if Add(bar)/Subt is high, then one of every NXOR gate\'s inputs is high too. Sin

Question

if Add(bar)/Subt is high, then one of every NXOR gate's inputs is high too. Since NXOR's another input is B(0-3), if B0 = 1, then at the first Full adder, the B is going to be 1 too, which is not its complement form. May I know how the NXOR gate works in the diagram? Thanks

6. The circuit shown in Figure 6-71 is a 4-bit circuit that can add or subtract numbers in a form used in computers (positive numbers in true form; negative numbers in complement form). (a) Explain what happens when the Add/Subt. input is HIGH. (b) What happens when AddiSub is LOW? As B3 A2 B2 Ao Bo Add/Sub. A B Cin A B Cin A B Cin A B Cin out FIGURE 6-71

Explanation / Answer

Yes you are correct. if Add(bar)/Subt is high, B will not get complemented and hence addition will occur. if Add(bar)/Subt is low, then B will get complemented and substraction will occur.

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