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+19 votes

The number of full and half-adders required to add 16-bit numbers is

  1. 8 half-adders, 8 full-adders

  2. 1 half-adder, 15 full-adders

  3. 16 half-adders, 0 full-adders

  4. 4 half-adders, 12 full-adders

asked in Digital Logic by Veteran (59.5k points) | 4k views

1 Answer

+32 votes
Best answer
Answer is B.

Ffor LSB addition we do not need a full adder.

For addition of subsequent bits we need full adders since carry from previous addition has to be fed into the addition operation.
answered by Loyal (9k points)
edited by
But why to take C0 as 0.
Maybe because,if we don not take C0 as 0 then we will need 16 full adders which is not in option.
ppl here are not explaining the answers.. just writing the answrs.. very bad
The explanation is present in the selected answer. The Carry In of the LSB Adder will always be 0. So, the LSB adder need not be full. It can be a half adder. Therefore 15 full adders and 1 half adder.
plz expalin more not geting?????
C0(carry at LSB) will always be 0 for addition , it will be 1 in case we want to do subtraction using an adder, so we need 15 FA for Most significant 15 bits & 1 half adder for two bits at least significant position.

we know that HA adds 2 bits & FA adds 3 bits, at LS position, there will be two bits only(we can ignore C0).

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