4.1.3 but subtracts using the twos complement method described in Digital Electronics Module 1.5 (Ones and Twos Complement). This circuit adds in the same way as the adder in Fig. This is an 8-bit parallel adder/subtractor.
A further development of the parallel adder is shown in Fig.4.1.4. To carry out arithmetic however, it is also necessary to be able to subtract. 4.1.4 8−Bit Twos Complement Adder/Subtractor.
