This set of Logic Design Multiple Choice Questions & Answers (MCQs) focuses on “Serial Data Code Conversion”.
1. What is the function of the clock recovery circuit in the serial data and code converter?
a) To transmit serial data
b) To regenerate clock signal at the receiver
c) To activate the sequential circuit
d) To recover lost data
View Answer
Explanation: At the receiver end, we need to sample the received signal within the clock period same as at the transmitter end. So a clock recovery circuit is needed at the receiving end to recover the clock pulse from the received signal. The clock recovery circuit is used in a serial data code converter to regenerate the clock signal at the receiving end. This is also called digital phase locked loop.
2. Which one of the following is a characteristic of NRZI code?
a) For each 0 in the original sequence, the bit transmitted is the same as the previous bit transmitted. For each 1 in the original sequence, the bit transmitted is the complement of the previous bit transmitted
b) For each 1 in the original sequence, the bit transmitted is the same as the previous bit transmitted. For each 0 in the original sequence, the bit transmitted is the complement of the previous bit transmitted
c) Gray code of the original sequence is transmitted
d) Bit by bit complement of the original sequence is transmitted
View Answer
Explanation: NRZI code stands for Non Return Zero Inverted code. In this code, for a zero in bit stream, the original previously sent bit is sent again and for each 1 in the bit stream, the complement of the previously sent bit is sent.
3. What is the NRZI code for the bit sequence 01110010?
a) 01101100
b) 00001001
c) 01011100
d) 10001101
View Answer
Explanation: In NRZI code, for a zero in bit stream, the original previously sent bit is sent again and for each 1 in the bit stream, the complement of the previously sent bit is sent. If we follow the rule here, we get,
0 1 1 1 0 0 1 0 0 1 0 1 1 1 0 1
Hence the right answer is 01011101.
4. Which one of the following codes are called a “Bi-phase code”?
a) NRZI code
b) Gray code
c) Excess 3 code
d) Manchester code
View Answer
Explanation: In Manchester coding, each bit is encoded by a positive or negative 90° phase shift. A logic 0 is represented by a zero to one transition and a logic 1 is represented as an one to zero transition. That’s why it is termed as a bi-phase code.
5. If B is the bandwidth of a specific digital signal, what will be the bandwidth of it’s Manchester code?
a) 2B
b) B/2
c) B
d) 4B
View Answer
Explanation: In Manchester coding, each bit is encoded by a positive or negative 90° phase shift. Bandwidth of the Manchester code of any digital signal is always twice that of the signal. So the answer will be 2B.
6. Which one of the following is the correct data package for the NRZI code 01101110?
a) 01001011
b) 01011001
c) 00101100
d) 01101010
View Answer
Explanation: To get the actual data package, at first we take the MSB as of the data same as that of the code. Then for every next bit, if the next bit is complement of the previous one, then a 1 is added to the original data stream. Otherwise a 0 is added. Thus we get,
0 1 1 0 1 1 1 0 0 1 0 1 1 0 0 1
Hence, the right answer is 01011001.
7. What will be the equivalent Manchester code for the NRZ code 0011111100001100?
a) 0110101001011001
b) 0100111001010100
c) 0101000110101001
d) 1101010110010010
View Answer
Explanation: For NRZ to Manchester code conversion, we have to examine the NRZ code. MSB of the Manchester code is taken same as that of the NRZ code. If the next bit of NRZ is complement of the present one, the next bit of the Manchester code is kept as same as the previous bit. Else if the next bit in NRZ is same as that of the present bit, the next bit in Manchester code is complement of the previous one. Thus,
NRZ(x) 0 0 1 1 1 1 1 1 0 0 0 0 1 1 0 0 Manchester 0 1 1 0 1 0 1 0 0 1 0 1 1 0 0 1
Thus the right answer is 0110101001011001.
8. Which one of the following OSI layers uses the Manchester code?
a) Data link layer
b) Physical layer
c) Network layer
d) Application layer
View Answer
Explanation: Manchester coding is a coding scheme where each bit is encoded by a positive or negative 90° The physical layer of the Open System Interconnection (OSI) system uses the Manchester code to encode the clock and data of synchronous bit stream.
9. In Manchester coding, how logic 1 and 0 are represented?
a) 1 is high to low transition and 0 is low to high transition
b) 0 is high to low transition and 1 is low to high transition
c) 1 is a positive spike and 0 is negative spike
d) 0 is positive spike and 1 is negative spike
View Answer
Explanation: Manchester code is a self synchronizing code or bit representation. We can extract the timing and clock frequency of a transmitted signal. For that purpose, a logic 1 is represented as a high to low transition and a logic 0 is represented as a low to high transition.
10. Which one of the following is true for NRZ-S line code?
a) 1 is high to low transition and 0 is low to high transition
b) 0 is high to low transition and 1 is low to high transition
c) 1 is a positive spike and 0 is negative spike
d) 0 is represented by a transition in voltage and 1 is represented by no transition in voltage
View Answer
Explanation: Line coding is the process of converting digital data to digital signals. By this technique we convert a sequence of bits to a digital signal. At the sender side digital data are encoded into a digital signal and at the receiver side the digital data are recreated by decoding the digital signal. NRZ-S is a specific line code where 0 is represented by a transition in voltage and 1 is represented by no transition in voltage.
11. Which one of the following is used to represent 1s in unipolar signaling?
a) Rectangular pulse
b) Triangular pulse
c) Sine pulse
d) Cosine pulse
View Answer
Explanation: Unipolar signalling is also called as On-Off Keying or simply OOK.
The presence of pulse represents a 1 and the absence of pulse represents a 0.
The 1s are represented by a rectangular pulse in unipolar code and 0 is represented by no pulse.
12. What is the full form of AMI?
a) Additive Mark Inversion
b) Alternative Marking Innovation
c) Alternate Mark Inversion
d) Alternate Machine Industry
View Answer
Explanation: AMI stands for Alternate Mark Inversion. This is a special type of bipolar coding scheme.
Here, For a 1, the voltage level gets a transition from + to – or from – to +, having alternate 1s to be of equal polarity. A 0 will have a zero voltage level.
13. Which one of the following is the fourier transform of a rectangular pulse?
a) Sinc pulse
b) Cos wave
c) Sine wave
d) Triangular pulse
View Answer
Explanation: Fourier transform is a mathematical tool by which we represent any time domain signal in frequency domain. By the general laws of fourier transform we can see that in the frequency domain, it takes the shape of a sinc function.
Rect(t/T) ⟵ FT ⟶ Tsinc(wT/2)
14. What will be the polarity of the last 1 of the following data sequences if a bipolar signaling scheme is used with first logic 1 represented as a positive pulse?
110110110101
a) Positive
b) Negative
c) Zero level
d) Can’t be determined
View Answer
Explanation: Bipolar signaling is a specific line coding scheme where logic 0s are represented by no pulse and consecutive 1s are represented by opposite pulse I.e. the 1st 1 in the data is represented by a positive pulse and the 3rd 1 is represented as a negative pulse. We can see that there are even number of 1s in the data stream. So obviously the last 1 will be represented by a negative pulse as the first one is positive.
15. Which of the following Line code is a self-synchronizing one?
a) AMI
b) Polar Code
c) Bipolar Code
d) Manchester Code
View Answer
Explanation: In telecommunication and data storage, Manchester code (also known as phase encoding, or PE) is a line code in which the encoding of each data bit is either low then high, or high then low, for equal time. So the clock intervals can be recovered from the code itself. The other options have no such features.
16. In alphanumeric code which type of symbols are used to represent state transitions?
a) 0s and 1s
b) Special characters
c) Alphabets
d) Digits other than 0 and 1
View Answer
Explanation: The alphanumeric state graph notation is named after the alphanumeric input variables used instead of 0 and 1 in the state graph. Hence, the right answer is alphabets.
17. Which of the following is an advantage of alphanumeric state graph notation?
a) It makes easier to understand the state transitions
b) It reduces the number of transitions
c) It makes the design more efficient
d) Number of inputs and outputs are reduced
View Answer
Explanation: When a state sequential circuit has several inputs, then the state graph arcs are marked with alphanumeric state transition symbols that makes it easier to understand the graph.
Sanfoundry Global Education & Learning Series – Logic Design.
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