The addition of the two numbers is done bit by bit, starting with the least significant bits.

Adding two bits can result in a carry-over wich has to be added to the next two bits. There are two ways to "remember" the carry-over:

  1. The carry-over is written on the field underneath the next digits to be added (solution 1).
  2. The carry-over is saved using additional states (solution 2).

Remembering the carry-over using states


The states "carry" and "no carry" are used to remember the carry-over.