Binary subtraction is performed using one’s complement and 2’s complement methods

One’s complement method

Step 1: Find the ones complement of the subtrahend

Step 2: Add the subtractor and ones complement of the subtrahend

Step 3: If carry is present add the carry to the result

Step 4: If carry is not obtained the number is in its negative ones complement form

Example 25: find 12-3 using ones complement method

 Ones complement of subtrahend 3 = 1100.

12 – 3  =+9 → 1100₂+0011₂=1001₂

Example 26: find 12-15 using ones complement method

Ones complement of subtrahend 15 = 0000

Taking the ones complement of the result 1100 → (-)0011