Part 5.1: 4-Bit Adder/Subtractor Circuit | Building 4-Bit ALU From Basic Logic Gates | Logisim
Part 5.1 shows how to make a 4-bit Adder/Subtractor assembly. Every Adder has an EXOR gate IC in front of it. Also for input/output lines, transmission gates are used to decide whether to transmit a bit signal or not. It is also used to equate both inputs. Remember, moving the circuit may give you an error by showing all lines blue. Just save your project it will resolve that issue.