# MCQs on Digital Electronics

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01․ The code used in digital systems to represent decimal digits, letters, and other special characters such as + , – , . , * , etc. is
octal
natural BCD
ASCII

Except ASCII code given remaimg codes are used for number representation only. The code used in digital systems to represent decimal digits, letters, and other special characters such as +, –, ., *, etc. is ASCII code.

02․ The codes in which each successive code word differs from the preceding one in only one bit position are called
BCD codes
sequential codes
self-complementing codes
cyclic codes

The sequence used in k map is not in binary sequence which would be 00, 01, 10, 11. It is 00, 01, 11 10, which is Gray code or cyclic code sequence. Gray code sequence only changes one binary bit as we go from one number to the next in the sequence, unlike binary. That means that adjacent cells will only vary by one bit, or Boolean variable. This is what we need to organize the outputs of a logic function so that we may view commonality. Moreover, the column and row headings must be in Gray code order, or the map will not work as a Karnaugh map.

03․ Unit distance code is the other name of
sequential code
self-complementing code
cyclic code
XS-3 code

In Gray code successive numbers will differ by only one bit. It is also known as unit distance code or cyclic code or reflective code. It is a unweighted code.

04․ (11011) 2 in BCD 8421 code is
00011011
00100111
11011001
01101100

In BCD there are 6 invalid BCD combinations are present with 4 bits. Using logic circuit design consider invalid BCD combinations into don't care. During BCD addition, if invalid BCD code is present then add '0110' to get correct result.

05․ (1D)16 in BCD 8421 code is
00011101
00101001
00011111
00100100

In BCD there are 6 invalid BCD combinations are present with 4 bits. Using logic circuit design consider invalid BCD combinations into don't care. During BCD addition, if invalid BCD code is present then add '0110' to get correct result.

06․ (44)8 in BCD 8421 code is
01000100
00100100
00110110
01100011

In BCD there are 6 invalid BCD combinations are present with 4 bits. Using logic circuit design consider invalid BCD combinations into don't care. During BCD addition, if invalid BCD code is present then add '0110' to get correct result.

07․ For a code to be self-complementing, the sum of all its weights must be
6
9
10
12

Weighted self complimented codes are 2421, 3321, 5211 and 4311. Therfore, the sum of all its weights must be '9' for a self-complementing code.

08․ The following code is not a BCD code.
Gray code
XS-3 code
8421 code
all of these

XS-3 code is obtained by adding '0011' to the BCD code. Therefore, XS-3 code is not a BCD code.

09․ The parity of the binary number 11011001 is
even
not known
odd
same as the number of zeros

Parity of a binary number is even parity when the number of 1's present in the number is even otherwise odd parity. Therefore, the given binary number is a odd parity number.

10․ 2-out-of-5 code is
weighted code
self-complementing code
non-weighted code
alphanumeric code

A two-out-of-five code is an encoding scheme which uses five bits consisting of exactly three 0s and two 1s. This provides ten possible combinations, enough to represent the digits 0–9. This scheme can detect all single bit-errors, all odd numbered bit-errors and some even numbered bit-errors (for example the flipping of both 1-bits). However it still cannot correct for any of these errors.

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