I have 2 inputs,

input A = 0101

input B = 1111

Looking to perform the operation, A minus B and the function table of the ALU mentions that Cn must equal 1.

There is room for a carry out but not an overflow.

By looking at it I can see the answer is -5. But how can this be represented in a 4-bit output number?

So far I have read to complement B so it becomes 0000, and added this to 0101 and the carry in of 1.

But this results in 0110. Not sure about this so any help is welcomed.