Digital Design 2nd Edition F Vahid Need help filling in the

Digital Design (2nd Edition) F. Vahid. Need help filling in the blanks and want to verify what I believe it is, thanks.

Solution

for the first and second box:

it is seen that we have total 3 external input

that is a , b , wi

as given we have

a = a₂a₁a₀

b = b₂b₁b₀

so we can say that we have two inputs which are a nd b which is 3 bits each.

also as it is a full subtractor

we can tell that it is a 3 bit full subtractor.

for third box:

as the 3 bit full subtractor is build with 3 one bit full subtractor we can say that it is a 3 bit full subtractor build with 3 full one bit subtractor.

for the fourth box:

we can see that borrow out of the previous full subtractor is coonected to the borrow in of the next full subtractor.

so it is borrow look ahead kind of thing.

hence we cam say that,

it is a 3 bit full subtractor build with 3 full one bit subtractor connected in a borrow look ahead manner.

for the fifth box and sixth box:

as seen from the figure borrow out of the previous full subtractor is connected to the borrow in of the next subtractor.

borrow out bit is nothing but the wo and borrow in is nothing but the wi

so we can say that w0 is connected to the wi

hence statement is like this:

it is a 3 bit full subtractor build with 3 full one bit subtractor connected in a borrow look ahead manner (that is where output wo of the one subtractor is connected to the input wi of the next subtractor).

here bold letters show the contents of the box