digital electronics objective questions and answers MCQ

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digital electronics objective questions and answers

MCQ Objective Test

objective questions and answers in digital electronics

Science and Engineering digital electronics objective questions with answers

objective qns and answers. on digital elctronic flip flops

basic electronics multiple choice questions
Basic Questions on

Digital Electronics

Flip Flops

Number System

Logic gates

Logic Families


1. The voltage levels for a negative logic system

(a) must necessarily be negative

(b) could be negative or positive

(c) must necessarily be positive

(d) must necessarily be either zero or —5 V

2. The output Qn of a J-K flip-flop is zero. It changes to 1 when a clock pulse is applied. The inputs Jn and Kn are respectively

(a) 1 and X

(b) 0 and X

(c) X and 0

(d) X and 1

3. The larger the RAM of a computer, the faster is its speed, since it eliminates

(a) need for ROM

(b) need for external memory

(c) frequency disk I/O s

(d) need for a data-wide path

4. DB, DW and DD directives are used to place data in particular location or to simply allocate space without preassigning anything to space. The DW and DD directories are used to generate

(a) offsets

(b) full address of variables

(c) full address of labels

(d)offsets of full address of labels and variables

5. The number of bits needed to address 4K memory is


(b) 8


(d) 16

6. The ESC instruction of 8086 may have two formats. In one of the formats, no memory operand is used. Under this format, the number of external op-codes (for the co-processor) which can be specified is?

(a) 64

(b) 128

(c) 256

(d) 512

7. The TRAP is one of the interrupts available its INTEL 8085. Which one of the following statements is true of TRAP?

(a) It is level triggered

(b) It is negative edge triggered

(c) It is positive edge triggered

(d) It is both positive edge triggered and level triggered

8. In a 16-bit microprocessor, words are stored in two consecutive memory locations. The entire word can be read in one operation provided the first

(a) word is even

(b) word is odd

(c) memory location is odd

(d) memory address is even

9. A 3 x 8 decoder with two enable inputs is to be used to address 8 blocks of memory. What will be the size of each memory block when addressed from a sixteen bit bus with two MSBs used to enable the decoder

(a) 2K

(b) 4K


(d) 64K

The following . items consist of two statements, one labeled as ‘Assertion A ‘ and the other labeled the ‘Reason R’. You are to examine these two statements carefully and decide if the Assertion A and the Reason R are individually true and if so, whether the Reason is a correct explanation of the Assertion. Select your answers to these items using the codes given below and mark your answer sheet accordingly:


(a) Both A and R are true and R is the correct explanation of A.

(b)Both A and Rare true but R is NOT a correct explanation of A.

(c) A is true but R is false

(d)A is false but R is true

10. Assertion (A): TTL and CMOS cannot be normally used together.

Reason (R) : .TTL operates on a (±5 0.25) V regulated supply voltage and some mA, while the CMOS operates on unregulated supply voltage of +3 to +15 and some microA.

11. Assertion (A): Machine language program is written in hexadecimal.

Reason (R) : Microprocessor can understand hexadecimal number system.

12.A JK flip-flop has its J input connected to logic level 1 and its K input to the Q

output. A clock pulse is fed to its clock input. The flip-flop will now

(a) change its state at each clock pulse

(b) go to state 1 and stay there

(c) go to state 0 and stay there

(d) retain its previous state

13.A decade counter requires

(a) 10 flip-flops

(b) 4 flip-flops

(c) 3 flip-flops

(d) 2 flip-flops.

14 The decimal value for the BCD coded number 00010010 is

(a) 6

(b) 10



15. The Boolean expression (A+C÷D) (B+D+C)

may be simplified as

(a) AB + CB


(c) A+BC+D

(d) A+B+CD.

16. An adder takes……. Input/s and produces………. Output/s

(a) one, two

(b) two, two

(c) three, two

(d) two, three.

17.1 Increasing the precision of the REAL data type requires using at least one additional bit in

(a) the mantissa

(b) the exponent

(c) both the mantissa and the exponent

(d) none of the above.

18. Let * be the binary operation on rational numbers given

a*b=a+b+2ab. Which of following are true?

I. * is commutative

II. There is a rational number that is a*identity

III. Every rational number. has as a* inverse.

(a) I only

(b) II only

(c) I and II

(d) I,II and III

19..How many 1 are present in the binary

representation of 15 x 256 + 5 x 16 + 3?

(a) 8

(b) 9

(c) 10


20. Which of the following combinations of gates does not allow the implementation

of an arbitrary Boolean function?

(a) OR gates and inverters only

(b) NAND gates only

(c) OR gates and exclusive – OR gates only

(d) OR gates and NAND gates.

21.Which logic circuit is the fastest?

(a) TTL

(b) DTL

(c) RTL

(d) All have same speed.

22.A half adder has

(a) 2 inputs and 2 outputs

(b) 2 inputs and 3 outputs

(c) 3 inputs and 3 outputs

(d) None of the above.

23. The main advantage of flip-flops over transistor circuit is

(a) immunity from noise

(b) low heating

(c) low propagation delay time

(d) high propagation.

24. The Integrated injection Logic has higher density of integration than TT’L because it

(a) does not require transistors with high current gain and hence they have smaller geometry

(b) uses bipolar transistor

(c) does not require isolation diffusion

(d) uses dynamic logic instead of static logic.

25.In a positive edge triggered JK flip-flop, a

low J and a low K produce the……. state A

high J and a high K mean that the output

will …….on the rising edge of the clock

(a) active…. race

(b) inactive ……dead

(c) inactive …..toggle

(d) active …..constant

26.How many bits does one need to encode all twenty-six letters, ten symbols, and ten


(a) 5

(b) 6

(c) 7

(d) 46

27. Consider the representation of six-bit numbers by two’s complement, one’s

complement, or by sign = and magnitude.In which representation is there overflow

from the addition of the integers 1000 and 011000 ?

(a) Two’s complement only

(b) Sign and magnitude and one’s complement only

(c) Two’s complement and one’s complement only

(d) All three representations.

28. Which of the following sets represents a universal logic family?




(d) None of the above.

29. The maximum propagation value in case of 7400 NAND gates is

(a) 1 second

(b) 20 milli seconds

(c) less than 20 nano seconds

(d) less than 20 pico seconds.

30 . The total number of Boolean functions which can be realized with your variables

Is ?

(a) 4


(c) 256

(d) 65,536

Answers :

1 b
2 a
3 c
4 d
5 c
6 b
7 d
8 d
9 c
10 b
11 d
12 a
13 d
14 c
15 b
16 c
17 a
18 c
19 a
20 d
21 a
22 a
23 c
24 b
25 c
26 b
27 d
28 a
29 c
30 b

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