of logic circuit symbols which represent inversion of a particular signal.

244. A circuit that goes through 2n-1 states in a random fashion.

245. BCD code has always ________ bits per number.

246. A logic circuit that depends on the status of its selected inputs will channel its data input to one of ​ several data outputs.

247. Which of the following choices is NOT a characteristic of analog quantity?

248. Which of the following items below is not a part of the hardware organization in a computer?

249. An abbreviation that represents the opcode of a computer instruction.

250. What two types of inputs that a clocked flip-flop has?