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1.For this circuit, if the result is A or B, then therewill be an output and no carry out. If a carry in is addedon top of those 2 outcomes, then there will also be a carry out. If both A and B are 1, then there’sa carryout. Basically, adding a carry in is like adding a 1, and the result is the output and the c out is like thecarry in an addition problem. I verified this by turning on A and B in different ways and seeing the LEDs’reactions.
2.When you subtract 2 numbers, the result is equal to the sum of the number with the 2’s complement of theother number. Therefore, for subtraction, one of the inputs is the 2’s complement of the original number.So x XOR 0 = x and x XOR 1 = x’. I verified this by inserting 0’s or 1’s into the xor gates and seeing theLEDs’ reactions.A3A2A1A0B3B2B1B0BoutS3S2S1S01000001000110100010000000000101000110100001011111010
10101011111110110001100011111011111111110101101111013.A BCD adder adds two BCD digits together and outputs a sum digit in BCD.