Tuesday, August 16, 2011

Half Adder Circuit


Half adder circuit is essential circuit for computer hardware components. The device which can calculate some integer or floating point wants half adder circuit. It is used for performing mathematical calculation in hardware. In computer, calculator and other counting device use half adder. It is the great invention for the scientists to sum the numbers easily. It consists of a XOR gate and two input pin and output sum and carry. Numbers of n bit are connected serially to add numbers.


Truth Table 

        Input A
        Input B
        Output C
        Output S
          0
           0
            0
           0
          0
           1
            0
           1
          1
           0
            0
           1
          1
           1
            1
           0


Circuit Diagram


 









Implementation of Half Adder using Boolean function

 A half adder is a logic circuit . It adds two single-bit numbers and produces sum(S) and carry(C). The simplest half-adder designing consists of an XOR gate for S and an AND gate for C Half.
When some numbers are added, it adds column by column. We're adding two bits. So, the adder we want to create should have two inputs bits. It generates a sum bit for that column, plus a carry. So there should be two bits of output. It is called half adder.

                >It takes two data inputs (call them x and y)
                >It outs two outputs (sum s and carry c)

For example we added two numbers   A and B
              
 Addition:
                                A (Augends)
    +B (Added)
                 __________________
     C S (output)
 Where,

                 A=1-bit number
                 B=1-bit number
                 S=Sum Bit output 
            C=Carry-Bit                                                          
                                                                
         

S=x'y+xy'  
C=xy

In half adder one adder and one XOR gate exists.
Ripple carry adder and carry look –ahead adder are consists of half adder and full adder.
 Various kinds  of adder is a ripple carry adder, since each carry bit "ripples" to the next full adder. Note that the first (and only the first) full adder may be replaced by a half adder.





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