im using a 4 bit adder and i would like to know does the A pin get plus or minus by the B pin or is it the other way around. e.g A + B = S A - B = S or
B + A = S B - A = S

 

im using a 4 bit adder and i would like to know does the A pin get plus or minus by the B pin or is it the other way around. e.g A + B = S A - B = S or
B + A = S B - A = S

I'm not sure what you are asking. A 4-bit two's complement adder does not use or understand signs. The process is the same regardless of whether A and B are signed or unsigned. If A and B are unsigned then they are in the range [0..15] and the result is as well. the state of the carry out will not affect the 4-bit sum but can be used to affect the next higher order operation. If A and B are signed, then they are in the range [-8..+7]. The result and the carry out can be used to detect the occurrence of an overflow or underflow.

 

im using a 4 bit adder and i would like to know does the A pin get plus or minus by the B pin or is it the other way around. e.g A + B = S A - B = S or
B + A = S B - A = S

I can't understand what you're asking for. An adder can only add.

Is this schoolwork?