This set of Logic Design Multiple Choice Questions & Answers (MCQs) focuses on “Sequential Circuit Design”.
1. How do we convert to excess 3 code from BCD code?
a) By adding binary 3 to every binary coded decimal digit
b) By performing bit by bit XOR operation
c) By performing bit by bit XNOR operation
d) By subtracting binary 3 from each bit
View Answer
Explanation: Excess 3 codes are always obtained by adding binary 3 or 11 to every binary coded decimal digit. Hence it’s called excess 3. Bit by bit XOR is performed in case of binary to grey code conversion. So the right option is by adding binary 3 to every BCD digit.
2. What is the excess 3 code for the BCD code 1011?
a) 1100
b) 1110
c) 1001
d) 1111
View Answer
Explanation: BCD to excess 3 code conversions are performed by adding binary 3 or 11 to the BCD code.
Hence, the right answer is (1011 + 11) = 1110 or decimal 14.
3. Which of the following code conversions needs a bit by bit XOR operation?
a) BCD to Excess 3
b) Excess 3 to BCD
c) Binary to Gray Code
d) Gray code to binary
View Answer
Explanation: Binary to Grey code conversion needs a bit by bit XOR operation for every successive bit to be performed. The other conversions mentioned don’t need this. Hence, Binary to gray code is the right answer.
4. Which of the following is the equivalent gray code for binary 1011010?
a) 1011011
b) 1111001
c) 1110111
d) 0110111
View Answer
Explanation: To convert the binary code to equivalent grey code, we take the first bit as it is and perform bit by bit XOR operation for every following consecutive bits.
1 (+) 0 (+) 1 (+) 1 (+) 0 (+) 1 (+) 0
1 1 1 0 1 1 1
Hence, the right gray code is 1110111.
5. Which one of the following is the equivalent binary code for the grey code 1010110?
a) 1101010
b) 1110110
c) 1100100
d) 1001001
View Answer
Explanation: The MSB of the binary code is always equal to that of the grey code. Other bits can be obtained by checking grey code bit at that index. If grey code bit is 0, them copy previous binary code bit. Else copy invert of the binary code bit. Thus we get,
Grey 1 0 1 0 1 1 0
Binary 1 1 0 0 1 0 0
Hence, the correct binary equivalent is 1100100.
6. Which one is the equivalent BCD code for the excess 3 code 1000?
a) 0101
b) 1100
c) 1011
d) 1101
View Answer
Explanation: To get the equivalent BCD digit, we have to subtract binary 3 or 11 from the given excess 3 code.
1000 - 11 = 0101
Hence the correct answer is 0101.
7. What is the function of the following circuit?
a) BCD to excess 3 converter
b) Excess 3 to BCD converter
c) Gray code to binary converter
d) Binary to Gray code converter
View Answer
Explanation: The circuit shown is a binary to gray code converter. It is clear that if we consider I0, I1, I2 and I3 as a 4 bit input word, then the MSB I0 and output MSB F0 is same and bit by bit XOR is performed between every two consecutive bits following the MSB. Thus, the circuit acts as a binary to gray code converter.
8. Which one of the following is a non-weighted code?
a) Gray code
b) Binary
c) Octal
d) Decimal
View Answer
Explanation: Only the bits of gray code have no weight. But the others like binary, decimal and octal has weighted digits by the weight of 2, 10 and 8. Hence, gray code is the right answer.
9. What is length of a gray code obtained from a binary code?
a) Length of binary code – 1
b) Length of binary code + 1
c) Equal to the length of binary code
d) Length of binary code + 2
View Answer
Explanation: We are taking the MSB of gray code same as that of the decimal code. After performing bit by bit XOR for every next consecutive binary bit, total bits obtained = length of binary code – 1
So, total bits in gray code = length of binary code – 1 + 1 = length of binary code.
10. Which one is the equivalent grey code for the excess 3 code 1001?
a) 0111
b) 0011
c) 0110
d) 0100
View Answer
Explanation: To convert the excess 3 to gray code, first convert it to BCD.
Thus, 1001 – 11 = 0110 BCD
Now, converting this BCD to gray code, we get,
BCD 0 1 1 0
Gray 0 1 0 0
Hence the right answer is 0100.
11. Gray code is also known as which of the following?
a) Reflected Binary code
b) Line cod
c) Excess 3 code
d) RGB code
View Answer
Explanation: The Gray Code is a sequence of binary number systems, which is also known as reflected binary code. The reason for calling this code as reflected binary code is the first N/2 values compared with those of the last N/2 values in reverse order.
12. How many XOR gates are required to build a n bit gray code converter?
a) n
b) 3
c) n-1
d) n+1
View Answer
Explanation: In a grey code converter, we take the MSB as it is and perform XOR operation between every two of the remaining bits. Thus, if we have a n bit sequence, then we have to perform n-1 XOR operations. So, we need n-1 XOR gates.
13. What is the BCD code for the number 687?
a) 0110 1000 0111
b) 1010101111
c) 1001 0001 0101
d) 1001 100 100
View Answer
Explanation: In computing and electronic systems, binary-coded decimal (BCD) is a class of binary encodings of decimal numbers where each digit is represented by a fixed number of bits, usually four or eight. Here, the equivalent binary representations of each group are
6 -➔ 0110
8 -➔ 1000
7 -➔ 0111
Hence the BCD representation is 0110 1000 0111.
14. Which one of the following is needed to build a BCD to Excess 3 code converter?
a) Full Adder
b) Half Adder
c) Full Subtractor
d) Half Subtractor
View Answer
Explanation: Excess 3 code is generated by adding binary 3 to each BCD digits. Thus, we need a full adder circuit to get a BCD to excess 3 converters.
15. What is the equivalent grey code for 11001010?
a) 10101111
b) 11001100
c) 10001100
d) 10101010
View Answer
Explanation: The MSB of the binary code is always equal to that of the grey code. Other bits can be obtained by checking grey code bit at that index. If grey code bit is 0, them copy previous binary code bit. Else copy invert of the binary code bit.
Thus,
1 1 0 0 1 0 1 0
1 0 0 0 1 1 0 0
The grey code is 10001100.
Sanfoundry Global Education & Learning Series – Logic Design.
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