$0.$ Build a $4-$bit adder from AND, OR$,$ and NOT gates as follows.

a$.$ Write out the truth table for a $1-$bit adder, which has three $1-$bit inputs: a$,$ b$,$ and

carry$\_$in$,$ and two $1-$bit outputs: result and carry$\_$out.

b$.$ Implement, in Logisim, the circuit for the $1-$bit adder corresponding to the above

truth table.

c$.$ In Logisim, create the four$-$bit adder by making three more copies of the above $1-$

bit adder, and then connecting them together. The resulting four$-$bit adder should

have the following inputs: a$0,$ a$1,$ a$2,$ a$3,$ b$0,$ b$1,$ b$2,$ b$3$ and carry$\_$in$.$ It should

have the following outputs: result$0,$ result$1,$ result$2,$ result$3,$ and carry$\_$out. $($Note:

To copy and paste the $1-$bit adder, select the entire $1-$bit adder by dragging the

mouse over the adder, copy by typing either control$-$C or command$-$C$,$ and then

paste by typing control$-$V or command$-$V$.$ You$$ll need to drag each new copy

into the right position$).$

d$.$ Be sure to test the adder to make sure it is getting the right outputs. Once you

have it working, you should:

i$.$ Give the circuit a name by clicking on $$main$$ under the $$untitled$$ folder

in the upper left$-$hand window and then, in the bottom left where it says

$$main$$ next to circuit name, typing in the name you want to give the

circuit. In this case $$one$\_$bit$\_$adder$$ is a good name, but it$$s up to you.

ii$.$ Save the circuit $($by clicking $$File$$ and $$Save$)$ to a file named

$$adder$.$circ$.$