UGC NET CS 2014 Dec-Paper-2
October 7, 2023
Graphs
October 7, 2023
UGC NET CS 2014 Dec-Paper-2
October 7, 2023
Graphs
October 7, 2023

UGC NET CS 2014 Dec-Paper-2

Question 6
The BCD adder to add two decimal digits needs minimum of
A
6 full adders and 2 half adders
B
5 full adders and 3 half adders
C
4 full adders and 3 half adders
D
5 full adders and 2 half adders
Question 6 Explanation: 
→ Each digit is represented by a 4-bit BCD code.
→ To add two 4-bit number, we need 1 Half Adder(to add LSBs) and 3 Full Adders(remaining three bits of both number along with carry bits).
→ To make the resultant Sum as valid BCD sum, we need to add 0110 to the sum.
→ This can be done with 1 Half adder and 2 Full Adder
(Note: LSB bit of 0110 is always zero. So there is no need of ADDER to add LSBs.)
→ Here, Half adder is used to add next significant bits.
Total 5 Full Adders and 2 Half Adders are needed
Correct Answer: D
Question 6 Explanation: 
→ Each digit is represented by a 4-bit BCD code.
→ To add two 4-bit number, we need 1 Half Adder(to add LSBs) and 3 Full Adders(remaining three bits of both number along with carry bits).
→ To make the resultant Sum as valid BCD sum, we need to add 0110 to the sum.
→ This can be done with 1 Half adder and 2 Full Adder
(Note: LSB bit of 0110 is always zero. So there is no need of ADDER to add LSBs.)
→ Here, Half adder is used to add next significant bits.
Total 5 Full Adders and 2 Half Adders are needed
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