Question 10.24: Compare and contrast parallel and serial adders....

Parallel adders require more circuits than serial adders but allow all inputs to be presented at once instead of sequentially. The advantage of adding serially is that just one adder is needed. A parallel adder consists of full-adders connected in cascade, with the output carry from one full-adder connected to the input carry of the next full-adder. The inputs to the serial adder are two series of signals for the addend and the augend. The output S is a series of signals for the sum. The carry output C_{0} is delayed one clock pulse by a \mathrm{flip-flop} and fed back as a carry input C_{1}. Basically, a serial adder adds magnitudes. We need a circuit to test the carries into and out of the sign bit if the numbers to be added are in two’s complement. Using one’s complement we not only have to test sign bit carries but also have to provide an end-around carry.