Digital Electronics - Combinational Logic Circuits - Discussion


The carry propagation can be expressed as ________.

[A]. Cp = AB
[B]. Cp = A + B

Answer: Option B


No answer description available for this question.

Sudeep Kumar Rana said: (May 21, 2012)  
This happens in parallel adders. (Where we try to add numbers in parallel via more than one adders).

A carry propagation occurs when carry from one adder needs to be forwarded to other adder and that second adder is holding the computation (addition) because carry from first adder has not come yet. So there is a slight delay for second adder and this is known as carry propagation.

Naren said: (May 5, 2016)  
Carry propagate is Cp= A XOR B.

The number of gate levels for the carry propagation can be found from the circuit of full adder.

For reference see M. Morris Mano digital design page no. 159 (V th edition).

Manju said: (May 31, 2017)  
The Expression for carry AB, for sum A XOR B.

Ayan said: (Aug 14, 2017)  
It must be A.B.

Brjesh Kumar said: (Sep 18, 2017)  
It must be A.B.

Sai Krishna said: (Sep 16, 2018)  
It must be A XOR B.

Reshma said: (Jan 24, 2019)  
A XOR B is correct.

Sunil said: (Jun 16, 2019)  
A XOR B is correct. I too agree.

Sai Krishna said: (Feb 6, 2020)  
A B Cin Cout
0 0 0 0
0 0 1 0
0 1 0 0
0 1 1 1
1 0 0 0
1 0 1 1
1 1 0 1
1 1 1 1

Carry propagation means the carry input (C in)bit should be '1' and it should be propagated to C out. If you observe the truth table (for C in=1), C out=A+B.

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