Last Updated :
19 Nov, 2018
Consider an eight-bit ripple-carry adder for computing the sum of A and B, where A and B are integers represented in 2’s complement form. If the decimal value of A is one, the decimal value of B that leads to the longest latency for the sum to stabilize is _____________
[This Question was originally a Fill-in-the-blanks Question]
(A) -1
(B) 2
(C) 1
(D) -2
Answer: (A)
Explanation:
Here \"longest latency for the sum to stabilize\" means maximum delay that
ripple carry adder would take to add A and B, we are given value of A and
need to find the value of B.
The Delay in Ripple Carry Adder is as follows
- For sum there are 2 XOR gates.
- For carry there is 1 XOR,1 AND and 1 OR gate.
i.e total 3 gate delays in case of carry and 2 gate delays in sum.
If we do 2\'s complement of 1 in 8 bit we get \"00000001\".
same we do for each option
-1 : \"11111111\"
2 : \"00000010\"
1 : \"00000001\"
-2 : \"11111110\"
So in case of -1 the carry bit will change and thus it will take 1 extra
gate delay, hence we could see that the maximum delay we could get when
input at B will be -1, i.e. add \”00000001\” with \”11111111\” and would get Maximum delay.
This explanation has been provided by Harshit Sidhwa.
Quiz of this Question
Share your thoughts in the comments
Please Login to comment...