Half adder... sum and carry

Discussion in 'Homework Help' started by fadax, Apr 19, 2010.

  1. fadax

    Thread Starter New Member

    Apr 19, 2010
    4
    0
    Hi
    I am revising for an exam next week and I came across this question when answering questions about computer arithmetic:

    http://i40.tinypic.com/15dmkvt.png

    I am confused because the truth table shows S=1, C=1 for a half adder with inputs A=1, B=1. But I learnt that with these inputs, a half adder would always output S=0, C=1. (making the sum function XOR, not OR)

    So why is it different here? I thought it might be a mistake in the question.. or am I missing something??

    thanks
     
  2. JDT

    Well-Known Member

    Feb 12, 2009
    658
    85
  3. fadax

    Thread Starter New Member

    Apr 19, 2010
    4
    0
    That gives the truth table which I've learnt for the half adder.. with S=0,C=1 for input A=1,B=1.

    Does this mean that there is a mistake in the question or is there some other way a half adder can work??
     
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