Question

Explain about Ripple Adder/Subtractor using 1’s complement method.

Answer 1

Ripple Adder

it is the combination of 4 full adder connected as shown in the figure .

S₀ , S₁ , S₂ , S₃ are output as shown in figure

$A_o,A_1,A_2,A_3$ and $B_o,B_1,B_2,B_3$ are at input terminal with combinations inside the full adder as shown

with alternate combinations

this works as !'s compliment addition means , LSB dinotes the sign of number , after addition we we have change the number like in bannary to get the desired answer 1 to 0 , 0 to 1.

ripple Subtractor 

ripple Subtractor  using 1's complement as shown in the figure above ,

it uses 4 XOR gates as shown in the figure , the inputs are done parallel as shown in the figure

it also uses 4 full adder as shown in the figure ,

and ouput comes out to be $S_3 , S_2,S_1,S_0$ , the main thing in this combination is to manage the carry , that is carry out , it is done as shown in the figure.

$A_0,A_1,A_2,A_3$ are given input parallel to XOR gates and corresponding full adder as shown in the figure,

$B_0,B_1,B_2,B_3$ are given input directly to the XOR gates and their output is acts input to the corresponding full adder .