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A and B are summed and the sum appears at Y and carry-out.
* Add with carry: A, B and carry-in are summed and the sum appears at Y and carry-out.
* Subtract: B is subtracted from A (or vice versa) and the difference appears at Y and carry-out. For this function, carry-out is effectively a "borrow" indicator. This operation may also be used to compare the magnitudes of A and B; in such cases the Y output may be ignored by the processor, which is only interested in the status bits (particularly zero,

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