Let's consider how we would solve our problem of subtracting 1_{10} from 7_{10} using 1's complement.

0111 (7)  0001  (1) 

0001 > 1110 

0111 (7) + 1110 +(1) 10101 (?) 

0101 + 1 0110 (6) 

0111 (7)  0001  (1) 0110 (6) 
Now let's look at an example where our problem does not generate an overflow bit. We will subtract 7_{10} from 1_{10} using 1's complement.

0001 (1)  0111  (7) 

0001 (1) + 1000 +(7) 1001 (?) 

0001 (1) + 1000 +(7) 1001 (6) 
The animation below demonstrates how to subtract the 5bit binary numbers 01101_{2} and 01001_{2} using 1's complement representation. Click on the "Start Tutorial" button to view the animation.
Let's review the steps for subtracting x from y with an nbit 1's complement representation.
 Negate x using 1's complement.
 Reverse all the bits in x to form x.
 Add x and y.
 If the sum exceeds n bits, add the extra bit to the result.
 If the sum does not exceed n bits, leave the result as it is.