ripple carry adder

Question

Consider a 4 bit Ripple carry adder for computing the sum of A and B , where A and B are unsigned integers.If the decimal values of A is 7, the smallest decimal value of B that leads to the longest latency for stabilizing the result is ____________

Comments

To get the longest delay, the adder should generate a carry at the last bit, because the last carry will take the most of the time in ripple carry adder. So if 1st number is 7 i.e. 0111. I think 1001(9) should be the smallest number that will generate a carry at the last bit, and hence give the longest latency for stabilizing the result. Am I right?

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Yes 1001.

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@rishab how did u find 1001..by brute force?

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Please read my first comment carefully, I gave the explanation. Basically, we want a carry at the last bit, i.e. MSB. So the minimum number that will do the job is 1001. You can kinda say it as brute force, but much of this you can do it in your head. Just think how to get a carry at the last bit.