Having trouble forming an equation on 2 bit subtractor

[AilingLore21]

Homework Statement

We are asked to make a subtractor circuit which has a 2 bit, 2 input data.

Homework Equations

A₁A₀

_

B₁B₀

_________________________________

The Attempt at a Solution

I would have a 3 bit output with one borrow. The problem is I am stuck at this point and am having troubles forming an equation. Someone lent me their diagram and this is what I have

I have tried building this on the breadboard but it gives off an erroneous result at the 7 segment cathode with the ls48 decoder for the 4th time I assembled this. It only gives off 0 and 4 at the LED matrix when it should be 3,2,1,0. The upper LED is the rightmost bit while the third led is the third bit

 

[berkeman]

Homework Statement

We are asked to make a subtractor circuit which has a 2 bit, 2 input data.

Homework Equations

A₁A₀

_

B₁B₀

_________________________________

The Attempt at a Solution

I would have a 3 bit output with one borrow. The problem is I am stuck at this point and am having troubles forming an equation. Someone lent me their diagram and this is what I have

I have tried building this on the breadboard but it gives off an erroneous result at the 7 segment cathode with the ls48 decoder for the 4th time I assembled this. It only gives off 0 and 4 at the LED matrix when it should be 3,2,1,0. The upper LED is the rightmost bit while the third led is the third bit

Can you show us the truth table for the subtractor? And the K-maps that correspond to each of the outputs?