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2. Full adder and full subtracter implemented by NAND Requirements: (1) You know, the basic elements of digital logic are gates. In this topic, you should design both full adder and full subtracter in a single circuit using NAND. (2) If you choose this topic, the course paper should be at least 2 pages, includes the principle and the circuit you designed. Hint (a): The truth tables of full adder and full subtracter are as the following: Tab 1 Truth table of full adder Tab 2 Truth table of full subtracter A B Cin S Cout B Cin S Cout WA 0 0 0 0 0 O 0 0 O O O 0 0 1 1 0 0 1 1 1 0 0 1 0 1 0 0 1 0 1 1 0 1 1 0 1 0 1 1 0 1 1 0 O 1 0 1 O 0 1 0 1 0 1 0 1 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 1 1 1 1 1 1 1 1 1 1 Hint (b): You can use one common switch to control the function of adder and subtracter. When the switch is on (its value is 1), the function of circuit is a full adder, when the switch is off (its value is 0), the function of circuit is a full subtracter. a