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Digital Electronics
NUMBER SYSTEM
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ADDER
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Q- Design and implement the following with a combinational circuit (with A and B being 4-bit numbers):

S1           S0                           Output

0              0                              A plus B

0              1                              left shift A

1              0                              A plus B plus 1

1              1                              2A + 1

Ans: We need one 4-bit parallel ADDER and MUX to implement the above. As we can see that we need atleast one A at the input of ADDER so put A at one of the inputs

And for the 2nd input we have to choose out of different options, hence we use a MUX

And we see that we have to add an extra 1 when s1=1 & s0=0 and  s1=1 & s0=1. In both cases we have s1=1 so we attach s1 to carry pin also.

Left shifting A would make it 2A hence we add A to A to get left shift of A.

The circuit required is as follow:

 

 

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