Logic design - Full subtractor question -

[minhkhoa2011]

Logic design - Full subtractor question - need help !

Homework Statement

My professor gave my class this question but I really do not know how to solve.

The circuit will perform the subtraction where A<3:0>; B<3:0>; C<3:0>; D<3:0> represent 4-digit binary number.
a) Complement the schmetic by entering the node name S<4:0>; P<4:0>; C<3:0>; D<3:0>


Any help will be appreciated!
thanks all .

Homework Equations

The Attempt at a Solution

I know that I have to use the diagram but I do not know where to start from :-[

 

[berkeman]

Homework Statement

My professor gave my class this question but I really do not know how to solve.

The circuit will perform the subtraction where A<3:0>; B<3:0>; C<3:0>; D<3:0> represent 4-digit binary number.
a) Complement the schmetic by entering the node name S<4:0>; P<4:0>; C<3:0>; D<3:0>


Any help will be appreciated!
thanks all .

Homework Equations

The Attempt at a Solution

I know that I have to use the diagram but I do not know where to start from :-[

Use what diagram? Were you given a diagram? If so, please post it as an attachment, or give us a link to follow to see it.

Also, what are you subtracting from what? A-B? B-C? A full subtractor has two inputs (and maybe a borrow bit in), and one output (and maybe a borrow bit out)...