I have a true table of full adder. Now i want to complete the adder so that it can also used used for subtraction (with overflow indicator). (OF = XYS'+ X'Y's)
x y cin --- cout s
0 0 0 --- 0 0
0 0 1 --- 0 1
0 1 0 --- 0 1
0 1 1 --- 1 0
1 0 0 --- 1 1
1 0 1 --- 1 0
1 1 0 --- 1 0
1 1 1 --- 1 1
cout = xy + xc + yc s = x'y'c+ x'yc'+ xy'c'+ xyc
I was thinking that the true table for subtraction will be like this :
sub s x y --- overflow
0 0 0 0 --- 0
0 0 0 1 --- 0
0 0 1 0 --- 0
0 0 1 1 --- 1
0 1 0 0 --- 1
0 1 0 1 --- 0
0 1 1 0 --- 0
0 1 1 1 --- 0
is this table right ?
or i need to use this one
0 0 0 0 --- 0
0 0 0 1 --- 0
0 0 1 0 --- 0
0 0 1 1 --- 1 === can any one explain why i got 1 in the overflow here?
0 1 0 0 --- 1
0 1 0 1 --- 0
0 1 1 0 --- 0
0 1 1 1 --- 0
1 0 0 0 --- 0
1 0 0 1 --- 0
1 0 1 0 --- 1 is this the correct true table ?
1 0 1 1 --- 0
1 1 0 0 --- 0
1 1 0 1 --- 1
1 1 1 0 --- 0
1 1 1 1 --- 0
Is this true table correct with the function (of = overflow) OF = XYS'+ X'Y's
How to make AU for this one ?
Need help plz
