I am stumped on writing the logic to test my four bit adder with inputs X[0:3],

Question

I am stumped on writing the logic to test my four bit adder with inputs X[0:3], Y[0:3], and Cin, and outputs S[0:3], Cout, and OVF. I think my problem is either with my adder layout, or more likely, with the way I am assigning values to the busses.

The full adders that my four bit adder is based on are correct, and I am pretty sure my four bit adder is correct, but I must test the adder to be certain.

I am trying to do a simple test to see if the overflow is correct when Cin=0, and the results show that something is wrong. Here is an example of what the adder is finding:

X= 10 Y= 9 Cin= 0 S= 7 Cout= 0 OVF= 0;

I think it should instead be X=10, Y=9, Cin=0, S=3, Cout=1, OVF=1

Where am I going wrong?

Here is my four bit adder and my test fixture:

Explanation / Answer

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